Cue dimensionality in the three-choice pentylenetetrazole-saline-chlordiazepoxide discrimination task

Sprague-Dawley rats were trained in a three-choice drug discrimination task utilizing 5mg/kg chlordiazepoxide (CDP), saline (SAL), and 15mg/kg pentylenetetrazole (PTZ) as stimulus conditions. Generalization tests of the three training conditions resulted in exclusively injection-appropriate lever selection. Cross-generalization tests with PTZ or CDP resulted in dose-dependent lever selections confined to the training drug and SAL levers. Morphine and ethanol cross-generalization tests produced saline-appropriate responding, whereas cocaine and caffeine produced PTZ-appropriate responding at high doses. Tests conducted after concomitant administration of both training drugs demonstrated a reciprocal antagonism between the two drugs. More importantly, when the training dose of CDP was held constant and combined with increasing doses of PTZ, a shift from CDP- to PTZ-appropriate responding through a dose range of exclusive SAL-appropriate responding was demonstrated. Overt behavioral indices of seizure activity occurred at dose combinations that engendered only saline responding, but PTZ-appropriate responding did not correspond with the development of overt seizure episodes. These data suggest that the PTZ discriminative cue in the present three-choice paradigm is not primarily linked to its proconvulsant effects. The data are discussed in terms of an hypothesis in which the discriminable interoceptive cues for PTZ and CDP lie at opposite ends of a single continuum that has a neutral centroid, and this continuum more likely reflects an anxiolysis-anxiogenesis dimension than an anticonvulsant-seizure dimension.