, Volume 224, Issue 4, pp 537-548
Date: 05 Jul 2012

Discrimination of ethanol–nicotine drug mixtures in mice: dual interactive mechanisms of overshadowing and potentiation

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Abstract

Rationale

One possible basis for the proclivity of ethanol and nicotine co-abuse is an interaction between the discriminative stimulus (SD) effects of each drug.

Objectives

The current work sought to assess the discriminative control of ethanol and nicotine cues in mice trained with drug mixtures and to determine whether interactive mechanisms of overshadowing and potentiation occur.

Methods

Male C57BL/6J mice were trained to discriminate ethanol (1.5 g/kg) alone or ethanol plus nicotine (0.4, 0.8, or 1.2 mg/kg base) in experiment 1 and nicotine (0.8 mg/kg) alone or nicotine plus ethanol (0.5, 1.0, or 2.0 g/kg) in experiment 2. Stimulus generalizations of the training mixtures to ethanol, nicotine, and the drug combination were assessed.

Results

Ethanol (1.5 g/kg) retained discriminative control despite the inclusion of a progressively larger nicotine dose within the training mixtures in experiment 1. Although the nicotine SD was overshadowed by ethanol training doses > 0.5 g/kg in experiment 2, nicotine did potentiate the effects of low-dose ethanol.

Conclusions

These findings are suggestive of dual mechanisms whereby ethanol (>0.5 g/kg) overshadows the SD effects of nicotine, and at lower doses (<1 g/kg) the salience of ethanol’s SD effects is potentiated by nicotine. These mechanisms may contribute to the escalation of concurrent drinking and smoking in a binge-like fashion.