Selective enhancement of AMPA receptor-mediated function in hippocampal CA1 neurons from chronic benzodiazepine-treated rats.

Two days following one-week administration of the benzodiazepine, flurazepam (FZP), rats exhibit anticonvulsant tolerance in vivo, while reduced GABA(A) receptor-mediated inhibition and enhanced EPSP amplitude are present in CA1 pyramidal neurons in vitro. AMPA receptor (AMPAR)-mediated synaptic transmission in FZP-treated rats was examined using electrophysiological techniques in in vitro hippocampal slices. In CA1 pyramidal neurons from FZP-treated rats, the miniature excitatory postsynaptic current (mEPSC) amplitude was significantly increased (33%) without change in frequency, rise time or decay time. Moreover, mEPSC amplitude was not elevated in dentate granule neurons following 1-week FZP treatment or in CA1 pyramidal neurons following acute desalkyl-FZP treatment. Regulation of AMPAR number was assessed by quantitative autoradiography with the AMPAR antagonist, [(3)H]Ro48-8587. Specific binding was significantly increased in stratum pyramidale of hippocampal areas CA1 and CA2 and in proximal dendritic fields of CA1 pyramidal neurons. Regulation of AMPAR subunit proteins was examined using immunological techniques. Neither abundance nor distribution of GluR1-3 subunit proteins was different in the CA1 region following FZP treatment. These findings suggest that enhanced AMPAR currents, mediated at least in part by increased AMPAR number, may contribute to BZ anticonvulsant tolerance. Furthermore, these studies suggest an interaction between GABAergic and glutamatergic systems in the CA1 region which may provide novel therapeutic strategies for restoring BZ effectiveness.