NICOTINE AND HEROIN AUGMENT COCAINE-INDUCED DOPAMINE OVERFLOW IN NUCLEUS-ACCUMBENS

The current public debate on nicotine concentrates on the abuse potent ial of nicotine per se. However, little is known about the interaction of nicotine with other drugs of well-established abuse liability such as cocaine. Indeed, cigarette smoking increases the intake of cocaine and other drugs of abuse. In order to test iii these epidemiological data are reflected in a neurochemical correlate of the reinforcing eff ects of drugs of abuse, i.e., dopamine overflow in the nucleus accumbe ns, in vivo brain microdialysis was used to examine the effects of nic otine and cocaine either alone or in combination in freely moving rats . Furthermore, the effects of the nicotine + cocaine combination were compared to another drug combination of high abuse potential, i.e., he roin + cocaine ('speedball'). Both nicotine + cocaine as well as heroi n + cocaine stimulated nucleus accumbens dopamine overflow in an addit ive manner. Repeated intermittent administration of nicotine did not s ignificantly alter the effects of a subsequent challenge with the nico tine + cocaine combination. These data suggest that the clinical-epide miological findings on either drug combination are reflected in a stim ulatory interaction on nucleus accumbens dopamine overflow that is add itive. No significant tolerance seems to develop to this effect of nic otine. These neurochemical findings support behavioral data suggesting that the reinforcing effects of cocaine and heroin are additive and p redict that nicotine will enhance the reinforcing effects of cocaine. (C) 1997 Elsevier Science B.V.