Y A Gonchar | PubMed Health

PubMed1995

GABA-immunopositive neurons in rat neocortex with contralateral projections to S-I.

The callosal projection is traditionally believed to be exclusively excitatory in function. A new method combining lectin-conjugated colloidal gold for retrograde tracing with immunofluorescence for GABA was used to investigate this question. The large majority of neurons retrogradely labeled after injections of tracer into contralateral S-I were GABA-negative cells in layers II-VI. However, GABA-positive neurons projecting to contralateral S-I were also seen. The majority of double-labeled cells were only weakly labeled with tracer; they were located both in superficial and deep cortical layers and represented at least 1% of all retrogradely labeled neurons. Neurons double-labeled for both tracer and GABA in upper layers were found mainly within the central patch of callosally projecting neurons, whereas those in deep layers were scattered throughout contralateral cortex.

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Minicolumnar activation patterns in cat and monkey SI cortex.

The distribution of stimulus-evoked 14C-2-deoxyglucose (2DG) labeling in primary somatosensory cortex (SI) of monkey (Macaca fascicularis) and cat was investigated. Reconstructions of the global pattern of labeling reveal that discrete skin stimuli evoke activity within an extensive region of SI, and that the activation pattern typically consists of multiple, elongated regions of above-background labeling ("modules," typically 0.5-1.0 mm wide, and 1-4 mm long). Evidence obtained using recently developed methods (Tommerdahl, 1989) for quantitative analysis of 2DG activity patterns is shown to be consistent with the idea (Whitsel et al., 1991) that SI modules typically are bounded by zones dominated by stimulus-evoked inhibition. The labeling pattern within individual 2DG modules in SI of both cats and monkeys is analyzed quantitatively (in the frequency domain). Within-module spatial activation patterns are demonstrated to be periodic, consisting of radially oriented profiles of above-background labeling separated from each other by less strongly labeled radial profiles. The spectral characteristics of within-module 2DG labeling change systematically with location along the module's long axis: spatial frequencies between 18 and 35 cycles/mm are prominent in the labeling that occupies both the middle and upper layers at central locations in the module, but are a less obvious component of the labeling in both the middle and upper layers at locations remote to the module center. Since the radially oriented periodic variation both (1) in 2DG labeling in regions of SI outside modules and (2) in optical density in images of Nissl-stained sections of SI consists predominantly of spatial frequencies in the range of 18-35 cycles/mm, it is concluded that the radial profiles of labeling within individual 2DG modules correspond to groupings of minicolumns distinguishable from their neighbors on the basis of labeling intensity. The findings raise the possibility that highly structured, within-module spatial patterns of SI minicolumnar activation encode information about the physical properties of tactile stimuli.

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