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Stress Inhibits Hair Growth in Mice by Induction of Premature Catagen Development and Deleterious Perifollicular Inflammatory Events via Neuropeptide Substance P-Dependent Pathways

      It has been much disputed whether or not stress can cause hair loss (telogen effluvium) in a clinically relevant manner. Despite the paramount psychosocial importance of hair in human society, this central, yet enigmatic and controversial problem of clinically applied stress research has not been systematically studied in appropriate animal models. We now show that psychoemotional stress indeed alters actual hair follicle (HF) cycling in vivo, ie, prematurely terminates the normal duration of active hair growth (anagen) in mice. Further, inflammatory events deleterious to the HF are present in the HF environment of stressed mice (perifollicular macrophage cluster, excessive mast cell activation). This provides the first solid pathophysiological mechanism for how stress may actually cause telogen effluvium, ie, by hair cycle manipulation and neuroimmunological events that combine to terminate anagen. Furthermore, we show that most of these hair growth-inhibitory effects of stress can be reproduced by the proteotypic stress-related neuropeptide substance P in nonstressed mice, and can be counteracted effectively by co-administration of a specific substance P receptor antagonist in stressed mice. This offers the first convincing rationale how stress-induced hair loss in men may be pharmacologically managed effectively.
      “An intense psychic shock may also exert pronounced effects on the skin, eg, graying and generalized loss of hair.”
      • Selye H
      This quote from Hans Selye,
      • Selye H
      a pioneer in research into stress more than half a century ago reflects in laymen and physicians the deeply rooted assumption that stress can be associated with hair loss and changes in hair color. Many anecdotal observations of sudden hair loss concomitant with emotional stress have been reported supporting the above quote.
      • Trepat L
      • Petre AJ
      ‘Pelada Universal por shock emotiva.’.
      • York J
      • Nicholson T
      • Minors P
      • Duncan DF
      Stressful life events and loss of hair among adult women, a case-control study.
      • Garcia-Hernandez MJ
      • Ruiz-Doblado S
      • Rodriguez-Pichardo A
      • Camacho F
      Alopecia areata, stress and psychiatric disorders: a review.
      • Sinclair R
      Diffuse hair loss.
      Such observations prompted many retrospective studies, the majority of which date back to the 1950s or 1960s.
      • York J
      • Nicholson T
      • Minors P
      • Duncan DF
      Stressful life events and loss of hair among adult women, a case-control study.
      • MacAlpine I
      Is alopecia areata psychosomatic? A psychiatric study.
      • Van der Steen P
      • Boezeman J
      • Duller P
      • Happle R
      Can alopecia areata be triggered by emotional stress? An uncontrolled evaluation of 178 patients with extensive hair loss.
      • Russiello F
      • Arciero G
      • Decaminada F
      • Corona R
      • Ferrigno L
      • Fucci M
      • Pasquini M
      • Pasquini P
      Stress, attachment and skin disease: a case-control study.
      Although a medically benign condition, hair loss (alopecia areata, telogen effluvium) is nevertheless a significant psychosocial issue for most of the affected patients that greatly reduces quality of life and as such effectuates both additional stress perception and secondary morbidity.
      • Chrousos GP
      Stressors, stress, and neuroendocrine integration of the adaptive response. The 1997 Hans Selye Memorial Lecture.
      Despite the fact that an association between stress and hair loss is well accepted among patients and clinicians, it remains to be convincingly demonstrated in appropriate stress models that a defined psychoemotional stressor can actually inhibit or damage hair growth in vivo. Moreover, in the absence of a clear-cut pathophysiological concept, no specific pharmacological intervention is currently available to manage stress-induced hair loss. To be effective, any such therapeutic intervention that attempts to counteract stress-induced telogen effluvium or alopecia areata would have to prevent premature termination of the growth phase of the hair cycle (anagen) and would have to inhibit the onset of catagen.
      • Paus R
      • Cotsarelis G
      The biology of hair follicles.
      Recently, we have introduced an animal model for telogen effluvium that allows for the testing of whether stress-induced hair growth inhibition is fact or fiction, which offers the opportunity to gain insights into the pathomechanism involved in stress-triggered hair growth inhibition and that permits the exploration of various strategies for therapeutic intervention.
      • Arck PC
      • Handjiski B
      • Hagen E
      • Joachim R
      • Klapp BF
      • Paus R
      Indications for a ‘brain-hair follicle axis (BHA)’: inhibition of keratinocyte proliferation and up-regulation of keratinocyte apoptosis in telogen hair follicles by stress and substance P.
      This animal model uses mice, because they display a highly synchronized hair cycle (which facilitates experimentation and allows to detect even subtle hair growth alterations by stress). Further the hair follicle (HF) cycle has nowhere been better characterized than in mice.
      • Paus R
      • Cotsarelis G
      The biology of hair follicles.
      • Chase HB
      Physical factors which influence the growth of hair.
      • Maurer M
      • Handjiski B
      • Paus R
      Hair growth modulation by topical immunophilin ligands: induction of anagen, inhibition of massive catagen development, and relative protection from chemotherapy-induced alopecia.
      • Stenn KS
      • Paus R
      Controls of hair follicle cycling.
      Exposure of mice to a well-defined experimental psychoemotional stressor (sound stress)
      • Clark DA
      • Banwatt D
      • Chaouat G
      Stress-triggered abortion in mice prevented by alloimmunization.
      resulted in significantly increased keratinocyte apoptosis and decreased keratinocyte proliferation in resting (telogen) HFs in situ.
      • Arck PC
      • Handjiski B
      • Hagen E
      • Joachim R
      • Klapp BF
      • Paus R
      Indications for a ‘brain-hair follicle axis (BHA)’: inhibition of keratinocyte proliferation and up-regulation of keratinocyte apoptosis in telogen hair follicles by stress and substance P.
      These data are further supported by observations from Aoki and colleagues,

      Aoki E, Shibasaki T, Kawana S: Intermittent foot shock stress prolongs the telogen stage in the hair cycle of mice. Exp Dermatol, in press

      who used a different stressor to investigate the effect of stress on the HF, the so-called intermittent foot shock, which prolonged the telogen stage in the murine hair cycle and may delay exogen.

      Aoki E, Shibasaki T, Kawana S: Intermittent foot shock stress prolongs the telogen stage in the hair cycle of mice. Exp Dermatol, in press

