Date of Degree


Document Type


Degree Name





Nancy Hemmes

Committee Members

Bruce Brown

Robert Ranaldi

Carolyn Pytte

Joshua Peck

Subject Categories

Experimental Analysis of Behavior


conditioned reinforcement, heroin, rats, associative learning, natural rewards


Repeated-intermittent heroin use has been implicated in altering learning processes. Ranaldi et al. (2009) and Morrison et al. (2011) demonstrated that repeated-intermittent heroin administration leads to an enhancement of conditioned reinforcement by a food-paired light stimulus; however, the mechanism governing this effect is still largely unknown. The aims of the present study were to examine modifications in Pavlovian and operant associations for cues paired with natural rewards after a series of intermittent heroin injections. The study consisted of three phases: (1) Pavlovian Conditioning Phase (4 days)- in which three groups of rats had a light stimulus paired with food, and one group had unpaired food and light presentations, (2) Repeated Intermittent Heroin Injections (Behavioral Sensitization Test) (9 days)- rats in each group were injected daily with either saline or heroin and tested for behavioral sensitization, (3) Associative Learning Test Phase (99 days)- rats were assigned to one of four conditions based on conditioning history (light paired or unpaired with food) and type of operant consequence for lever pressing (contingent or non-contingent). In this phase, rats were exposed to two test conditions (15 days each), two spontaneous recovery conditions (10 days each), and an additional two test conditions, one with no heroin (7 days) and the other with an additional heroin injection seven days prior (7 days). There was a 7-day break in between each experimental condition. The first test condition measured conditioned reinforcement of operant responding. The light stimulus from the Conditioning Phase was presented contingent or non-contingent upon lever pressing, depending on group assignment, in the absence of primary reeinforcement. The second test condition was extinction of operant responding in which lever pressing in all groups resulted in no programmed consequence (light). The third condition was identical to the first test condition, except that animals received an additional injection of heroin or saline prior to testing. The results show that after repeated-intermittent heroin administration rats that received light-food pairings and a contingent presentation of a light stimulus demonstrated greater lever pressing for a stimulus paired with food (active lever) compared to saline controls and all other experimental conditions. These findings are consistent with the conclusion that chronic heroin administration leads to an enhancement of conditioned reinforcement, an effect that is primarily mediated by operant contingency learning.