Anagen Phase Research Articles

Histochemistry of the human hair follicle with consideration of anagen phases I to VI.

The hair follicle is composed of different epithelial layers under participation of mesenchymal and nerval factors. The present study is an attempt to localize differentiation and functional markers in the human hair follicle during anagen phases I to VI. Monoclonal antibody K 8.12 against keratins 13 and 16 showed an increasing reactivity with certain types of the follicle epithelia during anagen I to VI. Ki67 was expressed within the innermost layer of the outer hair root sheath. Scattered Ki67-positive matrix cells could be additionally identified during anagen V and VI but were absent in anagen I to IV. During anagen Merkel cells became more abundant in the bulbar area. Neuropeptide-like immunoreactivity expressed by bulbar (especially matrix) cells were evenly seen during the early anagen I and II. The findings are in favour of a neurohumoral modulatory role during anagen phases accompanied by an increase of expression of certain proliferation-associated antigens like keratin 16 and Ki67 among the complex epithelia of human hair follicles.

Investigation of germinative cells in generating and renewed anagen hair apparatus in mice using anti-bromodeoxyuridine monoclonal antibody

To elucidate the cell kinetics in generating and renewed anagen hair apparatus in mice, S-phase cells in dorsal skin of new-born and 14 to 25-day-old mice were labeled with bromodeoxyuridine (BrdU) and stained immunohistochemically using anti-BrdU monoclonal antibody. In primary hair germ, lower and outer cells were positively stained. In hair peg, the positive cells were divided into upper and lower portions. In bulbous hair peg, the lower positive cells gathered at the suprapapillary area, whereas the upper positive cells were located in the outer part of the hair apparatus. The latter positive cells were further divided in the middle and upper parts of the epithelial cord. The upper cells were going to form a sebaceous gland. From the suprapapillary group of germinative cells, hair cortex through the innermost cell layer of the outer root sheath were considered to be produced. The positive cells of the outer middle group may be important for elongation of hair apparatus and produce outer root sheath cells. At the end of anagen phase, first the suprapapillary cells became negative and then the outer root sheath cells became negative. BrdU-positive cells reappeared at the bottom of telogen hair apparatus and formed a secondary hair germ. Then, a similar cell kinetics was repeated in the renewed anagen hair apparatus. The germinative cells were separated into a few groups during the generation and cyclic changes of hair apparatus. Each cell group formed the individual part of the hair apparatus in a coordinate fashion, resulting in dynamic changes of the hair apparatus.