      These intriguing findings had pointed to the existence of a brain-hair follicle axis,
      • Arck PC
      • Handjiski B
      • Hagen E
      • Joachim R
      • Klapp BF
      • Paus R
      Indications for a ‘brain-hair follicle axis (BHA)’: inhibition of keratinocyte proliferation and up-regulation of keratinocyte apoptosis in telogen hair follicles by stress and substance P.
      however, this pilot study had examined only resting (telogen) HFs and did not yet prove that stress can inhibit the growth of actually growing hair shaft producing (= anagen) HF by premature induction of HF regression (catagen), as necessary prerequisite for being capable of inducing telogen effluvium and massive catagen development, as it is seen in alopecia areata (AA) in man.
      • Paus R
      • Cotsarelis G
      The biology of hair follicles.
      • Clark DA
      • Banwatt D
      • Chaouat G
      Stress-triggered abortion in mice prevented by alloimmunization.
      In the context of the ancient debate on whether or not, and how, stress can negatively impact hair growth, investigating the effect of a defined psychoemotional stressor on the cycling activity of anagen HF in vivo and therefore remaining the immediate research priority, based on the hypothesis that stress-induced immunoactivation causes apoptosis, which, in a rather mild expression, would lead to telogen effluvium and in a more profound manifestation associated with dysregulation of calcitonin gene-related peptide (CGRP),
      • Daly TJ
      Alopecia areata has low plasma levels of the vasodilator/immunomodulator calcitonin gene-related peptide.
      triggers alopecia areata.
      Our previous pilot study had suggested that the neuropeptide substance P (SP) is one candidate mediator along the brain-HF axis because the anti-proliferation and proapoptotic effects could be reproduced in fact by SP.
      • Arck PC
      • Handjiski B
      • Hagen E
      • Joachim R
      • Klapp BF
      • Paus R
      Indications for a ‘brain-hair follicle axis (BHA)’: inhibition of keratinocyte proliferation and up-regulation of keratinocyte apoptosis in telogen hair follicles by stress and substance P.
      Also we had previously demonstrated that SP potently manipulates murine HF cycling in vivo and in skin organ cultures,
      • Paus R
      • Heinzelmann T
      • Schultz KD
      • Furkert J
      • Fechner K
      • Czarnetzki BM
      Hair growth induction by substance P.
      • Peters EM
      • Botchkarev VA
      • Botchkareva NV
      • Tobin DJ
      • Paus R
      Hair-cycle-associated remodeling of the peptidergic innervation of murine skin, and hair growth modulation by neuropeptides.
      making SP a particularly attractive candidate mediator in these stress studies. After von Euler and Gaddum
      • von Euler US
      • Gaddum JH
      An unidentified depressor substance in certain tissue extracts.
      had first described SP more than 70 years ago, much evidence has accumulated to suggest that this undecapeptide can indeed be considered as the prototypic stress-related neuropeptide.
      • Paus R
      • Heinzelmann T
      • Schultz KD
      • Furkert J
      • Fechner K
      • Czarnetzki BM
      Hair growth induction by substance P.
      • Peters EM
      • Botchkarev VA
      • Botchkareva NV
      • Tobin DJ
      • Paus R
      Hair-cycle-associated remodeling of the peptidergic innervation of murine skin, and hair growth modulation by neuropeptides.
      • von Euler US
      • Gaddum JH
      An unidentified depressor substance in certain tissue extracts.
      • Rathsack R
      • Oehme P
      • Roske I
      • Hilse H
      Substance P-like immunoreactivity in plasma and adrenal medulla of rats with spontaneous hypertension and WKY rats under acute stress.
      • Arck PC
      • Merali FS
      • Stanisz AM
      • Stead RH
      • Chaouat G
      • Manuel J
      • Clark DA
      Stress-induced murine abortion associated with substance P-dependent alteration in cytokines in maternal uterine decidua.
      • Zhu GF
      • Chancellor-Freeland C
      • Berman AS
      • Kage R
      • Leeman SE
      • Beller DI
      • Black PH
      Endogenous substance P mediates cold water stress-induced increase in interleukin-6 secretion from peritoneal macrophages.
      • Vaupel R
      • Jarry H
      • Schlomer HT
      • Wuttke W
      Differential response of substance P-containing subtypes of adrenomedullary cells to different stressors.
      This concept is further supported by two recent studies reporting that when the function of SP or its receptor is genetically disrupted, such mice show a significantly reduced response to moderate to intense pain.
      • Cao YQ
      • Mantyh PW
      • Carlson EJ
      • Gillespie AM
      • Epstein CJ
      • Basbaum AI
      Primary afferent tachykinins are required to experience moderate to intense pain.
      • De Felipe C
      • Herrero JF
      • O'Brien JA
      • Palmer JA
      • Doyle CA
      • Smith AJ
      • Laird JM
      • Belmonte C
      • Cervero F
      • Hunt SP
      Altered nociception, analgesia and aggression in mice lacking the receptor for substance P.
      In line with the distinct pharmacological properties of various neurokinins (NKs), which constitute a family of neuropeptides that comprises SP, three distinct receptors for SP have been cloned: the NK1 receptor, where SP is the preferred high affinity ligand, and the NK2 and NK3 receptors.
      • Teichberg VI
      • Cohen S
      • Blumberg S
      Distinct classes of substance P receptors revealed by a comparison of the activities of substance P and some of its segments.
      • Lee C-M
      • Iversen LL
      • Hanley MR
      • Sandberg BEB
      The possible existence of multiple receptors for substance P.
      • Buck SH
      • Burcher E
      The tachykinins: a family of peptides with a brood of receptors.
      • Nakanishi S
      Mammalian tachykinin receptors.
      Because the NK1 receptor has become a model for how neuropeptides and corresponding receptor-blocking drugs interact,
      • Gether U
      • Johansen TE
      • Snider RM
      • Lowe AJ
      • Nakanishi S
      • Schwartz TW
      Different binding epitope for substance P and the non-peptide antagonist, CP-96, 345, on the NK1 receptor.
      more than 30 nonpeptide NK1 antagonists are available to date.
      • Folkers K
      • Hörig J
      • Rosell S
      • Björkroth U
      Chemical design of antagonists of substance P.
      • Wang ZY
      • Tung SR
      • Strichartz GR
      • Håkanson R
      Investigation of the specificity of FK 888 as a tachykinin NK1 receptor antagonist.
      • Garret C
      • Carruette A
      • Fardin V
      • Moussaoui S
      • Peyronel JF
      • Blanchard JC
      • Laduron PM
      Pharmacological properties of a potent and selective nonpeptide substance P antagonist.
      • Snider RM
      • Constantine JW
      • Lowe III, JA
      • Longo KP
      • Lebel WS
      • Woody HA
      • Drozda SE
      • Desai MC
      • Vinick FJ
      • Spencer RW
      A potent nonpeptide antagonist of the substance P (NK1) receptor.
      • Betancur C
      • Azzi M
      • Rostène W
      Nonpeptide antagonists of neuropeptide receptors: tools for research and therapy.
      Availability of these selective and sensitive NK1 antagonists now allows to dissect the functional role of endogenous SP in stress-associated responses, including the effects stress may exert on HF cycling.
      For this reason the present study aimed at dissecting the impact of both stress and SP on the anagen/catagen transition of the murine hair cycle. We used the most studied mouse strain in hair research, C57BL/6 mice, and CBA/J mice, which have previously been demonstrated to be highly susceptible to stress.
      • Clark DA
      • Banwatt D
      • Chaouat G
      Stress-triggered abortion in mice prevented by alloimmunization.
      • Arck PC
      • Merali FS
      • Stanisz AM
      • Stead RH
      • Chaouat G
      • Manuel J
      • Clark DA
      Stress-induced murine abortion associated with substance P-dependent alteration in cytokines in maternal uterine decidua.
      Specifically, we investigated whether sound stress 1) promotes premature catagen development in anagen HFs in C57BL/6 and/or CBA/J mice with an originally synchronized hair cycle, as it can be identified by the hair cycle score (HCS);
      • Maurer M
      • Handjiski B
      • Paus R
      Hair growth modulation by topical immunophilin ligands: induction of anagen, inhibition of massive catagen development, and relative protection from chemotherapy-induced alopecia.
      • Müller-Röver S
      • Handjiski B
      • van der Veen C
      • Eichmuller S
      • Foitzik K
      • McKay IA
      • Stenn KS
      • Paus R
      A comprehensive guide for the accurate classification of murine hair follicles in distinct hair cycle stages.
      2) changes the physiological patterns of apoptosis in situ during the anagen/catagen transformation of HFs in both mouse strains, using terminal dUTP nick-end labeling (TUNEL) as markers;
      • Betancur C
      • Azzi M
      • Rostène W
      Nonpeptide antagonists of neuropeptide receptors: tools for research and therapy.
      3) alters the number, perifollicular location, and/or activation status of perifollicular macrophages and/or mast cells in murine back skin,assessed by quantitative (immuno-)histochemistry;
      • Maurer M
      • Paus R
      • Czarnetzki BM
      Mast cells as modulators of hair follicle cycling.
      • Eichmüller S
      • van der Veen C
      • Moll I
      • Hermes B
      • Hofmann U
      • Müller-Röver S
      • Paus R
      Clusters of perifollicular macrophages in normal murine skin: physiological degeneration of selected hair follicles by programmed organ deletion.
      4) induces changes in the skin of both mouse strains that can be abrogated by using the highly selective NK1-receptor antagonist (NK1-RA) RP 67580;
      • Garret C
      • Carruette A
      • Fardin V
      • Moussaoui S
      • Peyronel JF
      • Blanchard JC
      • Laduron PM
      Pharmacological properties of a potent and selective nonpeptide substance P antagonist.
      5) in addition, we tested whether SP is up-regulated in murine skin after stress exposure and if the systemic administration of SP alone sufficed to reproduce the observed effects of stress on selected parameters of skin immunology and hair biology in C57BL/6 and CBA/J mice.

      Materials and Methods

      Animals

      Six- to 8-week-old female CBA/J and C57BL/6 mice (Charles River, Sulzfeld, Germany) were chosen because mice at this age show the most reliable and profound stress response
      • Clark DA
      • Banwatt D
      • Chaouat G
      Stress-triggered abortion in mice prevented by alloimmunization.
      • Arck PC
      • Merali FS
      • Stanisz AM
      • Stead RH
      • Chaouat G
      • Manuel J
      • Clark DA
      Stress-induced murine abortion associated with substance P-dependent alteration in cytokines in maternal uterine decidua.
      and are in the telogen stage of the hair cycle.
      • Müller-Röver S
      • Handjiski B
      • van der Veen C
      • Eichmuller S
      • Foitzik K
      • McKay IA
      • Stenn KS
      • Paus R
      A comprehensive guide for the accurate classification of murine hair follicles in distinct hair cycle stages.
      The animals were housed in community cages at the animal facilities of the Charité, Virchow Hospital (Berlin, Germany) with 12-hour light periods, and were fed water and mouse chow ad libitum. Animal care and experimental procedures were approved by the state authority for animal research conduct (LaGetSi, Berlin, Germany) and performed in compliance with guidelines of the LaGetSi for the use of laboratory animals.

      Anagen Induction

      Anagen was experimentally induced by depilation, as previously published.
      • Chase HB
      Physical factors which influence the growth of hair.
      • Handjiski BK
      • Eichmuller S
      • Hofmann U
      • Czarnetzki BM
      • Paus R
      Alkaline phosphatase activity and localization during the murine hair cycle.
      Briefly, a wax/rosin mixture was applied to the dorsal skin (from neck to tail) of mice with all HFs in telogen, as evidenced by the homogeneously pink skin color on the back. Peeling-off the wax/rosin mixture removes all hair shafts and immediately induces homogeneous anagen development over the entire depilated back skin area of the mouse, thus inducing a highly synchronized anagen development. After full anagen development, the consecutive stages (catagen and telogen) then develop spontaneously in a relatively homogeneous wave-like pattern starting in the neck region.

      Application of Stress

      The CBA/J and C57BL/6 mice were exposed to sound stress for the duration of 24 hours starting on day 14 after depilation, ie, when all back skin HFs were in late anagen.
      • Müller-Röver S
      • Handjiski B
      • van der Veen C
      • Eichmuller S
      • Foitzik K
      • McKay IA
      • Stenn KS
      • Paus R
      A comprehensive guide for the accurate classification of murine hair follicles in distinct hair cycle stages.
      The ultrasound stress was emitted by a rodent repellant device (Conrad Electronics, Berlin, Germany) at a frequency of 300 Hz in intervals of 15 seconds. The stress device was placed into the mouse cage so that the mice could not escape the sound perception.
      • Arck PC
      • Handjiski B
      • Hagen E
      • Joachim R
      • Klapp BF
      • Paus R
      Indications for a ‘brain-hair follicle axis (BHA)’: inhibition of keratinocyte proliferation and up-regulation of keratinocyte apoptosis in telogen hair follicles by stress and substance P.
      • Clark DA
      • Banwatt D
      • Chaouat G
      Stress-triggered abortion in mice prevented by alloimmunization.
      • Arck PC
      • Merali FS
      • Stanisz AM
      • Stead RH
      • Chaouat G
      • Manuel J
      • Clark DA
      Stress-induced murine abortion associated with substance P-dependent alteration in cytokines in maternal uterine decidua.

