Effect of pentobarbital on unit activity of reticular and ventrolateral thalamic nuclei in cats

Abstract

Responses of single units in the reticular and ventrolateral thalamic nuclei were studied in acute experiments on curarized cats before and after intravenous injection of small doses (0.5–15 mg/kg) of pentobarbital, with simultaneous derivation of activity by two electrodes. After injection of pentobarbital, unit activity in the reticular nucleus consisted of high-frequency grouped (52.5% of 40 neurons) or continuous (30%) discharges as long as barbiturate spindles were present in the electrocorticogram. Activity of only four neurons (10%) of this nucleus was inhibited during the presence of spindles. In all other neurons of the reticular nucleus (7.5%) the character of discharges was unchanged after injection of pentobarbital. The appearance of grouped discharges, repeated several times (66.5% of 40 neurons), or blocking of activity (30%) throughout the period of spindle recording was observed in neurons of the ventrolateral nucleus. The remaining neurons of that nucleus (3.5%) did not respond to intravenous pentobarbital. The appearance of high-frequency discharges in neurons of the reticular nucleus while spindles were recorded coincided with a period of silence in neurons of the ventrolateral nucleus (58.5% of 34 pairs of neurons). High-frequency electrical stimulation of the mesencephalic reticular formation led to asynchronous activation of neurons of the ventrolateral nucleus (82%) and inhibition of unit activity in the reticular nucleus (88%).