The Variation Of α7nAChR And NNOS In Central Expressions And Its Effects On Learning And Memory Abilities Of Aβ-induced Cognitive Dysfunction Rats

Objective:The aim is to explore the temporal and spatial distributions and variations of nicotinic acetylcholine receptor(n ACh R) and neuronal nitric oxide synthetase(n NOS) in cerebral cortex and hippocampus of Aβ-induced cognitive dysfunction rats and its effects on learning and memory. To observe α7n ACh R and n NOS level and distribution in cerebral cortex and hippocampus of Aβ-induced cognitive disordered rats in different endurance time, and analyze the spatial characteristics and laws with time prolong of the Aβadministration. Meanwhile, to analyze the level of n NOS and α7n ACh R in cerebral cortex and hippocampus and the influence on learing and memory abilities after repeatly injecting L- arginine( L-Arg, the NO precursor) or choline chloride(an agonist of α7 nicotinic acetylcholine receptor) and L-Arg+CC into lateral ventricle, to explore the interaction of NOergic and cholinergic system in cognitive dysfunction rats.Methods :Firstly, 60 SD rats were randomly divided into six groups. Three experimental groups were intracerebroventricularly(i.c.v.) injected with condensed-amyloid beta peptides 1-42(Aβ1-42, 2.5 μg/ μl, 4μl) and were observed consecutive seven days(7 d Aβ group),fourteen days(14 d Aβ group) or twenty-one days(21 d Aβ group), respectively; three control groups were i.c.v. injected with the same amount of normal saline and were observed the same length of time as the three experimental groups. The learning and memory abilities of rats was tested with Y-maze; the locations of α7n ACh R and n NOS in the cerebral cortex and hippocampal CA1, CA3 and DG regions were measured by immunohistochemistry and the expressions of α7n ACh R and n NOS were measured by Western blot. Secondly, 40 SD rats were randomly divided into four groups. Rats were i.c.v.injected with condensed-amyloid beta peptides 1-42(Aβ1-42)(2.5 μg/ μl, 4μl); and 30 minutes after injected with Aβ1-42, rats were i.c.v. injected with L-arginine(L-Arg, the NO precursor) 17.5 μg/ μl(Aβ+L-Arg group) or choline chloride(CC, an agonist of α7n ACh R)8 μg/ μl(Aβ+CC group), and with combined injection of equal amount of L-Arg and CC(Aβ+L-Arg+CC group) and normal saline was used as control(Aβ+NS group),respectively, 5 μl every time, once daily for seven consecutive days. Behavioral detection,immunohistochemistry and Western-blot were carried 30 minutes after the last day of the i.c.v. administration.Results:(1) The first part: 1) The results of Y-maze test showed that the numbers of stimulations to reach the learning and memory criterions of rats were decreased with the increased of testing days. Whereas, the stimulating times increased in three experimental groups as compared with three saline groups(all were P<0.01). A comparison among three experimental groups showed that the stimulations to criterion increased in 14-day group in comparison with 7-day group(all were P<0.05), and in 21-day group in comparison with14-day group(P<0.05 or P<0.01). There were no significant differences in the above indicators of the three control groups. 2) The results of the optical density of n NOS-LI andα7n ACh R-LI in cortex and hippocampal regions with immunocytochemistry decreased in three experimental groups as compared with three NS groups, as well as the results of the protein expressions with Western-blot(P<0.05 or P<0.01). Especially the superficial layer of prefrontal cortex and hippocampal CA3 region have a larger range of variation. All the above parameters of the three experimental groups were decreased in 14-day group as compared with 7-day group(P<0.05 or P<0.01), and in 21-day group as compared with14-day group(P<0.05 or P<0.01). There weren’t significant differences in the results of the three saline groups.(2) The second part: 1) The numbers of stimulations to reach the learning and memory criterions on Y-maze were decreased in Aβ + L-Arg group(all were P<0.05) or Aβ + CC group(P<0.05 or P<0.01) as compared with Aβ + NS group, and the numbers were decreased in Aβ + L-Arg + CC group compared with that in Aβ + L-Arg group or Aβ + CC group(all were P<0.05 or P<0.01). 2) The optical density of n NOS-LI and α7n ACh R-LI and the protein expressions in prefrontal cortex and hippocampal regions were increased in Aβ + L-Arg group(all were P<0.05) or Aβ + CC group(P<0.05 or P<0.01) as compared with Aβ + NS group, these indicators were increased in Aβ + L-Arg+ CC group compared with that in Aβ + L-Arg group or Aβ + CC group(all were P<0.05 or P<0.01).Conclusion:(1) The abilities of learning and memory, the expressions of α7n ACh R and n NOS in the prefrontal cortex and hippocampus showed progressive decline with the extension of the application of A beta in the model of cognitive dysfunction of Aβ-induced rats.Especially the superficial layer of prefrontal cortex and hippocampal CA3 region have a larger range of variation.(2) Intracerebroventricular administration of L-Arg combined with choline chloride can significantly promote the single action of the L-Arg or choline chloride on the expressions of n NOS and α7n ACh R in the prefrontal cortex and hippocampus along with the improvement of cognitive dysfunction of rats. The results suggest that the synergistic effects between n NOS and nicotinic system can be conductive to the improvement of cognitive dysfunction in rats.