| Abstract: | Two experiments were carried out to assess the effects of the opioid antagonist, naloxone, on the acquisition and extinction of shock avoidance by rats in the jump-up apparatus. In Experiment 1 naloxone pretreatment facilitated acquisition but had no effect on extinction of avoidance behavior. In the second experiment the effect of naloxone on acquisition was replicated and in addition, it was shown that naloxone enhanced freezing when a response prevention or flooding procedure was introduced. Again naloxone failed to alter the course of extinction, nor did it interact with the effects of flooding which, by itself, facilitated extinction. The results suggest that naloxone's effects are limited to increasing the functional intensity of the US, and provide further support for the dissociation between extinction of avoidance behavior and other indices of fear. |
