Adult male P, NP and W rats (n = 20/strain), 90-100 days old at the time of the experiment, were used in this study. P and NP rats were from the 60th generation, and were obtained from breeding facilities on the Indiana University School of Medicine campus. P and NP rats were originally derived from an out-bred W stock at Walter Reed Army Institute of Research (Lumeng et al., 1977). W rats used in the present study were purchased from Harlan Industries (Indianapolis, IN). Animals were received in our facilities 3 weeks prior to the experiment. Rats were double housed on a reverse 12:12 light-dark cycle with lights off at 0900 hours. Rats had water and rat chow ad libitum. Animals were habituated to handling and injection procedures for 5 days prior to initiating the experiment. The animals used in these experiments were maintained in facilities fully accredited by the Association for the Assessment and Accreditation of Laboratory Animal Care (AAALAC). All research protocols were approved by the Institutional Animal Care and Use Committee and are in accordance with the
