Some enkephalinergic pathways in the brain of Rana esculenta: an experimental analysis

The distribution of proenkephalin-like immunoreactivity in the brain of Rana esculenta was examined after either unilateral transection of the lateral forebrain bundle or unilateral ablation of the optic tectum. Following transection of the lateral forebrain bundle, proenkephalin-like immunoreactivity could no longer be detected on the ipsilateral side of the brain in either the pretectal area or the nuclei of the mesencephalic tegmentum which receive projections from the ipsilateral lateral forebrain bundle. Following ablation of the optic tectum, proenkephalin-like immunoreactivity could no longer be detected in the area of the ipsilateral isthmic nucleus which receives projections from the ipsilateral optic tectum. These results suggest that both enkephalinergic projection neurons and enkephalinergic local-circuit neurons regulate visual information processing in the frog. It is proposed that the descending telencephalic enkephalinergic pathway regulates avoidance and prey-catching behavior in the frog. The role(s) of the enkephalinergic tecto-isthmic pathway in the visual behavior of the frog remain(s) to be determined.