Adenohypophysitis Associated with Sebaceous Gland Atrophy in a Dog

Sebaceo us adeniti s is a granulomatous or pyogranul ornatous dermatitis with inflammation located around sebaceous glands. In chronic cases, these gland s are replaced by fibrous connective tissue} Many breeds of dogs have been affected , but adult Standa rd Poodles, Sam oyeds, Vizlas, and Akitas are appare ntly predisposed.' Etiologic facto rs are unknown. Seconda ry pyoderma is often a complicati ng factor. Sebaceous aden itis should be considered in the different ial diagnosis of dogs with seborrhea sicca that is unresponsive to medic al therap y.' A 9-year-old, castrated male Samoyed dog was euthanatized and presented to the Colorado Stat e University Veterinary Teaching Hospital for necropsy. It had a 3-year history of a generalized derm at itis and blepharitis that was unresponsive to conventional medical therapy. Serologic and endocrine function tests were never performed. Th e entire hair coat was thin, and the skin was rough, dry, and scaly. Th ere was partial alopecia and crusting of the eyelids . Th e externa l ear canal s were dirty and scaly. A postmort em examination of the abdomen, thorax, and brain revca led no other gross lesions. Th e tissues that were examined histologically were multiple areas of trun cal skin, external auditory canal, upper and lower eyelids, nictitating membrane, th yroid , adrenal, hypophysis, and both eyes. Sebaceo us gland s were absent in all areas ofskin examined. Dorsal thoracic and dorsal lumbar skin had mild to moderate epidermal and follicular orthoke ratotic hyperkeratosis and moderate infiltrat ion aro und hair follicles by lymph ocytes and plasma cells (Fig. I). Ove r 150 sections from one sample of skin were cut and examined. No sebaceo us glands were found in any section. Focal areas of epidermis were mi ldly acanthotic, varying from two to five cell layers thi ck. Sma ll numbers of lymphocytes and plasma cells were scatt ered in the papillary derm is. Hair follicles were in catagen and anagen phases. Apocrine sweat glands were moderately dilated and were often surro unded by a Iymp hoplasmacytic infiltra te. Changes in ventral thoracic skin were simi lar but less pronoun ced. Hair follicles in an externa l auditory canal were hyperkeratotic. Ceruminous glands and hair follicles were surro unded by lymphocytes and lesser numbers of macroph ages, fibroblasts , and a few neutrophils. As in the skin , sebaceous glands were absent. Epith elium of an upp er eyelid was acanthotic and had parakerat otic hyperkeratosis. A superficial crust consisted of keratin debris and neut roph ils. Hair follicles were plugged with kera tin and often con tained neutrophils. Heavy infiltrations of lymphocytes, plasma cells, and macrophages surrounded hair follicles and the tubul ar gland s of Moll. Tarsal glands , which are modified sebaceous glands, were absent. Th e nictit at ing membrane contained a normal am ount of tubular lacrimal gland s with sma ll interstitial accumulations of plasma cells. Th ere were dense accumulatio ns of plasma cells in the subconjunctiva. The zona fasciculata and zona reticularis of an ad renal gland were j udged subjective ly to be thickened in relation to the zona glomeru losa and the medu lla. Examination of thyroid gland revealed no microscop ic abnormalities. Th e eyes had no microscopic lesions. In the adenohypophysis, multiple, large foci contained a Iymph oplasmacytic infiltrate and scattere d cells that were either chro mophobic pitu itary cells, which they closely resembled, or macroph ages. Th ese cells had vesicular , sometim es indented nuclei, and indi stin ct cytoplasm. Acidophilic and basophilic cells were greatly decreased or absent in the inflam ed areas (Fig. 2). Th ere was a pale, eosinophilic, loose, fibrillar matrix in affected foci. A Masson 's trichrome-stained sectio n failed to reveal an increase d amo unt ofcollagen. The neurohypoph ysis was not affected. Sebaceo us glands are normally present in all regions of haired skin.' Th e history, signalment, distribution of skin lesions , and absence of sebaceous gland s in thi s case are compatible with chronic or end-s tage sebaceous adenitis of dogs.'> In contrast to those cases of sebaceous adeniti s previously described in the literatu re, the dermatitis in thi s dog was not granulomato us. It is possible that the leukocytic infiltrate was modified as the sebaceo us glands disapp eared. It is also possible that thi s case represent s a non-granulomatous variant of the disease syndrome.

Hair anatomy for the clinician

The rational evaluation of hair disorders requires familiarity with follicular anatomy. Hair structure can be easily examined by studying clipped hair shafts, entire hairs gently pulled or forcibly plucked from the scalp, and scalp biopsies (sectioned vertically or transversely). Anatomic features will be different depending on whether a given hair is in the anagen, catagen, or telogen phase. Follicle size will also vary, from the minute vellus hair to the long, thick terminal hair. Each follicle can be divided into distinct regions--bulb, suprabulbar zone, isthmus, and infundibulum. Activity growing (anagen) hairs are characterized by a hair matrix surrounding a dermal papilla; inner and outer root sheaths are present and well developed. A catagen hair can be identified by its markedly thickened vitreous layer and fibrous root sheath, which surrounds an epithelial column; above this column, the presumptive club forms. A telogen hair is distinguished by its fully keratinized club, which is surrounded by an epithelial sac. Below this lies the secondary hair germ and condensed dermal papilla, waiting for the mysterious signal that initiates a new life cycle.

