BACKGROUND:Previous studies have found that neuronal damage caused by continuous excessive fluoride exposure is related to Ca2+overload,but the mechanism of Ca2+flow conversion between intracellular calcium stores and cell apoptosis damage is still unclear.OBJECTIVE:To investigate the effect of fluoride exposure on Ca2+transport channel proteins and apoptosis levels in the mitochondria-associated endoplasmic reticulum membrane of primary cultured neural cells.METHODS:Primary nerve cells of neonatal SD rats were cultured in vitro and identified by immunofluorescence staining with neuronal nucleus-specific antibody up to day 7.The nerve cells were divided into control group(containing 0 mmol/L sodium fluoride),low fluoride group(containing 0.5 mmol/L sodium fluoride),and high fluoride group(containing 1 mmol/L sodium fluoride).The cell morphological changes were observed by light microscope 24 hours after fluorine exposure.The expression levels of apoptosis-related protein BAX/BCL-2 and calcium transfer-related pathways VDAC1,GRP 75,and IP3R were detected using western blot assay.The expression levels of VDAC1,GRP 75,and IP3R mRNA were detected by RT-PCR.Ca2+levels were detected by Rhood-2AM Ca2+probe.Mitochondrial membrane potential detection kit was used to detect the change in mitochondrial membrane potential.The level of apoptosis was determined by flow cytometry and TUNEL staining.RESULTS AND CONCLUSION:(1)The purity of neurons cultured on day 7 had been determined to be over 90％,with few impurities,good growth status,and tight cell network connections,meeting the requirements of subsequent experiments.(2)Compared with the control group,growth of neural cell clusters in the low-fluoride group and the high-fluoride group increased;the processes were broken;the cell body was rounded,and the connection network between cells was destroyed.Compared with the low-fluoride group,the cell damage changes in the high-fluoride group were more obvious.(3)Compared with the control group,the protein expressions of VDAC1,GRP75,and IP3R were increased in the low-fluoride group and the high-fluoride group(P＜0.05),and the ratio of apoptosis-related protein BAX/BCL-2 was increased(P＜0.05).Compared with the control group,the expression of VDAC1 and GRP75 mRNA in the low-fluoride group was significantly increased(P＜0.05);the expression levels of VDAC1,GRP75,and IP3R mRNA in the high-fluoride group were significantly increased(P＜0.01).(4)The level of cell apoptosis increased significantly after fluoride exposure,and the high-fluoride group was significantly higher than the control and low-fluoride groups(P＜0.01).(5)After fluoride exposure,the concentration of mitochondrial Ca2+in nerve cells increased significantly(P＜0.05),the mitochondrial membrane potential decreased(P＜0.01),and the degree of damage in the high-fluoride group was more obvious(P＜0.05).The results show that fluoride exposure impairs the morphological structure of primary neural cells,resulting in upregulation of Ca2+transfer pathway protein expression between the endoplasmic reticulum and mitochondria,mitochondrial Ca2+overload,mitochondrial damage,and increased levels of apoptosis.

