A possible role for the eyes in the photoperiodic response of quail

The effects of blinding on the photoperiodic responses of male Japanese quail were investigated by measuring plasma luteinizing-hormone (LH) concentrations in intact and castrated birds. Blinded birds were still able to respond to short and long days with appropriate changes in LH levels, suggesting that the basic photoperiodic mechanisms do not require retinal photoreception. However, there were clear-cut differences between blinded and sighted birds with the LH levels being higher in blinded quail. This difference between blinded and sighted was greater in short than in long days, and was also enhanced by castration. In conclusion we propose that short day information transmitted by the eyes has an inhibitory effect for LH secretion independent from sex steroid negative feedback effects in quail.