Striatal projections from the lateral and posterior thalamic complexes. An anterograde tracer study in the cat.

Striatal projections from the lateral intermediate (LI) and posterior (Po) thalamic complexes were studied with the anterograde tracers wheat germ agglutinin-horseradish peroxidase and Phaseolus vulgaris leucoagglutinin. Projections to the lateral part of the head and body of the caudate nucleus (CN) and to the putamen (Pu) were found to arise from the ventral parts of the caudal subdivision of the LI besides the well established sources in the intralaminar and ventral thalamic nuclei. No projections to the CN and only a few to the Pu were found to arise from the medial division of the Po. The presence of terminal and intercalated varicosities in the thalamostriatal fibers suggests that they form both terminal and en passant synapses. Thalamostriatal fibers from these thalamic sectors were unevenly distributed within the CN, with patches of either low-density innervation or with no projections at all interspersed within irregular, more densely innervated areas. The former coincided with the acetylcholinesterase-poor striosomes and the latter areas of dense projection with the extrastriosomal matrix.