BACKGROUND:Previous studies have found that neuronal damage caused by continuous excessive fluoride exposure is related to Ca2+overload,but the mechanism of Ca2+flow conversion between intracellular calcium stores and cell apoptosis damage is still unclear.OBJECTIVE:To investigate the effect of fluoride exposure on Ca2+transport channel proteins and apoptosis levels in the mitochondria-associated endoplasmic reticulum membrane of primary cultured neural cells.METHODS:Primary nerve cells of neonatal SD rats were cultured in vitro and identified by immunofluorescence staining with neuronal nucleus-specific antibody up to day 7.The nerve cells were divided into control group(containing 0 mmol/L sodium fluoride),low fluoride group(containing 0.5 mmol/L sodium fluoride),and high fluoride group(containing 1 mmol/L sodium fluoride).The cell morphological changes were observed by light microscope 24 hours after fluorine exposure.The expression levels of apoptosis-related protein BAX/BCL-2 and calcium transfer-related pathways VDAC1,GRP 75,and IP3R were detected using western blot assay.The expression levels of VDAC1,GRP 75,and IP3R mRNA were detected by RT-PCR.Ca2+levels were detected by Rhood-2AM Ca2+probe.Mitochondrial membrane potential detection kit was used to detect the change in mitochondrial membrane potential.The level of apoptosis was determined by flow cytometry and TUNEL staining.RESULTS AND CONCLUSION:(1)The purity of neurons cultured on day 7 had been determined to be over 90％,with few impurities,good growth status,and tight cell network connections,meeting the requirements of subsequent experiments.(2)Compared with the control group,growth of neural cell clusters in the low-fluoride group and the high-fluoride group increased;the processes were broken;the cell body was rounded,and the connection network between cells was destroyed.Compared with the low-fluoride group,the cell damage changes in the high-fluoride group were more obvious.(3)Compared with the control group,the protein expressions of VDAC1,GRP75,and IP3R were increased in the low-fluoride group and the high-fluoride group(P＜0.05),and the ratio of apoptosis-related protein BAX/BCL-2 was increased(P＜0.05).Compared with the control group,the expression of VDAC1 and GRP75 mRNA in the low-fluoride group was significantly increased(P＜0.05);the expression levels of VDAC1,GRP75,and IP3R mRNA in the high-fluoride group were significantly increased(P＜0.01).(4)The level of cell apoptosis increased significantly after fluoride exposure,and the high-fluoride group was significantly higher than the control and low-fluoride groups(P＜0.01).(5)After fluoride exposure,the concentration of mitochondrial Ca2+in nerve cells increased significantly(P＜0.05),the mitochondrial membrane potential decreased(P＜0.01),and the degree of damage in the high-fluoride group was more obvious(P＜0.05).The results show that fluoride exposure impairs the morphological structure of primary neural cells,resulting in upregulation of Ca2+transfer pathway protein expression between the endoplasmic reticulum and mitochondria,mitochondrial Ca2+overload,mitochondrial damage,and increased levels of apoptosis.

Objective:To investigate the effects of excessive fluoride exposure on astrocytes and the expression of glial fibrillary acidic protein (GFAP), in vitro and in vivo. Methods:(1) In vivo experiment: 24 SPF SD rats, half male and half female, were randomly divided into control and fluoride exposed groups according to sex and body weight, 12 rats in each group. Rats were fed with < 1 mg/L and 50 mg/L sodium fluoride solution prepared by tap water for 6 months, respectively. The expression levels of GFAP protein in rat brain tissue were measured by immunofluorescence, immunohistochemistry and Western blotting. (2) In vitro experiment: adult (6-month-old) rat cortical astrocytes were extracted and cultured in primary culture (4 mmol/L sodium fluoride solution for 24 h), and the astrocytes were identified by immunofluorescence, and GFAP mRNA and protein expression levels were detected by real-time fluorescence quantitative PCR and Western blotting, respectively, and astrocytes apoptosis and calcium ion content were detected by flow cytometry. Results:(1) In vivo experiment: the results of immunofluorescence, immunohistochemistry and Western blotting showed that the GFAP protein expression level in brain tissue of rats exposed to fluoride was higher than that of control group (0.440 ± 0.200 vs 0.250 ± 0.120, t =-5.93, P = 0.027; 0.270 ± 0.020 vs 0.240 ± 0.050, t =-4.87, P = 0.040; 1.017 ± 0.001 vs 0.486 ± 0.006, t =-52.48, P = 0.001). (2) In vitro experiment: GFAP positive cells were identified as astrocytes by immunofluorescence; GFAP mRNA expression level was higher in fluoride exposed group than that of control group by real-time fluorescence quantitative PCR (2.780 ± 0.120 vs 0.134 ± 0.005, t =-37.84, P = 0.001). The Western blotting results showed that the GFAP protein expression level was higher in fluoride exposed group than that of control group (2.76 ± 0.10 vs 1.38 ± 0.05, t =-20.44, P = 0.002). Flow cytometry results showed that the apoptosis rate of astrocytes was higher in fluoride exposed group than that of control group (%: 55.0 ± 1.0 vs 3.5 ± 0.6, t =-10.28, P = 0.009) and the calcium ion content was lower than that of control group (%: 54 ± 9 vs 72 ± 13, t = 4.64, P = 0.043). Conclusion:Excessive fluoride exposure causes increased GFAP expression in astrocytes in vitro and in vivo, promotes apoptosis, and affects calcium signaling pathways.

