Coat colour changes in polar animals are related to seasonal variation in photic inputs. The present work was performed to study the photoresponses of hair follicular melanocytes in human skin. The melanocytes, being photosensitive cells, can function as UV biosensors, since dendrites extend towards the source of UV light. Fifty-one skin biopsies from the margin of vitiligo were subjected to whole skin organ cultures. These were exposed to a pulse of UV light to study hair bulb melanocytes in vitiligo. It is observed that the melanocytes are seen within the anagen matrix. These melanocytes are poorly dendritic in control and dark-incubated cultures. On UV exposure, they become highly dendritic, the dendrites extending towards the hair shaft in 93.5%. They show prominent catechol oxidase and noradrenaline positivity, all features of UV responsiveness. The melanocytes within the hair follicle are not directly exposed to UV light. The melanocyte dendricity and the alignment of dendrites towards the shaft on UV exposure indicate that the columns of the cells in the hair shaft act as an efficient fibre-optic system, transmitting UV light. Morphologically, the keratinocytes in the hair shaft are arranged in compressed linear columns which resemble the coaxial bundles of commercial fibre-optic strands as is observed in plants. Keratinocytes in the inner and outer sheaths do not show this arrangement. Thus the hair follicle functions as a specialised UV receptor in the skin responding to nuances of photic inputs in human skin. This is reflected in coat colour changes in animals exposed to large variations in day-night cycles.

Adolescent↗

PubMedDate not supplied

Photomodulation of the melanocyte cell cycle by indoleamines.

Melanocytes are photoresponsive cells which respond to varying doses of UV exposure in the G2 phase of the cell cycle by prominent dendricity. This photoresponse is related to indoleamine light sensitivity. The present study highlights the role of indoleamines in the photomodulation of the melanocyte cell cycle. The study was conducted on 40 whole-skin organ cultures taken from the marginal zone of vitiligo. Twenty organ cultures were subjected to G2-phase arrest, while 20 were incubated in tryptamine. The organ cultures were incubated in the dark, exposed to a pulse of 120 s UV at 2 h of incubation and harvested 3 and 6 h after UV exposure. It has been reported that the photosensitive enzymes N-acetyl transferase (NAT) and hydroxyindole-o-methyl transferase (HIOMT) are activated during the G2 phase. The conversion of serotonin to melatonin is inhibited by UV exposure as seen at 3 h. This activity recovers on continued dark incubation 6 h after UV exposure. On incubation with tryptamine, UV exposure results in utilisation of tryptamine as seen by prominent indoleamine positivity. Three hours after UV exposure, there is 75% dendricity indicating G2 phase traverse. There is a corresponding high serotonin positivity with a low melatonin positivity. This is reversed following 6 h of dark incubation with high melatonin positivity indicating reactivation of NAT and HIOMT. This is accompanied by a doubling of the melanocyte number due to mitotic traverse and an arrest in G1 phase with low utilisation of tryptamine. Thus tryptamine is utilised by melanocytes on UV exposure to be synchronised and traversed into G2 phase activating the photosensitive enzymes NAT and HIOMT. When followed by a dark phase, melatonin accumulates to traverse the melanocytes through M-phase of the cell cycle with doubling of the cell number. Thus the uptake and metabolisation of indoleamine precursors photomodulate the melanocyte cell cycle on UV exposure.

Acetylserotonin O-Methyltransferase↗

PubMedDate not supplied

Melatonin and melanocyte functions.

The effect of melatonin on melanocyte functions was studied by incubating whole-skin organ cultures with melatonin, as well as by assessing melatonin positivity in melanocytes versus dendricity and pigmentation, when arrested in the G(2) phase. From this study, it was observed that melatonin positivity is inversely related to the length of UV exposure. Increasing melatonin levels are related to decreasing dendricity and pigment donation during photoresponse in the G(2) phase. Melanocyte melatonin positivity increases with dark incubation and is higher with a pulse of UV exposure after dark incubation with melatonin. This increase is associated with a doubling of melanocyte number after dark incubation and a further doubling upon exposure to a pulse of UV. The melanocytes directly take up melatonin, which results in a marked increase in their numbers. Thus, extreme caution should be exercised when using melatonin as an anticancer drug. This finding also simulates the melanocyte repopulation of the skin with repigmentation during summer in polar animals.

Cell Count↗

PubMedDate not supplied

HBs antigenemia in chronic liver disorders in infancy and childhood.

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Carrier State↗