ELECTROLYTIC LESIONS TO THE OPTIC CHIASM AFFECT CIRCADIAN LOCOMOTOR RHYTHMS IN LIZARDS

ELECTROLYTIC lesions to 85-95% of both optic nerves at the level of th e optic chiasm (OC-X) induce a significant shortening of the free-runn ing period (tau) of locomotor rhythms in Podarcis sicula held in const ant temperature (29 degrees C) and constant darkness. Together with pr evious data in P. sicula, showing that retinalectomy (RET-X) in consta nt darkness also mostly induces a shortening of tau, the present resul ts demonstrate that the retinae play a central role in the control of behavioural circadian rhythmicity independently of light perception. T he fact that OC-X and RET-X affect locomotor rhythms in the same way ( mostly by shortening tau), strongly supports the contention that the i nfluence of the retinae on the circadian system is neurally mediated.