Pavlovian-Instrumental Transfer of the Discriminative Stimulus Effects of Nicotine and Ethanol in Rats

Abstract

To date, only 1 study has evaluated the impact of a Pavlovian drug conditional stimulus (CS) on operant responding. A withinsubject operant 1-lever go/no-go (across sessions) design was used to evaluate the impact of Pavlovian contingencies on the discriminative stimulus effects of nicotine (0.4 mg/kg) and ethanol (800 mg/kg) in male Sprague Dawley rats . Drugs were administered 10 min before each acquisition and test session. One drug predicted sessions of food reinforcement and the other drug predicted sessions of nonreinforcement; stimulus roles were counterbalanced . In Experiment 1 (n = 7), operant lever pressing was initially maintained on a VI-30 s schedule of food reinforcement. This phase was followed by 20 (CS+ vs . CS-) Pavlovian drug discrimination training sessions without the levers present. Two extinction tests revealed significantly more operant lever pressing under the CS+ drug conditions compared to the CS-drug conditions, suggesting evidence for Pavlovianinstrumental transfer. Operant training significantly strengthened stimulus control. In Experiment 2 (n = 7) , the drugs functioned as operant drug discriminative stimuli first. Next, the predictive roles of the drug SDs and SLlS were reversed under F'avlovian CS-and CS+ contingencies, respectively. The original stimulus control was significantly undermined but was not reversed. These studies suggest that Pavlovian drug-reinforcer contingencies embedded within the operant 3-term contingency may play a partial role in mediating the discriminative stimulus effects of drugs.A variety of drugs function as discriminative stimuli (SDs) (Stolerman, 2006) in that that they set the occasion (Skinner, 1938) for operant responding. A prototypical drug discrimination paradigm involves a twolever appetitive operant choice procedure. Responding on one lever is reinforced only under one drug condition but not under a nondrug (or

Pavlovian Extinction of the Discriminative Stimulus Effects of Nicotine and Ethanol in Rats Varies as a Function of Context

“…Nicotine-S ∆ responding was slower to decay than ethanol-S ∆ responding. It should be noted here that this observation has been replicated throughout every drug discrimination study conducted by this author (Troisi, 2003a(Troisi, , 2003bTroisi, 2006). Figure 2 displays the results of the 5-min nonreinforcement sessions.…”

“…Finally, it has been argued elsewhere (Troisi, 2003a(Troisi, , 2006) that the one-lever drug discrimination paradigm may simulate how interoceptive events can set the occasion for drug reinforcement (e.g., Beardsley, Anthony, & Lopez, 1992). For example, self-administration of one drug may frequently precede self-administration of another drug (e.g., alcoholà n icoti ne).…”

“…Importantly, this latter result occurred due to reestablishment of the context (operant chamber)àreinforcer relationship (Rescorla & Wagner, 1972 ). More recently, nicotine and ethanol were first treated as CS+'s or CS-'s correlated with a food-pellet US, in a Pavlovian discrimination procedure (i.e., Pavlov's method of contrast; Troisi, 2006). In a test phase, previously established free-operant lever pressing was tested under each drug CS.…”

“…That investigation demonstrated that Pavlovian contingencies can impact operant discriminative stimulus effects of drugs; imposing explicit CSàUS relationships on drug states impacts the function of drugs as operant discriminative stimuli. However, although such Pavlovian relationships may be sufficient to produce operant stimulus control, they are neither necessary nor sufficient (Troisi, LeMay, & Järbe, 2010) for establishing operant discriminative control by drug states (Troisi, 2006). The environmental context in which the acquisition and extinction of a Pavlovian CSàUS relationship takes place impacts recovery of responding following extinction-that is, renewal (Bouton & King, 1983).…”

Transfer of the discriminative stimulus effects of Δ9-THC and nicotine from one operant response to another in rats

“…Drug states can function similarly. For instance, nicotine and ethanol, after first functioning as either CS+ (predicted food) or a CS− (predicted no food) in a Pavlovian drug discrimination procedure (e.g., Struthers et al 2009), transferred, and differentially modulated, the rate of operant lever pressing (Troisi 2006). Moreover, reversing the role of the drug S D to a CS− while simultaneously reversing the role of the S Δ to a CS+ altered operant response rates but did not reverse the original discriminative control (Troisi 2006).…”