The results indicated that, similar to glucocorticoids and norepinephrine magnifying memory,33 CRH in the amygdala modulated learning and memory for aversive events.83 While glucocorticoids are essential in the development of fear,84 perhaps by the induction of central
CRH, glucocorticoids, and CRH both play a check details larger role in the organization of behavior.85-87 Nonetheless, glucocorticoids are secreted Inhibitors,research,lifescience,medical under a number of experimental conditions in which fear, anxiety, novelty, and uncertainty are experimental manipulations.9,78,88-90 In contexts where there is loss of control, or the perception of a loss of control (worry is associated with the loss of control), glucocorticoids are secreted. This holds across a number of species, including humans; perceived control reduces the levels of Inhibitors,research,lifescience,medical glucocorticoids.88 These findings
are congruent with those of Curt Richter91 who observed an enlarged adrenal gland in stressed, fearful wild rats when compared with unstressed laboratory analogs. Glucocorticoids in the basolateral complex of the amygdala appear to be necessary for aversive and fear conditioning. For example, injection of the glucocorticoid receptor antagonist RU-486 into the basolateral complex of the amygdala will reduce the consolidation of aversive conditioning92 Inhibitors,research,lifescience,medical in addition to other forms of conditioning, including contextual fear.93 Other experiments have shown that glucocorticoid injections into the amygdala can facilitate aversive conditioning.33 Experiments like these, which use
post-training injection procedures, demonstrate that glucocorticoids are necessary for consolidation of the memory of aversive conditioning and Inhibitors,research,lifescience,medical may facilitate the memory process.94,95 Glucocorticoid levels impact on learned fear.94-97 For example, in one study rats received conditioning trials in which the unconditioned stimulus (footshock) was presented concurrently with the conditioned stimulus (auditory tone). For several days after conditioning the rats were treated with Inhibitors,research,lifescience,medical corticosterone; conditioned fearinduced freezing was enhanced.96 Corticosterone, by the induction of central CRH expression, facilitates fear-related behavioral responses.76 Thus, in one study looking at contextual fear conditioning, groups of rats that were chronically treated with Megestrol Acetate corticosterone displayed more fear conditioning than the vehicle-treated rats. Glucocorticoid antagonists disrupt contextual fear conditioning.94,95 Thus, the data suggest that repeated high levels of corticosterone can facilitate the retention of contextual fear conditioning, perhaps by the induction of CRH gene expression in critical regions of the brain such as the amygdala. Importantly, amygdala infusion of corticosterone aimed at the central nucleus also increases milder forms of anxiety as measured with rats in the elevated plus maze.