A POSSIBLE RETINAL INFORMATION ROUTE TO THE CIRCADIAN PACEMAKER THROUGH PRETECTAL AREAS IN THE HAGFISH, EPTATRETUS-BURGERI

By recording the locomotor activity rhythm of hagfish, Eptatretus burg eri, in which surgical lesions of the pretectal areas were made, we se arched for the route of light information from the eyes to the circadi an pacemaker, which is considered to be located in the preoptic nucleu s. The entrainment of circadian activity rhythm to the light dark cycl e, under 12 h light/12 h dark (12L:12D) was lost in animals whose pret ectum was ablated with a pair of scissors and the animals then showed a free-running rhythm. Destruction of the pretectal areas with a high- frequency lesion generator also caused a free-running rhythm under 12L :12D. These findings indicate that retinal information may entrain the circadian rhythm via the pretectal areas, which have retinofugal conn ections.