POSTNATAL MATURATION OF GABA-IMMUNOREACTIVE NEURONS OF RAT MEDIAL PREFRONTAL CORTEX

A light microscopic immunocytochemical approach has been used to exami ne the distribution and maturation of gamma-aminobutyric acid- (GABA) containing cells in rat medial prefrontal cortex (mPFC) at progressive postnatal stages. Between P1 and P5, labeled cells in the cortical pl ate show less differentiated morphological characteristics when compar ed to cells in the deeper laminae. By P10, however, most labeled cells in superficial laminae show more differentiated characteristics with some having a distinctive multipolar appearance. Between P1 and P5, th ere is a significant increase (50%) in the density of GABA-containing cells in the superficial laminae, while concurrently there is an overa ll decrease in the subjacent deeper laminae. As the cortex continues t o expand, there is a corresponding decrease in the density of GABA-imm unoreactive cells in the outer two-thirds of the cortical mantle until approximately P15, stabilizing at 20-25 cells/100,000 mu m(2) for all laminae. Between P1 and P15, there is also a significant increase (13 3%) in the average size of labeled cells, followed by a gradual decrea se of 30% between P15 and P41. During P1-7, there is a marked increase in the density of labeled axosomatic terminals in both the superficia l (200%) and deep laminae (116%). In the superficial layers, however, the density of labeled terminals again increases by 86% between P12 an d P18. In general, the present findings are consistent with the idea t hat there is a progressive maturation of the intrinsic GABAergic syste m in rat mPFC in a classic ''inside-out'' pattern, and this involves e xtensive postnatal changes occurring during the first 3 postnatal week s. (C) 1995 Wiley-Liss, Inc.