Topical cyclosporin induces hair growth in human split skin grafted onto nude mice.

Previously we observed that systemic CyA induces hair growth in an experimental model of human scalp skin graft transplanted onto nude mice. In the present study we investigated the role of topical CyA in the murine transplantation model, using human split-thickness skin grafts (HSTSG). Ten mice grafted with 1-mm-thick skin and another 10 mice grafted with 0.4-mm-thick skin were treated topically with CyA in olive oil. Ten other mice, treated with olive oil only, served as a control group. At the end of the study we observed hair growth only on the grafted skin of the CyA-treated group. Four out of 10 grafts showed hair growth in each of the groups. Quantitative analysis of transverse sections of cylindrical punch biopsy specimens of HSTSG before transplantation revealed anagen follicles, including small ones and telogen/catagen follicles, whereas specimens after skin transplantation showed terminal follicles mostly in the anagen phase. The present study provides further support to previous observations regarding the beneficial effect of CyA on hair growth.

Direct analyses of in vivo colony survival after single and fractionated doses of radiation.

Several methods are described for analysing the results of in vivo colony assays using the statistical procedure called maximum-likelihood analysis. The methods differ in the way in which they take into account possible sources of variability in the data. The methods described here for analysing microcolony data are direct methods, in that they use the observed colony counts rather than transformed (e.g. Poisson-corrected) data. Each method can be used to estimate the average number of surviving cells per tissue structure (e.g. per jejunal crypt) in a single dose group, together with 95% confidence intervals, or to fit cell-survival models to data from a range of dose groups (e.g. to obtain estimates of D0 or of the linear-quadratic parameters alpha and beta). Experimental microcolony data from murine jejunum, colon, and hair follicles irradiated in anagen (proliferative) or telogen (resting) phase have been analysed. Estimates of D0 have been derived from single-dose data and estimates of alpha, beta, and the initial number of clonogenic cells per structure have been derived from fractionation data. For hair follicles, the half-time of repair of sublethal radiation injury has also been derived from fractionation data.

Cell kinetic study of human and mouse hair tissues using anti-bromodeoxyuridine monoclonal antibody

To determine sites of cell proliferation in hair tissues, in vitro and in vivo labeling with bromodeoxyuridine (BrdU) and immunohistochemical demonstration of BrdU incorporation sites by anti-BrdU monoclonal antibody were performed on human and mouse hairs and hair follicles. The germinative area of the hair bulb of human anagen hair was divided into three portions: (A) the upper and inner protion, (B) the middle portion and (C) the lowest outer portion. A-cells intermingled with melanocytes, were regarded as germinative cells of the hair cortex. B-cells appeared to develop into Huxley's layer, cuticle of inner roct sheath (IRS), and hair cuticle. C-cells seemed to develop into bulbar outer root sheath (ORS), the innermost cell (IMC) layer of the ORS and Henle's layer. The suprabulbar portion, where the ORS abruptly increased in thickness, was found to be the fourth main germinative portion (D). The ORS cells, except for the IMCs, seemed to originate mostly from the D-cells. In the late anagen phase, first, C-cells became BrdU negative, then, A- and B-cells gradually turned negative, and finally, D-cells lost their germinative activity. In catagen and telogen hair tissues, BrdU-positive cells were found in the two outer cell layers in the ORS. The structure of anagen hair tissues seems to be maintained by the coordinated mitotic activities of characteristically distribated germinative cells of various hair cell layers. The sequential cessation of mitotic activity of these cells is associated with the morphological changes from anagen through catagen to telogen. These findings were common to both human and mouse hair tissues.

Hair-specific expression of chloramphenicol acetyltransferase in transgenic mice under the control of an ultra-high-sulfur keratin promoter.

