Proconvulsant and 'anxiogenic' effects of n-butyl beta carboline-3-carboxylate, an endogenous benzodiazepine binding inhibitor from brain.

The discovery of n-butyl beta carboline-3-carboxylate (beta CCB) as an endogenous substance of brain capable of interacting with the central benzodiazepine receptor, and the fact that this beta carboline increases in the cerebral cortex of rats undergoing acute stress, led us to study the pharmacological properties of beta CCB in mice. Using 3-mercaptopropionic acid in subconvulsant doses, it was found that this beta carboline, although not being a convulsant, has a proconvulsant action, as indicated by the number of mice undergoing convulsions and the reduction in latency. This proconvulsant effect was observed both with IP or ICV injections and was blocked by the benzodiazepine receptor antagonist RO 15-1788. In an open-field test the injection of 0.3 mg/kg of diazepam increased the number of squares crossed, while beta CCB had the opposite effect, reducing the squares crossed in a dose dependent manner between 1 and 30 mg/kg. This drug also increased the time of freezing and decreased the number of rearings. These changes were partially counteracted by the injection of 3.6 mg/kg of RO 15-1788. In the plus-maze test, 10 mg/kg chlordiazepoxide increased the number of entries and the time spent in the open arms, while the beta carboline produced the opposite effect. The conclusion reached is that beta CCB has both proconvulsant and anxiogenic actions, behaving as an inverse agonist for the central benzodiazepine receptor.