Memory enhancing effects of nicotine, cocaine, and their conditioned stimuli; effects of beta-adrenergic and dopamine D2 receptor antagonists.

Abstract

BACKGROUND\nThere is evidence that post-training exposure to nicotine, cocaine, and their conditioned stimuli (CS), enhance memory consolidation in rats. The present study assessed the effects of blocking noradrenergic and dopaminergic receptors on nicotine and cocaine unconditioned and conditioned memory modulation.\n\n\nMETHODS\nMales Sprague-Dawley rats tested on the spontaneous object recognition task received post-sample exposure to 0.4\xa0mg/kg nicotine, 20\xa0mg/kg cocaine, or their CSs, in combination with 5-10\xa0mg/kg propranolol (PRO; beta-adrenergic antagonist) or 0.2-0.6\xa0mg/kg pimozide (PIM; dopamine D2 receptor antagonist). The CSs were established by confining rats in a chamber (the CS\u2009+) after injections of 0.4\xa0mg/kg nicotine, or 20\xa0mg/kg cocaine, for 2\xa0h and in another chamber (the CS\u2009-) after injections of vehicle, repeated over 10\xa0days (5 drug/CS\u2009+\u2009and 5 vehicle/CS\u2009-\u2009pairings in total). Object memory was tested 72\xa0h post sample in drug-free animals.\n\n\nRESULTS\nCo-administration of PRO or PIM blocked the memory-enhancing effects of post-training injections of nicotine, cocaine, and, importantly, exposure to their CSs.\n\n\nCONCLUSIONS\nThese data suggest that nicotine, cocaine as well as their conditioned stimuli share actions on overlapping noradrenergic and dopaminergic systems to modulate memory consolidation.