Internal coincidence of serotonergic and dopaminergic oscillations modulates photo sexual responses of Japanese quail, Coturnix coturnix japonica.

Specific temporal phase relation of neural oscillations appears to be the regulator of gonadal development in many seasonally breeding species. To find out the specific phase angle of two neural oscillations that triggers gonado-inhibitory or gonado-stimulatory response, and to test the internal coincidence model, sexually immature male Japanese quail were administered with the serotonin precursor, 5-hydroxytryptophan and the dopamine precursor, L-dihydroxyphenylalanine at hourly intervals of 6, 7, 8, 9, 10, 11 and 12 h (5 mg/100 g body weight/day for 12 days under continuous condition of light, LL). Thereafter all the groups were shifted to long photoperiod (LD16:8). During post-treatment period, in general, a significant suppression of gonadal activity was seen in the 7 h and 8 h quail and an increase in the 11 h and 12 h quail compared to the control and these effects were maintained until 105 days post treatment when the study was terminated. These findings suggest that, in addition to the effects of photoperiod, the gonadal development of Japanese quail may be also modulated by internal coincidence of serotonergic and dopaminergic oscillations (induced by the administration of their precursor drugs) and the gonadal response varies depending on the time interval between the administrations of two drugs on a circadian basis. These results also demonstrate inversion of gonadal response from 7/8 h (suppressive) to 11/12 h (stimulatory) phase relation of the two oscillations and suggest that similar to photoperiodic time measurement, Japanese quail may also detect changes in the phase angle of circadian oscillations to modulate its gonadal activity.