Figure 1. Experiment 1: Value-driven reward-seeking actions are elevated after reward experience/incentive learning opportunity in early opiate withdrawal.

Table: Experiment 1 Design- Rats were trained 4 h food deprived on the seeking-delivery chain of actions to earn sucrose. Following training rats were treated with either vehicle (early withdrawal: n=8; late withdrawal n=8) or morphine (early withdrawal: n=7; late withdrawal n=7) 1/d for 11 d. Testing commenced 24 h after the last drug injection and for Group Early Withdrawal and 14 d after last injection for Group Late Withdrawal. Rats were tested for the effects of opiate withdrawal on reward seeking (in 5 min non-rewarded extinction tests) both prior to and after an incentive learning opportunity (non-contingent exposure to sucrose in opiate withdrawal). A. Effects of early opiate withdrawal on reward-seeking action performance (normalized to pre-drug baseline reward-seeking response rate on the last pre-drug training session) prior to (Test 1a- open bars) and after (Test 1b- shaded bars) an opportunity to experience the sucrose training outcome in the opiate withdrawn state. B. Effects of early opiate withdrawal on sucrose palatability, assessed as lick frequency, during the non-contingent re-exposure to the sucrose in opiate withdrawal. C. Effects of early opiate withdrawal on goal approach (normalized to pre-drug baseline entry rate on the last pre-drug training session) during the non-contingent re-exposure to the sucrose in opiate withdrawal. D. Effects of protracted (i.e., late) opiate withdrawal on reward seeking (normalized to pre-drug baseline response rate) prior to (Test 1a- open bars) and after (Test 1b- shaded bars) an opportunity to experience the sucrose training outcome in the late opiate withdrawn state. The inset shows the effects of late opiate withdrawal (Morph) compared to vehicle-treated control (Veh) on reward seeking prior to and after sucrose re-exposure during the first two min of each test. E. Effects of late opiate withdrawal on sucrose palatability, assessed as lick frequency, during the non-contingent re-exposure to the sucrose in opiate withdrawal. F. Effects of late opiate withdrawal on goal approach (normalized to pre-drug baseline entry rate) during the non-contingent re-exposure to the sucrose in opiate withdrawal. *, p<0.05. 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.