Convulsant versus typical barbiturates: effects on locomotor activity.

The present studies examined the effects of a typical (secobarbital) and a convulsant (cyclohexylideneethyl-5-barbituric acid [CHEB]) barbiturate on spontaneous locomotor activity in rats. Administered alone, secobarbital produced a mild stimulation of activity at a low (2.5 mg/kg) dose, and a dose-dependent depression of locomotor activity at higher (5-20 mg/kg) doses. Surprisingly, the convulsant barbiturate CHEB produced a depression of locomotor activity at all subconvulsant doses tested (2.5-20 mg/kg). IP administration of CHEB was also observed to produce abdominal muscle contractions (writhing). In a second experiment, it was found that the writhe-inducing compound para-phenyl-quinone (PPQ) did not affect locomotor activity, indicating that the depression of activity produced by CHEB was not secondary to its writhe-producing effects. In a third experiment, the "barbiturate antagonist" potential of CHEB was examined. Treatment with 10 mg/kg CHEB did not significantly alter the depression of locomotor activity produced by 10 mg/kg secobarbital. These data suggest that (1) typical and convulsant barbiturates are not strict opposites in terms of all of their behavioral actions and (2) CHEB may not be effective as a "barbiturate antagonist."