      Application of SP

      Recombinant SP was dissolved in 2% dimethyl sulfoxide, diluted 1:10−5 in phosphate-buffered saline (PBS) and injected intraperitoneally at a concentration of 10 nmol/0.2 ml, as shown to be effective,
      • Arck PC
      • Handjiski B
      • Hagen E
      • Joachim R
      • Klapp BF
      • Paus R
      Indications for a ‘brain-hair follicle axis (BHA)’: inhibition of keratinocyte proliferation and up-regulation of keratinocyte apoptosis in telogen hair follicles by stress and substance P.
      into nonstressed mice as a single dose on day 14 after depilation to mimic stress-triggered, SP-mediated effects.

      Application of SP NK1 Receptor Antagonist (NK1-RA)

      In one set of experiments, the highly selective NK1-RA named RP 67580 (Rhône-Poulenc, France) was injected intraperitoneally at a dose of 200 μg/200 μl PBS/mouse every other day from day 2 until day 16 after depilation in control and stressed mice.

      Tissue Preparation

      On day 16 after depilation, ie, at the time when control mice are just about to spontaneously enter the catagen transformation of their depilation-induced anagen HFs,
      • Stenn KS
      • Paus R
      Controls of hair follicle cycling.
      • Müller-Röver S
      • Handjiski B
      • van der Veen C
      • Eichmuller S
      • Foitzik K
      • McKay IA
      • Stenn KS
      • Paus R
      A comprehensive guide for the accurate classification of murine hair follicles in distinct hair cycle stages.
      all mice were sacrificed. The mice were anesthetized by an intraperitoneal injection of a lethal overdose of ketanest and perfusion-fixed with a mixture of 4% paraformaldehyde and 14% saturated picric acid as previously described
      • Ljungberg A
      • Johansson O
      Methodological aspects on immunohistochemistry in dermatology with special reference to neuronal markers.
      • Botchkarev VA
      • Eichmüller S
      • Johansson O
      • Paus R
      Hair cycle-dependent plasticity of skin and hair follicle innervation in normal murine skin.
      • Botchkarev VA
      • Eichmuller S
      • Peters EM
      • Pietsch P
      • Johansson O
      • Maurer M
      • Paus R
      A simple immunofluorescence technique for simultaneous visualization of mast cells and nerve fibers reveals selectivity and hair cycle-dependent changes in mast cell-nerve fiber contacts in murine skin.
      or killed by cervical dislocation. Skin specimens from the neck region of murine back skin were harvested parallel to the vertebral line to obtain longitudinal sections through the hair units, which is an essential requirement for the quantitative histomorphology of the hair cycle,
      • Paus R
      • Peters EM
      • Eichmüller S
      • Botchkarev VA
      Neural mechanisms of hair growth control.
      folded, deep frozen in liquid nitrogen, and then covered with embedding medium, as described in detail.
      • Eichmüller S
      • van der Veen C
      • Moll I
      • Hermes B
      • Hofmann U
      • Müller-Röver S
      • Paus R
      Clusters of perifollicular macrophages in normal murine skin: physiological degeneration of selected hair follicles by programmed organ deletion.
      Cryosections were then processed for immunohistochemistry and TUNEL staining.

      Quantitative Histomorphometry of HF Cycling

      A previously published effective technique for follicle classification based on the alkaline phosphatase histochemistry of dermal papilla and sebaceous gland has been performed on the tissue sections.
      • Müller-Röver S
      • Handjiski B
      • van der Veen C
      • Eichmuller S
      • Foitzik K
      • McKay IA
      • Stenn KS
      • Paus R
      A comprehensive guide for the accurate classification of murine hair follicles in distinct hair cycle stages.
      • Handjiski BK
      • Eichmuller S
      • Hofmann U
      • Czarnetzki BM
      • Paus R
      Alkaline phosphatase activity and localization during the murine hair cycle.
      This allowed to accurately classify all HFs with respect to their exact stage in the transition from anagen VI via catagen I to VII to telogen.
      • Stenn KS
      • Paus R
      Controls of hair follicle cycling.
      For quantification, a previously described HCS was calculated:
      • Maurer M
      • Handjiski B
      • Paus R
      Hair growth modulation by topical immunophilin ligands: induction of anagen, inhibition of massive catagen development, and relative protection from chemotherapy-induced alopecia.
      every stage of anagen or catagen was assigned to an arbitrary unit in ascending numerical order (anagen VI, 0; catagen I, 1; catagen II, 2, and so forth). The total number of HFs in each specific hair cycle stage was then multiplied by its corresponding unit number. The resulting sum was divided by the total number of HFs counted, thus defining the average hair cycle stage of all HFs within the entire examined group.

      Immunohistochemistry

      Immunohistochemistry was performed following published protocols.
      • Arck PC
      • Handjiski B
      • Hagen E
      • Joachim R
      • Klapp BF
      • Paus R
      Indications for a ‘brain-hair follicle axis (BHA)’: inhibition of keratinocyte proliferation and up-regulation of keratinocyte apoptosis in telogen hair follicles by stress and substance P.
      • Eichmüller S
      • van der Veen C
      • Moll I
      • Hermes B
      • Hofmann U
      • Müller-Röver S
      • Paus R
      Clusters of perifollicular macrophages in normal murine skin: physiological degeneration of selected hair follicles by programmed organ deletion.
      Anti-mouse MHC class II antibody (ER-TR; BMA, Germany) was used in a 1:100 dilution for immunodetection of MHC-II+ cell cluster within murine skin). In brief, cryostat sections (10 μm) were fixed in acetone (10 minutes at −20°C) and preincubated with ready-to-use blocking solution (Immunotech, Germany), followed by an incubation with the primary antibody. Development was performed using diaminobenzidine. The rat anti-mouse MHC II+ antibody was incubated for 45 minutes at room temperature, followed by rabbit anti-rat secondary antibody (1:70, 30 minutes; DAKO, Germany), and the alkaline phosphatase anti-alkaline phosphatase technique was used for development.

      Fluoresence Immunohistochemistry for SP-Positive Nerve Fibers in the Skin

      For visualization of nerve fibers, perfusion-fixed cryostat sections (14 μm) were incubated overnight at room temperature in a humidity chamber with the primary antiserum to SP (1:100, rat, monoclonal; Chemicon, Temecula, CA). This was followed by an incubation of 1 hour at 37°C with tetramethylrhodamine-isothiocyanate-conjugated F(ab)2 fragments of goat anti-rat IgG (Jackson ImmunoResearch, West Grove, PA) at a dilution of 1:200.
      • Peters EM
      • Botchkarev VA
      • Botchkareva NV
      • Tobin DJ
      • Paus R
      Hair-cycle-associated remodeling of the peptidergic innervation of murine skin, and hair growth modulation by neuropeptides.
      After incubation, sections were rinsed in 0.1 mol/L Tris-buffered saline, pH 7.4, three times for 15 minutes each. After washing in Tris-buffered saline, all sections were mounted and stored at −20°C until analyzed. Three types of negative controls were done: 1) slides were incubated with the secondary antibody alone; 2) slides were incubated with the primary antibody after preincubation with control peptides for the specific antisera (10 to 20 μg/ml, 37°C, 1 hour; Sigma, St. Louis, MO); 3) slides were incubated with rabbit/rat IgG as primary antibody. As positive controls, cryostat sections of whole-mount mouse fetuses were used containing brain, spinal cord, heart, and gut. Negative controls did not reveal specific immunoreactivity. Sections were examined at ×400 magnification under a Zeiss Axioscope fluorescence microscope. The appearance of nerve fibers in defined areas such as the epidermis, the dermis including the arrector pili muscle, and the subcutis was assessed and the number of single nerve fiber profiles in dermis and subcutis was quantified by histomorphometry, as previously described in detail.
      • Peters EM
      • Botchkarev VA
      • Botchkareva NV
      • Tobin DJ
      • Paus R
      Hair-cycle-associated remodeling of the peptidergic innervation of murine skin, and hair growth modulation by neuropeptides.
      For each stage of HF cycling, at least 10 microscopic fields each of four to five different mice containing a minimum of 30 different HFs per mouse, were studied (ie, more than 200 microscopic fields were studied for each immunocytochemicalreaction).

      Giemsa Staining

      The presence of mast cells in murine back skin was detected using Giemsa staining (Merck, Germany). In brief, Giemsa was applied at a 1:10 dilution with 2% sodium borate solution for 45 minutes at room temperature. Differentiation was achieved using 0.02% acetic acid under microscopic control, slides were dehydrated and mounted. Mast cells were classified as degranulated when eight or more granules could be found outside the cell membrane.
      • Maurer M
      • Paus R
      • Czarnetzki BM
      Mast cells as modulators of hair follicle cycling.
      • Paus R
      • Maurer M
      • Slominski A
      • Czarnetzki BM
      Mast cell involvement in murine hair growth.

      TUNEL Staining

      To evaluate apoptotic cells in murine HFs, we used the TUNEL-staining method as described before.
      • Lindner G
      • Botchkarev VA
      • Botchkareva NV
      • Ling G
      • van der Veen C
      • Paus R
      Analysis of apoptosis during hair follicle regression.
      Ten-μm cryostat sections of murine back skin were freshly prepared and fixed in formalin, postfixed in ethanol/acetic acid, and incubated with digoxigenin-dUTP in the presence of terminal desoxynucleotidyl transferase (TdT), using a commercially available kit (Intergen, Germany). TUNEL-positive cells were visualized by anti-digoxigenin fluorescein isothiocyanate-conjugated F(ab)2 fragments, counterstaining was performed using 4,6-diamidino-2-phenylindole (DAPI) dye (1 μg/ml methanol; Roche, Germany) in a subsequent incubation step. Finally, sections were mounted using VectaShield (Vector Laboratories, Germany). Negative controls for the TUNEL staining were made by omitting TdT, according to the manufacturer's protocol.

