Figure 2. Experiment 2: In early opiate withdrawal a negative change in reward value is blocked resulting in reward seeking inconsistent with reward palatability.

Table: Experiment 2 Design- Rats were trained 22 h food deprived on the chain of actions to earn sucrose. Following chronic morphine (n=12) or vehicle (n=12) treatment all rats were tested in early withdrawal (1-5 d off drug). For the first testing phase all rats were deprived of food for 1 h prior to each day’s test. On the first test day rats were allowed to lever press on the sequence of actions non-rewarded in order to assess the general effects of satiety on reward seeking. On the second test day rats were given non-contingent re-exposure to the sucrose outcome sated (1 h food-deprived) for the first time, creating an opportunity for negative incentive learning in which the rat should learn that, when sated, the sucrose is less valuable (Balleine, 1992; Dickinson and Balleine, 1994; Wassum et al., 2011a). The next day rats were then tested for their reward-seeking performance (in a 5 min non-rewarded extinction test) following this opportunity for negative incentive learning. As a control rats were given both a reward seeking and palatability test in the 22 h food-deprived state. A. Effects of early opiate withdrawal on reward seeking (normalized to pre-drug baseline response rate) prior to (Test 1a- open bars) and after (Test 1b- shaded bars) a negative incentive learning opportunity- experience with sucrose training outcome sated (1 h food-deprived) for the first time. B. Effects of early opiate withdrawal on sucrose palatability, assessed as lick frequency, when in a hungry 22 h food-deprived control state relative to a novel 1 h food-deprived state. C. Effects of early opiate withdrawal on goal approach (normalized to pre-drug baseline entry rate) during the non-contingent re-exposure to the sucrose in opiate withdrawal when in a hungry 22 h food deprived control state relative to a 1 h food-deprived state. D. Correlation between sucrose palatability (lick frequency) during the 1 h food-deprived non-contingent re-exposure and subsequent reward-seeking rate 1 h food deprived the next day- separated for the vehicle-treated and opiate withdrawn (morphine) rats. RR-4, random-ratio 4; FR-1, fixed-ratio 1; LP_S, seeking lever press, LP_D, delivery lever press; Suc, 20% sucrose solution; Ø, no reward delivery; dep, deprived; *, p<0.05; **, p<0.01.