PERCEPTUAL MASKING OF THE CHLORDIAZEPOXIDE DISCRIMINATIVE CUE BY BOTHCAFFEINE AND BUSPIRONE

Twelve male Sprague-Dawley rats were trained to discriminate between t he interoceptive stimulus attributes of 5 mg/kg chlordiazepoxide (CDP) and saline in a two-lever operant task under a fixed-ratio 10 (FR-10) schedule of food reinforcement. Caffeine, buspirone, and Ro 15-1788 f ailed to engender complete generalization when tested in combination w ith saline. In drug interaction test sessions caffeine (56 mg/kg) bloc ked the discriminative stimulus properties of the training dose of CDP and shifted the CDP discriminative dose-response function to the righ t. This rightward shift in CDP discriminative function was paralleled by a concomitant downward shift in the rate-of-responding dose-respons e function. Drug interaction test sessions conducted with 3.2 mg/kg of buspirone in combination with various doses of CDP engendered a downw ard shift in both the discriminative and rate-of-responding dose-respo nse functions. Because 3.2 mg/kg buspirone in combination with the tra ining dose of CDP resulted in complete response rate suppression, addi tional combination tests were conducted with 3 mg/kg CDP, a dose which reliably engendered >90% CDP-appropriate responding, and various dose s of buspirone. Similar to the CDP-caffeine interactions, buspirone bl ocked the cueing properties of 3 mg/kg CDP with a parallel reduction i n response rates. Interaction test sessions conducted with Ro 15-1788 and CDP resulted in rightward shifts in both the discriminative and ra te functions of CDP. We suggest that the interactions between CDP and both caffeine and buspirone resulted from the perceptual masking of th e interoceptive (subjective) effects of CDP, whereas the interaction b etween Ro 15-1788 and CDP reflect pharmacological antagonism.