PHASE-RELATIONSHIP AND MUTUAL EFFECTS BETWEEN CIRCADIAN-RHYTHMS OF OCULAR MELATONIN AND DOPAMINE IN THE PIGEON

In order to study the mechanisms of ocular circadian rhythms in the pi geon, we measured melatonin and dopamine simultaneously from the eye u sing in vivo microdialysis. In experiment 1, the phase relationship be tween circadian rhythms of ocular melatonin and dopamine under light-d ark cycles (LD) and continuous dim light (LLdim) was examined. Under L D, melatonin was high during the dark and low during the light. On the other hand dopamine was high during the Light and low during the dark . These rhythms with the anti-phase relationship were maintained after the birds were transferred from LD to LLdim. In experiment 2, effects of a single light pulse on melatonin and dopamine rhythms were examin ed. A light pulse at CT18 rapidly suppressed melatonin release to the daytime level, whereas it rapidly increased dopamine release to the da ytime level. The light pulse also affected the phases of melatonin and dopamine rhythms, inducing phase advances of both rhythm without chan ging the anti-phase relationship before the Light pulse. In experiment 3, effects of an intraocular injection of dopamine or melatonin on th eir circadian rhythms were examined. A dopamine injection during the s ubjective night suppressed melatonin release and induced a light-pulse type phase shift in both melatonin and dopamine rhythms. On the other hand, a melatonin injection during the subjective day suppressed dopa mine release and induced a dark-pulse type phase shift. These results are compatible with either one or two oscillator models, but the inter action between melatonin and dopamine is, in either case considered as an important mechanism regulating ocular circadian rhythms of the pig eon. (C) 1998 Elsevier Science B.V.