2.2.2.2. Surgery and norbinaltorphimine intra-accumbal administration.
All surgeries were performed under isoflurane anaesthesia (1.5-2 minimum alveolar concentration, MAC) and under aseptic conditions. Before anesthetising the animals for the surgeries, they received injections (s.c.) of 1.8 mg/kg enrofloxacin (Bayer) and 2.5 mg/kg of carprofen (Pfizer). Then, we anesthetised animals in a induction chamber and used 0.1% topical lidocaine in the surgical area and in the ears before fixing animals to the stereotaxic frame (Stoelting, Wood Dale, USA). The skull of the rats were exposed, and a craniotomy was bilaterally performed above the posteromedial NAc shell. By means of a stainless steel microinjector (33-gauge) attached to a PE-10 tubing and a 25-mL Hamilton syringe mounted on a syringe pump (Kd Scientific, Holliston, USA) we injected aCSF (0.5 uL per side) or NorBNI (2 ug per hemisphere in 0.5 uL, REF #N1771, SigmaAldrich, St. Louis, USA) in the following coordinates: +0.96 mm anteroposterior, ±0.8 mm mediolateral, and -6.2 mm dorsoventral from bregma in a flat skull position (Massaly et al., 2019). Finally, we covered the craniotomies with bone wax (Ethicon, Cincinnati, USA) and the skin of each animal was sutured with a nylon monofilament suture (Ethicon, Cincinnati, USA). Rats were allowed to recover in a box provided with a heat pad and were closely monitored until they fully recovered from the anaesthesia. During the days following the surgery, rats were daily examined and received injections (s.c.) of 1.8 mg/kg enrofloxacin and 2.5 mg/kg of carprofen once a day the following 2 days.