Sixteen Long–Evans rats (eight females, eight males) were obtained at 175 to 200 g from Charles River Laboratories and weighed an average of 426.13 ± 36.7 g (males) and 286.38 ± 29.86 g (females) at the time of surgery. All rats were maintained on a 12-h light/dark schedule with lights on at 6 am. Food was provided ad libitum, but mice were water-restricted to 35 mL of water per day throughout training and testing. During weekends and the postsurgery recovery periods rats were provided with ad libitum access to food and water. All experimental procedures were approved by the University of Maryland Animal Care and Use Committee and conformed to the guidelines set forth by the National Research Council Guide for the Care and Use of Laboratory Animals (38).
