| Abstract: | Two groups of acute experiments were performed on cats anesthetized by ketamine and immobilized by myorelaxine to study reactions of neurons in ventral anterior (VA) and ventral lateral (VL) thalamic nuclei to stimulation of nucleus entopeduncularis (nEp) in normal animals and in those treated with chronic injections of neurotoxin--N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 5 mg/kg, i.m., daily, for five days). It was established that in normal cats 28% of the neurons studied have responded to nEp stimulation by inhibition with the latency shorter than 7 ms. In a half of inhibiting neurons after the first phase of inhibition which lasted 18 +/- 2 ms, the second inhibitory phase was registered. The duration of the latter was 25 +/- 4 ms. In MPTP-treated cats the number of neurons inhibited after nEp stimulation was practically the same as in normal ones (24.5%). A tendency of the first phase shortening and a statistically significant increase of the second inhibition phase duration up to 50 +/- 11 ms were found. It was suggested that changes in the inhibitory processes in VA-VL neurons receiving afferents from nEp might be explained by hyperpolarization of the nerve cell membrane evoked by increasing pallidothalamic inhibitory influences. That hyperpolarization created conditions for a decrease in Cl(-)-dependent and an increase in Ca(2+)-dependent K(+)-related phases of inhibitory postsynaptic potentials. |