Objective:To observe the expression levels of glial fibrillary acidic protein (GFAP), β-tubulin Ⅲ and synaptophsin, and explore the role of tripartite synapse in the mechanism of central nervous system (CNS) injury and the neuroprotective effect of chondroitin sulfate (CS).Methods:One month old clean grade, 48 female Sparague-Dawley rats and 48 male Sparague-Dawley rats, were randomly divided into 8 groups according to body weight (90 - 120 g) by random number table method, with 12 rats in each group, half male and half female. These rats were fed with water containing different concentrations of sodium fluoride (NaF) [ < 0.5 mg/L (control, CN), 10.0 mg/L (low dose fluoride, LF) and 50.0 mg/L (high dose fluoride, HF)]. Some rats were fed directly for 185 days (CN, LF and HF groups). In addition, rats of CN + normal saline (NS), LF + NS, HF + NS groups and LF + CS, HF + CS groups, were intraperitoneally injected with NS or 0.66 mg/kg CS for 5 consecutive days after 180 days of feeding. After the experiment, the pathological changes of hippocampal CA4 of brain tissue in each group were observed by hematoxylin eosin staining under light microscope, and the expression and distribution of GFAP, β-tubulin Ⅲ and synaptophsin in hippocampal CA4 of rats were detected by immunohistochemistry, the expression of GFAP, β-tubulin Ⅲ and synaptophsin at protein level in hippocampus of rats were detected by Western blotting.Results:Under light microscope, eosinophilic change, loss and irregular arrangement of neuron in the hippocampal CA4 were observed in LF, HF, LF + NS and HF + NS groups. The morphology of LF + CS and HF + CS groups was not significantly changed compared with CN group, but was significant changed compared with LF, HF, LF + NS and HF + NS groups. Immunohistochemical results showed that the rates of positive area of GFAP, β-tubulin Ⅲ and synaptophsin in female and male rats in LF and HF groups were significantly decreased than those in CN group ( P < 0.05); the positive area rates of female and male rats in LF + CS and HF + CS groups were higher than those in LF and HF groups, respectively ( P < 0.05). Western blotting results showed that the proten expression levels of GFAP, β-tubulin Ⅲ and synaptophsin of female and male rats in LF and HF groups (LF group: 0.90 ± 0.09, 0.82 ± 0.08, 1.43 ± 0.14, 0.92 ± 0.02, 1.21 ± 0.15, 0.87 ± 0.02, HF group: 0.58 ± 0.14, 0.73 ± 0.03, 0.63 ± 0.06, 0.67 ± 0.03, 0.87 ± 0.04, 0.70 ± 0.05) were lower than those in CN group (1.24 ± 0.08, 1.09 ± 0.10, 2.64 ± 0.30, 1.54 ± 0.09, 1.72 ± 0.10, 1.13 ± 0.06, P < 0.05). Conclusions:The tripartite synapse and extracellular matrix may take part in pathogenesis of the damages of CNS results from chronic fluorosis; CS may reduce the injury to a certain extent.

