Dependence of sensorimotor cortex neuron activity on noradrenergic and serotoninergic transmission in unspecific thalamic nuclei.

Background and evoked impulse activity of sensorimotor cortex neurons and conditioned reflex of trained cats were changed by blockers of noradrenaline and serotonin receptors applied through chemitrodes to thalamic complex of the centrum medianum and nucleus parafascicularis neurons. Application of obzidan, an antagonist of beta-adrenoreceptor to the complex of the centrum medianum and nucleus parafascicularis induced an initial increase and following decrease of the motor activity of cats. After obzidan application conditioned reflex remained unchanged at the initial, excitatory phase and started to decrease later. Lisergamide applied to the complex of the centrum medianum and nucleus parafuscicularis produced an initial decrease of movement activity and then drowsiness of the animals. Responses to conditioned stimuli were gradually decreased. The background impulse activity of the sensorimotor cortex neurons increased after obzidan application and decreased rapidly after lisergamide injection into the complex of the centrum medianum and nucleus parafascicularis. The responses of cortical neurons to conditioned stimuli were reduced, sometimes completely eliminated in both cases. Background and evoked impulse activity greatly increased by application of 5-hydroxytryptamine after preliminary lisergamide-induced depression of the impulse activity. It was concluded that under natural conditions the noradrenergic system exerts indirect inhibitor effects on the neocortex neurons through the centrum medianum and nucleus parafascicularis thalamic complex, whereas the serotoninergic system acting via the same complex increases the background and evoked impulse activity of the sensorimotor cortical neurons.