Changes in GABA(A) receptor function and cross-tolerance to ethanol in diazepam-dependent rats

Changes in gamma-aminobutyric acid(A) (GAB(A)) receptor function and their relation to cross-tolerance to ethanol (EtOH) were studied in diazepam (DZP)-dependent rats, Physical dependence on DZP was induced in male Fischer rats by using the drug-admired food method. The Cl-36(-) influx into cerebral cortical synaptoneurosomes induced by 10 mu M GABA in DZP-withdrawn rats was significantly increased, compared with control and DZP-tolerant rats. Although enhancement of GABA-dependent Cl-36(-) influx by the addition of EtOH and flunitrazepam (FZ) was recognized in the control, there was no such effect of EtOH or FZ in the DZP-tolerant animals. On the other hand, GABA-dependent Cl-36(-) influx was enhanced by FZ in the withdrawn group. The addition of picrotoxin and bicuculline inhibited GABA-dependent Cl-36(-) influx in each group, The stimulatory effect of FZ on GABA-dependent Cl-36(-) influx was inhibited by the addition of Ro 15-1788 in the control group. However, such an inhibitory effect was not observed in the withdrawn group. The antagonistic effect of Ro 15-4513 on EtOH stimulation of GABA-dependent Cl-36(-) influx observed in the control was not recognized in the withdrawn group. In a [H-3]FZ assay of binding to benzodiazepine (BZ) receptors, B-max values were significantly increased in DZP-withdrawn animals, but decreased in the DZP-tolerant group, compared with the control. When [H-3]muscimol binding was examined, the K-d of high-affinity sites of the GABA(A) receptor in withdrawn rats was significantly lower than in the control. In low-affinity binding sites, the values of K,and B-max were significantly decreased, compared with those in the control. The present study indicates that GABAergic transmission involving the regulation of GABA-dependent chloride channels is altered in DZP-dependent rats. Alterations of the GABA(A)/BZ/chloride channel complex function may be related to the cross-tolerance between BZ and EtOH.