Perinatal Exposure To Bisphenol A Affects The Synaptic Structural Development In Offspring Mice

Environmental endocrine disrupting chemicals, a kind of exogenous compounds, can disrupt the normal function of the endocrine system, including hormone synthesis, release, transportation, metabolism, combination or removal. They can simulate the natural hormones, and have significant effects on human. Bisphenol A (BPA) is one of the typical environmental endocrine disruptors. It is widely used in epoxy resin, packaging material for food, resins lining metal cans, dental solid sealing agent and additive. BPA threatens human’s health through entering into body directly from foods, or leaching from the rubbish into the environment. BPA has weak estrogenic activity and can interfere endogenous estrogen activity by binding to estrogen receptors.Recent studies have found that, BPA under no-observed-adverse-effect level also has effects on the central nervous system of rodents. Perinatal exposure to BPA profoundly disrupts structure and development of the brain cortex and the morphological development of hippocampal neuron of offspring rats, meaning that the developing brain is a sensitive target organ to BPA. Our previous study showed that exposure to BPA (0.05-50mg/kg/d) affected mobility, exploration, anxiety and depression, learning and memory of offspring; rapidly enhanced the motility and the density of dendritic filopodia in the hippocampal neurons cultured in vitro. Synapse is the key part of brain plasticity and information transmission, and is closely related to behaviors, such as learning and memory. Synaptic structural modification, including synapse interface structure, the numeric synaptic density, synaptic transmission, is vulnerable to environment and drug, therefore, we examined the effects of perinatal exposure to BPA on synaptic density and the structure of synapse interface in hippocampus CA1of male offspring during postnatal developing stage. The expressions of synapsin Ⅰ, PSD-95, NMDA receptor NR1and AMPA receptor GluR1subunit protein were also measured to further discuss the molecular mechanism of BPA on synaptic structure.Methods:In this study, we chose male and female ICR mice (weight30-35g and25-30g, respectively, clean grade). Pregnant dams were orally exposed to BPA dissolved in peanut oil (0.04,0.4or4mg/kg/day) or only peanut oil as a vehicle control from gestational day (GD)7to postnatal day (PND)21. The male pups (n=10for each group) were sacrificed on PND14, PND21and PND56, respectively. Hippocampus tissue samples were used to observe the structure of synapse interface in hippocampus CA1by transmission electron microscope, the expressions of PSD-95, synapsin Ⅰ, NMDA receptor NR1and AMPA receptor GluR1subunit protein by western-blot and immunohi stochemi stry.Quantity one and Image-Pro Plus6.0were used to measured the protien bands and immunohistochemical images, respectively. Finally, SPSS15.0software was used to analyse experimental data, the data were expressed as mean±S.E.M. Difference between groups was then tested using Tukey’s test. Statistical significance was accepted at P<0.05.Results:1. Perinatal exposure to BPA, especially BPA (0.04and4mg/kg/d) obviously inhibited the formation of synapses during postnatal developing stage (PND14) and puberty (PND56)(P<0.01or P<0.001). It indicates that perinatal exposure to BPA inhibited the formation of synapse.2. Perinatal exposure to BPA altered the structural parameters of the synaptic interface. All dose of BPA significantly enlarged the width of synaptic cleft (P<0.01); the thickness of PSD was reduced by perinatal exposure to BPA at all of the dosage (P<0.01); the length of active zone was shortened (P<0.05or P<0.01), and it was more significantly on PND21; the curvature of synaptic interface was increased mainly during the early developing stage (PND14and PND21)(P<0.05). These results indicated that the structural parameters of synaptic interface have different sensitive degree to BPA, the width of synaptic cleft and the thickness of PSD are more sensitive to BPA.3. Western blot analysis showed that all the dosage of BPA groups down-regulated synapsin I on PND21and PND56(P<0.05or P<0.01); there is an inhibition of the expressions of PSD-95(P<0.05, P<0.01or P<0.001), and it was more significantly on PND56; expressions of NMDA receptor subunit NR1in hippocampus varied during postnatal developing stage of male offspring. The higher dose of BPA (0.4and4mg/kg/d) significantly increased and decreased the expression of NR1on PND21, on PND56, all dose of BPA displayed marked down-regulation of the NMDAR subunit NR1in hippocampus (P<0.05, P<0.01or P<0.001); the expression of GluRl was decreased, the lower and the higher dosage (0.04and4mg/kg/d) significantly inhibited the GluRl protein expression (P<0.05or P<0.01).4. We further examined the immunohistochemistry of these proteins. We found that it was in accordance with the results of Western blot.Conclusion:BPA under tolerable daily intake (0.05mg/kg/d) can also affects the synaptic development and synaptic plasticity. Perinatal exposure to BPA affects the synaptic structure and down-regulates the expressions of NMDAR、AMPAR、PSD-95and synapsin I in hippocampus CAlof male offspring during during postnatal developing stage. We presume that perinatal exposure to BPA disrupts normal development of synapse in male offspring, and also permanently influences the behavior of offspring in adulthood.