Ultrasonic vocalization in rats self-administering heroin and cocaine in different settings: evidence of substance-specific interactions between drug and setting.

Riccardo Avvisati,Caterina Michetti,Christian Montanari,Laura Contu,Aldo Badiani,Maria Luisa Scattoni,Emiliana Stendardo

doi:10.1007/s00213-016-4247-4

Abstract

RationaleClinical and preclinical evidence indicates that the setting of drug use affects drug reward in a substance-specific manner. Heroin and cocaine co-abusers, for example, indicated distinct settings for the two drugs: heroin being used preferentially at home and cocaine preferentially outside the home. Similar results were obtained in rats that were given the opportunity to self-administer intravenously both heroin and cocaine.ObjectivesThe goal of the present study was to investigate the possibility that the positive affective state induced by cocaine is enhanced when the drug is taken at home relative to a non-home environment, and vice versa for heroin.MethodsTo test this hypothesis, we trained male rats to self-administer both heroin and cocaine on alternate days and simultaneously recorded the emission of ultrasonic vocalizations (USVs), as it has been reported that rats emit 50-kHz USVs when exposed to rewarding stimuli, suggesting that these USVs reflect positive affective states.ResultsWe found that Non-Resident rats emitted more 50-kHz USVs when they self-administered cocaine than when self-administered heroin whereas Resident rats emitted more 50-kHz USVs when self-administering heroin than when self-administering cocaine. Differences in USVs in Non-Resident rats were more pronounced during the first self-administration (SA) session, when the SA chambers were completely novel to them. In contrast, the differences in USVs in Resident rats were more pronounced during the last SA sessions.ConclusionThese findings indicate that the setting of drug taking exerts a substance-specific influence on the ability of drugs to induce positive affective states.

Highlights

Previous experiments have shown that the setting of drug taking exerts a powerful influence on the rewarding effects of heroin and cocaine and that this influence is substance-specific
Differences in ultrasonic vocalizations (USVs) in Non-Resident rats were more pronounced during the first self-administration (SA) session, when the SA chambers were completely novel to them
The differences in USVs in Resident rats were more pronounced during the last SA sessions

Summary

Introduction

Previous experiments have shown that the setting of drug taking exerts a powerful influence on the rewarding effects of heroin and cocaine and that this influence is substance-specific. Cocaine self-administration (SA), for example, is greatly facilitated when rats self-administer the drug in an environment that is distinct from the home environment (Non-Resident rats) relative to rats for whom the SA chamber is the home environment (Resident rats) (Caprioli et al 2007a, b). Non-Resident rats exhibit greater motivation for cocaine SA than Resident rats, as indicated by progressive ratio reinforcement schedule procedures. Resident rats self-administer more heroin than Non-Resident rats and exhibit greater motivation in break-point procedures (Caprioli et al 2008). Non-Resident rats tend to prefer cocaine to heroin in a choice procedure, whereas Resident rats tend to prefer heroin to cocaine (Caprioli et al 2009). Non-Resident rats are more vulnerable to relapse into

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Conclusion