Effect Of Fluoride-Arsenic Exposure On The Expression Of PI3K-mTOR Signal Molecules In Hippocampus And Cerebral Cortex In Rats Offspring

Objectives The study was designed to observe the effect of fluorine, arsenic exposure of rat pups on growth, neurobehavioral reflexology, spatial learning and memory ability and change of neurons and synaptic structure. The effect of PI3K-m TOR signaling pathway has been explored. The study would to provide scientific basis for the prevention and control of fluoride and arsenic exposure.Methods A total of 40 Sprague-Dawley pregnant rats were randomly divided into four groups, with 8 rats each. During the gestation and lactation periods(about 3 weeks), rats in the three exposure groups were exposed to 100 mg/L sodium fluoride( Na F, F group),75 mg/L sodium arsenite( Na As O2, As group), and 100 mg/L Na F and 75 mg/L Na As O2(F+As group) in drinking water, respectively. Control rats were provided drinking water without supplements. The changes of body weight, physiological development index and neurobehavior reflect of pups were observed. To detect the contents of fluoride and arsenic in the brain tissues of pups. The changes of the ultrastructure and synaptic structure of the hippocampal neurons were observed. Morris water maze was used to measure the spatial learning and memory ability of pups in PND21 and PND42, respectively. Then the protein expression levels of m TOR,phosphorylated m TOR(p-m TOR), PI3 K, AKT and phosphorylated AKT(p-AKT) in hippocampus and cerebral cortex of pup rats were detected by western blot assay.Results 1 The body weights of PND7-PND35 pups in F group and As group, PND7-PND42 pups in F+As group were lower than control group(P<0.05). 2 The positive rate of surface righting in PND5, PND7, PND10 and the positive rate of negative geotaxis in F+As group were lower than control group. 3 The escape latency period on training day 1of PND21 pups in arsenic group was significantly higher than control pups(P<0.05). The escape latency period(training day 11) of PND21 pups in fluoride plus arsenic group was significantly higher than fluoride group(P<0.05). Compared with the control pups, the first platform time(training day 4 and day 11) of PND21 pups exposed to fluoride and arsenic in combination significantly prolonged(P<0.05). The target quadrant time on training day 4 of PND21 pups in arsenic group was markedly shortened than controls(P<0.05). The frequency through the platform within 120 s on training day 4 of PND21 pups in fluoride plus arsenic group was much less than control pups(P<0.05). The frequency through the platform within 120 s on training day 11 of PND21 pups in arsenic group was much less than controls(P<0.05). The escape latency period(training day 4 and day 11) of PND42 pups in arsenic and fluoride plus arsenic group were significantly higher than control and fluoride group, pups in fluoride plus arsenic group on training day 2 was higher than control and arsenic group(P<0.05). On training day 4, the first platform time of PND42 pups exposed to fluoride and arsenic was much longer than other groups.Compared with the control pups, the first platform time and the frequency through the platform within 120 s of PND42 pups exposed were all much less than control pups, the frequency through the platform within 120 s of pups exposed to arsenic and in combination group were less than control and fluoride groups(P<0.05). On training day 11, the first platform time of PND42 pups in arsenic group and fluoride plus arsenic group were much longer than other groups. The target quadrant time of PND42 pups in exposed groups were markedly shortened than controls(P<0.05). There was no significant difference on the frequency through the platform within 120 s between four groups. 4 There were obvious changes such as cell shrinkage, nuclear deformation, perinuclear mitochondrial swelling and cavitating. The pathological changes of cynapses were also observed for synaptic vesicles of presynaptic and postsynaptic membrane and the mitochondria ridge was incomplete, the synaptic cleft was expanded, and the mitochondria in postsynaptic membrane was swelled and cavitated. 5 Compared with the controls,except the level of m TOR,p-m TOR and AKT protein expression of PND42 pups in fluoride group, the levels of PI3 K, AKT and p-AKT protein expression of PND21 and PND 42 pups in the hippocampus tissue in the three exposure groups was lower(P<0.05). The levels of p-m TOR protein expression of PND 42 pups in the cerebral cortex in the three exposure groups were lower than controls(P<0.05). The levels of AKT protein expression of PND21 and PND 42 pups in the hippocampus tissue in As group and F+As group were lower than the F groups(P<0.05). Except the levels of AKT protein expression of PND42 pups in cerebral cortex in F and As groups, the levels of PI3 K, AKT and p-AKT protein expression of PND21 and PND42 pups in cerebral cortex in the three exposure groups were lower than controls(P<0.05). Compared with the F+As group, the levels of AKT protein expression of PND42 pups in cerebral cortex in F and As groups showed the statistical difference(P<0.05).Conclusions 1 Fluoride and arsenic, either alone or combined, not only can impair growth and development but also decrease the ability of spatial learning and memory of pups. 2 Fluoride, arsenic and co-exposure can decrease the neuronal cell and synaptic structure in pups. 3 Fluoride and arsenic, either alone or combined, can up-regulation the apoptotic rate of neuron. 4 Fluoride and arsenic, either alone or combined, can downregulation the m TOR, p-m TOR, PI3 K and p-AKT protein expressions in brain of pups. 5In our study, co-exposure of fluoride and arsenic made more serious effect in growth, the ability of spatial learning and memory in PND42 pups and the neuronal cell and synaptic structure in pups than fluoride or arsenic exposed alone.