Mre 037

After the sucrose tests, a subpopulation of the rats (n = 30) randomly selected from the 41 rats were catheterized under the anesthesia with a mixture of ketamine (80 mg/kg) and xylazine (10 mg/kg), intramuscularly. The other 11 rats were used for other purposes and their BPs and sensitivity to punishment were not significantly differ from those of the 30 rats except for the sensitivity at three pellets between the two groups (t = 2.10, p = 0.04). However, the significance disappeared after adjusting for the four multiple tests (2 value × 2 behavior). The catheter was made of a ~12-cm polyurethane tubing (MRE-037; Braintree Scientific, Inc. MA, USA) connected to the rat vascular access button (VAB95BS; Instech, PA, USA). The button was placed subcutaneously in the mid-scapular region and the tubing was tunneled under the skin and inserted into the right external jugular vein with a length of ~3.5 cm. Buprenorphine (0.03 mg/kg, subcutaneously) was given for the post-surgical analgesia. Catheter patency was evaluated by injecting 0.1 ml Brevital (1%) through the catheters as necessary and loss of muscle tone within five seconds indicates a patent catheter.

The catheterization and stereotactic surgery were performed under anesthesia with isoflurane. The catheter was made of ~12-cm polyurethane tubing (MRE-037; Braintree Scientific, Inc. MA, USA) connected to the rat vascular access button (VAB95BS; Instech, PA, USA). The button was placed subcutaneously in the mid-scapular region and the tubing was tunneled under the skin and inserted into the right external jugular vein with a length of ~3.5 cm. The coordinates for the CeA were: AP, −2.8 mm, ML, ±4.2 mm, and DV, −7.5 mm (relative to bregma, midline and skull surface, respectively). Guide cannulas were bilaterally implanted into the area that is 2 mm above the target. An obturator (Plastics One, Roanoke, VA) was inserted into each guide cannula to prevent blockage. After surgery, buprenorphine (0.03 mg/kg, subcutaneously) was given for the post-surgical analgesia. All rats were allowed to recover for one week during which 0.1 ml of the antibiotic gentamicin (10 mg/ml, Biowhitaker, Walkersville, MD) was injected through the catheter daily, and the catheter was flushed twice a day with heparinized physiological saline (30 U/ml). Catheter patency was evaluated by injecting 0.1 ml Brevital (1%) through the catheter and loss of muscle tone within five seconds indicated the patency of the catheter.

A subpopulation of the rats (male = 30; female = 25) were catheterized under the anesthesia with a mixture of ketamine (80 mg/kg) and xylazine (10 mg/kg), intraperitoneally. The catheter was made of a ~12-cm polyurethane tubing (MRE-037; Braintree Scientific, Inc. MA, USA) connected to the rat vascular access button (VAB95BS; Instech, PA, USA). The button was placed subcutaneously in the mid-scapular region and the tubing was tunneled under the skin and inserted into the right external jugular vein with a length of ~3.5 cm. Catheter patency was evaluated by injecting 0.1 ml Brevital (1%) through the catheters as necessary and loss of muscle tone within five seconds indicated a patent catheter.