The thalamostriatal projection in the cat

Abstract

The organization of the projections from the intralaminar and other thalamic nuclei to the caudate nucleus (CD), putamen (PU), nucleus accumbens (Acc), and olfactory tubercle (TO) were examined in the cat by autoradiography after deposits of 3 H‐amino acids in individual thalamic nuclei and by retrograde cell labeling after intrastriatal deposits of wheat‐germ‐conjugated horseradish peroxidase. All of the rostral intralaminar nuclei, here considered to include the central lateral (CL), paracentral (PC), central medial (CeM), and rhomboid nuclei (Rh), project to the striatum. Projections closely associated with those of the rostral intralaminar group arise from cells of the paraventricular nucleus (PV) and a region lateral to the stria medullaris. These nuclei, which roughly form a ring around the mediodorsal nucleus, project in a highly particular, but loosely arranged topographic pattern to all parts of the striatum. The medially located cells in Rh, PV, and those alongside the stria medullaris project mainly to medial parts of Acc and CD; the dorsolaterally located cells of CL project mainly to the dorsolateral parts of CD and PU; cells in PC and CeM project to progressively more ventral and medial parts of CD and PU, and the lateral part of Acc. Superimposed on this projection from the rostral intralaminar region is the projection from the caudal intralaminar group including the centromedian (CM), parafascicular (PF), and subparafascicular nuclei (subPF). Together these nuclei project in a loosely but specifically organized topography to the entire striatum. The lateral and dorsal parts of CD and PU receive fibers mainly from CM. Ventral and medial parts of CD and PU and Acc receive fibers mainly from PF; TO receives fibers from subPF and the ventral part of PF. Several nuclei in the lateral nuclear mass of the thalamus also project to particular parts of the striatum. Thus, cells in the rostromedial part of the ventral anterior nucleus project to the head of CD and some cells in the rostral part of the ventromedial nucleus project to the head of CD and to PU. Several cells scattered in the lateral posterior complex project to lateral parts of the head of CD, and cells in the rostral extension of the medial subdivision of the posterior nuclear complex project to lateral parts of the head and body of CD. Finally, several cells of the paratenial nucleus project selectively to Acc. These data provide a detailed map of the total thalamostriatal projection in the cat and, hence, form a basis for more specific functional questions about this poorly understood system.