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Waddell, Jaylyn

Psychology

2005

PhD

The experiments presented here examined the contribution of the stress-related peptide corticotropin releasing factor (CRF) to the return of conditioned fear following extinction. Extinction, or the loss of responding following presentation of a Pavlovian signal without reinforcement, is often viewed as an effective approach to the treatment of anxiety disorders and phobias. Systematic exposure therapy, for example, consists of exposure to a fear-eliciting stimulus or situation until the individual no longer experiences or expresses fear. This approach does not, however, erase the fear elicited by the stimulus, but rather produces inhibition of fear that is susceptible to relapse, or a return of the extinguished fear. Experiment 1 demonstrated that central antagonism of CRF receptors blocked the reinstatement of extinguished fear elicited by re-exposure to the footshock. Experiments 2a and 2b found no disruption of the acquisition or expression of conditioned fear. Experiment 3 extended these results, and found that antagonism of CRF receptors also blocked the expression of reinstatement of fear, and that this was not state dependent. Experiments 4 and 5 assessed the effect of local infusion of the CRF antagonist into either the central nucleus of the amygdala or the bed nucleus of the stria terminalis. The results collectively suggest that CRF is an essential aspect of the neural systems required for the return of extinguished fear. CRF receptors within the central nucleus of the amygdala and the bed nucleus of the stria terminalis are required prior to re-exposure to the US, but neither completely disrupted the expression of reinstatement of extinguished fear.