A comparison of mecamylamine and bupropion effects on memory-related responses induced by nicotine and scopolamine in the novel object recognition test in mice.

The aim of the present study was to evaluate the involvement of the cholinergic receptors ligands in the memory-related responses in mice, using the novel object recognition (NOR) test. The NOR test is based on natural, exploratory abilities of animals exposed to a new environment. In the first session, two copies of the same object were presented. In the next sessions (30min and 24h after), one of the familiar object and a new object were presented. The mice injected with nicotine (0.035 and 0.175mg/kg, free base, sc) before the first session spent more time exploring the new object than the familiar one at the second and third session, indicating that nicotine improved cognition. In turn, the mice injected with scopolamine (0.3 and 1mg/kg, ip) before the first session spent less time exploring the new object than the familiar one at the second and third trial, indicating that scopolamine impaired the memory performance. Additionally, the acute injection of drugs used in smoking cessation in humans: mecamylamine (0.5 and 1mg/kg) and bupropion (5 and 10mg/kg), prior to injections of nicotine (0.035mg/kg) or scopolamine (1mg/kg), significantly prevented nicotine-induced memory improvement or scopolamine-induced memory impairment, at the second and third session. The results of our studies unveiling neuronal mechanisms for cholinergic system of memory processes, via both nicotinic and muscarinic cholinergic receptors, will be useful for development of more effective pharmacotherapies for memory impairment-like treatment of human disorders in which cholinergic pathways have been implicated.