Depression of extra-cellular GABA and increase of NMDA-induced nitric oxide following acute intra-nuclear administration of alcohol in the cerebellar nuclei of the rat

Gamma-aminobutyric acid (GABA) and nitric oxide are two key-transmitters in cerebellar nuclei, the major output of cerebellar circuitry. The aims of this study were to investigate the effects of acute intra-cerebellar administration of ethanol (20 mM) on extra-cellular levels of GABA and on the NMDA-induced nitric oxide (NO) production using microdialysis in the rat. We also studied: (i) the effects of a pre-administration of DNQX, a specific antagonist of AMPA receptors, on NO production, (ii) the effects of a pre-administration of 7-NI (7-nitroindazole, an inhibitor of neuronal nitric oxide synthase NOS) and APV (D-2-amino-5-phosphonovaleric acid, a specific blocker of the NMDA type glutamate receptors) on the actions of alcohol/NMDA on glutamate receptors, and (iii) thein vivo interaction between DNQX, ethanol and NMDA receptor activation. We found that ethanol decreased the amount of extra-cellular GABA, and that this effect was counterbalanced by administration of tiagabine 1 mg/kg, a potent inhibitor of GAT-1 GABA transporter, given by the i.p. route. In loco administration of NMDA increased the levels of NO, as previously reported. A pre-administration of DNQX (500 microM) increased significantly the production of NO up to toxic levels, as well as ethanol administration. A preadministration of 7-NI or APV reduced significantly the amounts of NO when NMDA and alcohol were infused simultaneously. The combination of ethanol with DNQX was associated with a marked enhancement of the concentrations of NO. The activity of GAT-1 in cerebellar nuclei and around this target, including in glial cells expressing GAT-1 activated by ambient GABA, seems to be spared by ethanol. Tiagabine could be considered as a candidate for future investigational treatments of acute ethanol-induced dysfunction of cerebellar nuclei. We found a potentiation of the production of NO when AMPA antagonists are given simultaneously to ethanol. The hypothesis of AMPA neurotoxicity, which has convincing arguments during chronic exposure, is challenged in this model of acute cerebellar nuclear toxicity of alcohol.