      Quantitative Histomorphometry and Statistical Analysis

      All sections were analyzed at ×200 or ×400 magnification under a Zeiss Axioscope light microscope (Zeiss, Germany), photo documentation was performed using a KS400 camera (Zeiss, Germany). A mean of 79.3 single HFs per mouse (range, 40 to 110 HFs) was assessed from the neck region because catagen development occurs here first.
      • Maurer M
      • Handjiski B
      • Paus R
      Hair growth modulation by topical immunophilin ligands: induction of anagen, inhibition of massive catagen development, and relative protection from chemotherapy-induced alopecia.
      • Stenn KS
      • Paus R
      Controls of hair follicle cycling.
      • Müller-Röver S
      • Handjiski B
      • van der Veen C
      • Eichmuller S
      • Foitzik K
      • McKay IA
      • Stenn KS
      • Paus R
      A comprehensive guide for the accurate classification of murine hair follicles in distinct hair cycle stages.
      The total number of mice per group is given in the figures. Immunoreactive cells were counted in distinct HF compartments and around the hair units using a scaled eye piece. A fluorescence microscope (Zeiss, Germany) with appropriate excitation emission filter systems for fluorescence induced by DAPI and fluorescein isothiocyanate were used for the detection of apoptotic cells. The photo documentation was performed by a digital image analysis system (ISIS Metasystems, Altusheim, Germany). Means of all counts ±SEM were calculated. Differences were judged as significant if the P value was ≤0.05 (*), P ≤ 0.01 (**), and P ≤ 0.001 (***), as determined by the Mann-Whitney U/Wilcoxon rank tests.

      Results

      Stress Promotes Premature Catagen Development

      To test whether stress affects the timing of spontaneous catagen induction in depilation-induced anagen HFs in vivo, the onset of catagen development after initiation of an experimental hair cycle was examined in CBA/J and C57BL/6 mice exposed to sound stress compared to nonstressed control mice. As depicted in Figure 1, a significant increase in the progression of the hair cycle was observed with most HFs of nonstressed mice still in anagen VI, and the majority of HFs in stressed mice in early catagen. Interestingly, this premature progression was more pronounced in the stress-prone CBA/J mice (Figure 1A), compared to C57BL/6 mice (Figure 1B). This indicates a premature development of catagen follicles in both mice strains exposed to stress. Representative skin section that were used to assess the HCS of control C57BL/6 mice are shown in Figure 2A; areas with a significantly advanced progression of HCS (showing primarily catagen IV and V HFs) are presented in Figure 2B.
      Figure thumbnail gr1
      Figure 1In both mouse strains increased vulnerability of HFs toward an advanced catagen progression was detectable in stressed mice and could be mimicked by injection of SP in nonstressed mice and abrogated by injection of the highly specific NK1 receptor antagonist. The results for the CBA/J mice are shown on the left (A) and the data for C57BL/6 on the right (B). HCS was assessed as suggested by Maurer and colleagues.
      • Maurer M
      • Handjiski B
      • Paus R
      Hair growth modulation by topical immunophilin ligands: induction of anagen, inhibition of massive catagen development, and relative protection from chemotherapy-induced alopecia.
      In brief the y axis depicts the mean ± 1 SEM of histometric score assessed on day 16 after anagen induction. For every mouse a minimum of 100 individual HFs was assigned to defined hair cycle stages. On the right of the graph, representative hair cycle stages for each HCS are depicted, ie, anagen VI is the dominant hair cycle stage with a score of 0.5. **, P < 0.01. The number of mice per group is given in the bars.
      Figure thumbnail gr2
      Figure 2The effect of stress on the hair cycle stage is depicted in A–D. A: A representative area of control mice 16 days after depilation with the majority of HFs in anagen VI (AVI). B mirrors the effect of stress on the hair cycle stage on day 16 after depilation with HFs in catagen IV (CIV) or catagen V (CV). C: HF of stressed mice that received injection of SP, which mimicked the effect of stress on the vulnerability of HFs toward catagen progression with HFs in catagen III to VI (CIII-VI). D: A representative example of mice exposed to stress and treated with the NK1-RA, in which the majority of HFs were scored as anagen VI, similar to the nonstressed control group. E–F: The effect of stress on immunocytes in murine skin. E: Distribution of MHC-II+ cells in parafollicular dermis of nonstressed mice or in similar distribution in stressed mice that received the NK1-RA (bright red staining), compared to F, increased number of MHC-II+ cells in the bulge region, forming cluster after stress exposure. Similar staining patterns were present after injection of SP. Original magnifications, ×200.

      Stress Increases Intrafollicular Apoptosis

      This premature onset of catagen after application of stress was independently confirmed by measuring the intrafollicular patterns of apoptosis, because the massive, yet temporospatially highly controlled occurrence of intraepithelial apoptosis in the HFs is a hallmark of catagen development.
      • Lindner G
      • Botchkarev VA
      • Botchkareva NV
      • Ling G
      • van der Veen C
      • Paus R
      Analysis of apoptosis during hair follicle regression.
      As shown in Figure 3, exposure to stress 2 days before the assessment of HFs on day 16 after depilation resulted in a significantly increased percentage of HF units with signs of apoptosis (TUNEL+ cells) in the bulge region of both CBA/J mice (Figure 3A) and C57BL/6 mice (Figure 3B), which exceeded substantially the physiological signs of apoptosis in catagen HFs, as previously indicated by the so-called apoptomap.
      • Lindner G
      • Botchkarev VA
      • Botchkareva NV
      • Ling G
      • van der Veen C
      • Paus R
      Analysis of apoptosis during hair follicle regression.
      Because this HF region harbors the crucial population of epithelial stem cells of the HF,
      • Cotsarelis G
      • Cheng SZ
      • Dong G
      • Sun TT
      • Lavker RM
      Existence of slow-cycling limbal epithelial basal cells that can be preferentially stimulated to proliferate: implications on epithelial stem cells.
      • Lavker RM
      • Miller S
      • Wilson C
      • Cotsarelis G
      • Wei ZG
      • Yang JS
      • Sun TT
      Hair follicle stem cells: their location, role in hair cycle, and involvement in skin tumor formation.
      these stress-induced up-regulations of TUNEL+ cells in this sensitive HF compartment is of particular biological importance. Similar observations of stress-triggered increase of TUNEL+ cells were detectable in the bulb area (Figure 3, C and D), where levels of significance were reached only in C57BL/6 mice exclusively (Figure 3D). Absolute numbers of TUNEL+ cells in bulge and bulb region are given in Table 1, supporting the data on percentages given in the figures. Figure 4 shows representative examples of apoptotic cells in HF bulge (Figure 4A) and bulb (Figure 4E) of nonstressed control C57BL/6 mice, compared to HFs with high numbers of apoptotic cells in bulge (Figure 4B) and bulb (Figure 4F) in mice of the same strain exposed to stress.
      Figure thumbnail gr3
      Figure 3The effect of stress on the percentage of HFs with TUNEL+ cells in bulge (A) and bulb (C) in CBA/J mice and TUNEL+ cells in bulge (B) and bulb (D) in C57BL/6 mice (mean ± SEM). Exposure to stress 2 days before assessment led to a significant increase of apoptotic cells/HF bulge (*, P < 0.05 for CBA/J; ***, P < 0.001 for C57BL/6) and bulb (***, P < 0.001 for C57BL/6). The effect of stress on HF apoptosis in bulge could be mimicked by injection of SP in both strains of nonstressed mice (A and B) and abrogated by treatment with NK1-RA in the bulge region of stressed mice (A and B). The number of mice per group is given in the bars.
      Table 1Absolute Cell Counts in CBA/J and C57BL/6 Mice (Mean ± SEM)
      ControlStressSPControl NK1-RAStress NK1-RA
      CBA/J mice
       TUNEL+ cells
        Bulge
      Bulge area of anagen VI/catagen I follicles covers 40-μm2 tissue.
      3.4 ± 1.17.9 ± 1.76.9 ± 1.13.4 ± 1.12.8 ± 0.9
        Bulb
      Bulb area of anagen VI/catagen I follicles covers 60-μm2 tissue.
      9.7 ± 2.613.7 ± 4.76.9 ± 2.92.6 ± 0.75.0 ± 1.7
       MHC II+
      Number of cell clusters per 12.5-mm epidermal length.
      2.0 ± 0.37.0 ± 1.1 8.3 ± 1.2 3.3 ± 0.32.7 ± 0.3
       Mast cells
        Dermis total/7.6 ± 0.5/8.6 ± 0.7/7.8 ± 0.4/NDND
        Degranulated
      Classified as degranulated when eight or more granules were seen outside the cell membrane.
      2.2 ± 0.34.1 ± 0.3 3.3 ± 0.3
        Subcutis total/3.6 ± 0.4/4.5 ± 0.5/3.7 ± 0.4/NDND
        Degranulated
      Classified as degranulated when eight or more granules were seen outside the cell membrane.
      1.0 ± 0.21.9 ± 0.2 1.3 ± 0.2
      C57BL/6 mice
       TUNEL+ cells
        Bulge
      Bulge area of anagen VI/catagen I follicles covers 40-μm2 tissue.
      6.7 ± 1.815.2 ± 1.7 21.7 ± 3 2.1 ± 0.47.5 ± 2.1
        Bulb
      Bulb area of anagen VI/catagen I follicles covers 60-μm2 tissue.
      6.2 ± 1.114.8 ± 5.0 22.0 ± 3 6.4 ± 1.18.2 ± 1.3
       MHC II+
      Number of cell clusters per 12.5-mm epidermal length.
      4.7 ± 0.611.8 ± 0.8 8.5 ± 0.9 7.0 ± 1.85.3 ± 0.5
       Mast cells
        Dermis total/6.8 ± 0.4/6.7 ± 0.9/5.7 ± 0.4/NDND
        Degranulated
      Classified as degranulated when eight or more granules were seen outside the cell membrane.
      0.7 ± 0.14.1 ± 0.9 2.5 ± 0.3
        Subcutis total/2.9 ± 0.3/3.0 ± 0.2/2.5 ± 0.3/NDND
        Degranulated
      Classified as degranulated when eight or more granules were seen outside the cell membrane.
      0.3 ± 0.11.8 ± 0.2 1.8 ± 0.2
      ND, Not determined.
      ↑, Significant increase compared to nonstressed control (P ≤ 0.05).
      ↓, Significant decrease compared to stressed, non-NK1 RA-treated group (P ≤ 0.05).
      * Bulge area of anagen VI/catagen I follicles covers 40-μm2 tissue.
      Bulb area of anagen VI/catagen I follicles covers 60-μm2 tissue.
      Number of cell clusters per 12.5-mm epidermal length.
      § Classified as degranulated when eight or more granules were seen outside the cell membrane.
      Figure thumbnail gr4
      Figure 4The effect of stress on HF keratinocyte apoptosis in bulge (A–D) and bulb (E and F) region in dermis of C57BL/6 mice. A and E: TUNEL staining in dermis of control mice, very few apoptotic cells can be observed in bulge (A) or bulb (E). HF keratinocyte nuclei appear in bright blue, resulting from DAPI counterstaining. B and F: Stress exposure 2 days before TUNEL staining caused an increase in apoptotic cells in the bulge (B) and bulb (F) region of the HF, as depicted by green fluorescence and pointed out in one case with an arrow. C and G: Injection of SP simulated the effect of stress in nonstressed C57BL/6 mice by causing an increase in apoptotic cells in the bulge (C) and bulb (G) region of the HF, as depicted by green fluorescence. D and H: HF from a stressed C57BL/6 mouse treated with NK1-RA. No signs of apoptosis in bulge (D) and bulb (H).