Objective To study the mechanism of central nervous system (CNS) injury in chronic fluorosis and the neuroprotective effect of chondroitin sulfate (CS).Methods Forty-eight female Sprague-Dawley rats weighting 90-120 g were divided into 8 groups according to body weight by random number table,6 rats in each group:control group,drinking tap water freely;low dose and high dose fluoride groups,freely drinking tap water with fluoride content of 10 and 50 mg/L,respectively;control + normal saline (NS),low dose fluoride + NS,and high dose fluoride + NS groups,each group was fed for 180 d,and treated with intraperitoneal injection of 0.66 mg/kg NS for 5 d (once a day);low dose fluoride + CS and high dose fluoride + CS groups,each group was fed for 180 d,0.66 mg/kg CS was injected intraperitoneally for 5 d (once a day).All groups were fed standard nutritive animal feed for 185 d and dissected for brain tissue.The pathologic change was observed after hematoxylin-eosin (HE)staining;the expression levels of phosphorylated extracellular signal-regulated protein kinase 1/2 (phospho-Erk1/2)and glutamate receptors 1,2 (GluR1,GluR2) in the brain cortex were detected by immunohistochemistry;the protein levels of Erk1/2,phospho-Erk1/2,GluR1,and GluR2 in the brain cortex were detected by Western blotting.Results Brain cortex of all rats in the fluoride groups showed eosinophilic degeneration,loss and disordered arrangement of neurons,and the brain morphological changes in each fluoride + CS groups were significantly improved compared with those in the fluoride groups.Immunohistochemistry results showed that compared with the control group [(0.44 ± 0.09)％,(1.49 ± 0.05)％,(2.51 ± 0.54)％],the expression levels of phospho-Erk1/2 [(1.47 ±0.09)％,(1.03 ± 0.05)％],and GluR2 [(2.37 ± 0.06)％,(3.38 ± 0.12)％] in the low dose and high dose fluoride groups were increased,and the expression levels of GluR1 [(1.49 ± 0.02)％,(0.99 ± 0.19)％] were decreased (P ＜ 0.05).Western blotting results showed that compared with the control group (1.00 ± 0.12,1.76 ± 0.33),the protein levels of Erk1/2 (3.10 ± 0.76,1.99 ± 0.01) and phospho-Erk1/2 (3.27 ± 0.25,2.67 ± 0.05) in low dose and high dose fluoride groups were significantly increased (P ＜ 0.05);compared with low dose fluoride group,the protein levels of Erk1/2,and phospho-Erk1/2 (1.30 ± 0.31,2.20 ± 0.34) in low dose fluoride + CS group decreased significantly (P ＜0.05).Compared with control group (1.86 ± 0.47,1.17 ± 0.27),the protein levels of GluR1 (1.09 ± 0.26,0.61 ± 0.14) in low dose and high dose fluoride groups decreased significantly,while the protein level of GluR2 (1.99 ± 0.42,3.38 ±0.27) increased significantly (P ＜ 0.05);compared with low dose and high dose fluoride groups,the protein levels of GluR2 in low dose fluoride + CS and high dose fluoride + CS groups (1.53 ± 0.41,2.65 ± 0.32) decreased significantly (P ＜ 0.05).The protein level of phospho-Erk1/2 was negatively correlated with GluR1 protein level (r =-0.975,-0.991,P ＜ 0.05) in low dose and high dose fluoride groups,and it was positively correlated with the protein level of GluR2 (r =0.986,0.993,P ＜ 0.05).Conclusion The CNS injury caused by chronic fluorosis may be related to GluR1 and GluR2 activated Erk1/2 signaling pathway,and CS has certain protection to the injury.

