Abstract

Stressors produce an array of effects on both aversively- and appetitively-motivated behaviors. Because aversive stimuli motivate behaviors in aversively-motivated tasks, assessing stressors effects in these tasks requires re-exposure to aversive stimuli. This is not the case in appetitively-motivated tasks. Based on research that stressors can potentiate responding to subsequent aversive stimuli, the current studies assessed the hypothesis that aversively-motivated behaviors are more sensitive to the effects of stressors than appetitively-motivated behaviors. The studies reported here compared the effects of footshock and restraint in several behavioral procedures that measure responses to aversive and appetitive stimuli. Because of evidence that novel stimuli may also be aversive, the impact of stressors on responding to novel stimuli were also evaluated. CTA studies indicated that footshock enhanced amphetamine CTA (aversive response) and saccharin neophobia (novelty) but not saccharin consumption in saline-injected rats (appetitive response). Runway studies showed that footshock enhanced the response to reward reduction (aversive response) but had not impact on runway responding when reward magnitude was unchanged or increased (appetitive response). Two studies examined the effect of restraint on drug self-administration. Restraint did not influence the acquisition or maintenance of cocaine self-administration, although restraint potentiated cocaine-induced locomotion. Restraint increased ethanol intake on the first post-restraint test only in animals deprived of ethanol on restraint days. Footshock decreased novelty-induced locomotion but only in the initial 5 min of the open-field test. Results of these studies indicate that stressors can alter response to aversive and novel stimuli without altering response to appetitive stimuli. The light/dark emergence test confirmed that Sprague-Dawley rats are more "anxious" than Long-Evans rats. The more reactive Sprague-Dawley rats exhibited a behavioral profile similar to that seen in stressed Long-Evans rats in the earlier studies. These studies support the hypothesis that exposure to stressors preferentially enhance the response to both aversive and novel stimuli without altering responses to appetitive stimuli.