SELECTIVE LOSS OF GABA NEURONS IN AREA CA1 OF THE RAT HIPPOCAMPUS AFTER INTRAVENTRICULAR KAINATE

The intraventricular injection of kainic acid (KA) in rats produces a loss of dentate hilar neurons and hippocampal CA3 pyramidal cells, and renders the dentate granule cells and the CA1 pyramidal cells hyperex citable. We have used immunocytochemical detection of glutamic acid de carboxylase (GAD), a marker of gamma-aminobutyric acid (GABA) cells, a s well as stereological cell counting techniques, to determine whether inhibitory cell loss was present 2 weeks after KA treatment. In area CA1, we found that the density of GAD-positive cells was reduced by KA , but only in stratum oriens and the alveus. Counts of Nissl-stained n eurons were also significantly reduced in this layer. These results de monstrate a loss of GABA cells in the basal dendritic layer of the CA1 region, which may underlie the hyperexcitability of CAI pyramidal cel ls following KA treatment. (C) 1998 Elsevier Science B.V. All rights r eserved.