Determinants of patchy metabolic labeling in the somatosensory cortex of cats: a possible role for intrinsic inhibitory circuitry.

Despite repeated experimental demonstration that somatic stimulation leads to an intermittent, "column-like" pattern of 2-deoxyglucose (2DG) label in the somatosensory cortex, the functional significance of this pattern remains uncertain. A number of recent studies have suggested that the putative inhibitory neurotransmitter GABA may play an influential role in the cortical processing of sensory information. To test the possibility that GABA-mediated inhibitory processes might participate in the formation of the 2DG patches, the 2DG pattern obtained under "normal" experimental conditions was compared with the pattern observed when cortical inhibition was modified by topical application of the GABA antagonist, bicuculline methiodide (BIC). Under "normal" experimental conditions, we found that somatic stimulation led to an intermittent, patch like distribution of 2DG uptake in cat somatosensory cortex, which exhibited consistent features in animals studied using the same stimulus and experimental condition. Reconstructions of the stimulus-evoked activity patterns revealed that the label was confined to territories known to receive input from the stimulated body region and was organized into elongated strips. Topical application of BIC to the somatosensory cortex dramatically altered the dimension of the metabolic patches, which were often embedded in a field of elevated 2DG uptake. In BIC-treated hemispheres the average width of 2DG patches was 1266 microns, whereas the average width of patches in the opposite untreated hemisphere (elicited by identical stimuli) was 713 microns. Unfolded maps of the labeling pattern revealed that in the BIC-treated hemispheres adjacent "strips" of 2DG label tended to fuse, leading to a less intermittent distribution than that observed in the untreated hemispheres. An important role for GABA in the formation of the normal cortical response to somatic stimulation is suggested.