Effect of excitotoxic striatal lesions on the discharge pattern in globus pallidus and entopeduncular nucleus of the cat.

Abstract

An objective of these experiments was to characterize the discharge pattern of neurons in the globus pallidus and entopeduncular nucleus of the awake, unanesthetized and quietly sitting cat. A further objective of this work was to examine the effects of excitotoxic striatal lesions on the neuronal discharge in these nuclei. Three patterns of discharge have been described in the primate pallidum: (1) a high frequency discharge; (2) a high frequency discharge interrupted by long periods of silence; and (3) a discharge in bursts. The first pattern of discharge is evident in the internal pallidal segment only, whereas the latter two patterns are observed in the external segment exclusively. The major physiologic function of striatal discharge appears to be inhibition of neurons in the globus pallidus and entopeduncular nucleus. Thus, it was hypothesized that excitotoxic lesions of the striatum would result in: (1) increased discharge rate; (2) increased bursting; (3) increased variability of discharge; and (4) decreased proportion of units showing cross-correlations indicative of simultaneous inhibition--in both the globus pallidus and entopeduncular nucleus. In the present study, all patterns of discharge observed in the primate pallidum were evident in the cat pallidum, however, none of these patterns was exclusive to a particular segment of the pallidum. Units that discharged in bursts and units that contained long periods of silence were evident in both segments. After striatal lesions, the discharge rate in globus pallidus increased significantly whereas the discharge rate in the entopeduncular nucleus was unaffected by the lesion. Contrary to prediction, variability of discharge, amount of bursting, and the proportion of units containing long intervals all decreased significantly in both globus pallidus and entopeduncular nucleus. The striatal lesion had no effect on the cross-correlation histograms observed in the globus pallidus and entopeduncular nucleus.