The Effect On Learning And Memory And The Changes Of NMDA Receptor Expression Of Offspring Rats After Arsenic Exposure During Different Perinatal Periods

Arsenic is a half-metal element,which widely exists in the environment as the form of compound. Dissipating to surrouding environment,Original and oxidative arsenic can cause air,water and field crops pollution.People intaking arsenic-polluted water and food or fume containing arsenic can cause acute and chronic arseniasis,and also increase the attack rate of cancer.People pay more attention to arsenic because as a neuropoison arsenic can impair the nervous system.These years,epidemiologic survey showed that youngsters,who drank water with arsenic for a long period,had decreased memory,attention and linguistic capacity.Animal experiment also demonstrated that arsenic can delay neurobehavior and impair learning and memory ability of offspring rats.Learning and memory ability is closely associated with activity of human life.The function of central nervous system can be affected by lots of factors,and it is more sensitive to the toxic effects than other organizations.Glutamic acid is the highest content amino acid in the central nervous system,and it is a general and intensive excitatory neurotransmittcr in the nervous system.N-methyl-D-aspartate(NMDA) receptor is one of the glutamate receptor subtypes,and its channel only open in the process of learning and memory.Consequently,NMDA receptor is considered to play a key role in the learning and memory function.This research focused on the channel subunits of NMDA receptor genc and protein expression level in order to study the relationship between NMDA receptor and learning and memory impairment caused by arseniasis.The aim of this study was to find out the molecular mechanism of learning and memory impairment caused by arsenic exposure during developmental period of offspring rats.It could provide a new target for interventing the dangers of arseniasis at cellular and molecular level,and it also provided experimental evidence for preventing the harm of teenagers arsenic poisoning.Sprague-dawley male rats were exposed to arsenite(100 mg/L in drinking water) in three groups (pregnancy,lactation and the whole range) from gestation day 0 until F1 pups 42 days old.The control group drunk distilled water.The weight changes of F1 pups was observed and the indicators of physiological development and neurobehavior changes was recorded.Till postnatal 42 days,pups were taken three experimental tests of hidden platform acquisition,probe trial and subsequent visible platform in the Morris water maze(MWM).Hippoeampus was collected for detecting the subunits mRNA and protein expression level of the NMDA receptor,respectively using RT-PCR and Western-blot assay.The results was taken statistical analysis using Quantity one software system.2-week-old neonatal rats were selected to collect hippocampal slices for patch clamp test.Using whole-cell recording technique,the action potentials of hippocampal slices and changes of NMDA receptor channel current were recorded after hippocampal slices were incubated by arsenite.The results were used to authenticate the neurobehavior test and molecular biological experiment.The weight of F1 pups in groups of lactation and the whole range were much lower than in control group after postnatal day 7(P＜0.05).But other physiologic markers(eye opening,pinna detachment,hair growth,tooth growth,et al) were not affected by arsenic exposure.In contrast to the control group,surface righting,cliff avoidance and negative geotaxis in group of the whole range were significantly delayed (P＜0.05).In Morris water maze tests,the time of F1 pups in arsenite exposed group during lactation swimming correctly to the hidden-platform were much longer than the whole range group(P＜0.05),and the times of F1 pups swimming across the target region were also much fewer than the whole range group(P＜0.05). There were no significant difference among any other groups.The result showed that the learning and memory ability of offspring can be inhibited by arsenite during lactation exposure.When arsenite concentration of offspring rats reached a certain degree after postnatal,it could present some promotion in a short period,because that arsenic is the minor element for the development of animals.In contrast to the control group,the NR2A gene and protein expression in pregnancy exposure and lactation exposure group was significantly decreased(P＜0.05).But NR1 and NR2B subunit expression level had not obvious effect.NR1 is the basic subunit in learning and memory ability,while NR2 is the accommodation subunit.NR2A expression being inhibited may be one of the molecule mechanism of the learning and memory ability of offspring rats being damaged by arsenic exposure during pregnancy and lactation period.The results of patch clamp experiment showed that the action potentials of hippocampal slices and channel current of NMDA receptor were both significantly diminished,and the difference became bigger on account of the concentration of arsenite was higher.This result showed that arsenic could certainly cause NMDA receptor channel damage,which could inhibit neurobehavior development and learning and memory ability of offspring rats.These researches showed that lactation arsenite exposure can obviously inhibit the growth and neurobehavior development of offspring rats.Arsenite exposure during lactation period can impair the learning and memory ability of offspring rats.But in a short period after postnatal,moderate arsenite also can cause a certain auxoaction.Therefore,the effect on the learning and memory ability of offspring rats exposed to arsenite at different development period should be further studied.Among NR1,NR2A and NR2B subunits,NR2A plays an important role in the process of arsenite impairing learning and memory ability of offspring rats,which is only one of the numerous mechanisms.More subunits and channels should be studied in order to more clearly understand the molecular mechanism of learning and memory impairment caused by arsenite exposure.People should pay more attention to arseniasis in early development period,for that organism has particular sensitivity to the environmental poison during pregnancy and lactation development stage.The content of arsenic in drinking water and milk product should be strictly controled in order to more effectively prevent teenagers from arsenic poisoning.