Journal of Neuroscience, Vol 13, 4193-4213, Copyright © 1993 by Society for Neuroscience
Differential metabolic and electrical activity in the somatic sensory cortex of juvenile and adult rats
DR Riddle, G Gutierrez, D Zheng, LE White, A Richards and D Purves
Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710.
We have examined relative levels of metabolic and electrical activity
across layer IV in the primary somatic sensory cortex (S1) of the rat in
relation to regions of differential postnatal cortical growth. Each of
several indices used--mitochondrial enzyme histochemistry, microvessel
density, Na+/K+ pump activity, action potential frequency, and deoxyglucose
uptake--indicate regional variations of metabolic and electrical activity
in this part of the brain in both juvenile (1-week- old) and adult
(10-12-week-old) animals. At both ages, areas of the somatic sensory map
related to special sensors such as whiskers and digital pads showed
evidence of the most intense activity. Thus, mitochondrial enzyme staining,
blood vessel density, and Na+/K+ ATPase activity were all greatest in the
barrels and barrel-like structures within S1, and least in the adjacent
interbarrel cortex and the cortex surrounding S1. Multiunit recordings in
and around the posteromedial barrel subfield of anesthetized animals also
showed that the average ratio of evoked to spontaneous activity was greater
in barrels than in the surrounding, metabolically less active cortex.
Furthermore, autoradiograms of labeled deoxyglucose accumulation in awake
behaving animals indicated systematic differences in neural activity across
S1 barrels and barrel-like structures showed more deoxyglucose accumulation
than interbarrel, nonbarrel, or peri-S1 cortex. These regional differences
in neural activity correspond to regional differences in neocortical growth
(Riddle et al., 1992). The correlation of greater electrical activity,
increased metabolism, and enhanced cortical growth during postnatal
maturation suggests that neural activity foments the elaboration of
circuitry in the developing brain.
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