      Stress Increases Perifollicular Macrophage Clusters

      We had previously shown that the exposure to stress significantly boosts the occurrence of perifollicular MHC class II+ cell clusters. These MHC class II+ cell clusters represent primarily activated macrophages and are associated with a substantially higher risk of HFs to be immunosurgically eliminated by a process termed “programmed organ deletion.”
      • Eichmüller S
      • van der Veen C
      • Moll I
      • Hermes B
      • Hofmann U
      • Müller-Röver S
      • Paus R
      Clusters of perifollicular macrophages in normal murine skin: physiological degeneration of selected hair follicles by programmed organ deletion.
      The current study revealed a significant increase of HFs that displayed prominent perifollicular MHC class II+ cell clusters (>5 cells) in both stressed strain of mice (CBA/J, Figure 5A; C57BL/6, Figure 5B). Absolute numbers of MHC class II+ cells per 12.5-mm epidermal length are given in Table 1, also indicating the significant increase in actual cell cluster numbers positive for MHC class II around the HF. Figure 2E shows representative immunohistochemistry of control HFs with low numbers of perifollicular MHC II+ cells in nonstressed C57BL/6 mice. For comparison, an example of high numbers of perifollicular MHC II+ cells in stressed C57BL/6 mice is depicted in Figure 2F.
      Figure thumbnail gr5
      Figure 5The effect of stress on the percentage of HFs with MHC-II+ perifollicular cell cluster in CBA/J (A) and C57BL/6 (B) mice (mean ± SEM). Exposure to stress 2 days before assessment led to a significant increase of MHC-II+ cells cluster (***, P < 0.001 for both strains). Injection of SP in nonstressed mice mirrored the effect of stress in both strains and injection of NK1-RA abrogated the effect of stress on number of MHC-II+ cells cluster in CBA/J (A) and C57BL/6 (B) mice (***, P < 0.001 for both strains). The number of mice per group is given in the bars.

      Stress Stimulates Mast Cell Degranulation

      Mast cells have been shown to play a key role in the neuroimmunological linkage of stress to defined inflammatory events.
      • Bienenstock J
      • Denburg J
      • Scicchitano R
      • Stead R
      • Perdue M
      • Stanisz A
      Role of neuropeptides, nerves and mast cells in intestinal immunity and physiology.
      • Williams RH
      • Bienenstock J
      • Stead RH
      Mast cells—the neuroimmune connection.
      • Theoharides TC
      • Singh LK
      • Boucher W
      • Pang X
      • Letourneau R
      • Webster E
      • Chrousos G
      Corticotropin-releasing hormone induces skin mast cell degranulation and increased vascular permeability, a possible explanation for its proinflammatory effects.
      We therefore evaluated activated (degranulated) mast cells in the current stress model. Interestingly, a significantly increased percentage of degranulated mast cells was seen in the dermis (Figure 6A) and in the subcutis (Figure 6C) of stressed CBA/J mice. Similar observations were made with C57BL/6 (Figure 6, B and D) after exposure to stress. Absolute numbers of total and degranulated mast cells in dermis and subcutis are given in Table 1, indicating that the total number of mast cells did not significantly differ among the groups.
      Figure thumbnail gr6
      Figure 6The effect of stress on the percentage of degranulated (= activated) mast cells calculated from the total number of mast cells (mean ± SEM) in dermis (A and B) and subcutis (C and D) in CBA/J (A and C) or C57/BL6 (B and D) mice. Exposure to stress 2 days before assessment led to a significant increase of degranulated mast cells in murine dermis and subcutis in both strains. Injection of SP mimicked the effect of stress in nonstressed control mice. The number of mice per group is given in the bars.
      Figure 7A and, at a higher magnification in B, show a representative example of nondegranulated (nonactivated) mast cells (white arrow) in the dermis near a HF in the skin of control C57BL/6 mice, compared to the degranulated (activated) mast cells in stressed C57BL/6 mice (purple arrow), where extracellular granules can be seen in the dermis (Figure 7, C and D).
      Figure thumbnail gr7
      Figure 7A: Mostly nonactivated mast cells in dermis of nonstressed C57BL/6 mice (dark purple staining). B: A magnification of the region marked in A with the stippled line. No extracellular granules are present in the vicinity of the resting mast cell, as pointed out by the white arrow. C: Stress exposure caused an increase in activated (degranulated) mast cells in dermis. The region magnification indicated in C and presented in D shows a representative example of an activated, degranulated mast cell with more than eight extracellular granules, as indicated by the purple arrow. E–H: Fluorescence immunohistochemistry of SP nerve fibers (delicate red lines) in the dermis (bulge area) of nonstressed mice is presented in E. A mast cell appears in bright green. F: SP nerve fibers in the dermis (bulge area) of a mouse exposed to stress. In this section, an increase in mast cell number can also be observed. Interestingly, we frequently observed SP-positive nerve fibers in the direct vicinity (<2 μm) of mast cells in dermis and subcutis (G) of stressed mice. H: Higher magnification of the stippled square in G.

      Stress Exposure Up-Regulates Protein Expression of SP Nerve Fibers in Dermis

      To directly prove that exposure to stress affects the density and expression pattern of neuropeptide in skin, we included perfusion-fixed mice and demonstrated that stress indeed triggered a significant increase of SP-positive nerve fibers in dermis and in subcutis, whereby in subcutis, levels of significance could not be reached (P = 0.064) (Figure 8). Fluorescence immunohistochemistry of SP nerve fibers (delicate red lines) in the dermis (bulge area) of nonstressed mice is presented in Figure 7. A mast cell appears in bright green. Figure 7H depicts SP nerve fibers in the dermis (bulge area) of a mouse exposed to stress. In this section, an increase in mast cell number can also be observed. Interestingly, we frequently observed SP-positive nerve fibers in the direct vicinity (<2 μm) of mast cells in dermis and subcutis (Figure 7G) of stressed mice. Figure 7H shows the higher magnification of the stippled square in Figure 7G.
      Figure thumbnail gr8
      Figure 8A: Stress exposure significantly up-regulates number of SP nerve fibers/visual field in dermis of C57BL/6 mice. B: A tendency of up-regulation could also be observed in the subcutis.

      Stress-Induced Premature Catagen Development, Intrafollicular Apoptosis, and Deleterious Inflammatory Events around the HF Are Reproduced by Injection of SP

      Next, we wished to determine whether the effects of stress on premature catagen development and intrafollicular apoptosis could be reproduced by systemic injection of one key modulator implicated in stress responses, the neuropeptide SP. CBA/J or C57BL/6 mice received a single intraperitoneal injection of recombinant SP 2 days before skin harvesting. As presented in Figure 1, A and B, a significant hair cycle progression toward catagen could be induced by injection of SP in both strains of mice in absence of the experimental stressor, thus mimicking the effect of stress. Histology of a representative area of catagen III to IV HF is given in Figure 2C.
      As shown in Figure 3, A and B, a significant increase of TUNEL+ HFs was indeed seen after SP injection in the bulge region in both (nonstressed) mouse strains, simulating the highly significant increase of apoptotic cells triggered by stress. The effect of SP injection on apoptotic cells in the bulb region showed similar tendencies, however, levels of significance were only reached in C57BL/6 mice (Figure 3, C and D). Representative bulge or bulb areas of SP-injected C57BL/6 mice are shown in Figure 4, C and G, respectively.
      SP mimicked the effect of stress exposure on the percentage of HFs with MHC II+ cell cluster in CBA/J and C57BL/6 mice (Figure 5, A and B) and further simulated the effect of stress on the activation status of mast cells in dermis in both strains (Figure 6, A and B) and in subcutis for C57BL/6 mice (Figure 6D).

      NK1 Receptor Antagonist Normalizes Most Stress-Induced Alterations

      Further, we investigated whether co-administration of a SP receptor antagonist in stressed mice would abrogate the effects of sound stress on catagen induction and intrafollicular apoptosis. Injection of the highly specific NK1-RA significantly down-regulated the effects of stress on the premature progression of catagen in both mouse strains (Figure 1, A and B, and Figure 2D for histology). The same was true for intrafollicular apoptosis in the bulge (Figure 3, A and B) of both strains and in bulb region of C57BL/6 mice (Figure 3D). Representative histology is shown in Figure 4, D and H.
      The effect of stress exposure on the percentage and number of MHC II+ cell clusters could be significantly abrogated by NK1-RA in both mouse strains (Figure 5, A and B). Because we previously demonstrated that murine skin mast cells appear not to express the NK1 receptor,
      • Arck PC
      • Handjiski B
      • Hagen E
      • Joachim R
      • Klapp BF
      • Paus R
      Indications for a ‘brain-hair follicle axis (BHA)’: inhibition of keratinocyte proliferation and up-regulation of keratinocyte apoptosis in telogen hair follicles by stress and substance P.
      we did not investigate the effect of the NK1-RA in the present study.

