Surgical procedures
Seven days before the experiments, animals were anaesthetized with 2,2,2-tribromoethanol (250 mg/kg, i.p.) and placed in a stereotaxic apparatus (Stoelting, USA). After local anaesthesia with 2% lidocaine, the skull was exposed through an incision in the skin. The periosteum was removed with a 10% H2O2 solution. Stainless-steel guide cannulas (11 mm long, 0.55 mm outside diameter) were implanted bilaterally in the IC according to coordinates obtained from the rat brain atlas of Paxinos and Watson (1997) (anteroposterior, +3.2 mm from bregma; lateral, +3.75 mm from bregma; vertical, -4.5 mm from skull; incisor = -3.2 mm) (Paxinos & Watson, 1997). Self-curing acrylic resin and screws were used for fixation of the cannulas to the skull, and a 0.2 mm diameter mandrel was inserted into the cannulas to avoid obstruction during the animals’ recovery. As a prophylactic measure, the animals received a veterinary pentabiotic (Fontoura Wyeth, Brazil; 80,000 UI, i.m.) and the non-steroidal anti-inflammatory drug flunixin meglumine (Banamine®, Schering-Plough, Brazil; 2.5 mg/kg, s.c.) after the surgery.
Twenty-four hours before the experiments, the animals were anaesthetized with 2,2,2-tribromoethanol (250 mg/kg, i.p.), and a polyethylene catheter was inserted into the inferior abdominal aorta via the femoral artery for cardiovascular recording and blood sampling. The catheter was exteriorized on the animal’s dorsum and fixed to the skin by surgical suture. At the end of the surgery, the animals received the non-steroidal anti-inflammatory drug flunixin meglumine (Banamine®, Schering-Plough, Brazil; 2.5 mg/kg, s.c.). The animals were kept in individual cages throughout the postoperative period, and cardiovascular parameters were recorded. On the day of the experiments, microinjections into the IC were randomized in a non-blind manner.