Electrophysiological correlates among the radial nerve, the caudate and the entopeduncular nuclei in cats.

The entopeduncular nucleus (EPN), as the medial part of the globus pallidum, has been considered the efferent structure of the striatum. Based on this, we decided to study its possible somatosensory projections and the electrophysiological relationship with the caudate nucleus (CN). Radial nerve stimulation produced evoked responses (ER) in CN and EPN. The ERs recorded in EPN are of shorter latencies (11 msec) than those in CN (23 msec). Electrical stimulation of CN elicited ERs in EPN. These ERs are bigger when the stimulation sites coincide with the regions of CN where somatic stimulation also elicited ERs. The same regions of CN yielding ERs by somatic stimulation respond to EPN stimulation. The ERs recorded in EPN by radial nerve stimulation diminished when the CN was stimulated 7 msec after the radial nerve, while other intervals were less effective. The results show that the radial nerve probably has direct ipsi and contralateral projections to the EPN and a bidirectional connection between EPN and CN. We suggest a feedback response of EPN to CN stimulation, an arrangement which would be the functional basis for the central motor regulation.