      Discussion

      Extending our previous pilot study in telogen mouse skin,
      • Arck PC
      • Handjiski B
      • Hagen E
      • Joachim R
      • Klapp BF
      • Paus R
      Indications for a ‘brain-hair follicle axis (BHA)’: inhibition of keratinocyte proliferation and up-regulation of keratinocyte apoptosis in telogen hair follicles by stress and substance P.
      we show here for the first time that a well-defined psychoemotional stressor indeed alters actual HF cycling in vivo, ie, prematurely terminates the normal duration of hair growth in mice and up-regulates apoptosis and deleterious inflammatory events in and around the murine HFs. This provides the first solid pathophysiological mechanism for how stress may actually cause telogen effluvium and/or may even be involved in triggering the development of alopecia areata: 1) induction of premature catagen induction; 2) up-regulation of keratinocyte apoptosis in the hair bulb and bulge, the most damage-sensitive epithelial component of the HF; 3) induction of mast cell degranulation; 4) attraction of potentially damaging perifollicular infiltrates of activated macrophages home in on the bulge, the site of HF epithelial stem cells, thus reflecting an immunoactivation.
      Furthermore, we show that most hair growth-inhibitory effects of stress can be imitated by the prototypic stress-related neuropeptide, SP, and, with respect to premature catagen onset, increased apoptosis and MHC class II+ cell infiltrates, can be counteracted effectively by co-administration of a specific SP receptor antagonist.
      To date, SP has been implicated in diverse pathophysiologies, especially diseases of the central nervous system, which have been examined in the greatest detail.
      • von Euler US
      • Gaddum JH
      An unidentified depressor substance in certain tissue extracts.
      • Raffa RB
      Possible role(s) of neurokinins in CNS development and neurodegenerative or other disorders.
      • Hokfelt T
      • Pernow B
      • Wahren J
      Substance P: a pioneer amongst neuropeptides.
      Although SP is best known as a pain-mediating neuropeptide, it also controls various behavioral, neurochemical, and cardiovascular responses to stress
      • Cao YQ
      • Mantyh PW
      • Carlson EJ
      • Gillespie AM
      • Epstein CJ
      • Basbaum AI
      Primary afferent tachykinins are required to experience moderate to intense pain.
      • De Felipe C
      • Herrero JF
      • O'Brien JA
      • Palmer JA
      • Doyle CA
      • Smith AJ
      • Laird JM
      • Belmonte C
      • Cervero F
      • Hunt SP
      Altered nociception, analgesia and aggression in mice lacking the receptor for substance P.
      • Hokfelt T
      • Pernow B
      • Wahren J
      Substance P: a pioneer amongst neuropeptides.
      • Grelot L
      • Dapzol J
      • Esteve E
      • Frugiere A
      • Bianchi AL
      • Sheldrick RL
      • Gardner CJ
      • Ward P
      Potent inhibition of both the acute and delayed emetic responses to cisplatin in piglets treated with GR205171, a novel highly selective tachykinin NK1 receptor antagonist.
      • Fukuda H
      • Koga T
      • Furukawa N
      • Nakamura E
      • Shiroshita Y
      The tachykinin NK1 receptor antagonist GR205171 prevents vagal stimulation-induced retching but not neuronal transmission from emetic vagal afferents to solitary nucleus neurons in dogs.
      • Onuoha GN
      • Alpar EK
      • Chukwulobelu R
      • Nicholls DP
      Distributions of VIP, substance P, neurokinin A and neurotensin in rat heart: an immunocytochemical study.
      and exerts a wide range of immunomodulating properties.
      • Hokfelt T
      • Pernow B
      • Wahren J
      Substance P: a pioneer amongst neuropeptides.
      • Agro A
      • Stanisz AM
      Neuroimmunomodulation: classical and non-classical cellular activation.
      • Singh VK
      Neuropeptides as native immune modulators.
      • McGillis JP
      • Mitsuhashi M
      • Payan DG
      Immunomodulation by tachykinin neuropeptides.
      The development of small molecule antagonists of the SP-preferring tachykinin NK1 receptor during the past decade
      • Gether U
      • Johansen TE
      • Snider RM
      • Lowe AJ
      • Nakanishi S
      • Schwartz TW
      Different binding epitope for substance P and the non-peptide antagonist, CP-96, 345, on the NK1 receptor.
      • Cotsarelis G
      • Cheng SZ
      • Dong G
      • Sun TT
      • Lavker RM
      Existence of slow-cycling limbal epithelial basal cells that can be preferentially stimulated to proliferate: implications on epithelial stem cells.
      offers an important opportunity to exploit these molecules as novel therapeutic agents for hair growth disorders. In addition, recent clinical trials have confirmed the efficacy of NK1 receptor antagonists to alleviate depression and emesis but, surprisingly, not pain.
      • Rupniak NM
      • Kramer MS
      Discovery of the antidepressant and anti-emetic efficacy of substance P receptor (NK1) antagonists.
      In the future, clinical trials, targeted to appropriate patient populations, ie, patients with telogen effluvium or alopecia areata, may establish the therapeutic potential of novel neuropeptide ligands in such hair growth disorders.
      In the present study we compared a well-established CBA/J mouse model for stress-related research (based on activation of the immune system and hypothalamo-pituitary-adrenal axis),
      • Clark DA
      • Banwatt D
      • Chaouat G
      Stress-triggered abortion in mice prevented by alloimmunization.
      • Arck PC
      • Merali FS
      • Stanisz AM
      • Stead RH
      • Chaouat G
      • Manuel J
      • Clark DA
      Stress-induced murine abortion associated with substance P-dependent alteration in cytokines in maternal uterine decidua.
      with the in hair research widely used mouse strain C57BL/6.
      • Maurer M
      • Handjiski B
      • Paus R
      Hair growth modulation by topical immunophilin ligands: induction of anagen, inhibition of massive catagen development, and relative protection from chemotherapy-induced alopecia.
      • Eichmüller S
      • van der Veen C
      • Moll I
      • Hermes B
      • Hofmann U
      • Müller-Röver S
      • Paus R
      Clusters of perifollicular macrophages in normal murine skin: physiological degeneration of selected hair follicles by programmed organ deletion.
      • Handjiski BK
      • Eichmuller S
      • Hofmann U
      • Czarnetzki BM
      • Paus R
      Alkaline phosphatase activity and localization during the murine hair cycle.
      • Paus R
      • Maurer M
      • Slominski A
      • Czarnetzki BM
      Mast cell involvement in murine hair growth.
      Published data indicate that different strains of mice react differently to various methods of stress application, ie, restraint stress affects C3H/HeJ, however, CBA/J or A/J mice proved resistant to restraint stress.
      • Clark DA
      • Banwatt D
      • Chaouat G
      Stress-triggered abortion in mice prevented by alloimmunization.
      By contrast, noise stress would affect CBA/J mice and C57BL/6 mice, both of which have been used in the present study.
      • Clark DA
      • Banwatt D
      • Chaouat G
      Stress-triggered abortion in mice prevented by alloimmunization.
      • Spehner V
      • De Wazieres B
      • Nicod L
      • Harraga S
      • Robert JF
      • Seilles E
      Auditory stress induces changes in membrane functions of mouse peritoneal macrophages.
      Comparing different strains in stress models, one might further question the hearing ability of the genetically different strains of mice, particularly when an audio stressor has been used. In our present study we observed that both strains, CBA/J and C57BL/6, showed high similarities in their response to stress/SP and skin immune environment. This is supported by published data indicating that C57BL/6 mice at the age of 6 weeks, as used in the present study, showed the same susceptibility to noise than CBA/J mice at the same age.
      • Ohlemiller KK
      • Wright JS
      • Heidbreder AF
      Vulnerability to noise-induced hearing loss in ‘middle-aged’ and young adult mice: a dose-response approach in CBA, C57BL, and BALB inbred strains.
      An important focus of research on stress-induced hair growth inhibition is to identify stress-vulnerable areas of the HF. One such area might be the residence of stem cell areas within the skin, because stem cells are vital for the homeostasis of self-renewing tissues and their manipulation may have wide-ranging consequences.
      • Cotsarelis G
      • Cheng SZ
      • Dong G
      • Sun TT
      • Lavker RM
      Existence of slow-cycling limbal epithelial basal cells that can be preferentially stimulated to proliferate: implications on epithelial stem cells.
      Rodent HF stem cells have been localized to the follicle bulge, whereas the location of human HF stem cells is less clear, and their characterization has been hampered by a lack of cellular markers for the bulge area.
      • Cotsarelis G
      • Cheng SZ
      • Dong G
      • Sun TT
      • Lavker RM
      Existence of slow-cycling limbal epithelial basal cells that can be preferentially stimulated to proliferate: implications on epithelial stem cells.
      These cells acquire the ability to produce a new hair.
      • Panteleyev AA
      • Jahoda CA
      • Christiano CA
      Hair follicle predetermination.
      The up-regulation of TUNEL+ cells in this key area of the HF, the bulge, by stress, as observed in the present study, is particularly striking because this region is one of the most sensitive targets for hair growth inhibitory agents and an abnormally high number of apoptotic cells in the epithelial stem cell region of the bulge carries the risk of permanent HF loss by programmed organ deletion.
      • Stenn KS
      • Paus R
      Controls of hair follicle cycling.
      • Eichmüller S
      • van der Veen C
      • Moll I
      • Hermes B
      • Hofmann U
      • Müller-Röver S
      • Paus R
      Clusters of perifollicular macrophages in normal murine skin: physiological degeneration of selected hair follicles by programmed organ deletion.
      This observation further supports our previously published data on increased signs of apoptosis in stressed mice with all HFs in resting telogen stage.
      • Arck PC
      • Handjiski B
      • Hagen E
      • Joachim R
      • Klapp BF
      • Paus R
      Indications for a ‘brain-hair follicle axis (BHA)’: inhibition of keratinocyte proliferation and up-regulation of keratinocyte apoptosis in telogen hair follicles by stress and substance P.
      Thus, we propose that such delicate area as the bulge region of the cycling HF is one key target for immune cells, particularly activated macrophages and mast cells, activated by systemic stress mediators and that have the potential to damage the HF morphology by up-regulation of apoptosis through the secretion of inflammatory cytokines, ie, tumor necrosis factor-α, interleukin-1β, and interferon-γ.
      • Yeh WC
      • Hakem R
      • Woo M
      • Mak TW
      Gene targeting in the analysis of mammalian apoptosis and TNF receptor superfamily signaling.
      • Totpal K
      • Singh S
      • Lapushin R
      • Aggarwal BB
      Qualitative and quantitative differences in the cellular responses mediated through Fas antigen and tumor necrosis factor.
      • Manna SK
      • Mukhopadhyay A
      • Aggarwal BB
      IFN-α suppresses activation of nuclear transcription factors NF-κB and activator protein 1 and potentiates TNF-induced apoptosis.
      • Ruckert R
      • Lindner G
      • Bulfone-Paus S
      • Paus R
      High-dose proinflammatory cytokines induce apoptosis of hair bulb keratinocytes in vivo.
      Longitudinal studies are now required to elucidate if a stress-triggered attack of HF stem cells would be associated with permanent or reversible hair growth inhibition. Further, based on our current data, we cannot differentiate whether the apoptotic cells in the bulge region are really stem cells or may be transient amplifying cells. Therefore we hope that the findings of the present study may foster research with label-retaining cells,
      • Wilson C
      • Cotsarelis G
      • Wei ZG
      • Fryer E
      • Margolis-Fryer J
      • Ostead M
      • Tokarek R
      • Sun TT
      • Lavker RM
      Cells within the bulge region of mouse hair follicle transiently proliferate during early anagen: heterogeneity and functional differences of various hair cycles.
      which would tell us whether we are dealing with stem cells or not.
      Clinical experience has long suggested that psychological factors play a role in triggering or exacerbating hair loss.
      • Selye H
      • Paus R
      Stress and the skin.
      • Williamson D
      • Gonzalez M
      • Finlay AY
      The effect of hair loss on quality of life.
      The present study now reports the first experimental evidence available in the literature that psychoemotional stress indeed negatively affects the cycling activity of HFs as well as their immune environment in vivo, thus strongly suggesting the concept that stress-induced hair loss is a clinical reality that should and can be treated. Once confirmed for the human system, the data presented here together with the recent emergence of NK1 antagonists as promising anti-depressants, SP receptor antagonists might serve a dual clinical role, ie, for alleviating both stress-induced hair loss itself, and secondary the depressive mood that comes with it.

