Abstract

The prevalence of alcohol, nicotine and caffeine place these substances among the most widely consumed in the world. Over the years studies have documented a strong positive relationship in the use of these drugs. Increasing attention within both the human and animal literature has been devoted to the study of the potential interactive effects between these recreational substances. The goal of this thesis was to examine the relationship between the positive reinforcing and conditioned taste aversion (CTA)-inducing properties of alcohol, caffeine and nicotine, and in so doing, to further elucidate the nature of the relationship between the phenomena of positive reinforcement and conditioned taste aversion. Experiments 1a-c and 2a-c showed that acetaldehyde, the putative reinforcing metabolite of ethanol may share common stimulus properties with nicotine and may also mediate the previously observed interaction between nicotine and ethanol in the preexposure CTA paradigm. Experiment 3 demonstrated that caffeine and nicotine shared common stimulus properties in the preexposure CTA procedure. Experiment 4 showed that mecamylamine, the nicotinic acetylcholine receptor antagonist, reversed the nicotine-induced attenuation of caffeine CTA and also blocked the formation of a caffeine-induced CTA. Experiments 5a and 5b demonstrated that caffeine facilitated the acquisition and maintenance of ethanol drinking in free feeding ethanol naïve animals. Experiments 5c and 5d revealed that the caffeine-induced elevation in ethanol drinking while unrelated to alteration in blood ethanol, might have been related to an increase in corticosterone. Experiments 6a-c showed that caffeine's facilitation of ethanol drinking might have resulted in an increase in the reinforcing efficacy of ethanol as reflected in CTA. Experiments 7a-c indicated that while locomotion responses to an inescapable novel environment appeared to be differentially related to the development of CTAs to amphetamine and morphine in rats it was unrelated to the expression of a LiCl induced CTA. Finally, the results of experiment 8 demonstrated a positive relationship between the amount of saccharin consumed orally and the expression of c-Fos -like immunoreactivity (FLI) in the Nucleus of the Solitary Tract suggesting that FLI may be more reactive to positive rather than aversive conditioning effects. Taken together, the studies reported here further shed light on the nature of the relationship between commonly co-used recreational substances and also support the hypothesis that the positively reinforcing and CTA inducing properties of self-administered drugs are indeed related and possibly governed by a shared neurobiological substrate.