Discriminative effects of phenazepam and gidazepam in rats: Comparison with other GABA-related drugs

The present study assessed the discriminative stimulus effects of phenazepa m (PHZ) (2 mg/kg, IF), gidazepam (GDZ) (10 mg/kg, IF), pentobarbital (PB) ( 10 mg/kg, IF), and buspirone (B) (5 mg/kg, IF) by testing GABA-related drug s in the two-lever liquid reinforced operant discrimination procedure in ra ts. Diazepam (5-30 mg/kg, IF) dose dependently and completely substituted i n GDZ-trained rats and in only 40% PHZ-trained rats. Following phenobarbita l (40-100 mg/kg, IF) injections the mean percentages of PHZ- and GDZ-lever responding generally were a monotonically increasing function of dose, but peaked at 39.3 and 52.9%, respectively. The PB discriminative cue was gener alized completely to PHZ, GDZ; and phenobarbital. Picrotoxin (2 mg/kg, SC) did not inhibit the PHZ and GDZ discriminations, while it antagonized the P B (10 mg/kg, IF) cue. Calcium valproate (200 mg/kg, IF) failed to produce P HZ effects, and partially substituted for GDZ. B failed to substitute for t he discriminative effects of PHZ, GDZ, or PB, producing a maximum 9.3, 18.0 , and 33.3% drug lever responding, respectively. These results suggest that the discriminative stimuli of PHZ and GDZ are similar to those of other be nzodiazepine agonists. However, the PHZ cue is more selective than that of GDZ. (C) 1999 Elsevier Science Inc.