Effects Of Fluoride And Arsenic Exposure On The Growth And Learning And Memory Of Offspring In Rats And Mechanism

Objectives The study was designed to observe the effect of fluoride, arsenic and co-exposure on growth and development,neurobehavioral reflex, spatial learning and memoryability in offspring of rats. The levels of second messengers and retrograde messenger,amino acid neurotransmitters were measured to explore the molecular mechanisms oflearning and memory impairment induced by fluoride, arsenic and their combinedexposure. The study would provide a scientific basis for molecular mechanisms inneurotoxicity induced by chronic exposure to fluoride, arsenic and combined fluoride andarsenic, and prevention for chronic fluoride and arsenic combined poisoning.Methods Eighty SD rats mated according to male and female ratio of1:1. Pregnant ratswere divided into four groups including control, fluoride, arsenic and fluoride-arsenicgroup, each group included10pregnant rats. These pregnant rats in fluoride, arsenic andfluoride-arsenic group were exposed to100mg/L NaF,75mg/L NaAsO2,100mg/L NaFplus75mg/L NaAsO2mixed solution through drinking water ad libitum, respectively, untilpostnatal day21(PND21) of offspring. The control pregnancy rats drunk water freely. Thechanges of body weight, physiological development index and neurobehavior reflect ofoffspring were observed. The learning and memory function was evaluated with Morriswater maze.The concentration of Ca2+in hippocampus cell was detected by flow cytometry.The levels of NO and NOS in hippocampus, cortex tissue and serum were measured by akit.The levels of Glu and GABA in the hippocampus and cortex tissue and serum ofoffspring were detected by HPLC. The protein expression of mGluR1ɑ and mGluR5in thehippocampus were detected using western-blot assay.Results1The body weights of PND4and PND21pups in arsenic group and PND4,PND7, PND14and PND21pups in fluoride-arsenic group were much lower than controlpups (P<0.05). Compared with the control pups, the positive rate of surface righting andslop turning in PND5pups and the positive rate of slop turning in PND6pups exposed tofluoride decreased (P<0.0083). Compared with the control pups, the positive rate of slopturning in PND6pups exposed to arsenic and the positive rate of slop turning and cliffavoidance in PND6pups exposed to fluoride-arsenic decreased (P<0.0083).The arms hangtime of PND12,PND13and PND14pups in arsenic and fluoride-arsenic group were muchshorter than those of controls (P<0.05).2The escape latency periods on training day4ofPND21and PND42pups in arsenic group and fluoride plus arsenic group weresignificantly higher than control pups (P<0.05).The escape latency period (training day4)of PND42pups in fluoride plus arsenic group was significantly higher than fluoride andarsenic exposure alone (P<0.05). Compared with the control pups, the first platform timeof PND21and PND42pups exposed to fluoride and arsenic individually and incombination significantly prolonged, the target quadrant time markedly shortened (P<0.05),and the frequency through the platform within120s of PND42pups were all much lessthan control pups (P<0.05). The differences of escape latency, the first platform time，thetarget quadrant time and the frequency through the platform between PND21and PND42 pups in the four groups were not statistically significant.3Compared with the controlgroup, the content of NO in serum of PND21pups in arsenic group and fluoride-arsenicgroup increased. Compared with the fluoride group, the content of NO in serum of PND21pups increased.The NO content and iNOS activity in the hippocampus of PND21pups inarsenic group and fluoride-arsenic group were higher than the control pups. The iNOSactivity in hippocampus of PND21pups in fluoride group was higher than the control pups(P<0.05). Compared with the control group, the content of NO in the hippocampus ofPND42pups in arsenic group and fluoride-arsenic group were higher than the control pups.The TNOS and iNOS activity in the cortex tissue of PND21pups in arsenic group werehigher than the other three groups (P<0.05). The TNOS activity in cortex tissue of PND42pups in fluoride-arsenic group were lower than fluoride and arsenic group,the iNOSactivity was lower than the other three groups (P<0.05).4Compared with the controlgroup, the level of Glu in the hippocampus tissue of PND21and PND42pups in arsenicgroup and fluoride-arsenic group decreased, the level of Glu of PND42pups inhippocampus significantly decreased; the level of GABA in hippocampus of PND42pupsin arsenic group and fluoride-arsenic group decreased. The level of Glu in cortex tissue ofPND21and PND42pups in fluoride-arsenic group and the level of Glu of PND42pups influoride and arsenic group decreased. The levels of GABA in cortex tissue of PND21andPND42pups in fluoride, arsenic and fluoride-arsenic group significantly decreased(P<0.05). The level of Glu in cortex tissue of PND21pups in fluoride-arsenic group,andthe level of GABA in cortex tissue of PND42pups in arsenic and fluoride-arsenic groupwere all lower than the fluoride group (P<0.05).5Compared with the control group, thelevels of mGluR1ɑ protein expression of PND21pups in arsenic group and fluoride-arsenic group decreased (P<0.05). The mGluR5protein expression in the hippocampustissue of PND21pups in fluoride group, arsenic group and fluoride-arsenic group waslower than the control group. The levels of mGluR5protein expression of PND42pups inarsenic group and fluoride-arsenic group were lower than the control group. Comparedwith fluoride group, the levels of mGluR1ɑ protein expression of PND21pups in fluoride-arsenic group decreased (P<0.05).Conclusions1Fluoride and arsenic, either alone or combined, can impair growth anddevelopment and neurobehavioral reflect of rats offspring.2Fluoride and arsenic, eitheralone or combined, could decrease the ability of spatial learning and memory in ratoffspring.3Fluoride, arsenic and co-exposure can affect the NO content and NOS activity,decrease Glu and GABA levels, mGluR1ɑ and mGluR5protein expressions in thehippocampus tissues in pups.4The effect of fluoride plus arsenic on NO content,Glucontent and mGluR1ɑ protein expression in hippocampus tissue was greater than fluorideor arsenic exposure, suggesting that there may be interactions between fluoride and arsenic.