Projections of the central medial nucleus of the thalamus in the rat: node in cortical, striatal and limbic forebrain circuitry.

The central medial nucleus (CM) of thalamus is a prominent cell group of the rostral intralaminar complex of the thalamus. No previous report in the rat has comprehensively described the projections of CM. Using the anterograde anatomical tracer, Phaseolus vulgaris leucoagglutinin, we examined the efferent projections of CM, comparing projections from rostral (CMr) and caudal (CMc) regions of CM. We showed that the central medial nucleus distributes substantially to several cortical sites and to a limited number of subcortical structures. The primary CM targets were anterior and posterior regions of cortex, the claustrum, the caudate-putamen, the nucleus accumbens (ACC), the olfactory tubercle, and the amygdala. CMr and CMc distribute to several of the same structures but essentially to different parts of these structures. By comparison, CMr more strongly targets limbic structures, CMc more heavily sensorimotor structures. Main CMr projection sites were the medial agranular, anterior cingulate, prelimbic, dorsolateral orbital and dorsal agranular insular cortices, the dorsal striatum, the ACC, and the basolateral nucleus of the amygdala. Main CMc cortical projection sites were the ventrolateral, lateral and dorsolateral orbital cortices, dorsal, ventral and posterior agranular insular cortices, visceral cortex, primary somatosensory and motor cortices, and perirhinal cortex. Main CMc subcortical projection sites were the dorsal striatum and the lateral, central, anterior cortical, and basomedial nuclei of amygdala. The largely complementary output of CMr and CMc to diverse areas of cortex and to regions of the striatum and amygdala suggest a combined CM influence over a widespread area of the anterior cortex and throughout the dorsal and ventral striatum and the amygdala. CM projections to limbic and sensorimotor structures of the rostral forebrain suggest that CM may serve to integrate affective, cognitive and sensorimotor functions for goal-directed behavior.