The striato-entopeduncular pathway in the rat. A retrograde transport study with wheatgerm-agglutinin-horseradish peroxidase.

The projection from the caudate-putamen to the entopeduncular nucleus was studied in rats using the wheatgerm-agglutinin--horseradish peroxidase (WGA-HRP) tracing technique. After iontophoretic injections of WGA-HRP into subregions of the entopeduncular nucleus, numerous HRP-labeled cells were found in the ipsilateral caudate-putamen. In all cases, the labeled neurons were localized in a restricted part of the caudate-putamen rostral to the cross-over of the anterior commissure. Labeled cells in the nucleus accumbens or the olfactory tubercle were never observed. The striato-entopeduncular projection was topographically organized: dorsal caudate-putamen projects to the dorsal part of the entopeduncular nucleus and ventral caudate-putamen to the ventral part. These results demonstrate that the striato-entopeduncular pathway is topographically organized as are a number of other neuronal circuits of the basal ganglia system.