Nitric oxide in the nucleus accumbens is involved in retrieval of inhibitory avoidance memory by nicotine

In the present study, the possible effect of nitric oxide agents injected into the nucleus accumbens (NAc) in the presence or absence of nicotine on morphine state-dependent memory in adult male Wistar rats was investigated. As a model of memory, a step-through type inhibitory avoidance task was used. Post-training injection of morphine (4 and 6 mg/kg) dose dependently induced the impairment of memory retention. Administration of morphine (4 and 6 mg/kg) before retention induced state-dependent retrieval of the memory acquired under post-training morphine (6 mg/kg) influence. Injection of nicotine before retention (0.25 and 0.5 mg/kg) alone and nicotine (0.1, 0.25 and 0.5 mg/kg) plus an ineffective dose of morphine (2 mg/kg) reversed the post-training morphine-induced memory impairment. The amnesia elicited by morphine (6 mg/kg) was also prevented by pre-retention intra-NAc administration of a nitric oxide synthase (NOS) inhibitor, l-NAME (0.24 μg/rat, intra-NAc). Interestingly, an ineffective dose of nicotine (0.1 mg/kg) in combination with low doses of l-NAME (0.06 and 0.12 μg/rat, intra-NAc) synergistically improved memory performance impaired by morphine given after training. It is important to note that intra-NAc administration of l-NAME before retention impaired memory retrieval by itself. In contrast, pre-retention administration of l-arginine, a nitric oxide (NO) precursor (0.25 and 0.5 μg/rat, intra-NAc), which had no effect alone, prevented the nicotine reversal of morphine effect on memory. The results suggest a possible role for nitric oxide of nucleus accumbens in the improving effect of nicotine on the morphine-induced amnesia and morphine state-dependent memory.