Retinal modulation of the hypothalamic sensitivity to testosterone feedback in photoperiodism of quail

This experiment was performed on two groups of male Japanese quail. One had been maintained in our laboratory as a closed colony (S-group), and the other had been obtained from a commercial source (R-group). Different responses of gonadal function were found between two groups following either testosterone treatment or exposure to short days. Immature birds of these groups responded to long days with rapid gonadal growth, but after sexual maturity, exposure to short days for 3 weeks induced testicular atrophy only in S-group. Involvement of the feedback effect of androgen in the photoperiodic response was then examined. Under long-day conditions, intraperitoneal placement of testosterone propionate (TP)-filled Silastic tube for 2 weeks decreased testicular weights in S-group but not in R-group. Apparently, sensitivity to short days is closely correlated with sensitivity to testosterone in the adult male. By bilateral enucleation, quail of S-group became less sensitive to both gonad inhibitory effect of short days and the negative feedback effect of TP. These results suggest that the photoperiodic mechanisms that are primarily mediated by the retinal system play a role in altering sensitivity to steroid feedback at the hypothalamus.