Conditioned Locomotion Is Not Correlated with Behavioral Sensitization to Cocaine: An Intra-Laboratory Multi-Sample Analysis

Abstract

Pre-clinical and clinical studies have demonstrated the importance of associative factors in regulating craving for drugs of abuse. To model these conditioned effects, we have examine cue-induced conditioned locomotion in rodents. The present study involved analysis of several of our prior studies to evaluate the relationship between conditioned locomotion and behavioral sensitization using a within-subjects analysis. Both are animal models used to study addiction, so it is important to know if one is predictive of the other, and more generally, if drug effects are predictive of conditioned effects. In all of our studies, Paired subjects received cocaine during presentation of conditioned stimuli while Unpaired subjects received saline with the stimuli and cocaine at the home cages an hour later. Paired subjects typically displayed behavioral sensitization over the course of training. After the completion of training, all subjects were tested with the conditioned stimuli in the absence of drug and conditioned locomotion was measured. The response of Unpaired subjects on the last training day was positively correlated with their response on test day, as expected since both days were nearly identical (stimuli presented without cocaine). However, for Paired subjects, the magnitude of conditioned locomotion on the drug-free test day was not positively correlated with the magnitude of behavioral sensitization. These results underscore the importance of focusing research on drug-free conditioned behaviors when attempting to model conditioned responses to drug related cues in human addicts.