EQUIVALENT CELL-DENSITY IN 3 AREAS OF NEONATAL RAT CEREBRAL-CORTEX

Using the disector method, equivalent cell densities (number of cells per unit volume) were found in the frontal (motor), parietal (somatose nsory) and occipital (visual) cortex of neonatal rat (1.2 x 10(6) cell s/mm(3)). As determined with GABA post-embedding immunocytochemistry o n semithin sections, at least 11% of these cells expressed GABA. Becau se neonate frontal cortex is thicker than the parietal or the occipita l cortex, the number of cells under an unit area of pial surface was g reater in this cortex. This clearly differed from the adult pattern, w here the greatest number of cells beneath an unit pial area is that of the somatosensory versus the frontal and the occipital cortex. It sug gests that the attainment of the adult number of cells in a cortical c olumn is achieved through differential cell death in the different are as and that the amount of thalamic input could be a crucial determinan t of the adult cytoarchitecture.