Rapamycin pellets

All animal procedures used in this study were approved by the Harry S. Truman Veterans Memorial Hospital (HSTVMH) Subcommittee for Animal Safety and University of Missouri IACUC before commencing. All animals were cared for in accordance with the Guidelines for the Care and Use of Laboratory Animals (National Institutes of Health publication 85-23). Zucker obese (fa/fa) (ZO) and lean (ZL) rats (Charles River Laboratories) were used in this study. Rats were maintained on ad libitum food and water and housed singly at the HSTVMH animal housing facility under standard laboratory conditions. Room temperature was maintained at 21-22°C. Light and dark cycles were for 12 hours, but animals were entrained to have dark cycle (awake time) during the day and light cycle (sleep time) during the night. At 8 weeks of age, Rapamycin pellets designed to deliver Rap at a concentration of 750 μg/kg/day for 21 days (from Innovative Research of America Inc., Sarasota, FL) or placebo (sugar) pellets were placed surgically under the skin behind the shoulder blades under brief isoflurane anesthesia and this procedure was repeated 3 times to achieve a 12-week treatment. ZL and ZO rats that received placebo pellets are referred to as ZL-C and ZO-C and those implanted with Rapamycin pellets are referred to as ZL-Rap and ZO-Rap, respectively, in the text.

Rapamycin pellets were made by Innovative Research (Sarasota, Florida, USA) with a dose of 9.45 mg per pellet with a 21-day release time. This results in a 2.5 mg/kg dose per day across the 21-day period. This pellet dose and window of administration was chosen based on a prior study [97 (link)]. The pellets were implanted in the midscapular region using a 7-gauge trocar under isoflurane anesthesia. Rats were given oral meloxicam (1.0 mg/kg) for pain before and 24 hours following the surgery. Pellet implantation was done at 3 weeks of age and the 21-day rapamycin release ending at 6 weeks of age. As a control, rats were implanted with a vehicle pellet. Y-maze testing was done when rats were 6 weeks old, novel object when rats were 6.6 weeks old, and social behavior when rats were 7.1 to 7.4 weeks old.