A ROLE FOR BRAIN GLUCOCORTICOID RECEPTORS IN CONTEXTUAL FEAR CONDITIONING - DEPENDENCE UPON TRAINING INTENSITY

We studied the possible involvement of corticosteroids in the establis hment and long-term expression of contextual fear conditioning and que stioned whether a corticosteroid action might be dependent upon stimul us intensity at training. Experiments included: (i) the intracerebrove ntricular administration of specific antagonists for the two types of intracellular corticosteroid receptors to rats trained at either 1 mA or 0.4 mA shock intensity at conditioning; and (ii) the administration of corticosterone after conditioning rats to 0.2 mA shocks. The resul ts showed that the administration of a type II glucocorticoid, but not a type I mineralocorticoid, receptor antagonist before conditioning r ats to the intermediate shock condition attenuated long-term expressio n of contextual fear conditioning. However, treatment with the antagon ists before conditioning to the high shock intensity failed to influen ce the extent of fear conditioning. In addition, an intraperitoneal co rticosterone injection, given immediately after training rats at the l ow shock intensity, enhanced long-term expression of the fear response . The results support the view that post-training levels of circulatin g corticosterone, through an interaction with central type II glucocor ticoid receptors, modulate the strength to which memory for contextual fear conditioning is established and maintained. (C) 1998 Elsevier Sc ience B.V.