Baclofen and γ-aminobutyric acid differentially suppress the cutaneous responsiveness of primary somatosensory cortical neurones

Abstract

Extracellular recordings from neurones in the cat's primary somatosensory cortex (S1) have been made with carbon fibre-filled multibarrel pipettes used for microiontophoresis. γ-Aminobutyric acid (GABA) and baclofen elevated the thresholds to tactile and airpuffer stimulation, reduced the sizes of cutaneous receptive fields (RFs), depressed spontaneous activity and decreasd the magnitudes of thalamically evoked responses. However, the manner in which baclofen produced its alterations in response properties could be differentiated from that of GABA in several respects. Specially, responses which reflected spatially integrated driving of cutaneous RFs across peripheral and central regions were suppressed more readily by GABA than by baclofen. Furthermore, baclofen was observed to exert suppressions of responses which were evoked from the peripheral regions of cutaneous RFs more effectively than it could those responses which were evoked from the central regions. GABA affected central and peripheral RF subregions relatively indiscriminately. These results suggest that not only bicuculine-sensitive processes, but also those activated by baclofen, are involved in controlling the sensitivity of S1 cortical neurones to afferent stimuli.