The majority of these studies were conducted with adult male Sprague-Dawley rats from a selective-breeding colony which has been previously described14 (link). The data presented here were obtained from bHR and bLR rats from generations S18–S22. Equipment and procedures for Pavlovian conditioning have been described in detail elsewhere 13 (link),15 (link). Selectively-bred rats from generations S18, S20 and S21 were transported from the University of Michigan (Ann Arbor, MI) to the University of Washington (Seattle, WA) for the FSCV experiments. During each behavior session, chronically implanted microsensors, placed in the core of the nucleus accumbens, were connected to a head-mounted voltammetric amplifier for detection of dopamine by FSCV23 (link). Voltammetric scans were repeated every 100 ms to obtain a sampling rate of 10 Hz. Voltammetric analysis was carried out using software written in LabVIEW (National Instruments, Austin, TX). On completion of the FSCV experiments, recording sites were verified using standard histological procedures. To examine the effects of flupenthixol (Sigma, St. Louis, Missouri; dissolved in 0.9% NaCl) on the performance of sign-tracking and goal-tracking behavior, rats received an injection (i.p.) of 150, 300 or 600 μg/kg of the drug one hour prior to Pavlovian conditioning sessions 9, 11 and 13. Doses of the drug were counterbalanced between groups and interspersed with saline injections (i.p., 0.9% NaCl; prior to sessions 8, 10, 12 and 14) to prevent any cumulative drug effects. To examine the effects of flupenthixol on the acquisition of sign-tracking and goal-tracking behavior, rats received an injection of either saline (i.p.) or 225 μg/kg of the drug one hour prior to Pavlovian conditioning sessions 1–7.
Detailed methods and any associated references are available in the online version of the paper at www.nature.com/nature.