Modulation of presynaptic GABA release by oxidative stress in mechanically-isolated rat cerebral cortical neurons

Reactive oxygen species (ROS), which include hydrogen peroxide (H ₂O₂), the superoxide anion (O₂ ^-·), and the hydroxyl radical (OH·), are generated as by-products of oxidative metabolism in cells. The cerebral cortex has been found to be particularly vulnerable to production of ROS associated with conditions such as ischemia-reperfusion, Parkinson's disease, and aging. To investigate the effect of ROS on inhibitory GABAergic synaptic transmission, we examined the electrophysiological mechanisms of the modulatory effect of H₂O ₂ on GABAergic miniature inhibitory postsynaptic current (mIPSCs) in mechanically isolated rat cerebral cortical neurons retaining intact synaptic boutons. The membrane potential was voltage-clamped at - 60 mV and mIPSCs were recorded and analyzed. Superfusion of 1-mM H₂O₂ gradually potentiated mIPSCs. This potentiating effect of H₂O₂ was blocked by the pretreatment with either 10,000-unit/mL catalase or 300-μM N-acetyl-cysteine. The potentiating effect of H₂O₂ was occluded by an adenylate cyclase activator, forskolin, and was blocked by a protein kinase A inhibitor, N-(2-[p-bromocinnamylamino] ethyl)-5- isoquinolinesulfonamide hydrochloride. This study indicates that oxidative stress may potentiate presynaptic GABA release through the mechanism of cAMP-dependent protein kinase A (PKA)-dependent pathways, which may result in the inhibition of the cerebral cortex neuronal activity.