The chlordiazepoxide/pentylenetetrazol discrimination: characterization of drug interactions and homeostatic responses to drug challenges

Rats were trained to discriminate chlordiazepoxide (CDP) from pentylenetetrazol (PTZ) in a two-lever food motivated discrimination task. Training drug doses were adjusted until subjects emitted approximately 50% of their responses on each of the two drug-appropriate levers during saline injection tests. Tests that followed injection of CDP/PTZ combinations illustrated a reciprocal antagonism between the two drugs. Saline-injection tests that followed large dose injections of CDP revealed a period of predominantly PTZ-appropriate responding that persisted after the initial period of predominantly CDP-appropriate responding. These data are interpreted to suggest that, unlike some other drugs that have been shown to antagonize the behavioral and CNS effects of benzodiazepines, the interoceptive stimulus generated by PTZ occupies a position opposite to that of CDP along some single affective continuum. In addition, these data suggest that drug/drug (DD) discriminations are capable of characterizing the interactions between training drugs. Finally, the data suggest that the CDP/PTZ discrimination is a sensitive detector of bidirectional shifts in interoceptive stimulus state along the CDP/PTZ continuum.