Involvement of nitric oxide in insulin induced memory improvement

Although brain was considered as an insulin-insensitive organ, recently it has appeared that insulin has some interesting effects on some brain regions like hippocampus. It has been known that intra-hippocampally administered insulin can improve learning and memory. Knowing that insulin can stimulate nitric oxide (NO) synthesis via eNOS activation and also that NO synthase (NOS) inhibitors can affect learning and memory, the aim of this study was to assess if NO is involved in insulin induced memory improvement. Wistar male rats were intra-CA1 cannulated and the effect of post-training and pre-probe trial intra-hippocampal administration of N-nitro-l-arginine methyl ester (l-NAME) (5, 10, 30 μg), insulin + l-NAME ± l-arginine were assessed in a single-day testing version of Morris water maze (MWM) task. Our results show that, l-NAME can prevent insulin induced memory improvement. This drug had no effect on escape latency of a non-spatial visual discrimination task. Therefore, it seems that endogenous nitric oxide has a role in spatial learning and memory improvement caused by insulin.