PHOTOSENSITIVITY IN THE SKIN OF THE LIZARD, Anolis carolinensis

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Abstract
Skin of the lizard, Anolis carolinesis, is remarkably sensitive to light. Illuminated in vitro with visible light from a tungsten source (110 W m-2), skin changes from brilliant green to dark brown (50% reduction in reflectance) within 2-4 min as a result of dispersion of melanin from a perinuclear position within dermal melanophores into superficial dendritic processes. Reversal of the process, reaggregation of pigment, will occur within 2.0 min upon return to darkness. This photic response can be initiated with light levels as low as 5.0 W m-2 and is maximized by light levels only 5% that of midwinter sunshine. Pigment dispersion in response to both melanocyte stimulating hormone and to light is inhibited by cytochalasin-B, indicating that microfilaments may be the motor element for pigment movement in that direction. Colchicine, but no cytochalasin-B, totally blocks pigment reaggregation following melanocyte stimulating hormone exposure and partially blocks it in the dark phase of the photic response. The results of this study are consistent with a model for pigment movement in A. carolinensis that provides microfilaments for pigment dispersion and microtubule involvement in both dispersion and aggregation. Finally, because it is readily visible, easily quantitified, rapid and reversible, photic response in the skin of A. carolinensis is recommended as a valuable model system for the study of saltatory movement of organelles within cells.