Discriminative stimulus and rate-decreasing effects of pregnanolone (n=12), flunitrazepam (n=10), pentobarbital (n=8), β-CCE (n=8) and morphine (n=9) in rats discriminating pregnanolone while responding under a fixed-ratio 20 schedule of food presentation. Ordinates: top panel, percentage of total responses emitted on the drug (i.e., pregnanolone) lever (% DR ± 1 SEM); bottom panel, average rate expressed as a percentage of control response rates (± 1 SEM). Abscissa: dose in mg/kg. Points above V represent the effects of vehicle.