Modulation of Inhibitory Synaptic Transmission in the Cat Motor Cortex Related to Realization of an Operant Reflex Evoked by a Complex of Stimuli

Abstract

In non-anesthetized cats, we examined the effects of iontophoretic microinjections of GABA, a blocker of GABAergic synaptic transmission, and modulators of noradrenergic transmission on impulse activity (IA) generated by motor cortex neurons in the course of realization of an operant motor reflex to the action of a complex of stimuli (warning and imperative ones). We tried to elucidate the role of different membrane receptors in modulation of spiking of cortical neurons. Microiontophoretic applications of GABA and noradrenaline resulted in decreases in the frequency of background IA of cortical neurons and suppression of their reactions related to realization of the operant reflex. The use of selective adrenoactive substances showed that applications of an α1 agonist, Mezaton, suppressed background spiking and impulsation generated within an interspike interval and in the course of the movement. An α2 blocker, yohimbine, exerted an opposite effect; the neuronal IA was intensified within the background period and other examined time intervals. There are reasons to believe that noradrenergic modulation of IA of cortical neurons is realized via direct effects on pyramidal neurons and also indirectly, through changes in the activity of inhibitory cortical interneurons.