S-Nitrosoglutathione Reductase Null Mice Display Increased Brain Glutamic Acid Decarboxylase Activity and Seizure Resistance in Hyperbaric Oxygen
An imbalance between glutamatergic and g-aminobutyric acid (GABA)ergic synaptic transmission is associated with hyperbaric oxygen (HBO2) induced seizures. Here we explored the impact of S-nitrosylation in preventing oxygen toxicity in S-nitrosoglutathione reductase (GSNOR) null mice and tested whether S-nitrosylation of brain glutamic acid decarboxylase (GAD) may alter its activity, thus the synthesis of inhibitory GABA. Wild type (WT) and GSNOR -/- mice were exposed to HBO2 at 4 ATA for up to 100 min and seizure latency was recorded. The medulla, cerebellum and forebrain were harvested from HBO2 exposed and control mice for determination of GAD activity (fluorometrically) and S-nitrosylated GAD-65 (Biotin-switch). The mean (± SE) seizure latency was significantly delayed in the GSNOR -/- (63 ± 7 min) compared to WT (34 ± 6 min) mice, and the proportion of GSNOR -/- mice that experienced seizures (56%) was significantly less than WT mice (87%). Relative to controls, GAD activity in the medulla and cerebellum was significantly increased in the GSNOR -/- compared to a reduction in WT mice: medulla (GSNOR -/-: +22% and WT: -13%) and cerebellum (GSNOR-/-: +23% and WT: -12%). A significant fall in the degree of GAD-65 S-nitrosylation was observed in GSNOR -/- (-63%) compared to WT (-17%) mice suggesting augmented denitrosylation after GSNOR deletion. Dysregulated S-nitrosylation increased seizure latency and reduced the percentage of mice that developed seizures. The protection afforded by reduced S-nitrosylation may be explained in part by increased GAD activity that would favor GABA synthesis, thus inhibit neuronal excitation and seizures.
