Sign-tracking predicts increased choice of cocaine over food in rats

Abstract

The purpose of this study was to determine whether the tendency to sign-track to a food cue was predictive of rats' choice of cocaine over food. First, rats were trained on a procedure where insertion of a retractable lever was paired with food. A sub-group of rats - sign-trackers - primarily approached and contacted the lever, while another sub-group - goal-trackers - approached the site of food delivery. Rats were then trained on a choice task where they could choose between an infusion of cocaine (1.0 mg/kg) and a food pellet (45 mg). Sign-trackers chose cocaine over food significantly more often than did goal-trackers. These results support the incentive-salience theory of addiction and add to a growing number of studies which suggest that sign-trackers may model an addiction-prone phenotype.

Keywords: Addiction; Choice; Cocaine self-administration; Goal-tracking; Sign-tracking.

Figure 1. Screening for ST vs. GT

a) Pavlovian Conditioned Approach index scores (averaged over last two days of PCA training) are shown for each animal in the experiment. White bars represent animals which dropped out of the experiment. These animals did not contribute data to any statistical analyses. b) Mean (±SEM) PCA scores of ST and GT rats (that completed the experiment) across PCA training. c) Mean (±SEM) lever contacts and nose pokes made during CS periods by STs and GTs, averaged over all sessions of PCA training. *** p ≤ 0.005, **** p < 0.001.

Figure 2. Operant Lever-Press Acquisition

a) Mean reinforcers (±SEM) per session earned by STs and GTs during acquisition of food- and cocaine-maintained lever pressing (averaged over the last 5 sessions of each type). b) Mean total (±SEM) food and cocaine reinforcers earned by STs and GTs upon meeting the response acquisition criterion for each response/reinforcement alternative. * p < 0.05.

Figure 3. Cocaine vs. Food Choice

Mean percentage (±SEM) of free choice trials (14 per session) on which STs and GTs chose drug in preference to food, averaged over the last two choice sessions. * p < 0.05.