Objective To evaluate the influence of fluoride on mitochondrial membrane potential of neuroblastoma SH-SY5Y cells,and on the expression levels of mitochondrial proteins mitofusion 1 (Mfn1) and fission 1 (Fis1).Methods A stable and feasible culture method of SH-SY5Y cells in vitro was established with different concentration of sodium fluoride [0.0 (control),0.4,2.0 and 4.0 mmol/L],and various periods exposure of 6,12,24,48 h;the mitochondrial membrane potential of SH-SY5Y cells was detected by mitochondrial membrane potential assay kit (JC-1);and the expression levels of Mfn1 and Fis1 proteins were detected by Western blotting.Results Compared with the control group (1.63 ± 0.18,1.13 ± 0.15,1.30 ± 0.02) for various periods exposure (6,12,48 h),the red/green fluorescence ratios of the mitochondrial membrane potential of SH-SY5Y cells exposed to 2.0 and 4.0 mmol/L of sodium fluoride were decreased significantly (1.01 ± 0.10,0.80 ± 0.04;0.75 ± 0.13,0.62 ± 0.10;0.82 ± 0.01,0.56 ± 0.04,P ＜ 0.05);compared with the control group (0.93 ± 0.03,1.05 ± 0.07,1.17 ± 0.04) for various periods exposure,the expression levels of mitochondrial Mfn1 protein were decreased significantly in 0.4,2.0,4.0 mmol/L sodium fluoride groups (6,12,48 h:0.75 ± 0.02,0.65 ± 0.05,0.57 ± 0.06;0.83 ± 0.06,0.79 ± 0.06,0.69 ±0.06;0.98 ± 0.05,0.73 ± 0.07,0.62 ± 0.09,P ＜ 0.05).Compared with the control group (0.90 ± 0.05) for exposure time 12 h,the expression levels of Fis1 protein were increased significantly in 2.0,4.0 mmol/L sodium fluoride groups (1.14 ± 0.06,1.23 ± 0.06,P ＜ 0.05).Conclusions The mitochondrial membrane potential and the expression levels of mitofusion 1 and fission 1 of SH-SY5Y cells treated with fluoride are abnormal,which might be associated with the theory of nerve cell damage from high oxidative stress.

Objective To investigate the changes of extracellular regulated protein kinases (Erk)1/2,phospho-Erk1/2,matrix metalloproteinases (MMP)-2 and MMP-9 in rats with experimental chronic fluorosis and the role of chondroitin sulfate in treatment of rat with experimental chronic fluorosis.Methods Using a group design and cell culture methods,the SH-SY5Y cells were divided into control group (culture medium with 0.0 mmol/L fluoride ion),fluoride group (fluoride ion:4.0 mmol/L) and chondroitin sulfate group (fluoride ion:4.0 mmol/L,chondroitin sulfate:0.4 g/L).The ultrastructural changes of the SH-SY5Y cells were observed through electron microscope after 24 h treatment.The SH-SY5Y cells were cultured for 72 h,the number of cells survived in three groups.were detected after stained by trypan blue.Fifteen clean grade SD rats with body weight of 100-120 g were divided into control group (tap water:fluorine content less than 0.5 mg/L),fluoride group (fluoride ion:10.0 mg/L) and chondroitin sulfate group (fluoride ion:10.0 mg/L,the rats were performed intraperitoneal injection with 0.66 mg/kg chondroitin sulfate for 5 days after intaking fluoride for 90 days) on the basis of random number table.Five rats were in each group,and the experiment was carried out for 95 days.The capability of learning and memory of rats were tested by Morris water maze test;the expression of phospho-Erk1/2,Erk1/2,MMP-2 and MMP-9 protein in brain tissue was detected by Western blotting;the expression of phospho-Erk1/2,MMP-2 and MMP-9 in hippocampus CA2 area of brain was detected by immunohistochemistry.Results More vesicles and swelling of mitochondria or endoplasmic reticulum were observed in SH-SY5Y cell treated with fluoride through electron microscope,but relatively less in chondroitin sulfate group.Survival rate and amount of SH-SY5Y treated with chondroitin sulfate [(92 ± 23)％ and (7.83 ± 1.38) × 106/ml] were significantly higher than that of fluoride group [(55 ± 2)％,(2.19 ± 1.26) × 106/ml,P ＜ 0.05].Animal experiment results showed that most rats in control group and chondroitin sulfate group used spatial direct search strategy,and the amount of this search strategy (2.20 ± 1.09,3.40 ± 1.34) was more than that in fluoride group (0.40 ± 0.54,P ＜ 0.05).The expression of phospho-Erk1/2 in brain tissue of rats in fluoride group (3.26 ± 0.88) was significantly higher than that in control group (1.53 ± 0.28) and chondroitin sulfate group (2.36 ± 0.87,P ＜ 0.05).Immunohistochemistry results showed that average gray value of phospho-Erk1/2 in chondroitin sulfate group (220.20 ± 3.09) was significantly higher than that of the control group and the fluoride group (100.00 ± 0.00,130.98 ± 1.27,P ＜ 0.05).The average gray value of MMP-2 in the fluoride group (294.52 ± 5.18) was significantly higher than that in control group and chondroitin sulfate group (100.00 ± 0.00,117.95 ± 1.55,P ＜ 0.05).The average gray value of MMP-9 protein of the fluoride group (993.64 ± 3.66) and the chondroitin sulfate group (1 167.30 ± 239) was significantly higher than that of control group (100.00 ± 0.00,P ＜ 0.05).Conclusions Erk1/2 pathway possibly maintains the stability of cell survival by regulating the expression of MMP-2 and MMP-9.Chondroitin sulfate can protective nerve cells and reduce the nervous damage caused by fluorosis to some certain extent.

