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Caffeine, a common active adulterant of cocaine, enhances the reinforcing effect of cocaine and its motivational value

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Abstract

Rationale

Caffeine is one of the psychoactive substances most widely used as an adulterant in illicit drugs, such as cocaine. Animal studies have demonstrated that caffeine is able to potentiate several cocaine actions, although the enhancement of the cocaine reinforcing property by caffeine is less reported, and the results depend on the paradigms and experimental protocols used.

Objectives

We examined the ability of caffeine to enhance the motivational and rewarding properties of cocaine using an intravenous self-administration paradigm in rats. Additionally, the role of caffeine as a primer cue during extinction was evaluated.

Methods

In naïve rats, we assessed (1) the ability of the cocaine (0.250–0.125 mg/kg/infusion) and caffeine (0.125–0.0625 mg/kg/infusion) combination to maintain self-administration in fixed ratio (FR) and progressive ratio (PR) schedules of reinforcement compared with cocaine or caffeine alone and (2) the effect of caffeine (0.0625 mg/kg/infusion) in the maintenance of responding in the animals exposed to the combination of the drugs during cocaine extinction.

Results

Cocaine combined with caffeine and cocaine alone was self-administered on FR and PR schedules of reinforcement. Interestingly, the breaking point determined for the cocaine + caffeine group was significantly higher than the cocaine group. Moreover, caffeine, that by itself did not maintain self-administration behavior in naïve rats, maintained drug-seeking behavior of rats previously exposed to combinations of cocaine + caffeine.

Conclusions

Caffeine enhances the reinforcing effects of cocaine and its motivational value. Our results highlight the role of active adulterants commonly used in cocaine-based illicit street drugs.

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Acknowledgments

The authors report no conflicts of interest. This study was supported by University of Cagliari and Fondazione Banco di Sardegna (local grant, CAR 2013-2014); Grant FCE 3/2013/1/100466, Smoked Cocaine in South Cone Countries Grant CICAD-OEA/USINL and PEDECIBA (Uruguay). José Pedro Prieto and Martín Galvalisi had postgraduate fellowships from ANII.

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    Authors and Affiliations

    1. Department of Experimental Neuropharmacology, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay

      José Pedro Prieto, Cecilia Scorza & Martín Galvalisi

    2. Department of Neurochemistry, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay

      Juan Andrés Abin-Carriquiry

    3. Department of Biomedical Sciences, University of Cagliari, Cagliari, Italy

      Gian Pietro Serra, Valentina Perra, Giovanna Piras & Valentina Valentini

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    1. José Pedro Prieto
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    2. Cecilia Scorza
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    Correspondence to Valentina Valentini.

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    José Pedro Prieto and Cecilia Scorza contributed equally to this work.

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    Prieto, J.P., Scorza, C., Serra, G.P. et al. Caffeine, a common active adulterant of cocaine, enhances the reinforcing effect of cocaine and its motivational value. Psychopharmacology 233, 2879–2889 (2016). https://doi.org/10.1007/s00213-016-4320-z

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