Activation of the Nitric-Oxide System in Nucleus Accumbens Inhibits the Nicotine Reversal Effects upon Ethanol-Induced Amnesia

Abstract

The present study investigated the possible involvement of the nucleus accumbens’ (NAc) nitric oxide system in nicotine's reversal effect upon ethanol-induced amnesia. The hypothesis was tested through ethanol state-dependent memory assessment in adult male Wistar rats. Bilateral chronic cannulae were implanted in the NAc and the animals were trained in a step-through type inhibitory avoidance memory task. The step-through latency was examined 24 h after animals’ training. The pre-training or pre-test intraperitoneal (i.p.) injection of ethanol (0.9 g/kg) decreased the step-through latency, indicating an amnesic effect of the drug. Meanwhile, the pre-test administration of ethanol (0.6 and 0.9 g/kg) could reverse the pre-training ethanol (0.9 g/kg)-induced amnesia, suggesting a state-dependent effect. Similar to ethanol, the pre-test intra-NAc microinjection of nicotine (0.25 and 0.5 µg/rat) alone or nicotine (0.1, 0.25 and 0.5 µg/mouse, intra-NAc) in combination with an ineffective dose of ethanol (0.3 g/kg) could significantly reverse the (pre-training) ethanol-induced memory impairment. The ethanol (0.9 g/kg)-induced amnesia was similarly prevented following the pre-test intra-NAc administration of a nitric oxide synthase (NOS) inhibitor, L-NAME (0.4 and 0.8 µg/rat). Of note, the co-administration of L-NAME (0.04 and 0.08 µg/rat, intra-NAc) with an ineffective dose of nicotine (0.1 µg/rat, intra- NAc) could significantly potentiate the memory-improving effect of nicotine on ethanol-induced amnesia and resembled the effects of pre-test administration of a higher dose of nicotine. Furthermore, while the pre-test intra-NAc injection of L-NAME impaired the memory retrieval by itself, the pre-test intra-NAc administration of L-arginine, a nitric oxide precursor (0.3 and 0.6 µg/rat, intra-NAc), did not exert any effect either alone or in combination with an effective dose of nicotine (0.5 µg/rat, intra-NAc) on pre-training ethanol-induced memory impairment. Our findings indicated a possible role of the nucleus accumbens’ nitric oxide system in the improving effects of nicotine on ethanol-induced amnesia and the related state-dependent learning.