Rate-dependent Effects of drugs. II. effects of some major tranquilizers on multiple fixed-ratio, fixed-interval schedule performance.

The effects of promazine, chlorpromazine, triflupromazine, prochlorperazine, trifluoperazine, perphenazine, fluphenazine, haloperidol, benzquinamide, tetrabenazine and chlorprothixene were determined on the rate of conditioned key pecking of pigeons under a multiple fixed-ratio 30, fixed-interval 5-minute schedule of food presentation. Chlorpromazine, prochlorperazine, perphenazine, chlorprothixene and tetrabenazine decreased responding relatively more within the fixed-interval component than within the fixed-ratio component and also produced rate-dependent effects within the fixed interval component, increasing the low rates of responding early in the fixed-interval but decreasing the high rates of responding in the terminal parts of the fixed interval. Triflupromazine, trifluoperazine, fluphenazine and haloperidol also decreased responding relatively more within the fixed-interval component than within the fixed-ratio component, but did not produce rate-dependent effects within the fixed-interval component. Both low and high rates of responding within the fixed interval were decreased only by these four drugs and they produced small and inconsistent decreases in the quarter-life values. Promazine and benzquinamide decreased responding relatively more within the fixed-ratio component than within the fixed-interval component and also produced rate-dependent effects within the fixed-interval component. There was a structure-activity relationship between the chemical group on the benzene ring of the phenothiazine nucleus and the rate-dependent effect on responding within the fixed-interval component. Phenothiazines with a hydrogen or chlorine group on the benzene ring produced a rate-dependent effect on responding within the fixed interval, while phenothiazines with a trifluoromethyl group on the benzene ring did not produce a rate-dependent effect on responding within the fixed interval.