We have generated a transgenic mouse line by microinjection of a chimeric DNA fragment (KER-CAT) containing a hair-specific, murine ultra-high-sulfur keratin promoter (KER) fused to the coding region of the bacterial chloramphenicol acetyltransferase (CAT) gene. A 671-base pair (bp) stretch of the 5' promoter region was used to direct the expression of the CAT gene in this construct. Of the tissues tested for CAT activity in these transgenic animals only skin with growing hair, isolated hair follicles, and microdissected vibrissae showed substantial levels of activity. These are the same tissues where the endogenous ultra-high-sulfur keratin gene is expressed as shown by in situ hybridization. Furthermore, analysis of the CAT activity during the developmental stages of the hair growth cycle shows that the chimeric gene is expressed during the anagen phase of the hair growth cycle; this is the expected time during development for its expression. From these results we conclude that 671 bp of the promoter sequence from the ultra-high-sulfur keratin gene is sufficient to direct the correct development-specific and tissue-specific expression of the reporter gene construct in transgenic mice. The appropriate expression of the KER-CAT construct in transgenic mice is an important step in understanding the regulation of this gene during hair organogenesis.

Angiogenic Activity is Defective in Monocytes from Patients with Alopecia Universalis

Monocyte/macrophages are important components of cell-mediated immune responses in presentation of antigen, as regulators of lymphocyte function, and as sources of cytokines that modulate functions of cells other than those of the immune system. Their role in the pathogenesis of alopecia areata (AA) and universalis (AU) has not been explored. This study is an investigation of the function of peripheral blood monocytes from normal subjects and patients with AA, AU, and alopecia totalis (AT), with respect to the principal macrophage-derived angiogenic factor, tumor necrosis factor alpha (TNF alpha). Because neovascularization is a necessary component in the anagen phase of hair growth and may play a role in the pathology of these disorders, we asked whether monocyte/macrophage angiogenic activity was compromised in these alopecias. Purified preparations of monocytes were activated in culture. Conditioned media were assessed for angiogenic activity on the chick chorioallantoic membrane and for concentration of TNF alpha by enzyme-linked immunosorbent assay (ELISA). Both angiogenic and the TNF concentration were significantly diminished in conditioned media from AU monocytes when compared to those from normal subjects and patients with AA. These results show that the function of AU monocytes may be abnormal and that the abnormality may distinguish AU from AA. Defective monocyte/macrophage function could also play a pathogenic role via effects on neovascularization and/or modulation of the immune response.

The effects of topical diazoxide on hair follicular growth and physiology of the stumptailed macaque

Diazoxide, an anti-hypertensive agent, has diverse pharmacologic effects; hypertrichosis, hyperglycemia associated with suppression of insulin release, and elevation of serum levels of androgens. Taking advantage of the hypertrichotic side effects of diazoxide, we examined the effect of topical application of the drug on hair regrowth in the bald frontal scalp of stumptailed macaques ( Macaca arctoides); we also monitored systemic side effects. Using 7 adult stumptails, we applied diazoxide (5% solution in a vehicle) topically on the bald frontal scalp, once a day, 5 days per week. Two of seven macaques had vehicle alone applied. Hair growth was monitored by photographic recording (once every month) and by sequential analysis of folliculograms from biopsied skin (once every 4 months). We also examined body weight, hematology, blood pressure, heart rate, serum levels of testosierone and dihydrotestosterone, and glucose tolerance for a 4-month period. All 5 diazoxide-treated animals showed thickening and maintenance of the frontal hair during the entire treatment period (16 months). Analysis of folliculograms showed progressive enlargement of hair follicular size and acceleration of its cyclic growth from telogen to anagen phase and prolongation of anagen phase in all treated animals. Controls showed no consistent progressive changes of follicular growth. None of the animals treated with diazoxide showed abnormal changes in physical growth, cardiovascular function, serum levels of androgens, glucose tolerance (including insulin levels), or hematology.

