Effect of stimulation of the nucleus entopeduncularis on neurons of thalamic motor nuclei under normal conditions and after injury of the nigrostriatal dopaminergic system by the neurotoxin mptp

Abstract

In two series of acute experiments on cats anesthetized with ketamine and immobilized with succinylcholine chloride, we investigated the reactions of neurons of the ventral anterior (VA) and ventral lateral (VL) motor nuclei of the thalamus to stimulation of the nucleus entopeduncularis (nEp) in intact animals and in animals administered the neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). It was established that in intact animals 28.0% of the investigated VA-VL neurons reacted to stimulation of nEp by inhibition with a latent period of less than 7 msec. In half of the inhibited neurons the first phase of inhibition, lasting 18 ± 2 msec on average, was followed by a second inhibitory wave lasting 25 ± 4 msec. In cats treated with MPTP the number of neurons inhibited after stimulating nEp practically did not change (24.5%). A tendency toward shortening of the first phase of inhibition and a statistically significant increase of the duration of its second phase (50 ± 11 msec) were noted. The changes in inhibitory processes in VA-VL neurons receiving afferents from nEp in cats with injury of the nitrostriatal dopaminergic system are explained by the more pronounced hyperplarization of the membrane of these neurons than in intact animals due to intensification of pallidothalamic inhibitory influences, which leads to weakening of Cl−-and strengthening of Ca2+-dependent K+ phase of postsynapic inhibition.