One wall of the chamber included two horizontally aligned retractable levers that were positioned 3 cm above the selleck chemical Imatinib Mesylate floor. A pellet dispenser was centrally positioned between the levers, 2 cm above the floor. Three 125-V horizontally aligned stimulus lights were located 5 cm above each lever, but only the central light (white) was operable. A 28-V houselight was centrally located 1 cm from the ceiling on the opposite wall. Extraneous sounds were masked by a fan located within the cubicle. Experimental events were controlled and recorded by Med-PC? software (Med Associates, St Albans, VT). Procedures Drugs Solutions were delivered via subcutaneous (s.c.) injections or 28-day osmotic minipumps (Model-2004 Alzet?, Cupertino, CA). Nicotine bitartrate (3.
16 mg/kg/day; dose expressed as free base) for the chronic phase was administered via osmotic minipump; to maximize stability in solution, pH was not adjusted (Matta et al., 2007). This dose of nicotine has been reported to produce stable nicotine plasma levels of 44 ng/ml for up to 28 days (Kenny, Gasparini, & Markou, 2003), which are equivalent to those obtained in humans who smoke approximately 30 cigarettes/day (Benowitz, 1988). For acute injections, nicotine was dissolved into 0.9% saline solution, and the pH was adjusted to 7.0 �� 0.2 with NaOH. An acute injection of nicotine (0.4 mg/kg) or saline occurred 5 min before or 1 hr after the session in the subjects�� home cage. Mecamylamine was dissolved into 0.9% saline solution with pH adjusted to 7.0 �� 0.2 with NaOH. Injections of mecamylamine (1.0 mg/kg s.c.
) were delivered 1 hr before the session. All s.c. injections were located caudal to the minipump, near the hip. Surgery Minipumps containing either nicotine or saline were implanted under isoflurane anesthesia. Minipumps were filled 24 hr prior to surgery and incubated in a saline bath. An incision was made in the skin between the scapulae, and the minipump was inserted into an s.c. pocket with the flow moderator pointed away from the incision. An analgesic agent (0.5% bupivacaine) was applied topically before the incision and when the site was closed with sutures. Isoflurane was terminated after the incision site was closed; the next test session began 2�C3 hr later. Behavioral Procedure Sessions occurred once daily at roughly the same time during the dark cycle and lasted for 1 hr.
Response shaping procedures, which reinforced responding equally on both the left and the right levers with 45 mg food pellets, are described in detail elsewhere (Palmatier et al., 2006). After shaping behavior on both levers, one was randomly assigned to be active and the other inactive. Both levers were available during sessions, but the inactive lever was not associated with any programmed consequence. The chamber was illuminated Anacetrapib by a white houselight during experimental sessions.