The Role of Free Oxygen Radicals in Lasting Hyperexcitability of Rat Subicular Neurons After Exposure to General Anesthesia During Brain Development
A large number of preclinical studies have established that general anesthetics (GAs) may cause neurodevelopmental toxicity in rodents and nonhuman primates, which is followed by long-term cognitive deficits. The subiculum, the main output structure of hippocampal formation, is one of the brain regions most sensitive to exposure to GAs at the peak of synaptogenesis (i.e., postnatal day (PND) 7). We have previously shown that subicular neurons exposed to GAs produce excessive amounts of reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), which is a known modulator of neuronal excitability. To further explore the association between GA-mediated increase in ROS levels and long-term functional changes within subicular neurons, we sought to investigate the effects of ROS on excitability of these neurons using patch-clamp electrophysiology in acute rat brain slices. We hypothesized that both acute application of H2O2 and an early exposure (at PND 7) to GA consisting of midazolam (9 mg/kg), 70% nitrous oxide, and 0.75% isoflurane can affect excitability of subicular neurons and that superoxide dismutase and catalase mimetic, EUK-134, may reverse GA-mediated hyperexcitability in the subiculum. Our results using whole-cell recordings demonstrate that acute application of H2O2 has bidirectional effects on neuronal excitability: lower concentrations (0.001%, 0.3 mM) cause an excitatory effect, whereas higher concentrations (0.01%, 3 mM) inhibited neuronal firing. Furthermore, 0.3 mM H2O2 increased the average action potential frequency of subicular neurons by almost twofold, as assessed using cell-attach configuration. Finally, we found that preemptive in vivo administration of EUK-134 reduced GA-induced long-lasting hyperexcitability of subicular neurons ex vivo when studied in neonatal and juvenile rats. This finding suggests that the increase in ROS after GA exposure may play an important role in regulating neuronal excitability, thus making it an attractive therapeutic target for GA-induced neurotoxicity in neonates.
KeywordsFree oxygen radicals Lasting hyperexcitability Rat subicular neurons
This study was funded in part by grants from the National Institutes of Health (Grant No. R01GM102525 to S.M.T. and Grant No. R01GM118197 to V.J-T.).
Compliance with Ethical Standards
The experiments were approved by the Institutional Animal Use and Care Committee of the University of Colorado Anschutz Medical Campus, Aurora, CO, and by the Animal Use and Care Committee of the University of Virginia, Charlottesville, VA. All experiments were done in accordance with the Public Health Service’s Policy on Humane Care and Use of Laboratory Animals.
Conflict of Interest
The authors declare that they have no conflict of interest.
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