CORTICAL ORGANIZATION OF THE POSTERO-MEDIAL BARREL-SUBFIELD IN MICE AND ITS REORGANIZATION AFTER DESTRUCTION OF VIBRISSAL FOLLICLES AFTER BIRTH

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Abstract
The postero-medial barrel-subfield (PMBSF) of the SI corte of normal adult mice contains clusters of cells called barrels. Each barrel histochemically shows increased succinate, lactate and G-6-P dehydrogenase, and GABA-T [transaminase] activity. Some neuronal perikarya in the barrel walls show GABA-T activity. Mitochondrial .alpha.-GPDH [.alpha.-glucose phosphate dehydrogenase] and AChE [acetylcholinesterase] show equal activities in the hollows and in the walls of the barrels. On this cortical vibrissa field, the contralateral and ipsilateral vibrissa project somatotopically in a way which coincides with the barrels. The mystacial vibrissa and the common fur of the muzzle project to different loci. The cortical surface area for the normal fur is 0.025 mm2; the cortical vibrissal area is 1.0 mm2. In mice with lesioned whisker pads the succinate dehydrogenase activity of the 4th layer in the vibrissal area becomes a continuous sheet similar to the adjacent 4th layer, the thickness of the cortex is relatively preserved and the total enzyme activities, biochemically assayed, are unchanged. These features are explained by a functional substitution. In mice with whisker pads lesioned since birth, the vibrissal area is still identified by the projections from ipsilateral vibrissa (undamaged side). This vibrissal area only is invaded by projections from the contralateral common fur of the muzzle. The compensatory process may result from an invasion of the vibrissal area by a new set of ascending fibers and not merely from axonal sprouting at the periphery or at the cortical level.