      Acknowledgements

      We thank R. Pliet and P. Busse for their excellent technical assistance.

      References

        • Selye H
        The Physiology and Pathology of Exposure to Stress. Medical Publishers, ACTA Inc., Montreal1950: 727
        • Trepat L
        • Petre AJ
        ‘Pelada Universal por shock emotiva.’.
        Semana Méd. 1942; 1: 65
      1. Whitlock FA Rook A Psychophysiological aspects of skin disease. Major Problems in Dermatology. vol 8. Saunders, London1976
        • York J
        • Nicholson T
        • Minors P
        • Duncan DF
        Stressful life events and loss of hair among adult women, a case-control study.
        Psychol Rep. 1998; 82: 1044-1046
        • Garcia-Hernandez MJ
        • Ruiz-Doblado S
        • Rodriguez-Pichardo A
        • Camacho F
        Alopecia areata, stress and psychiatric disorders: a review.
        J Dermatol. 1999; 26: 625-662
        • Sinclair R
        Diffuse hair loss.
        Int J Dermatol. 1999; 38: 8-18
        • MacAlpine I
        Is alopecia areata psychosomatic? A psychiatric study.
        Br J Dermatol. 1958; 70: 117-131
        • Van der Steen P
        • Boezeman J
        • Duller P
        • Happle R
        Can alopecia areata be triggered by emotional stress? An uncontrolled evaluation of 178 patients with extensive hair loss.
        Acta Dermatol Venereol. 1992; 72: 279-280
        • Russiello F
        • Arciero G
        • Decaminada F
        • Corona R
        • Ferrigno L
        • Fucci M
        • Pasquini M
        • Pasquini P
        Stress, attachment and skin disease: a case-control study.
        J Eur Acad Dermatol Venereol. 1995; 5: 234-239
        • Chrousos GP
        Stressors, stress, and neuroendocrine integration of the adaptive response. The 1997 Hans Selye Memorial Lecture.
        Ann NY Acad Sci. 1998; 851: 311-335
        • Paus R
        • Cotsarelis G
        The biology of hair follicles.
        N Engl J Med. 1999; 341: 491-497
        • Arck PC
        • Handjiski B
        • Hagen E
        • Joachim R
        • Klapp BF
        • Paus R
        Indications for a ‘brain-hair follicle axis (BHA)’: inhibition of keratinocyte proliferation and up-regulation of keratinocyte apoptosis in telogen hair follicles by stress and substance P.
        FASEB J. 2001; 5: 2536-2538
        • Chase HB
        Physical factors which influence the growth of hair.
        in: Montagna W Ellis RA The Biology of Hair Growth. Academic Press, New York1953: 435-440
        • Maurer M
        • Handjiski B
        • Paus R
        Hair growth modulation by topical immunophilin ligands: induction of anagen, inhibition of massive catagen development, and relative protection from chemotherapy-induced alopecia.
        Am J Pathol. 1997; 150: 1433-1441
        • Stenn KS
        • Paus R
        Controls of hair follicle cycling.
        Physiol Rev. 2001; 81: 449-494
        • Clark DA
        • Banwatt D
        • Chaouat G
        Stress-triggered abortion in mice prevented by alloimmunization.
        Am J Reprod Immunol. 1993; 29: 141-147
      2. Aoki E, Shibasaki T, Kawana S: Intermittent foot shock stress prolongs the telogen stage in the hair cycle of mice. Exp Dermatol, in press

