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 p allidus (GP) and the pars reticulata (SNR) of the substantia nigra (SN ) upon the reticular thalamic nucleus (Rt) in the rat. Thus, 13 animal s were deeply anesthetized and stereotaxically injected with horseradi sh peroxidase (HRP) conjugated with wheat germ agglutinin (HRP-WGA) mi xed with HRP free in different portions of GP and SN. Next, we evaluat ed the anterograde terminal labeling in the rostral two-thirds of Rt. Confirmatory results were obtained in our case material about the enti ty of GP reticular projections, and some new data are presented here r egarding the projections from GP and SNR upon Rt. Among them we emphas ize 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 projec ts more abundantly to the ventral sectors of Rt; and d) the central co re of Rt is more innervated by GP than by SNR, which innervates Rt mai nly in its peripheral portions. These results raise the possibility of multiple and differentiated assignments of the output nuclei of the b asal ganglia upon the thalamus and its connectivity.