Abstract
Environmental stimuli that are reliably paired with alcohol may acquire incentive salience, a property that can operate in the use and abuse of alcohol. Here we investigated the incentive salience of Pavlovian alcohol cues using a preclinical animal model. Male, Long-Evans rats (Harlan) with unrestricted access to food and water were acclimated to drinking 15% ethanol (v/v) in their home-cages. Rats then received Pavlovian autoshaping training in which the 10 s presentation of a retractable lever served as the conditioned stimulus (CS) and 15% ethanol served as the unconditioned stimulus (US) (0.2 ml/CS; 12 CS presentations/session; 27 sessions). Next, in an operant test of conditioned reinforcement, nose pokes into an active aperture delivered presentations of the lever-CS, whereas nose pokes into an inactive aperture had no consequences. Across initial autoshaping sessions, goal-tracking behavior, as measured by entries into the fluid port where ethanol was delivered, developed rapidly. However, with extended training goal-tracking diminished, and sign-tracking responses, as measured by lever-CS activations, emerged. Control rats that received explicitly unpaired CS and US presentations did not show goal-tracking or sign-tracking responses. In the test for conditioned reinforcement, rats with CS-US pairings during autoshaping training made more active relative to inactive nose pokes, whereas rats in the unpaired control group did not. Moreover, active nose pokes were positively correlated with sign-tracking behavior during autoshaping. Extended training may produce a shift in the learned properties of Pavlovian alcohol cues, such that after initially predicting alcohol availability they acquire robust incentive salience.
Highlights
Pavlovian cues that are associated with drugs of abuse can have robust and lasting influences on behavior
The reduction in g/kg from session 1 to session 27 is attributable to the volume of alcohol delivered per session remaining constant, but rat weights increasing over the course of the experiment
We found that a Pavlovian cue associated with unsweetened alcohol acquired incentive salience, as measured by sign-tracking and conditioned reinforcement, in rats with unrestricted access to food and water
Summary
Pavlovian cues that are associated with drugs of abuse can have robust and lasting influences on behavior. Burgeoning research (Yager and Robinson, 2010, 2013; Flagel et al, 2011a; Meyer et al, 2012a; Anselme et al, 2013; Lesaint et al, 2014; Morrow et al, 2015) indicates that during presentation of the lever-CS a subset of rats approaches the location where the US is delivered, learned behavior referred to as “goaltracking.” Another subset comes to approach and vigorously engage the lever-CS This learned behavior, referred to as “signtracking,” is interpreted as evidence of the CS having acquired incentive salience. This inference is supported by the finding that the lever-CS serves as a conditioned reinforcer for a novel operant response only in rats that have been categorized as sign-trackers (Robinson and Flagel, 2009)
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