Studies In The Effect Of Choline Supplementation On Memory And Its Mechanism In Hypoxia Exposed Mice

Objective：Highland areas are of strategic importance, its low pressure, low oxygen, cold andother environmental factors have a significant impact on human systems, including thecentral nervous system which is sensitive to hypoxia. The fact that hypoxia can affect thenervous system has been confirmed, the mechanism of hypoxic influence on the nervoussystem and cognitive function is a hot spot. A variety of diseases of the nervous systemare associated with nerve cells related tau, which is a microtubule binding protein. Whenit hyperphosphorylation it will affect their normal physiological functions. How hypoxicexposure changes cognitive function? What is the specific mechanism? Whether thischange is related to tau? Can the damage be improved by nutritional supplements? It willhave great meaning to the prevention and treatment of the cognitive dysfunction andprovide guidance to the workers in hypoxia environment caused by hypoxia if thesequestions were solved.Method：In this study, a mice model of chronic hypoxic exposure is established. Then weexamine the learning and memory function after being exposed in hypoxia, detect tauphosphorylation by western blotting. To evaluate the cholinergic system we detected theactivity of enzymes related to acetylcholine. Neuronal morphology changes are watchedby HE staining. After confirm the neuronal deficit caused by hypoxia, the mice weresupplement B complex vitamins. The improvement effect was evaluation on an overalllevel and molecular level. Research is about two parts. Thus the study contains two parts:1. Hypoxic influence on the mice cognition,2. the improvement to mice under hypoxicexposure after taking nutrients. Results:1. The influence of exposure time on learning and memory ability of miceThe experimental animals were randomly divided into four groups: control group(control),8hour hypoxia exposed group (8h),7day hypoxic exposure group (7d),28dayhypoxic exposure group (28d). The animals were placed in a hypobaric chamber,simulating environmental conditions for the height of5500m above sea level. Open-fieldtest demonstrate that after being exposed in hypoxia for8h the frequency of locomotionrear is decreased which is no statistical significance. After being exposed in hypoxia for28d the latent period is lengthened (P0.05) and the frequency of locomotion rear isdecreased(P0.05) Passive avoidance test demonstrated that after being exposed inhypoxia for28d the latent period in the bright room become shortened (P0.05) and themistake times are increased. It illustrates that chronic hypoxia chronic hypoxia hasgreater damage on the cognitive function and nervous system.With the increasing of hypoxia time tau phosphorylation has significantly increasedafter hypoxia exposure. In hippocampus after being exposed in hypoxia for28d thephosphorylation is aggravated in the site of Thr181, Ser262, and Ser396. While in cortexthe phosphorylation of these sites grows to the top after7d. As an important proteinphosphokinase GSK-3β is increased after being exposed in hypoxia for28d, whichmeans hypoxia exposure influence tau phosphorylation via GSK-3β. The activity ofenzymes about acetylcholine has changed too. The activity of ChAT decreased and AChEincreased compared with normoxic environment which means chronic hypoxiaenvironment exerts worse impact on the cholinergic system. HE staining indicates thatafter being exposed in hypoxia for28d the neuron arranges looser and the shape is not asmuch regular as the control group, which means hypoxia exerts effect on the neuronshape though the effect is slightly.2. The influence on cognitive function after supplemental B complex vitaminsexerted on mice exposed to hypoxiaThe mice were divided into five groups: control group (CONTROL), hypoxicexposure model group (HYPOXIA), hypoxic exposure while supplement complexvitamin B (HB), hypoxic exposure while supplement choline group (HC), hypoxiaexposure while supplement choline and complex vitamin B (HBC). Open-field testdemonstrate that after being supplemented choline and complex vitamin B the latent period is shortened (P0.05) and the frequency of locomotion rear is increased (P0.05)which means choline and complex vitamin B deviate the hypoxia causing depression byacting on nervous system Passive avoidance test demonstrated that after taking cholineand complex vitamin B the latent period in the bright room become lengthened (P0.05)which shows no significant change in the group HB and HC. It illustrates that takingcholine and complex vitamin B could deviate the memory damage caused by chronichypoxia. Compared with HYPOXIA group the eight arm test shows that supplementingvitamin B the mistake times and exploration time makes no difference. While aftersupplement choline the exploration time is shortened. When supplement choline andcomplex vitamin B mistake times and exploration time are both declined which illustratethat choline could improve the decreasing of space memory caused by chronic hypoxia.By detecting the enzyme joining Ach’s metabolism we find that the activity of ChATincreased compared with mice in hypoxia environment without nutrients supplement. It’smeans that choline and vitamin B could improve the central cholinergic system whichwas harmed by hypoxia. Western blotting results demonstrate that supplementing cholineand complex vitamin B the phosphorylation on the site of Thr181, Ser262and AT8oftau are decreased in hippocampus. While in cortex the site of Thr181, Ser262, AT8,AT180and Ser396are all attenuate, which means the choline and complex vitamin Bcould deviate the harm on cognition caused by hypoxia via tau’s phosphorylation.Conclusion:it was concluded that chronic hypoxia exposure could deteriorate the mice nervoussystem and cognitive function. The choline and complex vitamin B supplement willdecrease the damage. Its possible mechanism would be that the choline as a precursor ofneurotransmitter acetylcholine, through the blood brain barrier after administration, couldbe catalytic synthesized with acetyl coenzyme A to increase acetylcholine levels in thebrain. Then the neurons surface receptors are activated which start downstream signaltransduction, reduced levels of phosphorylated tau protein.