The Effect of Topical Minoxidil on Hair Follicular Cycles of Rats

To explore an easily accessible and reproducible model for examining the effect of minoxidil on hair growth, we studied the effect of minoxidil on the natural hair cycles of rats from birth to 80 days of age. During the 1st and 2nd postnatal cycles, the hair follicles grew very rapidly and the size of anagen follicles were markedly enlarged. In the 3rd cycle (50 days to approximately 100 days of age), duration of the telogen phase lasted approximately 20 days. Topical minoxidil, 1%, 3%, or 5% solution, applied on the backs of the rats from 23 days (weaning) to 80 days, induced a remarkable shortening of the telogen phase in the 3rd cycle. Although the dose-dependent response was very minimal, rats treated with 3% or 5% minoxidil showed similar effects in the 4th cycle. Minoxidil, however, did not induce prolongation of the anagen phase, but increased the rate of DNA synthesis in the anagen bulb during the 2nd and 3rd cycles. These results suggest that minoxidil specifically stimulates the secondary germ of the telogen follicles, resulting in rapid progression to anagen follicles.

Differential Expression of the 4F2 Activation Antigen on Human Follicular Epithelium in Hair Cycle

The expression of the 4F2 activation molecule has been studied on keratinocytes of human skin and hair follicle using immunoperoxidase staining with three different anti-4F2 monoclonal antibodies. Membranes of basal layer keratinocytes of the skin uniformly expressed this antigen, whereas a differential expression of this antigen was located in specific areas of the hair follicle. Follicles in the complete anagen phase displayed a strong 4F2 positive staining at the matrix and the outer root sheath cells. This positive staining gradually decreased along the proliferation zone, and became negative at the migration zone. Positivity was recovered in follicular cells at the duct of the sebaceous gland and was maintained in the upper outer root sheath where those cells fuse with the keratinocyte basal monolayer. Changes were also detected on different phases of the hair cycle. Follicles in the catagen-telogen phase expressed a very low number of positive cells in the matrix. Positive labeling progressively increased when the follicle was at the initial anagen stage, reaching a complete staining pattern in hair at the anagen phase. These results suggest that the expression of this activation antigen on hair keratinocytes may be related to the proliferation, active metabolism, and/or activation states of these cell types.

The stumptailed macaque as a model for androgenetic alopecia: Effects of topical minoxidil analyzed by use of the folliculogram

The use of the stumptailed macaque, which possesses hereditary balding characteristics similar in many respects to that of androgenetic alopecia in humans, enables us to obtain a morphometric assessment of the rate of cyclic change of the hair follicle. The analysis of folliculograms results in data that can determine the rate of cyclic progression (resting to regrowing phase, and regrowing to late anagen phase) and the overall change in follicular size. Topical minoxidil apparently activates the resting follicles in the bald scalp and stimulates their cyclic progression. It also increases DNA synthesis, resulting in relative enlargement of the growing anagen follicles. All minoxidil-treated animals had hair regrowth, although in varying degrees of restoration to the prebald condition and after varying durations of treatment. In general, the response was greater in the younger, early-bald stumptailed macaques compared with the older, advancedbald animals. The degree of response varied from regrowth of thicker, darker hairs over the entire bald area, with folliculograms showing corresponding large proportions of late anagen follicles, to the arresting of the balding process, with folliculograms showing maintenance of moderate populations of anagen follicles. Cessation of topical minoxidil treatment resulted in a renewal of the balding process, with folliculograms demonstrating increases in the proportion of resting follicles. This withdrawal from treatment apparently had no effect on hair regrowth during subsequent reapplications of minoxidil. Such treatment resulted in regrowth similar to that in the first treatment phase. Continuous treatment of topical minoxidil for 4 years has not resulted in systemic or local side effects in these animals.

