Study On The Effect Of LTP Induction Of Developing Rats Exposed To Aluminum During The Prenatal And Postnatal Periods And Related Mechanism

PrefaceAluminium is one of the most redundant elements in the crust of the earth.We are often exposed to Aluminium by many kinds of ways in our daily life.It has neural toxicity.Brain is the accumulation site and the main target organ.Aluminium is a main environmental factor to the disease of mentality and recognization decrease.The hippocampus is the most important encephalic region relative to function of learning and memory.Hippocampal long-term potentiation(LTP)is NMDA receptor-dependent persistent enhancement of efficacy in synaptic transmission,it is reputed that LTP represents the most intensively studied synaptic model and neural basis of learning and memory in the mammalian brain.So investigating the effect of aluminum exposure on LTP and the biochemical indicators relative to the LTP synaptic mechanism will help to elucidate the mechanism of aluminum damaging the learning and memory.Although Al has been reported to impair LTP following administration in vivo and in vitro,the underlying mechanisms of Al action on LTP are still unknown.In order to investigate the influence on leaming and memory after subchronic aluminum exposure from the prenatal and postnatal periods(3 months after birth),we will build the exposure model of rats,determine the aluminum level on brain and blood, monitor the learning and memory ability by the step-down test and the extraccllular micropipette recording technique will be used to recording electrophysiological changes.The content of aminoglutaric acid,NMDAR1 recepter and c-los protein will also be tested by immunohistochemistry.The subsequence of the test maybe offer some basic data and theory on how to prevent and cure the disease of mentality and recognization decrease early.Materials and methods1.Group and exposureHealthy adult Wistar rats(about 180 g)were exposed to aluminum through drinking 0%(distilled water)or 0.2g/100ml(represented by 0.2%-Al)and 0.4g/100ml (represented by 0.4%-Al)aluminum chloride(AlCl₃)solution,respectively,during the whole gestation and suckling period.Their offspring were distributed into three experimental groups:a control group,two exposed groups(0.2%-Al group and 0.4%-Al group)when aluminum exposure is ended at postnatal day 90.And the room temperature is 18℃～23℃,relative humidity is 45%～55%.2.Methods(1)Aluminium concentration analysisAtomic absorption spectrophotomery(AAS)was used to detect the content of Aluminium in blood and brain.(2)Ethology detectionEthology detection was detected by jumping stand experiment.(3)LTP recordThe technique of extracellular electrophysiological was used to record the effect of aluminium on long-term potentiation(LTP)in hippocampal CA1 area.(4)Glutamate content assay in hippocampus.The method of immunohistochemistry was used to measure the content of aminoglutaric acid in hippocampal CA1,CA3 and cortex area.(5)NMDAR1 receptor content assay in hippocampus.The method of immunohistochemistry was used to measure the content of NMDAR1 recepter in hippocampal CA1,CA3 and cortex area.(6)c-Fos protein content assay in hippocampus. The method of immunohistochemistry was used to measure the content of c-fos protein in hippocampal CA1,CA3 and cortex area.Results1.Aluminium concentration in blood and brainThe aluminum concentration in blood and brain tissue were significantly higher than the control group(P＜0.01)and increased with exposure dose.Futhermore,the difference between the two exposed group was statistically significant(P＜0.05 or P＜0.01).2.The comparison of learning and memory behavioural testThe behavioural data showed:the escape latency was remarkably prolonged (P＜0.01),the step-down latency was remarkably decreased(P＜0.01),and the number of errors both in learning and memory were significantly increased in the Al³⁺exposed groups(P＜0.01)as compared to the control group.Futhermore,the difference between the two exposed group was statistically significant(P＜0.05 or P＜0.01).3.The comparison of average PS enhancement rate after HFSWith the increase of exposure dose,the PS magnitude reduced evidently after HFS. As compared to the control group,the two exposed groups were significant reduced (P＜0.01),but the difference between the two exposed group was statistically non-significant.4.The comparison of aminoglutaric acid content in hippocampusCompared to the control group,the expression of aminoglutaric acid content in hippocampus were significantly reduced in Al³⁺exposed groups.5.The comparison of NMDAR1 recepter content in hippocampusCompared to the control group,the expression of NMDAR1 recepter content in hippocampus were significantly reduced in Al³⁺exposed groups(P＜0.01).Futhermore, the difference between the two exposed groups was statistically significant(P＜0.01). 6.The comparison of c-Fos protein content in hippocampusCompared to the control group,the expression of c-Fos protein content in hippocampus were significantly reduced in Al³⁺exposed groups.The expression in 0.4%-Al group were significantly reduced Compared to the control group and 0.2%-Al group(p＜0.01).Conclusion1.The experiment showed that subchronic Al exposure from prenatal to postnatal raised the level of Al in blood and brain and impaired the behaviour of the learning and memory in young rats.2.It can also impair the induction and maintenance of LTP.3.Al decreased the concentration of aminoglutaric acid,NMDAR1 recepter and c-fos protein in CA1 and CA3 region in hippocampus and cortical area of rats.