MELATONIN DOES NOT MODULATE TESTICULAR RESPONSIVENESS TO ALTERED PHOTOPERIODS - A STUDY DURING DIFFERENT PHASES OF THE ANNUAL GONADAL CYCLEIN ROSERINGED PARAKEETS (PSITTACULA-KRAMERI)

The roseringed parakeet has been shown to exhibit a variable testicula r responsiveness to both altered photoperiodic regimens and to treatme nt with melatonin during different phases of the annual gonadal cycle. Adult male roseringed parakeets were held under either natural photop eriods (NP), or long photoperiods (LP; 16L 8D), or short photoperiods (SP; 8L 16D) for a total period of 90 days. From day 46 onward, half o f the total birds in each group were administered with the vehicle of melatonin, and the other birds were injected daily in the afternoon wi th melatonin (25 mu g/100 g body wt.) till the end of the experiment. An identical experimental schedule was followed during the four differ ent (preparatory, progressive, pre-breeding, and breeding) phases of t he annual testicular cycle. The testicular activities in various bird groups were evaluated by volumetric, gravimetric, histometric and kary ometric measurements, and by quantitative histological studies. The fi ndings revealed that exogenous melatonin may exert either a suppressiv e influence or none at all on the testicular functions in relation to the photoperiodic schedule as well as to the reproductive phase of the concerned bird, but in no case modulates gonadal responsiveness to ar tificially altered photoperiods.