Conditioned stereotypy: Behavioral specification of the UCS and pharmacological investigation of the neural change

Previous work has shown that conditioned stereotypy can be produced by repeated treatments with d-amphetamine or apomorphine. We replicated this phenomenon and found that, as in previous reports, the amplitude of conditioned stereotypy was about one-third that of the unconditioned stereotypy. On the basis of the hypothesis that the UCS in this conditioning situation is a specific stimulation level of dopamine receptors expressed as a peak behavioral effect (UCR), rats were exposed to the experimental boxes for a brief interval during the peak behavioral effect of the drugs. This procedure produced an amplitude of conditioned stereotypy about two-thirds that of unconditioned stereotypy. The issue of the synaptic mechanism mediating conditioned stereotypy was addressed by examining the effect of pimozide on the behavior. A dose of pimozide that completely blocked apomorphine-unconditioned stereotypy also blocked apomorphine-conditioned stereotypy with no sign of motor impairment. d-Amphetamine-conditioned stereotypy was not completely blocked by a dose of pimozide that completely blocked d-amphetamine-unconditioned stereotypy. The implications of these findings for understanding the neural basis of conditioned stereotypy are discussed.