Alterations in Purkinje cell GABAA receptor pharmacology following oxygen and glucose deprivation and cerebral ischemia reveal novel contribution of ß1 -subunit-containing receptors.

ABSTRACT

Cerebellar Purkinje cells (PCs) are particularly sensitive to cerebral ischemia, and decreased GABA(A) receptor function following injury is thought to contribute to PC sensitivity to ischemia-induced excitotoxicity. Here we examined the functional properties of the GABA(A) receptors that are spared following ischemia in cultured Purkinje cells from rat and in vivo ischemia in mouse. Using subunit-specific positive modulators of GABA(A) receptors, we observed that oxygen and glucose deprivation (OGD) and cardiac arrest-induced cerebral ischemia cause a decrease in sensitivity to the ß(2/3) -subunit-preferring compound, etomidate. However, sensitivity to propofol, a ß-subunit-acting compound that modulates ß(1-3) -subunits, was not affected by OGD. The α/γ-subunit-acting compounds, diazepam and zolpidem, were also unaffected by OGD. We performed single-cell reverse transcription-polymerase chain reaction on isolated PCs from acutely dissociated cerebellar tissue and observed that PCs expressed the ß(1) -subunit, contrary to previous reports examining GABA(A) receptor subunit expression in PCs. GABA(A) receptor ß(1) -subunit protein was also detected in cultured PCs by western blot and by immunohistochemistry in the adult mouse cerebellum and levels remained unaffected by ischemia. High concentrations of loreclezole (30 µm) inhibited PC GABA-mediated currents, as previously demonstrated with ß(1) -subunit-containing GABA(A) receptors expressed in heterologous systems. From our data we conclude that PCs express the ß(1) -subunit and that there is a greater contribution of ß(1) -subunit-containing GABA(A) receptors following OGD.