Hippocampal Dysfunction Provoked by Mercury Chloride Exposure: Evaluation of Cognitive Impairment, Oxidative Stress, Tissue Injury and Nature of Cell Death

Abstract

Mercury (Hg) is a highly toxic metal, which can be found in its inorganic form in the environment. This form presents lower liposolubility and lower absorption in the body. In order to elucidate the possible toxicity of inorganic Hg in the hippocampus, we investigated the potential of low doses of mercury chloride (HgCl2) to promote hippocampal dysfunction by employing a chronic exposure model. For this, 56 rats were exposed to HgCl2 (0.375 mg/kg/day) via the oral route for 45 days. After the exposure period, the animals were submitted to the cognitive test of fear memory. The hippocampus was collected for the measurement of total Hg levels, analysis of oxidative stress, and evaluation of cytotoxicity, apoptosis, and tissue injury. It was observed that chronic exposure to inorganic Hg promotes an increase in mercury levels in this region and damage to short- and long-term memory. Furthermore, we found that this exposure model provoked oxidative stress, which led to cytotoxicity and cell death by apoptosis, affecting astrocytes and neurons in the hippocampus. Our study demonstrated that inorganic Hg, even with its low liposolubility, is able to produce deleterious effects in the central nervous system, resulting in cognitive impairment and hippocampal damage when administered for a long time at low doses in rats.

Effects of Bisphenol A Exposure during Pregnancy and lactation on Hippocampal Function in Newborn Rats

“…It was found that different concentrations of BPA did not affect the body weight of offspring, nor did they significantly regulate the weight of cerebellum, left hippocampus, right hippocampus, spleen, thyroid and pancreas of offspring. It has been reported that toxic exposure patterns can lead to cytotoxicity and cell apoptosis, affecting astrocytes and neurons in the hippocampus, but not necessarily affecting the weight of rats 22 , which is similar to our research. In vivo neuroelectrophysiological experiments showed that the increase of f-EPSP slope and PS amplitude in hippocampal CA1 region of male rats in BPA group was lower than that in control group after high frequency stimulation.…”

Toxic Mechanisms of Five Heavy Metals: Mercury, Lead, Chromium, Cadmium, and Arsenic

“… Aragão et al (2018) demonstrated cognitive impairment and hippocampal damage in rats with oral chronic administration of HgCl 2 . They also found that mercury levels in the hippocampus increased to 0.04 μg/g while the control group had Hg concentrations less than 0.01 μg/g ( Aragão et al, 2018 ). Another study indicated methylmercury chloride induced CNS injury in rats receiving different doses of 0.05, 0.5, and 5 mg/kg Hg against normal saline group.…”

Methylmercury Impact on Adult Neurogenesis: Is the Worst Yet to Come From Recent Brazilian Environmental Disasters?

“…Altered hippocampal structure and function induced by MeHg intoxication has been extensively reported (Falluel-Morel et al, 2012;Wu et al, 2016;Aragão et al, 2018). For example, a significant reduction in the total hippocampal DNA content has been found in the neonatal rat, 24 h after a single subcutaneous injection of MeHg (5 µg/g) on the postnatal day 7 (Falluel-Morel et al, 2007).…”