Differential responsiveness of dermal and epidermal melanocytes of Rana pipiens to hormones

Human pigmentation: A side effect adapted from a primitive organism's survival. Part 2: The melanocyte as mentor of the keratinocye

Pigmentation featured millions of years ago and perhaps began with an amoeba frightening off a predator with some agent such as dopamine to prevent its attachment for phagocytosis by an enemy. This paper suggests that the environmental forces of grip and stick, rather than pure chemical influences, deserve greater emphasis, and that the influence of the mechanical forces involved in grip and stick or release from attachment, all point to control of proteases as a function underlying pigmentation. How and why pigmentation varies with temperature and sunlight is discussed. The toxicity of melanin, pH, transepidermal water loss, and the influence of endocrine factors are also addressed.

Migration of epidermal melanophores to the dermis through the basement membrane during metamorphosis in the frog, Rana japonica

The number of epidermal melanophores of the skin decreases dramatically during metamorphosis in the frog, Rana japonica. This decrease may represent an adaptation for rapid color change, a property which the animal acquires after metamorphosis. We concluded that the decrease was due to the migration of epidermal melanophores to the dermis. Epidermal melanophores and epidermal cells are tightly associated with each other in the young tadpole. The association becomes looser at the metamorphic stage and, occasionally, small breaks in the basement membrane are seen. These breaks may facilitate the migration. The migration was observed exclusively at the metamorphic stage, in spite of careful observation of other stages under the electron microscope. The migration of epidermal melanophores was induced by treatment with thyroxine of cultured skin from tadpoles at stage 15, and this hormone may act directly on epidermal melanophores. Until now, the increase in the number of dermal melanophores during metamorphosis has been explained by the differentiation of dermal melanophores from melanoblasts and by their mitotic division. Our results show that the migration of epidermal melanophores to the dermis may be a factor which accounts for the increase in the number of dermal melanophores.

In vitro activation of amphibian dermal melanocytes by nicotine

Epidemiologic investigations have shown that nicotine could be a factor causing oral melanin pigmentation in man. Nicotine was therefore tested on amphibian skin melanocytes. Cell reactions were registered by spectrophotometry, in vitro light microscopy, photomicrography and light and electron microscopy. It was found that dermal melanocytes in the toad Bufo bufo and the frog Rana arvalis were activated by nicotine and that this activation was not mediated via beta-adrenergic receptors in melanocytes.