PINEALOCYTE-RESPONSE IN ROSERINGED PARAKEETS (PSITTACULA-KRAMERI) TO MELATONIN ADMINISTRATION VARIES IN RELATION TO THE REPRODUCTIVE PHASE OF THE ANNUAL TESTICULAR CYCLE

The effects of daily afternoon injection of melatonin (25 ug/ 100 g bo dy wt for 45 days) on the cytology of the pineal were studied during t he preparatory, progressive, pre-breeding and breeding phases of the a nnual testicular cycle in male roseringed parakeets. The cytological r esponses of the pineal to the melatonin administration in either case were evaluated by comparison with the pineals in parallel groups of co ntrol and sham-control (only ethanolic-saline injected) birds. It was found that the pinealocyte-response to exogenous melatonin was stimula tory to the pineal functions during the progressive phase and inhibito ry during the pre-breeding phase. But no changes in the pinealocytes o f melatonin treated birds were found during the preparatory and the br eeding phases. This is the first demonstration of cytological response s of the pineal to administration of its own hormone melatonin in any bird. The study implicates the involvement of hitherto unknown annual cyclic variable(s) related to the reproductive periodicity in the dete rmination of the responses of the pinealocytes to exogenous melatonin in male roseringed parakeets.