Temporal and regional regulation of α1, β2 and β3, but not α2, α4, α5, α6, β1 or γ2 GABA A receptor subunit messenger RNAs following one-week oral flurazepam administration

Abstract

The effect of prolonged benzodiazepine administration on GABA A receptor subunit (α1–6, β1–3, γ2) messenger RNAs was investigated in the rat hippocampus and cortex, among other brain areas. Rats were orally administered flurazepam for one week, a protocol which results in benzodiazepine anticonvulsant tolerance in vivo, and in the hippocampus in vitro, in the absence of behavioral signs of withdrawal. Autoradiographs of brain sections, hybridized with [ 35S]oligoprobes in situ, were examined immediately (day 0) or two days after drug treatment, when rats were tolerant, or seven days after treatment, when tolerance had reversed, and were compared to sections from pair-handled, vehicle-treated controls. α1 subunit messenger RNA level was significantly decreased in CA1 pyramidal cells and dentate granule cells at day 0, an effect which persisted only in CA1 neurons. Decreased “α1-specific” silver grain density over a subclass of interneurons at the pyramidal cell border suggested concomitant regulation of interneuron GABA A receptors. A reduction in β3 subunit messenger RNA levels was more widespread among hippocampal cell groups (CA1, CA2, CA3 and dentate gyrus), immediately and two days after treatment, and was also detected in the frontal and parieto-occipital cortices. Changes in β2 subunit messenger RNA levels in CA1, CA3 and dentate gyrus cells two days after ending flurazepam treatment suggested a concomitant up-regulation of β2 messenger RNA. There was a trend toward an increased level of α5, β3 and γ2 subunit messenger RNAs in CA1, CA3 and dentate gyrus cells, which was significant for the β3 and γ2 subunit messenger RNAs in the frontal cortex seven days after ending flurazepam treatment. There were no flurazepam treatment-induced changes in any other GABA A receptor subunit messenger RNAs. The messenger RNA levels of three (α1, β2 and β3) of nine GABA A receptor subunits were discretely regulated as a function of time after ending one-week flurazepam treatment related to the presence of anticonvulsant tolerance, but not dependence. The findings suggested that a localized switch in the subunit composition of GABA A receptor subtypes involving these specific subunits may represent a minimal requirement for the changes in GABA A receptor-mediated function recorded previously at hippocampal CA1 GABAergic synapses, associated with benzodiazepine anticonvulsant tolerance.