Buspirone, gepirone, ipsapirone, and zalospirone have distinct effects on the differential-reinforcement-of-low-rate 72-s schedule when compared with 5-HTP and diazepam

Abstract

The effects of four serotonin (5-HT)-1A compounds (buspirone, gepirone, ipsapirone and zalospirone) were compared with 5-hydroxytryptophan (5-HTP) [a 5-HT precursor with antidepressant (AD) efficacy], and diazepam (a benzodiazepine anxiolytic), on a differential-reinforcement-of-low-rate 72-s (DRL 72-s) schedule. Past research has shown that AD and anxiolytic compounds each have distinct effects on the DRL 72-s interresponse time (IRT) distribution profile. In the present paper, the profile of the IRT distribution was quantitatively characterized by three metrics: burst ratio, peak location and peak area. 5-HTP shifted the IRT distribution peak toward longer IRT durations, increased reinforcement rate and decreased response rate. The profile of the IRT distribution was not disrupted by 5-HTP. Diazepam disrupted the IRT distribution and increased bursting. In general, the arylpiperazine, 5-HT1A compounds increased reinforcement rate, decreased response rate and disrupted the profile of the IRT distribution. The effects of the four arylpiperazine 5-HT1A compounds on the IRT distribution profile were different from the AD profile of 5-HTP and the benzodiazepine anxiolytic profile of diazepam. Disruption of the IRT distribution by buspirone, gepirone, ipsapirone and zalospirone may result from decreased 5-HT transmission mediated by the presynaptic, somatodendritic 5-HT1A receptor.