ICV-CRH alters stress-induced freezing behavior without affecting pain sensitivity

Freezing is an adaptive response often induced by stressful, fear-eliciting stimuli. Three experiments with rats investigated the effects of intracerebroventricular (ICV) administration of corticotropin-releasing hormone (CRH) on freezing behavior and pain sensitivity. Experiments 1 and 3 demonstrated that ICV-CRH (300 ng) enhanced shock-elicited freezing. In Experiment 1, ICV-CRH also enhanced recovery from shock-elicited freezing, suggesting that the peptide has a biphasic effect. Experiments 2 and 3 established that CRH-induced freezing was not caused by heightened pain sensitivity. Interestingly, in Experiment 2, hot-plate exposure produced increased freezing that was attenuated by ICV-CRH. Thus, the direction of the ICV-CRH effect on freezing was found to depend on the nature of the stressor. These results suggest that endogenous CRH systems modulate stress-induced freezing.