Discriminative stimulus properties of pentylenetetrazol and bemegride: some generalization and antagonism tests

In an operant procedure of lever pressing on a FR 10 schedule of food reinforcement, male hooded rats were trained to respond with a lever on one side of a food cup following a drug injection, and to respond with a lever on the alternate side following a 1 ml/kg saline injection. All of 14 subjects learned to discriminate reliably between the effects of 20 mg/kg pentylenetetrazol (PTZ) and saline. Seven of eight rats learned to discriminate between the effects of bemegride (5 mg/kg) and saline. None of 14 rats learned to discriminate between 5mg/kg PTZ and saline. The bemegride discriminative stimulus generalized to PTZ (20mg/kg) and was antagonized by chlordiazepoxide (10 mg/kg). Chlordiazepoxide, diazepam, flurazepam, clobazam, and meprobamate were all effective antagonist of PTZ in a dose-dependent manner. Bemegride and cocaine generalized to the PTZ discriminative stimulus in a dose-dependent manner, but d-amphetamine, methylphenidate, and nicotine did not. Since bemegride and PTZ are convulsants at higher doses, the discriminative stimulus properties of these drugs might be based on a subtle convulsive brain state. The anxiolytic properties of benzodiazepines and meprobamate suggest that the discriminative stimulus produced by these convulsants is related to an "anxiety-inducing" action.