Both treatment groups were returned to their home cage 5 minutes following the last CS presentation, and then anesthetized 40 minutes later, using Nembutal (50 mg/kg i.p.). A second group of controls, the naïves, received no stimuli and no experience in the chamber and were anesthetized within their home cage. Four animals were allocated to each treatment group. Forty minutes following the last presentation of the CS and US, rats were anesthetized by i.p. injection with Nembutal (50 mg/kg; Abbott Laboratories, North Chicago, IL), in preparation for euthanasia by transcardial perfusion with fixatives.
