Journal of Neuroscience, Vol 9, 1-12, Copyright © 1989 by Society for Neuroscience
Determinants of patchy metabolic labeling in the somatosensory cortex of cats: a possible role for intrinsic inhibitory circuitry
SL Juliano, BL Whitsel, M Tommerdahl and SS Cheema
Department of Anatomy, USUHS, Bethesda, Maryland 20814.
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.
