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  • 1
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Epidermal melanocytes are easily identifiable in the skin of the Boa Constrictor throughout the whole skin cycle. Intensity of the dopa reaction, however, varies. It is at its peak just before the skin enters its resting phase when the melanization of the beta layer of the epidermis is complete. There is no pigment transfer when those layers of the epidermis are formed which contain alpha keratin. The melanocytes accumulate melanosomes, retain them throughout the resting phase of the epidermis, and donate them again during the subsequent growing period of the epidermal keratinizing system when beta keratin is again formed. Thus, when a new beta layer is formed, most of the melanosomes which are donated to this layer have been formed during a previous cycle. The dermal melanophores do not show morphological or histochemical changes during the shedding cycle of the epidermis.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The effects of UVL-B and/or testosterone replacement therapy are compared in normal and castrated rats in order to determine whether testosterone is required for UVL-B (280-315 nm) stimulation of melanogenesis in the testosterone-dependent epidermal melanocyte system of the scrotal skin of black Long Evans rats. Testosterone is not a prerequisite for UVL-B stimulation of melanocytes as in both castrates and normal animals the melanocytes respond to UVL-B by increases in size, length and number of dendrites (dendriticness), and tyrosinase activity (intensity of Dopa reaction). Addition of testosterone to castrates does enhance the effects of UVL-B. However, UVL-B with or without testosterone cannot maintain normal melanogenesis in rats irradiated immediately after castration nor can it restore normal melanogenesis following long term castration. Both the amount of UVL energy/exposure and the number of exposures are important variables in stimulation of the epidermal melanocytes. Administration of a dose of UVL-B to castrates in a single exposure is ineffective, while the same overall dose spread over several exposures increases the size and dendriticness of melanocytes. Testosterone and UVL-B act synergistically in affecting melanogenesis although neither singly nor in combination are they able to fully restore normal melanogenesis.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 135 (1988), S. 262-268 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Human melanocyte cultures were established using disaggregated epidermal cell suspensions derived from foreskins and plated onto culture dishes in medium containing 2% fetal bovine serum, growth factors, hormones, and melanocyte growth factor (MGF) extracted from bovine hypothalamus (Wilkins et al., J. Cell. Physiol., 122: 350, 1985). After 2 days in culture the cells were transferred to serum-free medium to eliminate keratinocyte and fibroblast growth. Melanocytes grew preferentially and pure melanocyte populations could be harvested after 12-16 days in vitro. Melanocytes were later subcultured in the presence of 1% FBS. Pure melanocyte cultures were characterized by light and electron microscopic criteria, as well as by cytochemical demonstration of the melanocytes specific enzyme, tyrosinase. At the ultrastructural level, cultured melanocytes derived from black (negroid) neonatal skin (B-M) had numerous mature rodshaped stage IV melanosomes, while white (caucasoid) skin-derived melanocytes (W-M) in culture contained no mature melanosomes. Growth rate, cell yield, and in vitro lifespan for B-M were more than twice that for W-M in pure melanocyte cultures in the presence of MGF. Our results suggest that MGF-dependent growth of B-M differs from that of W-M.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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