Scavenging ROS dramatically increase NMDA receptor whole-cell currents in painted turtle cortical neurons.

Area of Science:

• Neuroscience
• Cellular Physiology
• Comparative Biology

Background:

• Mammalian neurons undergo excitotoxic cell death due to excessive calcium influx via N-methyl-d-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors during oxygen deprivation.
• The western painted turtle exhibits remarkable resistance to neuronal damage during prolonged anoxia (oxygen deprivation), surviving overwintering periods without oxygen.
• Anoxia-induced neuroprotection in turtles involves decreased NMDA and AMPA receptor currents, modulated by mitochondrial calcium ([Ca(2+)]i) and potentially reactive oxygen species (ROS).

Purpose of the Study:

• To investigate the role of mitochondrial calcium release and reactive oxygen species (ROS) in regulating NMDA and AMPA receptor currents during anoxia in the western painted turtle.
• To determine if decreased ROS levels contribute to the anoxia-mediated decrease in glutamate receptor activity.
• To elucidate the mechanism by which turtles prevent excitotoxicity during prolonged oxygen deprivation.

Main Methods:

• Utilized electrophysiological recordings to measure NMDA and AMPA receptor whole-cell currents in turtle neurons.
• Manipulated intracellular reactive oxygen species (ROS) levels using scavengers (N-2-mercaptopropionylglycine, N-acetylcysteine) and hydrogen peroxide.
• Assessed the impact of mitochondrial ATP-sensitive potassium (mKATP) channel activation (diazoxide) on receptor currents and intracellular calcium ([Ca(2+)]i) and ROS levels.

Main Results:

• Scavenging ROS significantly increased NMDA receptor currents by 100%, while hydrogen peroxide decreased them, indicating ROS can modulate NMDA receptor activity.
• AMPA receptor currents and intracellular calcium ([Ca(2+)]i) concentrations were unaffected by ROS manipulation.
• Mitochondrial Ca(2+) release, triggered by diazoxide, decreased NMDA receptor currents, and this effect was independent of ROS levels and prevented ROS scavenger-induced potentiation.

Conclusions:

• Decreased ROS concentration is not the primary cause of anoxia-mediated decreases in NMDA/AMPA receptor currents; instead, it is associated with an increase in NMDA receptor currents.
• Mitochondrial calcium release plays a crucial role in preventing NMDA receptor potentiation during anoxia, thereby protecting neurons from excitotoxicity.
• The findings highlight a novel neuroprotective mechanism in turtles involving mitochondrial calcium dynamics during oxygen deprivation.