MODIFICATIONS OF SOMATOSENSORY-EVOKED POT ENTIALS (SEP) AFTER BICUCULLINE ADMINISTRATION TO PAPIO-PAPIO MONKEYS

SEPs were elicited by stimulation of the sciatic (proprioceptive) or s ural (exteroceptive) nerves. SEPs were recorded through epidural chron ic electrodes implanted in the related S1 cortical surface. They were studied after systemic or local cortical administration of subconvulsi ve doses of bicuculline (a specific GABAa antagonist). A powerful incr ease in the amplitude of the P16 component, along with an inhibition o f the N30 component were observed. From a cortical Current Source Dens ities analysis, the P16 facilitation was shown to result from blockade of the GABAa inhibitory synapses on the somas of pyramidal cells that are responsible for the P26 wave. Reduction of the N30 wave was attri buted to a bicuculline-induced reduction of an axo-dendritic depolaris ation of the apical dendrites belonging to pyramidal cells. A neurophy siological model of the SEP primary waves elicited by the thalamocorti cal proprioceptive or cutaneous inputs is suggested.