Behavioral pharmacology of abecarnil in baboons: self-injection, drug discrimination and physical dependence

The behavioral effects of abecarnil, a beta-carboline which has been suggested to function as a partial and/or selective agonist at the benzodiazepine receptor, were assessed in baboons. In a chronic administration study, 100mg/kg/day abecarnil for 6-8 weeks produced few signs of sedation: lip droop and intention tremor were observed in two of the four baboons. Flumazenil administration (5mg/kg, i.m.) on day 8 of chronic abecarnil produced only a mild precipitated benzodiazepine withdrawal syndrome. Vehicle substitution after 6-8 weeks of chronic abecarnil produced transient signs of a mild withdrawal syndrome, including decreased food intake, but did not produce vomiting, twitches/jerks or seizures. In a self-injection study, abecarnil (0.032-1.0mg/kg/injection) did not maintain rates of self-injection above vehicle control levels; higher rates of self-injection were maintained in the same animals by cocaine (0.32mg/kg/injection) and triazolam (0.01mg/kg/injection). The highest i.v. abecarnil dose (1.0mg/kg/injection) produced sedation and ataxia in two of the three baboons. In a drug discrimination study, generalization from lorazepam training conditions (1.8mg/kg, p.o.) to abecarnil was an increasing function of dose, and maximal drug lever responding occurred reliably in all baboons 5h after 10-32mg/kg, p.o. abecarnil administration. Flumazenil (0.32mg/kg, i.m.), given 4h after abecarnil, completely antagonized the abecarnil stimulus in test sessions 1h later. The present experiments show that the behavioral profile of abecarnil is clearly distinguisable from that of benzodiazepines.