CHRONIC BENZODIAZEPINE AGONIST TREATMENT PRODUCES FUNCTIONAL UNCOUPLING OF THE GAMMA-AMINOBUTYRIC-ACID BENZODIAZEPINE RECEPTOR IONOPHORE COMPLEX IN CORTICAL-NEURONS

We have investigated the effect of chronic flurazepam HCl treatment on the gamma-aminobutyric acid (GABA)(A) receptor complex in cultured ma mmalian cortical neurons. Chronic flurazepam (1-5 mu M, for 1-10 days) treatment did not produce any changes in the morphological appearance or the cell protein content of cortical neurons. The basal binding of [H-3]flunitrazepam, [H-3] Ro15-1788, and [H-3]Ro15-4513 was also not altered after the chronic treatment. However, chronic flurazepam treat ment produced uncoupling between GABA and pentobarbital sites and the [H-3]flunitrazepam binding site. The EC(50) values of GABA and pentoba rbital were not significantly altered after chronic flurazepam treatme nt; however, their E(max) values were decreased by similar to 50%. The effect of chronic flurazepam treatment on the observed uncoupling was both time and concentration dependent. Furthermore, the binding of [H -3]GABA and t-butylbicyclophosphoro[S-35]thionate was also not altered by chronic flurazepam treatment. The effect of GABA on Cl-36 influx w as not altered after chronic flurazepam treatment; however, treatment significantly attenuated the ability of diazepam to enhance GABA-induc ed Cl-36 influx. Chronic flurazepam-induced uncoupling and decreased d iazepam efficacy were reversed by the concomitant presence of the benz odiazepine antagonist Ro15-1788, suggesting that these events are medi ated via the benzodiazepine receptor site. Taken together, these resul ts suggest that chronic benzodiazepine treatment produces uncoupling o f GABA and pentobarbital sites from the benzodiazepine site and decrea sed coupling between the benzodiazepine site and GABA receptor-gated C l- channels. The uncoupling and decreased efficacy may be due to an al teration in the levels of various oc subunits and may be responsible f or the tolerance associated with chronic benzodiazepine agonist treatm ent.