An in vivo comparison of retinal and pineal melatonin production in C3H mice with normal and degenerate retinas

Purpose. To examine the effects of genetic retinal lesions on the ability of the eyes and pineal to produce melatonin and to regulate melatonin synthesis according to environmental light. Methods. This work compared C3H mice which were either +/+, homozygous for nlavrus alleles or carrying a transgene which selectively destroys cone pholoreceptors ( kindly donated by J Nathans and Y Wang, Johns Hopkins University). Pineals and eyes were dissected from animals at around 80 days of age, homogenised by exposure to ultrasound and assayed for melatonin using a direct radio immunoassay (after Fraser étal 1983. J.CIinical Chem 29:396-397). Tissue was collected at 2 hour intervals over 24 hours, from animals exposed to a 12:12 light:dark cycle. Results. Diurnal rhythms in+/+ pineal and retinal melatonin were observed tinder these conditions. In both eyes and pineals, melatonin content was low during the day. and peaked at night. Typically, maximal melatonin contents were around 400pg/pineal gland and around 50pg/pair of eyes. The diumal profile of melatonin production in the eye and pineal were significantly different in vivo. Pineal melatonin content was enhanced for a brief period during the second half of the night. By contrast, melatonin levels in the eye remained elevated for much of the dark period. Conclusions. There are significant differences in the diurnal profile of melatonin production in the eyes and pineal in viva. We are currently assessing the impact of photoreceptor degeneration on the ability of eyes and pineals to produce melatonin and to inhibit its synthesis on exposure to light.