Retinoids: Compounds important to hair growth

Although the mechanisms of follicular regression in androgenetic alopecia are not fully understood, retinoids may be important in changing the status of regressing follicles. There are many reports documenting reversal of epithelial dysplastic changes with retinoids. 13–18 Although none of the studies with retinoids have concentrated on the precise mechanisms of follicular growth (regression or regeneration), these limited observations1plt12 and our early studies2 suggest that further work should be done on the effect retinoids have on the hair follicle during the various growth and regression phases of the follicular life cycle in humans.We propose that certain retinoids increase the rate of hair growth, prolong the anagen phase of the hair cycle, play a role in converting vellus to terminal hairs, and act synergistically with minoxidil to produce more dense hair regrowth from regressing follicles than either compound alone. Larger controlled studies and better methods for assessing hair growth are necessary to support these early results, Other retinoids as well as certain minoxidil analogs should also be studied.

Hair Growth Induction by Ultraviolet Radiation in the Marsupial Monodelphis domestica

Hair follicles in the telogen stage of the hair cycle were induced into anagen phase after the skin of the South American opossum, Monodelphis domestica, was exposed to levels of ultraviolet B radiation (280 to 320 nm), which induced desquamation. Post-ultraviolet B exposure to long-wavelength radiation (320 to 400 nm, ultraviolet A) suppressed the induction of edema and desquamation and the induction of hair growth. Hair growth induction was also observed in skin damaged either by mechanical abrasion or by exposure to methoxsalen and ultraviolet A.

Seasonal moulting patterns in three fur bearing mammals: the European badger (Meles meles L.), the red fox (Vulpes vulpes L.), and the mink (Mustela vison). A morphological and histological study

Seasonal changes in the fur of three species of mammals at the adult stage, the European badger, the red fox, and the mink, were studied in the field. The badger had only one seasonal change of pelage during the summer and the fall (from July to December), and there was no seasonal variation of hair density. The fox moulted in the spring (between the end of April and the end of August) and again in the fall, but the fall change consisted only in the regrowth of a new fine undercoat that combined with the summer fur to form a denser winter coat. In the mink, the spring and fall moults were very distinct and gave rise to characteristic summer and winter coats that differed in density and number of fine hairs per surface unit. The histological study revealed a similarity in skin composition among the three species, but the relative importance of the different components (sebaceous glands, adipose tissue, keratine layer) varied with each species' way of life. Seasonal follicular activity was correlated with seasonal regrowth of the pelage; the active anagen phase was very long (badger, 5 months; fox, 4 months; mink, 2 months in the spring and 3 months in the fall). During the other part of the annual cycle, telogen, the hair follicles were in a resting phase. Differences in the annual moulting processes between the three species are discussed in terms of adaptive characteristics.[Journal translation]

8 Hair follicles and associated glands as androgen targets

The growth of hair, except that on the scalp, and the secretion of sebum are, in general, under the major influence of androgens. However, the responses of the hair follicles and their associated glands vary greatly between sites and between individuals. On the face, trunk and extremities the most important role of testosterone is to increase the period of activity, the anagen phase, of the hair follicle, though it also increases the rate of growth, thickness, extent of medullation and pigmentation of the hair. These effects involve high levels of hormone and its conversion to 5 alpha-dihydrotestosterone in the target organ. In contrast, the lower pubic triangle develops luxuriantly even in absence of 5 alpha-reductase. In the sebaceous glands, cell replication and lipid synthesis do not seem to be identically controlled, since they respond differently to inhibitors. The response of the sebaceous glands to androgens involves the interaction at the target site of pituitary factors, for which growth hormone, prolactin, and melanocyte stimulating hormone are all putative candidates. The most important scientific and clinical question is whether, in any particular circumstances, the degree of response of the hair follicles or sebaceous glands is determined by the level of available androgen or by the sensitivity of the target organ. While it is true that some patients with hirsutism or acne have above normal levels of plasma androgens or below normal levels of SHBG, a substantial proportion are normal in all respects. Moreover, the rates of hair growth on the extremities or of sebum excretion on the forehead do not seem to be correlated either positively with plasma androgens or negatively with SHBG, though they each have been shown to be correlated with circulating 5 alpha-dihydrotestosterone. The conclusion must be that, although male-type hair growth and high sebaceous secretion may be caused by, or at least accompanied by, high levels of free testosterone, the critical factor is more likely to be the peripheral response.

