Methylmercury Chloride-Induced Effects On Expression And Activity Of Protein Kinase C Subunits In Developing Rat Brain

Methylmercury chloride (MMC) is an accumulative environmental contaminant that threatens people's health. In fetal development MMC has a more profound toxic effects on central nervous system than in the adult. The lowest dosage, which impairs neurodevelopment as well as the exact mechanism underlying its neurotoxicity, is still unknown. Based on historical studies, MMC can cause the damage of neuron during the cerebral developmental stage by activating of signal transduction molecules, inhibiting neuron proliferation, inducing genes expression related to cell apoptosis and promoting cell death (apoptosis and necrosis). In this study, a rat cerebral developmental model was established using the dietary effects of MMC ingestion as is seen in human. The effects of MMC on developmental rat brain as well as expression and activity of PKC subunits were also studied. Our results demonstrated that MMC exposure during brain developmental stage could increase the concentration of brain mercury, which increases expression of PKC (α and δ), decreases expression of PKC (γ) and alters cytosolic and membrane PKC activity, causing the increase of PCD positive rate. The possible mechanism may be correlated with the These results would provide a reasonable interpretation of why children are more sensitive to the neurotoxicity of MMC and offer a theoretically experimental basis in order to discuss the mechanism. Establishment of developmental brain injured model of rats by chronic MMC exposureOne hundred and twenty female Wistar rats (120±20g) were randomly assigned to the experimental groups, dietary containing various amounts of MMC and one control group without MMC. The experimental groups were fed standard rat chow with 0.75 mg MMC (ExpⅠ),1.5mg MMC (ExpⅡ) and 3.0 mg MMC (ExpⅢ) respectively for 90 days before gestation to 30d post parturition. The number and weight of pups of ExpⅠwere nearly the same with that of control group, however which were lower in ExpⅡand ExpⅢ(data not shown), pups of different experimental group were normal in the appearance. Analysis of Hg concentrations in rat brainPups from each group were euthanized by decapitation on postnatal days(PND) PND3, 7,17,21 and 30. Whole brain were removed immediately, and the cerebra, cerebellum and hippocampus were dissected. Brain samples were numbered and weighed accurately on an electronic scale, then used for analysis of Hg concentrations by cold atom absorption Hg2+ concentration analysis apparatus. The results showed: there was no marked difference of MMC concentration among three brain regions (cerebra, cerebellum and hippocampus) within groups (p>0.05). The concentrations of Hg2+ in pups' brain of experimental groups at various postnatal days were markedly higher than those of the control group (p<0.05). Time-course studies in experimental group showed the concentrations of Hg2+ in pup's brain increased gradually during development and reached its peak at PND30. The results indicated that MMC could across blood-brain barrier which accumulated in pup's brain. The enhanced effect was dose-dependent.Investigation on morphology of developing rat brain injured by MMC Morphological changes of developing rat brain induced by MMCParaffin sections of brain samples were made of each group using standard methodology and stained with HE, then examined by light microscope. Apoptotic changes revealed cell shrinkage and nuclear pyknosis these were in the part of the neurons of the cerebra and hippocampus and were especially apparent in the Pukinje neurons of cerebellum. Apoptosis of neuron during development induced by MMCChanges of programmed cell death (PCD) rate of neuron from the cerebra, cerebellum and hippocampus caused by chronic MMC exposure were detected using ApoAlertTM DNA Fragmentation Assay Kit. The results showed that apoptosis were seen in developing neurons from both control and experimental groups, however the PCD rates in various experimental groups were significantly higher than that of control group acco...