EFFECT OF A GABA AGONIST ON THE EXPRESSION AND DISTRIBUTION OF GABA-A RECEPTORS IN THE PLASMA-MEMBRANE OF CULTURED CEREBELLAR GRANULE CELLS - AN IMMUNOCYTOCHEMICAL STUDY

The effect of the gamma-aminobutyric acid (GABA) agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP, 150-mu-M) on the localization and density of GABA(A) receptors in the plasma membrane of rat cerebellar granule cells in primary cultures was studied at the electron microscope (EM) level by preembedding immunogold staining using the monoclonal antibody bd-17 directed against the beta-subunit of the GABA(A) receptor complex. In THIP-treated as well as untreated control cultures, GABA(A) receptors were found to be evenly distributed in the plasma membrane of cell bodies as well as processes. However, the density of the GABA(A) receptors was significantly increased in the THIP-treated cultures as compared to the control cultures and this effect of THIP was particularly pronounced in the processes. GABA(A) receptors were occasionally observed to form 'hot spots' in process-like structures and again the frequency of these areas with an extremely high density of GABA(A) receptors was greatly increased in the THIP-treated cultures compared to the controls. It has thus been demonstrated that the ability of GABA agonists to induce formation of low-affinity GABA receptors can be directly visualized and quantified at the EM level using the preembedding immunogold technique. It is likely that low-affinity GABA(A) receptors are preferentially located in the cell processes and to a considerable extent in the form of 'hot spots'. However, these 'hot spots' also contain high-affinity receptors.