Search

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.

Terminal aborizations and synaptic boutons of cortical afferents to the cuneate nucleus were examined by light and electromicroscopy following intra-axonal staining with HRP. Two populations of afferents are described: (1) direct corticocuneate fibers, and (2) fibers destined for the spinal cord which issue collateral branches to the cuneate nucleus. Corticocuneate terminals primarily contact fine dendrites located in the ventral parts of the nucleus. These results are discussed in relation to previous anatomical findings and to new concepts of cuneate nucleus organization.

Treatment of pregnant rats with methylazoxymethanol acetate results in the invasion of mossy fibers into the infrapyramidal region of the hippocampus in the offspring. Since such an invasion of mossy fibers has also been reported in neonatal hyperthyroidism, prenatal ethanol exposure and neonatal lesion of CA3, a common etiology for this phenomenon is proposed.