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| Paper IPM / Cognitive Sciences / 12179 |
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| Abstract: | |||||
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In the present study, the possible involvement of nitric oxide systems in the ventral tegmental area (VTA) in nicotine?s effect on morphine-induced amnesia and morphine state-dependent memory in adult male Wistar rats was investigated. Step-through type inhibitory avoidance task was used to test memory retrieval. Post-training administration of morphine (5 and 7.5 mg/kg) induced amnesia. The response induced by post-training morphine was significantly reversed by pre-test administration of the drug. Pretest injection of nicotine (0.4 and 0.8 mg/kg s.c.) alone and nicotine (0.1, 0.4 and 0.8 mg/kg s.c.) plus an ineffective dose of morphine also significantly reversed the amnesia induced by morphine. Morphine amnesia was also prevented by pretest administration of L-arginine (1 and 3 �g/rat, intra-VTA), a nitric oxide (NO) precursor. Interestingly, an ineffective dose of nicotine (0.1 mg/kg s.c.) in combination with low dose of L-arginine (0.3 g/rat, intra-VTA) synergistically improved memory performance impaired by morphine given after training. In contrast, pre-test administration of NG nitro-L-arginine methyl ester hydrochloride (L-NAME), a nitric oxide synthase (NOS) inhibitor (2 �g/rat, intra-VTA) prevented the nicotine reversal of morphine effect on memory. The results suggest a possible role for nitric oxide of ventral tegmental area in the improving effect of nicotine on the morphine-induced amnesia.
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