Bidirectional effects of chronic treatment with agonists and inverse agonists at the benzodiazepine receptor.

We have studied in rodents the effects of beta-carboline inverse agonists on chronic treatment and after repeated administration of benzodiazepine agonists. Chronically, the inverse agonist FG 7142 caused chemical kindling, i.e., a decrease in the threshold to the convulsive effects of the drug. This change was accompanied by decreases in the effects of beta-carboline but not benzodiazepine agonists. In addition the effects of GABA receptor agonists were decreased and the effects of GABA antagonists marginally increased. The GABA stimulated benzodiazepine binding was lower after FG 7142 kindling. Some evidence was found in mice to suggest that these changes were accompanied by behavioural alterations, but studies in rats did not show any changes. Repeated administration of benzodiazepine agonists, sufficient to cause tolerance to their pharmacological actions and to those of beta-carboline agonists, increased all of the effects of the partial inverse agonists and some of the actions of the full inverse agonists. We suggest that this is due not to precipitation of withdrawal but to a "withdrawal shift" in the coupling at the receptor inophore. This would increase the intrinsic properties of inverse agonists and decrease those of agonists. Evidence for this hypothesis is summarised.