Leptin (5 μg/3 μl, purchased from the National Hormone & Peptide Program, CA, USA) and/or the melanocortin receptor antagonist SHU9119 (0.6 nmol/3 μl, Phoenix Pharmaceuticals, CA, USA) were administered into the LV of rats for 7 consecutive days. The doses of leptin and SHU9119 were chosen based on previous studies (Choi et al., 2003 (link), Fendt et al, 2009 (link), Inyushkin et al., 2009 , Mark et al., 2009 (link)). The rats were divided into the following groups: 1) daily leptin treatment alone, 2) daily SHU9119 treatment alone; 3) daily SHU9119 treatment combined with leptin treatment (30 min interval between injections); and 4) Vehicle control group that received daily phosphate buffer saline injections (PBS, pH=7.4, 3 μl). The LV injections were administered at 24-h intervals for 7 days between 11:00 am and noon. The injections were made with a Hamilton syringe (5 μl capacity) coupled with a polyethylene tubing (PE-10) connected to a needle (0.3 mm in diameter and 12 mm in length). Each injection was administered into the LV over 30 s and the injector was left in place for additional 30 s to allow the drug to diffuse in the CSF, followed by removal of the injector and replacement of the stylet into the guide cannula.