5 flow rate for a 5–7 min period through a Plexiglas chamber. Subjects received injections of rimadyl as an analgesic (rimadyl, 5 mg/kg, s.c.; Protease Inhibitor Library clinical trial Pfizer Animal Health, New York, NY) and baytril as an antibiotic (baytril, 2.5 mg/kg, i.p.; Bayer Animal Health, Pittsburgh,

PA). Prior to mounting the subjects on a stereotaxic apparatus, the experimenter clipped hairs from the surgical sites, washed areas of incision at least three times by alternating betadine scrub, ethanol, and sterile water, and finally with iodine solution. The rats were then placed in a stereotaxic apparatus and the Inhibitors,research,lifescience,medical skin above the skull was incised. One (for VTA only) or three (VTA, VHC, NAc) small burr holes (3-mm diameter) were drilled above the Inhibitors,research,lifescience,medical skull for cannulae placement. Three sterile plastic guide cannula each containing a sterile stainless steel dummy (CMA/Microdialysis, Acton, MA) were aimed at the right hemisphere of each brain area of interest as follows (dimensions in mm): (a) VHC: A/P −4.0, M/L +3.5, D/V −6.0; (b) the VTA:

A/P −5.2, M/L +0.8, D/V −6; and (c) the NAc: A/P +1.5, M/L +2.5, D/V −6.0 (Paxinos and Watson, 1998). The guides were slowly lowered to target nuclei via the holes and finally secured to the skull using bone screws and dental acrylic Inhibitors,research,lifescience,medical cement. During the postoperative care and treatment, rats were given once daily injections of rimadyl as analgesic (5 mg/kg s.c.) and baytril as antibiotics (2.5 mg/kg i.p.) for seven consecutive days. Occasionally and when necessary, baytril solution was added to water bottles (0.36 mL of the injectable form in 250-mL water bottles) for postoperative symptoms including loss of appetite, hair discoloration, or dehydrated skin. Inhibitors,research,lifescience,medical Behavioral apparatus Place conditioning: The apparatus is made of Plexiglas and was partitioned into three chambers (Fig. S1); black (left), gray (center), and white (right). The black and white chambers were equal in size (26 × 22 × 33 cm, each), while the central

chamber was smaller (18 × 22 × 33 cm) (Ricoy and Martinez 2009). Inhibitors,research,lifescience,medical The entire CPP apparatus was purchased from San Diego Instruments (San Diego Instruments, San Diego, CA) and had a Photo Activity System and software (PAS) that detects locomotion beam breaks and time spent in each chamber. The black and white chambers each had six photo beam sensors whereas the neutral central chamber had four. Previous studies from our oxyclozanide laboratory (Ricoy and Martinez 2009) and our current preliminary data showed that rats show place bias for one of the two ends of the CPP apparatus, with most of the rats significantly preferring the black compared to the white chamber. Behavioral assay Intracranial conditioned place preference (IC-CPP): IC-CPP was used as a behavioral model of place reinforcement learning, modified from Ricoy and Martinez, 2009 (Ricoy and Martinez 2009).