Objective To investigate the influence of chronic fluorosis on protein kinase Cβ (PKCβ)/p66shc signal pathway in the brain of rats,and reveal the molecular mechanism of brain damage.Methods According to body weight by the random number table method thirty SD rats were divided into three groups of 10 each (half females and half males),the normal control group [less than 0.5 mg/L of fluorine (prepared with NaF) in drinking water],low fluoride exposure group (10.0 mg/L fluorine),and high fluoride exposure group (50.0 mg/L fluoride).The experiment period was 6 months.The protein level of PKCβ,p66shc,phospho-p66shc and preserved ammonia acyl isomerase (Pin1) in rat brain was detected by Western blotting.The level of neuron nuclear antigen (NeuN),p66shc and phospho-p66sh in brain of rats was detected by immunohistochemistry.Results By Western blotting,the levels of PKCβ,Pin1 and phospho-p66shc protein in brain tissue in high fluoride exposure group [(193.00 ± 57.53)％,(228.21 ± 71.14)％,(201.54 ±:50.86)％] were higher than those of the normal control groups [(100.00 ± 21.24)％,(100.00 ± 40.55)％,(100.00 ± 13.35)％,all P ＜ 0.05].By immunohistochemistry,the numbers of NeuN staining in brain tissue of the rats in both high and low fluoride exposure groups [(49.50 ± 12.57)％,(65.66 ±14.58)％] were lower than that of the control group [(100.00 ± 18.32)％,all P ＜ 0.01].The level of phospho-p66shc protein in brain tissue in high fluoride exposure group [(242.66 ± 93.01)％] was higher than those of the low fluoride exposure and the normal control groups [(152.53 ± 60.65)％,(100.00 ± 25.63)％,all P ＜ 0.01].Conclusion Chronic fluorosis has increased the expressions of PKCβ,Pin1 and phospho-p66shc at protein level in brain of rats,which may be related to the molecular mechanism of brain damage resulted from chronic fluorosis.

