MDA effects on classical appetitive conditioning of the rabbit jaw movement response.

We determined MDA's effects on: (a) conditioning of the rabbit's jaw movement response (JMR) (Experiment 1); and (b) nonassociative JMRs and unconditioned JMRs (Experiment 2). Rabbits were administered 3,4-methylenedioxyamphetamine (MDA; 0, 2, or 4 mg/kg) into the marginal ear vein 20-30 min prior to each of 10 daily sessions. Experiment 1 involved 30 daily training trials of 15 tone- and 15 light-conditioned stimuli (CSs) paired with a 1-ml squirt of water, as the unconditioned stimulus (UCS), injected into the oral cavity. The study revealed that MDA impaired conditioned response (CR) acquisition to tone-CS trials while augmenting CRs to light-CSs. In Experiment 2, the animals received 15 tone- and 15 light CS-alone and 30 UCS-alone presentations daily. The study revealed that MDA produced a modest increase in nonassociative responses over days that interacted with CS modality. Accordingly, these nonassociative effects could not account for MDA's influences on CR acquisition. Moreover, MDA's decrementing and enhancing of CRs to tone- and light-CSs, respectively, appears to be attributable to the drug's enhancing or decrementing tone- and light-CS intensity.