Correlation Of Barin Injury Induced By Drinking Water Fluorosis And L-type Calcium Channel Of Neuron In Hippocampus Of Mice

Fluoride is a common and essential trace element in human life.It can enter the body through breathing,eating and drinking.However,excessive intake of fluoride can accumulate in the body,resulting in multiple organ damages.It is called endemic fluorosis,or fluorosis.Fluorosis damaged the bone organs,induced dental fluorosis and skeletal fluorosis,and damaged nonbone organs such as liver,kidney,reproductive system and the central nervous system.Not only dental fluorosis and skeletal fluorosis incidence increased in fluorosis area,but also appeared significantly lower IQ of children,and the elderly cognitive impairment and other phenomena.Hippocampus is an important part of brain in learning and memory,and also a target organ of fluorosis.CA1 region of hippocampus is an important part to memory conduction process of hippocampus.The L-type calcium channel is a voltage-gated channel on the cell membrane.It is also the main channel for calcium ions to flow into the cell.The change of its activity may lead to the intracellular calcium metabolism,thereby affecting the normal development and synaptic plasticity of brain cells.In recently years,"fluorosis induced calcium metabolism imbalance theory" has gradually aroused the attention,in this experiment,on the basis of preliminary studies,we detected learning and memory from behavior,brain oxidative stress related index of blood and L-type calcium channel current of vertebral neurons in CA1 region of hippocampal in mice after exposed to fluoride for 3 and 6 months,and mainly discussed the relationship between drinking water fluorosis induced brain injury of mice and L-type calcium channels of hippocampus neurons.Early weaned,SPF,healthy male ICR rats(60 rats aged 3 weeks)were randomly divided into four groups after 7 days in laboratory conditions.In the control group(CON),mice receiving tap water(<0.2 mg/L);low fluoride group(LF),mice receiving aqueous sodium fluoride(NaF,5 mg/L);and high fluoride group(HF),mice receiving aqueous sodium fluoride(NaF,30 mg/L).All of the mice were fed with a standard pellet diet(fluoride content<0.2 mg/kg,calcium content of 7-10g/kg).We observated learning and memory behavior of mice after exposed to fluoride for 3 months and 6 months,and the dental fluorosis and blood/urine fluoride content test results as the success replicate of the standard animal models of subchronic and chronic fluorosis,then we detected of serum total protein(TP)content and total antioxidant capacity(T-AOC),superoxide dismutase(SOD)activity,glutathione peroxidase(GSH-Px)activity and malondialdehyde(MDA)content,we used patch clamp to record the changes of L-type calcium channel current intensity of hippocampus CA1 region of mice,to explore the pathogenesis of brain injury caused by fluorosis,and provide the basis data for prevention and treatment of endemic fluorosis.In the experimental results,the results of fluorosis and blood fluorine/urine fluoride indicate that the subchronic/chronic animal model was successfully replicated;the results of the opening behavior showed that the mice in the fluorosis group had increased abnormal excitability and the inquiry behavior was significantly reduced;Morris water maze test The results showed that the ability of learning and memory of ICR mice with fluorosis was significantly decreased,and the decrease was correlated with the time and concentration of fluoride exposure.The blood oxidative stress related indicators showed that the total protein in the serum of mice infected with fluoride was detected.Content,GSH-Px,SOD,and T-AOC activity values decreased significantly,and MDA content increased significantly,suggesting that chronic and sub-chronic fluorosis can lead to reduced antioxidative stress and increased peroxidation in mice.The results of brain patch clamp study showed that the peak value of L-type calcium channel currents in pyramidal neurons in hippocampal CA1 region of mice exposed to fluoride increased significantly,and increased with the increase of exposure time;current relative values and steady-state coefficients Significant changes;current inactivation time and tail current time significantly increased,and the higher the fluorine concentration,the peak value and opening duration of LTCC increase in the hippocampal CA1 pyramidal neurons in mice treated with fluorosis increased,suggesting that L-type Calcium ion channels are sensitive to fluoride exposure.The electrophysiological mechanisms of brain injury induced by fluorine exposure may be:the activation voltage of calcium ion channels is reduced by fluorine exposure,the opening time of calcium channels is prolonged,and calcium influx per unit time is excessive,causing nerves Intracellular calcium overload,triggering a series of pathological reactions such as the significantly increased expression level of pro-apoptotic molecules,eventually lead to nerve cell injury.At the same time,the imbalance of calcium metabolism caused by fluorosis may be one of the pathogenesis of fluoride-induced brain injury.