Output organization of the feline entopeduncular and subthalamic nuclei.

Entopeduncular nucleus (EPN) cells which project to thalamic and non-thalamic sites were identified by antidromic discharge. Each population of cells, projecting to the ventral anterior nucleus of the thalamus (VA), centrum medianum (CM), the lateral habenula (LHB), and the pedunculopontine nucleus (PP), was distributed throughout the nucleus. While some cells projected to more than one region, particularly VA and CM, collaterals were not found in most cells. STN stimulation suppressed firing of some EPN cells for 80-120 msec in both barbiturate anesthetized and cerveau isolé cats. Suppression of activity was detected in most EPN cells projecting to LHB (73%); of all cells in which suppression of activity was detected, 84% projected to LHB and 15% to VA.