We studied the role of alpha-adrenoreceptors (AR) in the modulation of evoked neuronal activity in the primary motor cortex (PMC). Neurons receiving afferent inputs from the cerebellum were examined using a microiontophoretic technique. Activation of alpha-AR with octopamine resulted in most units (71%) on the intensification of background firing and in a prominent rise (in a dose-dependent manner) in the responsiveness of PMC neurons to stimulation of the superior cerebellar peduncle (SCP). A selective postsynaptic alpha1 antagonist, prazosin, evoked significant dose-dependent suppression of the background and evoked activity in 84% of the tested neurons. A selective presynaptic alpha2 antagonist, yohimbine, provided diverse effects. Its application exerted an excitatory effect in 50% of the studied neurons; however, in 33% of the cells qualitatively opposite alterations were observed: in low doses yohimbine increased the neuronal activity, but in high doses suppressed it. Our findings demonstrate the essential role of alpha-AR in the modulation of cerebro-cortical transmission and suggest their considerable involvement in motor functions.
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