Effects Of NO On α7NAChR Expressions In Cerebral Cortex And Hippocampus In Learning And Memory Processes In Rats

Objective To investigate the effects of different time application nitric oxide (NO) precursor L-arginine (L-Arg) and nitric oxide synthase (NOS) inhibitor Nω-nitro-L-arginine methylester (L-NAME) on nicotinic acetylcholine receptor (nAChR) expressions and in cerebral cortex and hippocampus in spatial learning and memory processes. Analyze of the effects of NO on a7nAChR expressions in learning and memory processes and its time-dependent.Methods Experiments were conducted in two parts. Firstly21healthy male Wistar rats were devided into three groups at random, and7in each group. Every group anaesthetized by chloral hydrate and cannulated in their right lateral brain ventricle with the help of Stereotaxic Frame. The rats flexibly response, no movement disorders after surgery, we admininstrated the NO precursor L-Arg0.5μmol/d, NOS inhibiter L-NAME5μmol/d once daily for seven days and the same amount of saline as control. The ability of learning with Y-maze was tested12h after the intracerebroventricular (i.c.v.) administration at the last day, and memory test were carried24h after learning test. And①the NO level with Nitric Oxide assay kit,②a7nAChR positive expression with immunocytochemistry③as well as a7nAChR protein expression with Western-blot in prefrontal cortex and hippocampus were detected. The second part of the experiment,42healthy male Wistar rats were devided into six groups at random, and7in each group, and have the same surgery with the first part. The rats flexibly response, no movement disorders after surgery, we respectively admininstrated the NO precursor L-Arg0.5μmol/d once daily separated for three days, seven days or fourteen days, and the other three group administrated the same periods and same dose of saline with the first three groups as control.12h after the intracerebroventricular (i.c.v.) administration at the last day, behavioral detection and immunohistochemistry were carried.Results (1) The first part:1) Behavioral results showed that the stimulating times achieved learning aim significantly shorten (23.6±10.5vs41.6±13.4, P<0.01), errors also significantly decreased during this process (8.6±4.5vs15.4±6.2, P<0.01), the errors also significantly decreased during the memory process (5.7±2.4vs9.9±4.0, P<0.05) in L-Arg group, as compared with normal saline group. Whereas, the indicators of the ability of learning and memory were both reduced in L-NAME group as compared with normal saline group (57.9±9.4vs41.6±13.4,23.7±5.3 vs15.4±6.2,16.6±3.7vs9.9±4.0, P<0.01).2) the content of NO, a7nAChR-LI with immunocytochemistry, and a7nAChR protein with Western-blot in prefrontal cortex and hippocampus significantly increased in L-Arg group as compared with normal saline group (NO in cerebral cortex5.41±0.27vs3.03±0.41, hippocampus4.60±0.56vs3.10±0.64; a7nAChR-LI in cerebral cortex39.4±5.10vs30.7±5.35, hippocampus25.3±4.29vs18.6±0.83; a7nAChR protein in cerebral cortex0.35±0.03vs0.44±0.01, hippocampus a7nAChR protein0.76±0.02vs0.69±0.02, P<0.05and P<0.01). whearse decreased in L-NAME groups as compaired with normal saline group (P<0.05and P<0.01).(2) The second part:1) Behabioral results showed that the stimulating times achieved learning aim in Y-maze significantly shorten (3d33.9±8.9vs46.6±12.6,7d23.6±10.5vs4l.6±13.4,14d14.4±3.90vs43.9±13.9, P<0.05and P<0.01), errors also significantly decreased during this process (3d13.6±5.1vs20.4±6.5,7d8.6±4.5vs15.4±6.2,14d3.7±2.4vs16.4±4.0, P<0.05and P<0.01), the errors during the memory process also significantly decreased (3d8.4±2.6v11.7±2.6,7d5.7±2.4vs9.9±4.0,14d3.0±1.6vs10.1±2.4, P<0.05and P<0.01) in3days,7days and14days of L-Arg group as compared with their respective the same time NS group. The content of NO, a7nAChR-LI with immunocytochemistry significantly increased in3days,7days and14days of L-Arg group as compared with their control group.2) Comparison between the three L-Arg group, the stimulating times achieved learning aim in Y-maze significantly shorten in7days group as compared with3days group (23.6±10.5vs33.9±8.9, P<0.05) and in14days group as compared with7days group (14.4±3.9vs23.6±10.5, P<0.05), errors also significantly decreased during learning and memory process in7days group as compared with3days group (8.6±4.5vs13.6±5.1,5.7±2.4vs8.4±2.6, P<0.05), and in14days group as compared with7days group (14.4±3.9vs23.6±10.5,3.0±1.6vs5.7±2.4, P<0.05); the content of NO, a7nAChR-LI with immunocytochemistry significantly increased in7days group as compared with3days group, and in14days group as compared with7days group. The above indicators were no significant differences in three NS groups.Conclusion (1) Multiple intracerebroventricular application NO precursor L-Arg could increased the content of NO in central nervous system, enhanced the ability of learning and memory, and significantly increased the a7nAChR expression in cerebral cortex and hippocampus; whereas, multiple administration of L-NAME led to lack of nitric oxide, inhibited the ability of learning and memory and the a7nAChR expression in prefrontal cortex and hippocampus.(2) The ability of learning and memory,and the expressions of α7nAChR increased with the extension of the application of L-Arg.