SCOPOLAMINE IMPAIRS ACQUISITION AND FACILITATES CONSOLIDATION OF FEARCONDITIONING - DIFFERENTIAL-EFFECTS FOR TONE VS CONTEXT CONDITIONING

Cholinergic antagonism impacts selected learning tasks. To understand where scopolamine exerts its action, learning tasks differentially sen sitive to hippocampus and amygdala lesions were used. Hippocampal lesi ons prevent context fear conditioning without effect on tone condition ing. These lesions also produce a time-dependent retrograde deficit in context conditioning. The amygdala is necessary for both tone and con text conditioning. To examine the possibility that cholinergic antagon ism mimics hippocampal damage or amygdala damage, rats were given scop olamine (1 mg/kg) either before or after fear conditioning. In the fea r conditioning procedure, rats received tone-footshock or context-foot shock pairings. Evidence of conditioning to the tone and the context w as provided by observation of freezing. When given prior to training, scopolamine blocked fear conditioning to the tone in a dose-dependent fashion but had no effect on context conditioning. The impairment of t one conditioning did not occur with methlyscopolamine, indicating the central action of the drug. Rats given scopolamine immediately followi ng fear conditioning, tested later in a drug-free state, froze more to the tone than rats given a control injection. The effect of scopolami ne on freezing to the context was not reliable. The present results su ggest that scopolamine's impact on fear conditioning is mediated by so me mechanism other than impaired hippocampal or amygdala functioning. (C) Academic Press, Inc.