OBJECTIVE:To establish a method for the 5 main components (original syringin,chlorogenic acid,eleutheroside E,isofraxidin and quercetin-3-rhamnoside) in the fruits and roots of wild Acanthopanax senticosus. METHODS:UPLC was per-formed on the column of Waters ACQUITY UPLC HSS T3 with mobile phase of acetonitrile-0.3% phosphoric acid (gradient elu-tion)at a flow rate of 0.2 ml/min. Detection wavelength was 300 nm,column temperature was 30 ℃,and injection volume was 10μl. RESULTS:The linear range was 24.56-184.2 μg/ml for syringin(r=0.9993),18.454-138.405 μg/ml for chlorogenic acid(r=0.9993),8.416-63.12 μg/ml for eleutheroside E (r=0.9997),3.286-24.645 μg/ml for isofraxidin (r=0.9993) and 2.522-18.915μg/ml for quercetin-3-rhamnoside(r=0.9998);RSDs of precision,stability and reproducibility tests were lower than 1%;recover-ies were 99.14%-100.50%(RSD=0.48%,n=6)for syringing in the fruits of A. senticosus、99.03%-100.45%(RSD=0.50%,n=6) for chlorogenic acid in the fruits of A. senticosus、99.22%-100.44%(RSD=0.44%,n=6)for eleutheroside E in the fruits of A. sen-ticosus、99.80%-100.80%(RDS=0.44%,n=6)for isofraxidin in the fruits of A. senticosus、99.76%-101.10%(RSD=0.51%,n=6) for quercetin-3-rhamnoside in the fruits of A. senticosus;99.21%-101.20%(RSD=0.73%,n=6)for syringing in the root of A. senti-cosus、99.81%-101.20%(RSD=0.52%,n=6)for chlorogenic acid in the root of A. senticosus、100.00%-101.50%(RSD=0.62%, n=6)for eleutheroside E in the root of A. senticosus、99.22%-100.40%(RSD=0.47%,n=6)for isofraxidin in the root of A. senti-cosus. CONCLUSIONS:The method is simple and stable with good reproducibility,and can be used for the simultaneous determi-nation of original syringin,chlorogenic acid,eleutheroside E,isofraxidin and quercetin-3-rhamnoside in the fruits and root of wild A. senticosus.

Objective Through observation of the expression and activity of extracellular regulated protein kinase 5 (ERK5) and its relationship with the learning and memory ability in rats with chronic fluorosis,to further study the pathogenesis of chronic fluorosis in nervous system.Methods Thirty SD rats were divided into 3 groups according to body weight by means of a random number table (10 rats in each group,half male and half female).The rats in control group were fed with free drinking tap water containing less than 0.5 mg/L fluoride (NaF);the rats in low fluoride group with 10.0 mg/L fluoride;the rat in high dose fluoride group with 50.0 mg/L fluoride.After 6months of experiment,rat brain tissue was took,mRNA expression level of ERK5 was detected by real-time fluorescence quantitative PCR (real-time PCR),protein expression level and activity of ERK5 were detected by Western blotting;the learning and memory ability of rats with chronic fluorosis were detected by Morris water maze test.Results The rat in groups exposed to fluoride exhibited different degrees of dental fluorosis and the fluoride content in urine of rats increased gradually with increase of fluoride doses (F =164.10,P ＜ 0.05).The protein levels of phosphor-ERK5 in the control group,low fluoride group and high fluoride group were 0.13 ± 0.03,0.29 ± 0.10and 0.43 ±0.17,respectively,the difference was statistically significant (F=11.96,P＜ 0.05),and low fluoride group and high fluoride group were higher than control group (all P ＜ 0.05).The total protein levels of ERK5 in control group,low fluoride group and high fluoride group were 0.32 ± 0.11,0.37 ± 0.13 and 0.49 ± 0.16,respectively,the difference was statistically significant (F =3.45,P ＜ 0.05),and high fluoride group was higher than control group (P ＜ 0.05).The expression of ERK5 mRNA in rat brains between groups was not significantly different (F =0.81,P ＞ 0.05).The second,third,and forth days of directional navigation experiment,the time of escape latency and the number of crossing the platform between groups were statistically significant (H =28.20,29.90,26.47,27.23,35.34,27.62,all P ＜ 0.01);the fifth day of space exploration experiment,the difference of the time of the first crossing platform and the number of crossing the platform between groups were statistically significant (H =31.41,30.80,all P ＜ 0.01);the protein level of phosphor-ERK5 in brain tissue of rats was negatively correlated with the number of the first crossing platform (r =-0.470,P ＜ 0.01),while positively related to escape latencies at the fifth day of the test (r =0.591,P ＜ 0.01).Conclusion The changes of ERK5 signaling pathway in rat brain tissue caused by chronic fluorosis are found,which are related to the decrease of leaming and memory ability of animals with chronic fluorosis.