ULTRAVIOLET REGULATION OF NEUROENDOCRINE AND CIRCADIAN PHYSIOLOGY IN RODENTS

UV wavelengths can regulate neuroendocrine and circadian responses in some rodent species. Appropriately timed UV exposures can block the sh ort photoperiod-induced collapse of the reproductive system, cause a r apid suppression of nocturnal melatonin synthesis, regulate melatonin rhythms and phase shift wheel running rhythms. These biological effect s of UV are not dependent on the Harderian gland or melanin in the eye , but appear to be related to the degree of transmission through the o cular lens. Such results are consistent with the hypothesis that eleme nts in the retina can transduce UV stimuli for circadian and neuroendo crine regulation.