Elsevier

Brain Research

Volume 657, Issues 1–2, 19 September 1994, Pages 236-244
Brain Research

Research report
Animals predisposed to develop amphetamine self-administration show higher susceptibility to develop contextual conditioning of both amphetamine-induced hyperlocomotion and sensitization

https://doi.org/10.1016/0006-8993(94)90973-3Get rights and content

Abstract

It has been shown that rats, like humans, display individual differences in the propensity to develop psychostimulant self-adiministration. Animals showing the highest locomotor reacitivity to novelty (HRs: High Responders) are more prone to develop amphetamine self-administration than rats having a low locomotor response to novelty (LRs: Low Responders). The present study was designed to ascertain whether individual differences are also present in the conditioning of drug effects, a process involved in the maintenance of addiction. After pairing the drug effect with a particular set of environmental cues, only HRs showed conditioned hyperlocomotion and evironment-specific sensitization to the effect of amphetamine. Unconditioned sensitization was, however, observed in LRs but not in HRs. The environment-specific sensitization disappeared on extinction of the conditioned hyperlocomotion in HRs, indicating that conditioning facilitates the expression of sensitization. In contrast, an inhibitory influence of conditioning on sensitization emerged from the analysis of the same results over all the experimental groups, without taking individual differences into account. In conclusion, our results show that: (i) locomotor reactivity to novelty predicts both vulnerability to develop self-administration and contextual conditioning of drug effects, which suggests that the two phenomena are two related features and that conditioning plays an important role not only in the maintenance of drug intake but also in its development; (ii) conditioned and unconditioned sensitization can be developd separately in different individuals which suggests that they are independent phenomena; (iii) analysis of individual is relevant to pharmacological studies, especially with respect to drugs of abuse.

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