Antagonism of pentobarbital induced discrimination in the gerbil

Previous work has shown that gerbils that could discriminate the effects of an injections of pentobarbital and the effect of saline, as shown by the animals' differential responding (left or right turn) in a T-shaped maze (state-dependent behavior), choose the saline associated position of the maze when challenged with bemegride in conjunction with the barbiturate. The present study examined whether differential responding in a T-maze would appear when gerbils were required to differentiate a pentobarbital (15 mg/kg)-bemegride (20 mg/kg) mixture from a saline condition (group 2) from the start of the discriminative training. The acquisition rate for this group was compared with that of another group which was required to discriminate the barbiturate, when given alone, from the no drug condition (group 1). Complete discrimination had occurred after 20 training sessions in group 1 whereas none was noted for group 2. Hereafter the bemegride was withdrawn and group 2 continued the regular training with pentobarbital solely vis-a-vis saline. Complete discrimination appeared within the next 10 sessions. After session 20 group 1 were given challenge trials which were interposed in the regular training with bemegride, metrazol, and cocaine. Bemegride (20 mg/kg), metrazol (40 mg/kg), but not cocaine (40 mg/kg), antagonized the pentobarbital (15 mg/kg) produced discrimination.