Somatostatin immunoreactivity in the entopeduncular projection to the lateral habenula in the rat

Many neurons within the ipsilateral entopeduncular nucleus were retrogradely labelled following the stereotaxic injection of the fluorescent tracer True Blue into the lateral habenula of the rat. These neurons also displayed somatostatin immunoreactivity when examined with a monoclonal antibody to cyclic somatostatin. Excitotoxic lesions of the entopeduncular nucleus resulted in a loss of the dense somatostatin terminal field normally present in the lateral habenula. These results indicate that the neuropeptide somatostatin is present in the projection from the entopeduncular nucleus to the lateral habenula.