Effect of Hair Growth Cycles on Experimental Cutaneous Candidiasis in Mice

Experimental cutaneous Candida albicans infections were produced in mice by inoculating the organisms onto areas of shaved flank skin where the hair follicles were in either the anagen (growing) or telogen (resting) phase of the growth cycle. Infection with Candida occurred in a majority of animals inoculated on either anagen or telogen skin, and the rate of clearance of the organisms was equivalent for infections on the 2 types of skin. Some of the animals inoculated on anagen skin developed foci of Candida infection in the well-developed hair follicles, below the skin surface. Deep foci of infection were not found after inoculation of the telogen areas. The infections resulted in increases in epidermal thickness and sensitization of the animals to Candida antigens, but these responses were not different between animals inoculated on the 2 types of skin. The results of these experiments indicate that although Candida albicans can infect skin containing either active or resting hair follicles, foci of infection below the skin surface occur only when well-developed hair follicles are present. These findings may have relevance to the consequences of human cutaneous candidiasis.

Dandruff: infection or not?

Synopsis The presence of apparently normal corneocytes as well as parakeratotic material in dandruff scales suggests that atypical keratinization in the scalp epidermis has not been of long duration. Abundance of hair fat on the scalp after puberty, colonization by fat-splitting micro-organisms (notably yeasts of the genus Pityrosporum) and transitory upsurges of epidermal mitosis in response to fatty acids produced by lipolysis of sebum triglycerides within the hair follicles, especially those in the anagen phase, seem likely to be implicated in the generation of dandruff scaling. Antidandruff efficacy apparently calls not only for antifungal potency demonstrable in vitro but also for the ability, when incorporated in a suitable formulation, to reach the microflora within the hair follicles and to inhibit the metabolic activity of these microorganisms even in the presence of sebum. The in vivo demonstration of an alleged 'anti-hyperproliferative'effect of an antidandruff compound has been described but probably has only coincidental relationship to its normal function in the control of dandruff, which seems more likely to depend on its antimicrobial properties. The available evidence thus tends to favour the view that the scalp microflora have a predominant role in the generation of dandruff. Pellicules: origine microbienne ou non microbienne?

Histogenesis of the intradermal melanocytic tumor in BDF1 mice induced by topical application of 9,10-dimethyl-1,2-benzanthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA).

The histogenesis of the intradermal melanocytic tumor induced in the skin of 88 female BDF1 mice by DMBA and TPA is studied light-and electron-microscopically. Four types of melanocytes were found in the mouse skin. The epidermal melanocytes transiently appeared several days after topical application of DMBA. Hair follicles turned into anagen phase and follicular melanocytes became apparent by week 3. After week 3, intradermal melanocytes of the perifollicular melanocytic networks (PFM), which were scattered in untreated mouse skin, proliferated to form the intradermal melanocytic tumors, and 267 tumors, composed of oval melanocytes in medullary growth, were induced in all of the 19 treated mice by week 32. Large dendritic melanocytes located deep in the reticular dermis, which did not participate in the formation of the tumor. Only 3 papillomas were induced in 2 of the 19. Light-and electron-microscopically, there was no evidence of migration of epidermal and hair follicular melanocytes into the dermis. Additionally, melanin-producing activity in the cytoplasm of Schwann cell and perineural epithelium was observed. The histogenesis of the intradermal melanocytic tumor was closely related to the melanocytes of the perifollicular melanocytic network (PFM).