DRUG STATES AS MODULATORS OF CONDITIONED IMMOBILITY IN A LATENT DISCRIMINATION PROCEDURE

Midazolam, amphetamine, and flesinoxan were used in four rat experimen ts to examine the usefulness of a latent Pavlovian discrimination proc edure to assess the discriminative-stimulus, or occasion-setting, prop erties of drugs. Experiment 1 first assessed the unconditioned effect of each of the drugs on the dependent measure used, which was immobili ty. Relative to saline, midazolam enhanced immobility, whereas flesino xan, and especially amphetamine decreased it. In each of the Experimen ts 2-4, subjects received a limited number of training sessions during which they consistently received a footshock in a distinctive box aft er a drug but not after saline, or vice versa. Subsequently, non-reinf orced test sessions were performed in the drug and saline states in bo th the conditioning box and a novel box. Relative to the saline state, rats previously shocked under midazolam were less mobile in the condi tioning box under midazolam, whereas rats previously not shocked under amphetamine or flesinoxan were more mobile under the drug. The remain ing animals did not show differential responding. The response profile s were accounted for in terms of the combined operation of an associat ive, or occasion-setting, effect and a non-associative effect of the d rug-induced states.