Caffeine, nicotine and mecamylamine share stimulus properties in the preexposure conditioned taste aversion procedure

Abstract

Rationale: The present study examined whether nicotine and caffeine, two of the most widely used psychoactive drugs, share stimulus properties in the preexposure conditioned taste aversion (CTA) procedure.

Objectives: To determine whether nicotine would attenuate the formation of a caffeine-induced CTA and further assess whether pretreatment with mecamylamine, a nicotinic receptor antagonist, would reverse nicotine's attenuating effect of a caffeine-induced CTA.

Methods: Male Wistar rats were preexposed with one of three doses of nicotine (0.6, 1.2 and 2.0 mg/kg, s.c.) for three consecutive days, then 24 h following the final preexposure injection were conditioned with caffeine (20 mg/kg and 30 mg/kg, i.p.) in a standard two-bottle test. There were four conditioning trials and four drug-free test days. In a follow-up study, rats were pretreated with mecamylamine (2 mg/kg, i.p.) prior to preexposure injections with nicotine (0.6 mg/kg, i.p.), then subsequently conditioned with caffeine (20 mg/kg, i.p.) as described above.

Results: The lowest nicotine dose (0.6 mg/kg) attenuated the caffeine induced CTAs (20 mg/kg and 30 mg/kg) but the higher nicotine doses showed no such attenuating effect. In addition, mecamylamine reversed the nicotine-induced attenuation of the caffeine-induced CTA and also directly attenuated it.

Conclusions: These results suggested that caffeine, nicotine and mecamylamine share overlapping stimulus properties and that the nature of this relationship may involve action at the nicotinic-cholinergic receptor.