Reverse glial glutamate uptake triggers neuronal cell death through extrasynaptic NMDA receptor activation

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Oxidative stress and prevention of the adaptive response to chronic iron overload in the brain of young adult rats exposed to a 150 kilohertz electromagnetic field.

International audienceIron surcharge may induce an oxidative stress-based decline in several neurological functions. In addition, electromagnetic fields (EMF) of frequencies up to about 100 kHz, emitted by electric/electronic devices, have been suggested to enhance free radical production through an iron dependent pathway. The purpose of this study was therefore to determine a possible relationship between iron status, exposure to EMF, and brain oxidative stress in young adult rats. Samples were micro-dissected from prefrontal cortex, hippocampus, striatum, and cerebellum after chronic saline or iron overload (IO) as well as after chronic sham exposure or exposure to a 150 kHz EMF or after combining EMF exposure with IO. The brain samples were used to monitor oxidative stress-induced lipid peroxidation and activity of the antioxidant enzymes superoxide dismutase and catalase. While IO did not induce any oxidative stress in young adult rats, it stimulated antioxidant defenses in the cerebellum and prefrontal cortex in particular. On the contrary, EMF exposure stimulated lipid peroxidation mainly in the cerebellum, without affecting antioxidant defenses. When EMF was coapplied with IO, lipid peroxidation was further increased as compared to EMF alone while the increase in antioxidant defenses triggered by the sole IO was abolished. These data suggest that EMF exposure may be harmful in young adults by impairing the antioxidant defenses directed at preventing iron-induced oxidative stress

Spatial learning, monoamines and oxidative stress in rats exposed to 900 MHz electromagnetic field in combination with iron overload

International audienceThe increasing use of mobile phone technology over the last decade raises concerns about the impact of high frequency electromagnetic fields (EMF) on health. More recently, a link between EMF, iron overload in the brain and neurodegenerative disorders including Parkinson's and Alzheimer's diseases has been suggested. Co-exposure to EMF and brain iron overload may have a greater impact on brain tissues and cognitive processes than each treatment by itself. To examine this hypothesis, Long-Evans rats submitted to 900 MHz exposure or combined 900 MHz EMF and iron overload treatments were tested in various spatial learning tasks (navigation task in the Morris water maze, working memory task in the radial-arm maze, and object exploration task involving spatial and non spatial processing). Biogenic monoamines and metabolites (dopamine, serotonin) and oxidative stress were measured. Rats exposed to EMF were impaired in the object exploration task but not in the navigation and working memory tasks. They also showed alterations of monoamine content in several brain areas but mainly in the hippocampus. Rats that received combined treatment did not show greater behavioral and neurochemical deficits than EMF-exposed rats. None of the two treatments produced global oxidative stress. These results show that there is an impact of EMF on the brain and cognitive processes but this impact is revealed only in a task exploiting spontaneous exploratory activity. In contrast, there are no synergistic effects between EMF and a high content of iron in the brain

Oxygen glucose deprivation-induced astrocyte dysfunction provokes neuronal death through oxidative stress

International audienceUnderstanding the role of astrocytes in stroke is assuming increasing prominence, not only as an important component on its own within the neurovascular unit, but also because astrocytes can influence neuronal outcome. Ischemia may induce astrogliosis and other phenotypic changes, but these remain poorly understood, in part due to limitations in reproducing these changes in vitro. Dibutyryl cyclic AMP-differentiated cultured astrocytes are more representative of the in vivo astroglial cell phenotype, and were much more susceptible than undifferentiated astrocytes to an ischemic-like stress, oxygen-glucose deprivation (OGD). OGD altered the expression/distribution and activity of glial glutamate transporters, impaired cellular glutamate uptake and decreased intracellular levels of glutathione preferentially in differentiated astrocytes. Resistance to OGD was conferred by inhibiting caspase-3 with DEVD-CHO and oxidative stress by the antioxidant N-acetylcysteine (NAC). The resistance of undifferentiated astrocytes to OGD may result from a transient but selective morphological transformation into Alzheimer type II astrocytes, an intermediary stage prior to transforming into reactive astrocytes. Co-culture of neurons with OGD-exposed astrocytes resulted in neurotoxicity, but at surprisingly lower levels with dying differentiated astrocytes. The antioxidant NAC or the 5-LOX inhibitor AA861 added upon co-culture delayed (day 1) but did not prevent neurotoxicity (day 3). Astrocytes undergoing apoptosis as a result of ischemia may represent a transient neuroprotective mechanism via ischemia-induced release of glutathione, but oxidative stress was responsible for neuronal demise when ischemia compromised astrocyte supportive functions