Effects of selective blockade of synaptic transmission in the parafascicular complex on activity of sensorimotor cortex neurons

Abstract

Neuronal firing activity pattern in the sensorimotor complex and conditioned reflexes produced by blockade of noradrenergic and serotoninergic input to the parafascicular complex (CM-PF) were investigated during chronic experiments on cats in which lever-pressing reflex had previously been set up. Micro-injection of obsidan, a beta-adrenergic blocker and lysergide, a serotonin blocker, were found to produce intensification and inhibition, respectively, of neuronal spontaneous firing activity in the sensorimotor cortex, with both blockers having a similar (inhibitory) effect on neuronal response induced by conditioned acoustic stimuli. Blockade of monoaminergic inputs to the CM-PF temporarily suppressed execution of the conditioned reflex and the non-conditioned reflex of lever-pressing (for 30–60 min). The study concludes that the pattern of effect produced by the monoaminergic system on the sensorimotor cortex is largely determined by indirect as well as direct agents and that such effects are mediated by neurons belonging to the CM-PF complex of the thalamic nuclei.