ANTISTRESS ACTION OF A CORTICOTROPIN-RELEASING FACTOR ANTAGONIST ON BEHAVIORAL REACTIVITY TO STRESSORS OF VARYING TYPE AND INTENSITY

Central administration of a Corticotropin-Releasing Factor (CRF) antagonist is well documented to attenuate a variety of behavioral responses to several distinct stressors; however, it is not yet clear whether the activation of CRF neurons is dependent on the type or intensity of the experimental stressor, or rather on the particular behavioral response to stress under study. To test the generality of the stress-protective effect of the CRF antagonist, alpha-helical CRF(9-41), (1, 5 or 25 mu g intracerebroventricularly), the present experiments employed a sensitive index of anxiogenic-like behavior by measuring suppression in exploration on the elevated plus-maze following exposure to social, swim, or restraint stressors. A 1 but not 5 or 25 mu g dose of the CRF antagonist administered just prior to social, swim, or restraint stress reversed the stress-induced inhibition of exploratory behavior. Chlordiazepoxide and the steroid anesthetic, alphaxalone, also attenuated the anxiogenic-like effect of restraint stress and elevated the baseline exploratory behavior of nonstressed control groups. Although the stressors produced a graded secretion of adrenocorticotropin (ACTH) with the ranking restraint > swim > social, the relative amplitude of behavioral reactivity to social, swim, and restraint stress was comparable. The relative efficacy of the CRF antagonist to reverse the stressor effects was also comparable. These results suggest that antagonism of activated brain CRF systems attenuates the behavioral response to stress regardless of the type or intensify of the stressor as measured by ACTH secretion.