Effect Of Chronic Toxicity Of Lead On Rat Brain Tissue

A series of study are designed on rats and the primary cultured hippocampal neurons. Many parameters are measured by pathologic, physiological and biochemical methods. To explore systematically and entirely the pathologic changes and mechanisms of toxicity for rat brain induced by chronic lead poisoning.Survival rate of hippocampal nerve cells was measured by MTT. 24 hours after different concentration of lead acetate (low, medium and high concentrations) imposed on hippocampal nerve cells respectively, Optical density of 570nm decrease became gradually Obvious, It showed a dose and time-dependent relationship. Release of lactate dehydrogenase in the Culture supertant significantly increased (p <0.01) and cholinesterase activity significantly decreased. By Nissl-staining, HE staining and Giemsa staining it can be found that lead made the surface of hippocampus neurons turn coarse, the cell became smaller, retracted, fracture, or even reduced, appeared nude nucleus, the network between the cells became loose, the boundaries between cell body and cytoplasma gradually blurred. It showed a dose and time dependent relationship.Quantitatively analysis of the average free Ca2 + fluorescence intensity of hippocampal neurons in the cytoplasm by laser scanning Confocal microscope indicated that the Ca2 + concentration in the hippocampus neurons increased significantly (p <0.01) in a certain lead concentration range and In a certain period. The increase of Ca2+ concentration in the neurons was related with the damage and apoptosis induced by lead. FCM results showed that the apoptosis number of lead acetate group significantly increased (p <0.01). It was of good relevance with the lead exposure dose. It was found that the number of positive neurons of Bcl-2 protein decreased significantly, while Bax protein positive neurons significantly increase by immunocytochemical staining. iNOS expression was significantly increased with the increase of lead concentration. Lead acetate can promote P53 gene expression in the hippocampus of rats, and there was a good dose-response relationship.The whole animal studies indicated that the food consumption and drinking amount of the experimental rats gradually reduced, particularly those exposed to high lead concentration 3 months and 6 months after exposed to lead water of 0.5 g / L, 1.0 g / L and 2.0 g / L (low, medium and high-lead group) 1 month, 3 months and 6 months. The average food consumption and drinking amount was significantly lower than the control group (p <0.01). The blood lead levels of each experimental group were significantly higher than the control (p <0.01).That of the group exposed to 2.0 g / L lead water were significantly higher than that of the group exposed to 0.5 g / L lead water(p <0.01), The blood lead levels raised with the prolong of time and increase of concentration. The differences of blood lead level between the three subgroups were not significant (p> 0.05).The lead level in the brain homogenate were significantly higher than the control (p <0.05). Drinking lead-higher water 1 month, 3 months, and 6 months later, Nissl body in the brain decreased at different degree, neurons shrunk, It was related with the exposure time and dose. Immunohistochemistry image analysis showed that Bcl-2 protein expression positive neuron in the hippocampus decreased with the increasing doses of lead exposure, and staining intensity decreased gradually, the average gray value gradually increased. Bax protein was opposite to Bcl-2.The expression of iNOS in the rat hippocampus and cortex obviously increased with the increase of lead exposure dose, there was a good dose-response relationship. P53 expression positive cell of all hippocampus in rat brain cells significantly increased. There was a positive correlation between the expression of P53 and lead-induced nerve cell apoptosis.From above all, it showed that long-term exposure to lead water would result in slow growth, chronic systemic diseases and damage in the rat brain. Some of the lead could go through the blood-brain barrier after the metabolism of the body, caused pathological morphological changes, such as damage of cerebral parenchyma, degeneration, shrinkage and necrosis of nerve cells, decrease of Nissl body and apoptosis in the hippocampus. Oxidative damage and apoptosis are likely to be the mechanisms of lead toxicity to brain.