FUNCTIONAL INACTIVATION OF THE LATERAL AND BASAL NUCLEI OF THE AMYGDALA BY MUSCIMOL INFUSION PREVENTS FEAR CONDITIONING TO AN EXPLICIT CONDITIONED-STIMULUS AND TO CONTEXTUAL STIMULI

The GABAa agonist, muscimol (0.5 mu g in 0.5 mu l saline), or vehicle was infused into the lateral and basal amygdala nuclei prior to fear c onditioning or testing in rats. Rats given muscimol before conditionin g and saline before testing showed much less freezing to the condition ed stimulus (CS) and the context than did controls given saline before training and testing. Rats given saline before training and muscimol prior to testing also showed low levels of freezing to the CS and the context. In follow-up procedures, rats with acquisition initially bloc ked by pretraining muscimol infusions froze in a manner similar to tha t of controls when retrained and retested with saline infusions. Rat:; trained with saline but tested with muscimol presumably became condit ioned but could express the learning. When retested with saline, they froze in the same manner as controls. Thus, activity in the lateral an d basal amygdala appears to play an essential role in the acquisition and expression of fear conditioning.