Pinealocyte‐response in roseringed parakeets(Psittacula krameri)to melatonin administration varies in relation to the reproductive phase of the annual testicular cycle

Abstract

Abstract The effects of daily afternoon injection of melatonin (25 ug/ 100 g body wt for 45 days) on the cytology of the pineal were studied during the preparatory, progressive, pre‐breeding and breeding phases of the annual testicular cycle in male roseringed parakeets. The cytological responses of the pineal to the melatonin administration in either case were evaluated by comparison with the pineals in parallel groups of control and sham‐control (only ethanolic‐saline injected) birds. It was found that the pinealocyte‐response to exogenous melatonin was stimulatory to the pineal functions during the progressive phase and inhibitory during the pre‐breeding phase. But no changes in the pinealocytes of melatonin treated birds were found during the preparatory and the breeding phases. This is the first demonstration of cytological responses 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 t...