Abstract
Mercury is a toxic metal that can be found in the environment in three different forms – elemental, organic and inorganic. Inorganic mercury has a lower liposolubility, which results in a lower organism absorption and reduced passage through the blood–brain barrier. For this reason, exposure models that use inorganic mercury in rats in order to evaluate its effects on the central nervous system are rare, especially in adult subjects. This study investigated if a chronic exposure to low doses of mercury chloride (HgCl2), an inorganic form of mercury, is capable of promoting motor alterations and neurodegenerative in the motor cortex of adult rats. Forty animals were exposed to a dose of 0.375 mg/kg/day, for 45 days. They were then submitted to motor evaluation and euthanized to collect the motor cortex. Measurement of mercury deposited in the brain parenchyma, evaluation of oxidative balance, quantification of cellular cytotoxicity and apoptosis and density of mature neurons and astrocytes of the motor cortex were performed. It was observed that chronic exposure to inorganic mercury caused a decrease in balance and fine motor coordination, formation of mercury deposits and oxidative stress verified by the increase of lipoperoxidation and nitrite concentration and a decrease of the total antioxidant capacity. In addition, we found that this model of exposure to inorganic mercury caused cell death by cytotoxicity and induction of apoptosis with a decreased number of neurons and astrocytes in the motor cortex. Our results provide evidence that exposure to inorganic mercury in low doses, even in spite of its poor ability to cross biological barriers, is still capable of inducing motor deficits, cell death by cytotoxicity and apoptosis, and oxidative stress in the motor cortex of adult rats.
Highlights
MATERIALS AND METHODSMercury is the third most toxic element on the planet, according to the US Government Agency for Toxic Substances and Disease Registry (Rice et al, 2014)
In our previous study (Teixeira et al, 2014a), we reported that inorganic mercury is able to accumulate in the brain parenchyma and that this finding is associated with functional alterations
The exposure for 45 days to inorganic mercury increased the mercury concentration deposited in the parenchyma of the motor cortex (Figure 4)
Summary
Mercury is the third most toxic element on the planet, according to the US Government Agency for Toxic Substances and Disease Registry (Rice et al, 2014). This substance can be found in three different forms in the environment: (i) elemental mercury or metallic mercury (Hg0); (ii) inorganic mercury (i.e., mercuric chloride, HgCl2); and (iii) organic mercury (i.e., methylmercury, MeHg) (Bernhoft, 2012). The toxic properties, biological behavior, toxicokinetics and clinical manifestations of mercury compounds are directly related to their chemical forms (Bernhoft, 2012; Rice et al, 2014). Studies involving the effects of inorganic mercury in adults are barely seen in the literature, due to factors such as low liposolubility, low corporal absorption and low passage through the blood–brain barrier (BBB) (Bernhoft, 2012; Rice et al, 2014)
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