NALTREXONE DOES NOT DISRUPT ACQUISITION OR PERFORMANCE OF INHIBITORY CONDITIONING

Previous research has demonstrated that naltrexone (NTX) enhances acqu isition of aversive excitatory Pavlovian conditioning. Both the condit ional opponent theory (Schull, 1979) and the perceived intensity hypot hesis (Fanselow, 1981; Young & Fanselow, 1992) accurately predict this result. Nevertheless, these two models make different predictions abo ut the effects of NTX on inhibitory conditioning. In the present exper iment, these predictions were tested by investigating the effect of NT X on the acquisition and expression of inhibitory conditioning. NTX wa s injected during conditioned inhibitory (CI) training or testing. To avoid an effect of NTX on excitatory conditioning, excitatory and inhi bitory trials were separated by 24 h. A control group was used to asse ss acquisition of CI. It was found that NTX did not disrupt acquisitio n or expression of CI. These results are inconsistent with the conditi onal opponent theory but are in accordance with the perceived intensit y hypothesis.