The UV-responsive melanocyte system: a peripheral network for photoperiodic time measurements. a function of indoleamine expression.

Earlier studies indicate the involvement of indoleamines in the melanocyte photoresponse and cell cycle. In this study whole skin organ cultures were done to study the location of indoleamine expression during the photoresponse. Whole skin organ cultures from marginal zone vitiligo were incubated in MEM containing adriamycin and exposed to varying pulses of UV at 2 h of incubation. The G2 phase marginal melanocytes show increasing dendricity in response to increasing UV exposure at 3 h of incubation. On immunohistochemical staining for serotonin and melatonin, it is observed that both are positive in these melanocytes. The proportion of serotonin-positive melanocytes rises with increasing UV exposure while that of melatonin positivity rises with decreasing UV exposure, thus simulating the pineal response to light entrainment. This is due to photoinhibition of enzymes converting serotonin to melatonin. This study shows that the melanocytes in the skin can serve as the peripheral neural net for photoperiodic time measurements - the biological calendar.