Astrocyte activation following nitrous oxide exposure is related to oxidative stress and glutamate excitotoxicity

Nitrous oxide is commonly used as an anesthetic agent and its exposure produces prolonged inactivation of vitamin B12. Nitrous oxide toxicity is associated with central nervous system changes which are similar to sub-acute combined degeneration (SACD). Astrocytes have important role in neurotoxic injuries, but have not been evaluated in N2O toxicity. In the present study, we have evaluated the changes in astrocytes in N2O exposed rats and correlated with neurobehavioral changes, oxidative stress and glutamate level. Adult wistar male rats were exposed to N2O oxygen mixture in 1:1 ratio at a rate of 2 L/min for 120 min for 60 days. Control rats underwent similar exposure to oxygen. At the end of exposure, spontaneous locomotor activities (total distance travelled, time resting, time moving, number of rearing, stereotypic count) and grip strength were evaluated. Plasma glutathione (GSH), total antioxidant capacity (TAC), serum malonodialdehyde (MDA) and serum homocysteine (Hcy) were measured by spectrophotometer. Glutamate in the cerebral cortex and cerebellum were measured by colorimetry. Immunohistochemistry for astrocyte (GFAP) phenotypic analysis and its activation in brain and spinal cord were measured using image J software in N2O exposed and control rats. The N2O exposed rats had significant reduction in total distance travelled, time moving and number of rearing whereas time resting increased compared to the control rats. Hcy, glutamate and MDA levels were significantly increased, however GSH and TAC level decreased in N2O exposed group compared to the controls. Astrocyte phenotype and its activation was significantly altered more so in spinal cord compared to cerebral cortex and was associated with neurobehavioral changes, oxidative stress and glutamate level. N2O related clinical dysfunction may be related to changes in astrocyte activation which is related to oxidative stress and glutamate neurotoxicity.