Descending efferent connections of the sub-pallidal areas in the cat: projections to the subthalamic nucleus, the hypothalamus, and the midbrain.

The efferent connections of the sub-pallidal regions to the mediodorsal thalamic nucleus, the subthalamic nucleus, the lateral hypothalamic area, and the midbrain were investigated in the cat, using Phaseolus vulgaris--leucoagglutinin (PHA-L) as an anterograde label. The results indicate that the sub-pallidal regions of the cat project to the (dorso)medial tip of the subthalamic nucleus and the adjoining lateral hypothalamic area as well as to the ventral tegmental area and the greater extent of the dorsolateral tier of the substantia nigra pars compacta. Extensive projections were also found to the peripeduncular nucleus. The central gray as well as the mesencephalic locomotor region receive some input from the basal forebrain too. In contrast only very limited projections were found to the mediodorsal thalamic nucleus. The results are discussed in view of the possible role of these output regions in oro-facial dyskinesia.