Chronic low-level arsenic exposure causes gender-specific alterations in locomotor activity, dopaminergic systems, and thioredoxin expression in mice.

Arsenic (As) is a toxic metalloid widely present in the environment. Human exposure to As has been associated with the development of skin and internal organ cancers and cardiovascular disorders, among other diseases. A few studies report decreases in intelligence quotient (IQ), and sensory and motor alterations after chronic As exposure in humans. On the other hand, studies of rodents exposed to high doses of As have found alterations in locomotor activity, brain neurochemistry, behavioral tasks, and oxidative stress. In the present study both male and female C57Bl/6J mice were exposed to environmentally relevant doses of As such as 0.05, 0.5, 5.0, or 50 mg As/L of drinking water for 4 months, and locomotor activity was assessed every month. Male mice presented hyperactivity in the group exposed to 0.5 mg As/L and hypoactivity in the group exposed to 50 mg As/L after 4 months of As exposure, whereas female mice exposed to 0.05, 0.5, and 5.0 mg As/L exhibited hyperactivity in every monthly test during As exposure. Furthermore, striatal and hypothalamic dopamine content was decreased only in female mice. Also decreases in tyrosine hydroxylase (TH) and cytosolic thioredoxin (Trx-1) mRNA expression in striatum and nucleus accumbens were observed in male and female mice, respectively. These results indicate that chronic As exposure leads to gender-dependent alterations in dopaminergic markers and spontaneous locomotor activity, and down-regulation of the antioxidant capacity of the brain.

Effects of inorganic arsenic exposure on glucose transporters and insulin receptor in the hippocampus of C57BL/6 male mice.

Children and adolescent populations chronically exposed to high doses of inorganic arsenic (iAs) in drinking water in some regions around the world have shown behavioral and memory deficits. Recent studies have also associated iAs exposure with dysregulation of glucose metabolism. The hippocampus is a cerebral region well known for its role in learning and memory. Studies in vitro and in vivo have shown that the hippocampus is vulnerable to iAs exposure, and to changes in glucose metabolism. The glucose transporters (GLUTs) and insulin receptor (IR) regulate glucose metabolism in brain; they are expressed by hippocampal cells, and alterations in these proteins have been associated with memory deficits. The aims of this study were to evaluate the effects of iAs exposure via drinking water (DW) on GLUT1, GLUT3 and insulin receptor (INSR) mRNA expression in the hippocampus, on performance in a spatial memory task, and on peripheral glucose regulation. C57Bl/6 male mice were exposed to 50 mg iAs/L via DW for one, two, or three months. The qRT-PCR analyses indicated that, compared to a control group, GLUT1 and GLUT3 mRNA levels were decreased, while INSR mRNA levels were increased in the hippocampus of iAs exposed animals. The levels of iAs and its methylated species in the hippocampus of the iAs-exposed group were significantly higher than in controls. Mice exposed to iAs learned the spatial task but showed increased latency to find the submerged platform 48 h after the last training session; these animals also showed dysregulation of peripheral glucose. These results suggest that the effects of iAs exposure on a spatial memory task performance could be mediated by disruptions of glucose regulation in the CNS.

Glutathione reductase inhibition and methylated arsenic distribution in Cd1 mice brain and liver.

Inorganic arsenic exposure via drinking water has been associated with cancer and serious injury in various internal organs, as well as with peripheral neuropathy and diverse effects in the nervous system. Alterations in memory and attention processes have been reported in exposed children, whereas adults acutely exposed to high amounts of inorganic arsenic showed impairments in learning, memory, and concentration. Glutathione (GSH) is extensively involved in the metabolism of inorganic arsenic, and both arsenite and its methylated metabolites have been shown to be potent inhibitors of glutathione reductase (GR) in vitro. Brain would be more susceptible to GR inhibition because of the decreased activities of superoxide dismutase (SOD) and catalase reported in this tissue. To investigate whether GR inhibition could be documented in vivo, we determined the activity and levels of GR in brain as well as in liver, the main organ of arsenic metabolism in mice exposed to 2.5, 5, or 10 mg/kg/day of sodium arsenite over a period of 9 days. In contrast to what has been observed in vitro, significant inhibition of the expression and activity of GR was observed only at the highest concentration used (10 mg/kg/day) in both organs. Although the disposition of arsenicals was higher in liver, significant amounts of inorganic and methylated arsenic forms were determined in the brain of exposed animals. The formation of monomethylarsenic (MMA) and dimethylarsenic (DMA) metabolites in the brain was confirmed by incubating brain slices for 24, 48, and 72 h with sodium arsenite.

In vivo GABA release and kinetics of transgene loss in a GABAergic cell line after long-term transplantation into the rat brain.

Ex vivo gene therapy uses modified cells to deliver substances into the brain. Cell line M213-2O CL-4 expresses human glutamate decarboxylase (hGAD(67)) by means of an Epstein-Barr virus-based plasmid. This cell line releases GABA in response to depolarizing stimuli in vitro, and after brain transplantation it modulates seizures in animal models. It is unclear if the functional effects observed can be attributed to GABA release by the grafted cells and if GABA release, in turn, is related to the kinetics of transgene permanence or loss under long-term transplantation conditions. To address these issues, two experiments were performed. The first one evaluated GABA levels in the vicinity of an intranigral transplant by microdialysis followed by high performance liquid chromatography (HPLC) quantification. GABA levels and GAD activity were higher in rats with 8-week-old transplants than in control animals, but this effect was lost in rats with 12-week-old transplants. The second experiment evaluated the number of copies of the plasmid containing the hGAD(67) (GAD1) transgene by real-time PCR after transplantation into the hippocampus at the same times. A time-dependent loss of the plasmid in the transplants was observed. The mechanism of plasmid loss was explored in vitro by analyzing the effects of DNA methylation and the absence of selection pressure. The results suggest that the loss of plasmid copies from transplants under long-term conditions may be related to methylation of plasmid regions involved in its nuclear retention. Taking these data together, we propose that the reported long-term functional effects of transplants of cell line M213-2O CL-4 may not be attributed exclusively to increased GABA release in the area of the graft, but that a paracrine-like action of GABA may lead to the remodeling of neural circuits in the host.