Role of retino-hypothalamic pathways in the entrainment of drinking rhythms

The role of retino-hypothalamic pathways in the re-entrainment of drinking rhythms after a 12 hr phase shift in the light-dark cycle was investigated by comparing the rate of re-entrainment of unilaterally blinded (UB) rats, with split optic chiasms (OCS) and controls. As reported previously, UB rats required more days to invert drinking rhythms than controls. The number of days required to re-entrain OCS rats fell between controls and UB rats but was not statistically significant from either group. Since OCS rats had the fewest retino-hypothalamic connections, the amount of retinal input to the surachiasmatic nuclei does not appear to play an important role in the rate of re-entrainment. The results are consistent with the hypothesis that the unequal distribution of retiono-hypothalamic fibers in UB rats interferes with the entrainment process. Compared to controls, both UB and OCS rats showed a small but significant post-operative reduction in the nocturnality of drinking.