        • Daly TJ
        Alopecia areata has low plasma levels of the vasodilator/immunomodulator calcitonin gene-related peptide.
        Arch Dermatol. 1998; 134: 1164-1165
        • Paus R
        • Heinzelmann T
        • Schultz KD
        • Furkert J
        • Fechner K
        • Czarnetzki BM
        Hair growth induction by substance P.
        Lab Invest. 1994; 71: 134-140
        • Peters EM
        • Botchkarev VA
        • Botchkareva NV
        • Tobin DJ
        • Paus R
        Hair-cycle-associated remodeling of the peptidergic innervation of murine skin, and hair growth modulation by neuropeptides.
        J Invest Dermatol. 2001; 116: 236-245
        • von Euler US
        • Gaddum JH
        An unidentified depressor substance in certain tissue extracts.
        J Physiol. 1931; 72: 74-87
        • Rathsack R
        • Oehme P
        • Roske I
        • Hilse H
        Substance P-like immunoreactivity in plasma and adrenal medulla of rats with spontaneous hypertension and WKY rats under acute stress.
        Biomed Biochim Acta. 1983; 42: 955-958
        • Arck PC
        • Merali FS
        • Stanisz AM
        • Stead RH
        • Chaouat G
        • Manuel J
        • Clark DA
        Stress-induced murine abortion associated with substance P-dependent alteration in cytokines in maternal uterine decidua.
        Biol Reprod. 1995; 53: 814-819
        • Zhu GF
        • Chancellor-Freeland C
        • Berman AS
        • Kage R
        • Leeman SE
        • Beller DI
        • Black PH
        Endogenous substance P mediates cold water stress-induced increase in interleukin-6 secretion from peritoneal macrophages.
        J Neurosci. 1996; 16: 3745-3752
        • Vaupel R
        • Jarry H
        • Schlomer HT
        • Wuttke W
        Differential response of substance P-containing subtypes of adrenomedullary cells to different stressors.
        Endocrinology. 1998; 23: 2140-2145
        • Cao YQ
        • Mantyh PW
        • Carlson EJ
        • Gillespie AM
        • Epstein CJ
        • Basbaum AI
        Primary afferent tachykinins are required to experience moderate to intense pain.
        Nature. 1998; 392: 390-394
        • De Felipe C
        • Herrero JF
        • O'Brien JA
        • Palmer JA
        • Doyle CA
        • Smith AJ
        • Laird JM
        • Belmonte C
        • Cervero F
        • Hunt SP
        Altered nociception, analgesia and aggression in mice lacking the receptor for substance P.
        Nature. 1998; 392: 394-397
        • Teichberg VI
        • Cohen S
        • Blumberg S
        Distinct classes of substance P receptors revealed by a comparison of the activities of substance P and some of its segments.
        Regul Pept. 1981; 1: 327-333
        • Lee C-M
        • Iversen LL
        • Hanley MR
        • Sandberg BEB
        The possible existence of multiple receptors for substance P.
        Naunyn-Schmiedeberg's Arch Pharmacol. 1982; 318: 281-287
        • Buck SH
        • Burcher E
        The tachykinins: a family of peptides with a brood of receptors.
        Trends Pharmacol Sci. 1986; 7: 65-68
        • Nakanishi S
        Mammalian tachykinin receptors.
        Annu Rev Neurosci. 1991; 14: 123-136
        • Gether U
        • Johansen TE
        • Snider RM
        • Lowe AJ
        • Nakanishi S
        • Schwartz TW
        Different binding epitope for substance P and the non-peptide antagonist, CP-96, 345, on the NK1 receptor.
        Nature. 1993; 362: 345-348
        • Folkers K
        • Hörig J
        • Rosell S
        • Björkroth U
        Chemical design of antagonists of substance P.
        Acta Physiol Scand. 1981; 111: 505-506
        • Wang ZY
        • Tung SR
        • Strichartz GR
        • Håkanson R
        Investigation of the specificity of FK 888 as a tachykinin NK1 receptor antagonist.
        Br J Pharmacol. 1994; 111: 1342-1346
        • Garret C
        • Carruette A
        • Fardin V
        • Moussaoui S
        • Peyronel JF
        • Blanchard JC
        • Laduron PM
        Pharmacological properties of a potent and selective nonpeptide substance P antagonist.
        Proc Natl Acad Sci. 1991; 88: 10208-10212
        • Snider RM
        • Constantine JW
        • Lowe III, JA
        • Longo KP
        • Lebel WS
        • Woody HA
        • Drozda SE
        • Desai MC
        • Vinick FJ
        • Spencer RW
        A potent nonpeptide antagonist of the substance P (NK1) receptor.
        Science. 1991; 251: 435-437
        • Betancur C
        • Azzi M
        • Rostène W
        Nonpeptide antagonists of neuropeptide receptors: tools for research and therapy.
        Trends Physiol Sci. 1997; 18: 372-386
        • Müller-Röver S
        • Handjiski B
        • van der Veen C
        • Eichmuller S
        • Foitzik K
        • McKay IA
        • Stenn KS
        • Paus R
        A comprehensive guide for the accurate classification of murine hair follicles in distinct hair cycle stages.
        J Invest Dermatol. 2001; 117: 3-15
        • Maurer M
        • Paus R
        • Czarnetzki BM
        Mast cells as modulators of hair follicle cycling.
        Exp Dermatol. 1995; 4: 266-271
        • Eichmüller S
        • van der Veen C
        • Moll I
        • Hermes B
        • Hofmann U
        • Müller-Röver S
        • Paus R
        Clusters of perifollicular macrophages in normal murine skin: physiological degeneration of selected hair follicles by programmed organ deletion.
        J Histochem Cytochem. 1998; 46: 361-370
        • Handjiski BK
        • Eichmuller S
        • Hofmann U
        • Czarnetzki BM
        • Paus R
        Alkaline phosphatase activity and localization during the murine hair cycle.
        Br J Dermatol. 1994; 131: 303-310
        • Ljungberg A
        • Johansson O
        Methodological aspects on immunohistochemistry in dermatology with special reference to neuronal markers.
        Histochem J. 1993; 25: 735-745
        • Botchkarev VA
        • Eichmüller S
        • Johansson O
        • Paus R
        Hair cycle-dependent plasticity of skin and hair follicle innervation in normal murine skin.
        J Comp Neurol. 1997; 386: 379-395
        • Botchkarev VA
        • Eichmuller S
        • Peters EM
        • Pietsch P
        • Johansson O
        • Maurer M
        • Paus R
        A simple immunofluorescence technique for simultaneous visualization of mast cells and nerve fibers reveals selectivity and hair cycle-dependent changes in mast cell-nerve fiber contacts in murine skin.
        Arch Dermatol Res. 1997; 289: 292-302
        • Paus R
        • Peters EM
        • Eichmüller S
        • Botchkarev VA
        Neural mechanisms of hair growth control.
        J Invest Dermatol Symp Proc. 1997; 2: 61-68
        • Peters EM
        • Botchkarev VA
        • Botchkareva NV
        • Tobin DJ
        • Paus R
        Hair-cycle-associated remodeling of the peptidergic innervation of murine skin, and hair growth modulation by neuropeptides.
        J Invest Dermatol. 2001; 116: 236-245
        • Paus R
        • Maurer M
        • Slominski A
        • Czarnetzki BM
        Mast cell involvement in murine hair growth.
        Dev Biol. 1994; 163: 230-240
        • Lindner G
        • Botchkarev VA
        • Botchkareva NV
        • Ling G
        • van der Veen C
        • Paus R
        Analysis of apoptosis during hair follicle regression.
        Am J Pathol. 1997; 151: 1601-1617
        • Cotsarelis G
        • Cheng SZ
        • Dong G
        • Sun TT
        • Lavker RM
        Existence of slow-cycling limbal epithelial basal cells that can be preferentially stimulated to proliferate: implications on epithelial stem cells.
        Cell. 1989; 57: 201-209
        • Lavker RM
        • Miller S
        • Wilson C
        • Cotsarelis G
        • Wei ZG
        • Yang JS
        • Sun TT
        Hair follicle stem cells: their location, role in hair cycle, and involvement in skin tumor formation.
        J Invest Dermatol. 1993; 101: 16S-26S
        • Bienenstock J
        • Denburg J
        • Scicchitano R
        • Stead R
        • Perdue M
        • Stanisz A
        Role of neuropeptides, nerves and mast cells in intestinal immunity and physiology.
        Monogr Allergy. 1988; 24: 134-143
        • Williams RH
        • Bienenstock J
        • Stead RH
        Mast cells—the neuroimmune connection.
        Chem Immunol. 1995; 61: 208-251
        • Theoharides TC
        • Singh LK
        • Boucher W
        • Pang X
        • Letourneau R
        • Webster E
        • Chrousos G
        Corticotropin-releasing hormone induces skin mast cell degranulation and increased vascular permeability, a possible explanation for its proinflammatory effects.
        Endocrinology. 1998; 139: 403-413
        • Raffa RB
        Possible role(s) of neurokinins in CNS development and neurodegenerative or other disorders.
        Neurosci Biobehav Rev. 1998; 22: 789-813
        • Hokfelt T
        • Pernow B
        • Wahren J
        Substance P: a pioneer amongst neuropeptides.
        J Intern Med. 2001; 249: 27-40
        • Grelot L
        • Dapzol J
        • Esteve E
        • Frugiere A
        • Bianchi AL
        • Sheldrick RL
        • Gardner CJ
        • Ward P
        Potent inhibition of both the acute and delayed emetic responses to cisplatin in piglets treated with GR205171, a novel highly selective tachykinin NK1 receptor antagonist.
        Br J Pharmacol. 1998; 124: 1643-1650
        • Fukuda H
        • Koga T
        • Furukawa N
        • Nakamura E
        • Shiroshita Y
        The tachykinin NK1 receptor antagonist GR205171 prevents vagal stimulation-induced retching but not neuronal transmission from emetic vagal afferents to solitary nucleus neurons in dogs.
        Brain Res. 1998; 802: 221-231
        • Onuoha GN
        • Alpar EK
        • Chukwulobelu R
        • Nicholls DP
        Distributions of VIP, substance P, neurokinin A and neurotensin in rat heart: an immunocytochemical study.
        Neuropeptides. 1999; 33: 19-25
        • Agro A
        • Stanisz AM
        Neuroimmunomodulation: classical and non-classical cellular activation.
        Adv Neuroimmunol. 1995; 5: 311-319
        • Singh VK
        Neuropeptides as native immune modulators.
        Prog Drug Res. 1995; 45: 9-31
        • McGillis JP
        • Mitsuhashi M
        • Payan DG
        Immunomodulation by tachykinin neuropeptides.
        Ann NY Acad Sci. 1990; 594: 85-94
        • Rupniak NM
        • Kramer MS
        Discovery of the antidepressant and anti-emetic efficacy of substance P receptor (NK1) antagonists.
        Trends Pharmacol Sci. 1999; 20: 485-490
        • Spehner V
        • De Wazieres B
        • Nicod L
        • Harraga S
        • Robert JF
        • Seilles E
        Auditory stress induces changes in membrane functions of mouse peritoneal macrophages.
        Scand J Immunol. 1996; 44: 643-647
        • Ohlemiller KK
        • Wright JS
        • Heidbreder AF
        Vulnerability to noise-induced hearing loss in ‘middle-aged’ and young adult mice: a dose-response approach in CBA, C57BL, and BALB inbred strains.
        Hear Res. 2000; 149: 239-247
        • Panteleyev AA
        • Jahoda CA
        • Christiano CA
        Hair follicle predetermination.
        J Cell Sci. 2001; 114: 3419-3431
        • Yeh WC
        • Hakem R
        • Woo M
        • Mak TW
        Gene targeting in the analysis of mammalian apoptosis and TNF receptor superfamily signaling.
        Immunol Rev. 1999; 169: 283-302
        • Totpal K
        • Singh S
        • Lapushin R
        • Aggarwal BB
        Qualitative and quantitative differences in the cellular responses mediated through Fas antigen and tumor necrosis factor.
        J Interferon Cytokine Res. 1996; 16: 259-267
        • Manna SK
        • Mukhopadhyay A
        • Aggarwal BB
        IFN-α suppresses activation of nuclear transcription factors NF-κB and activator protein 1 and potentiates TNF-induced apoptosis.
        J Immunol. 2000; 165: 4927-4934
        • Ruckert R
        • Lindner G
        • Bulfone-Paus S
        • Paus R
        High-dose proinflammatory cytokines induce apoptosis of hair bulb keratinocytes in vivo.
        Br J Dermatol. 2000; 143: 1036-1039
        • Wilson C
        • Cotsarelis G
        • Wei ZG
        • Fryer E
        • Margolis-Fryer J
        • Ostead M
        • Tokarek R
        • Sun TT
        • Lavker RM
        Cells within the bulge region of mouse hair follicle transiently proliferate during early anagen: heterogeneity and functional differences of various hair cycles.
        Differentiation. 1994; 55: 127-136
        • Paus R
        Stress and the skin.
        Exp Dermatol. 2001; 10: 367
        • Williamson D
        • Gonzalez M
        • Finlay AY
        The effect of hair loss on quality of life.
        J Eur Acad Dermatol Venereol. 2000; 15: 137-139