Afferent projections to the reticular thalamic nucleus from the globus pallidus and the substantia nigra in the rat.

This study was designed to explore the thalamic output of the globus pallidus (GP) and the pars reticulata (SNR) of the substantia nigra (SN) upon the reticular thalamic nucleus (Rt) in the rat. Thus, 13 animals were deeply anesthetized and stereotaxically injected with horseradish peroxidase (HRP) conjugated with wheat germ agglutinin (HRP-WGA) mixed with HRP free in different portions of GP and SN. Next, we evaluated the anterograde terminal labeling in the rostral two-thirds of Rt. Confirmatory results were obtained in our case material about the entity of GP reticular projections, and some new data are presented here regarding the projections from GP and SNR upon Rt. Among them we emphasize the following for the rostral two-thirds of this thalamic nucleus: a) the projections from GP are more abundant than those arising from SNR; b) a dorsoventral topographical design appears to be clear in the organization of the afferent connections from GP to Rt; c) SNR projects more abundantly to the ventral sectors of Rt; and d) the central core of Rt is more innervated by GP than by SNR, which innervates Rt mainly in its peripheral portions. These results raise the possibility of multiple and differentiated assignments of the output nuclei of the basal ganglia upon the thalamus and its connectivity.