A history of alternative reinforcement reduces stimulus generalization of ethanol-seeking in a rat recovery model

Background: Longer periods of recovery reduce the likelihood of relapse, which may be due to a reduced ability of various stimuli to occasion alcohol or drug seeking. However, this hypothesis remains largely uninvestigated. Methods: Here we assessed the ability of intermediate stimuli to occasion responding for ethanol in rats trained to discriminate an 8. kHz tone signaling a food fixed-ratio (FR) of 5 and an ethanol FR5, from a 16. kHz tone signaling a food FR150 and ethanol FR5. In the presence of the 8. kHz tone responding for food predominates, and in the presence of the 16. kHz tone, responding for ethanol predominates. Results: In the context of alternation between these conditions, varying the tone from 8 to 16. kHz produces a graded increase in ethanol (versus food) responding, consistent with a stimulus generalization function. A recent history of responding under food-predominant choice conditions, either during the test session or in the four sessions that precede it shifts the generalization function downwards. Extending this history to nine sessions shifts the curve further downwards. The stimulus generalization function was similar in a separate group, trained with different relative ratios for food and ethanol, but with similar behavioral allocation under each discriminative stimulus. Finally, withholding access to food and ethanol for 4 or 16 sessions did not affect the stimulus generalization gradient. Conclusion: These results suggest that longer histories of reinforced alternative behavior might reduce the likelihood of relapse by decreasing the control exerted over alcohol- or drug-seeking by stimuli similar to those that previously occasioned alcohol- or drug-seeking.