Preliminary assessment of the influence of caffeine on morphine - induced conditioned place preference in albino mice

Abstract

The rewarding effect of morphine is crucial to its addictive potential which limits its clinical use but enhances its recreational use. Caffeine is often concomitantly used with morphine due to its presence in dietary beverages. To this end, the present study was conducted to examine the influence of caffeine on morphine- induced reward, modelled as conditioned place preference (CPP). The influence of caffeine on acquisition of conditioned place preference, established by intraperitoneal injections of morphine (10 mg/kg) with or without caffeine (3 mg/kg) in an 8-day conditioning schedule, was determined in a final post conditioning test in albino mice. The effect of caffeine (3 mg/kg) on morphine- induced CPP expression was determined in a final post conditioning test after 8 conditioning sessions with morphine. The effect of caffeine on extinction of morphine induced CPP was determined on day 21 of daily extinction tests. Our results show that while caffeine did not influence the acquisition and extinction of morphine induced CPP, it significantly (p<0.05) reduced the expression of morphine induced CPP. Additionally, morphine induced CPP was resistant to extinction over a 21-day period. Altogether, given that caffeine is an antagonist of adenosine receptors, our findings suggest the involvement of adenosine receptors in morphine induced reward.