GABA PLASMA-MEMBRANE TRANSPORTERS, GAT-1 AND GAT-3, DISPLAY DIFFERENTDISTRIBUTIONS IN THE RAT HIPPOCAMPUS

This study evaluates the distribution of two high affinity gamma-amino butyric acid (GABA) transporters (GAT-1 and GAT-3) in the rat hippocam pus using immunocytochemistry and affinity purified antibodies. GAT-1 immunoreactivity was prominent in punctate structures and axons in all layers of the dentate gyrus. In Ammon's horn, immunoreactive processe s were concentrated around the somata of pyramidal cells, particularly at their basal regions. The apical and basal dendritic fields of pyra midal cells also displayed numerous GAT-1 immunoreactive punctate stru ctures and axons. The zone of termination of the messy fibers that inc ludes both the hilus of the dentate gyrus and stratum lucidum of the C A3 area was the lightest immunolabeled region of the hippocampal compl ex. Electron microscopic preparations demonstrated that GAT-1 immunore active axon terminals form symmetric synapses with somata, axon initia l segments, and dendrites of granule and pyramidal cells in the dentat e gyrus and Ammon's horn, respectively. Immunoreactivity was localized to the plasma membrane and the cytoplasm of axon terminals. The somat a of previously described local circuit neurons in the dentate gyrus a nd Ammon's horn contained GAT-1 immunoreactivity associated with the G olgi complex. Light, diffuse GAT-3 immunoreactivity was present throug hout the hippocampal formation. Thin, astrocytic glial processes displ ayed GAT-1 and GAT-3 immunoreactivity. This localization of GAT-1 and GAT-3 indicates that they are involved in the uptake of GABA from the extracellular space into GABAergic axon terminals and astrocytes. (C) 1996 Wiley-Liss, Inc.