Subjects

In total, 128 male Long Evans rats were received from a breeding colony maintained by the H.A. laboratory (University of Michigan, Ann Arbor, MI). Only male rats were used for these studies, which are a direct follow-up to prior studies that had been conducted with male rats (Flagel et al., 2011; Saunders and Robinson, 2012). The breeding colony originated in 2013 with 2 TH-Cre male Long Evans rats from the K.D. laboratory (Stanford University, Stanford, CA). The colony has since been maintained by breeding TH-Cre Long Evans male rats with WT Long Evans female rats. Rats were bred and weaned in either the Biological Science Research Building or the Molecular and Behavioral Neuroscience Institute building (University of Michigan, Ann Arbor, MI) and transferred to the S.B.F. laboratory in the Molecular and Behavioral Neuroscience Institute building around postnatal day (PND) 46. Rats were housed under a 12 h light-dark cycle (lights on at 6:00 A.M. or 7:00 A.M. depending on daylight saving time) with climate-controlled conditions (22 ± 2°C) and had ad libitum access to food and water throughout the study. They were pair- or triple-housed before surgery, and single-housed following surgery and for the duration of the experiment. Rats were acclimated to the housing room for a minimum of 1 week before experimenter handling began. Behavioral testing took place during the light-phase between 10:00 A.M. and 4:00 P.M. All procedures followed the Guide for the care and use of laboratory rat (National Academy of Sciences, 2011) and were approved by the University of Michigan Institutional Animal Care and Use Committee.