EXOGENOUS MELATONIN MAY ACT AS A REPRODUCTIVE-PHASE DEPENDENT MODULATOR OF THE RELATIONSHIP IN MORPHOLOGY BETWEEN PINEAL AND ADRENAL-CORTEX IN MALE BLOSSOMHEADED PARAKEET (PSITTACULA-CYANOCEPHALA) AND INDIAN WEAVER-BIRD (PLOCEUS-PHILIPPINUS)

The influence of melatonin, at a daily dose of 250 mu g/100 g b.w. for ten consecutive days on morphological parameters of the pineal and adrenal cortex was investigated in two diverse avian species, Blossomheaded parakeet (Psittacula cyanocephala) and Indian Weaver bird (Ploceus philippinus). The results suggest that melatonin administered during the breeding phase caused stimulation of the adrenal cortex as evidenced from the significant increase in adrenocortical cord width and nuclear size in both avian species. However, the pineal gland in both species remained unaltered during this phase. On the contrary, melatonin given during the non-breeding phase failed to alter the adrenal cortex but stimulated the pineal gland activity as evidenced from the significant increase in pinealocyte nuclear diameter in both species alike. It is suggested that melatonin can act as a reproductive-phase dependent modulator of the pineal gland and adrenal cortex in these birds.