NITROUS OXIDE ALLEVIATES STRESS AND MODULATES CENTRAL AMYGDALA HYPEREXCITABILITY

Stress induces persistent alterations in emotional and nociceptive processing through plastic changes within the central amygdala (CeA), a key hub for integrating stress- and pain-related signals. Stress exposure enhances CeA excitability, with accumulating evidence implicating NMDAR-dependent sensitization. Whether this sensitized state alters the neural responsiveness to NMDAR-targeting interventions remains unclear. Nitrous oxide (N₂O) is a clinically used anxiolytic and analgesic agent with partial NMDAR antagonistic properties. However, its effects on stress-sensitized amygdala activity have not been examined.

Here, we investigated how stress modifies the electrophysiological effects of prolonged N₂O exposure in the CeA. An immobilization stress (IS) model using restraint bags induced robust elevations in systolic blood pressure (SBP) and stress-related alterations in behavioral coping, as assessed by the open field and forced swim tests. N₂O exposure significantly reduced SBP elevation and attenuated behavioral alterations. To contextualize N₂O’s effects, comparisons were made with ketamine, a well-characterized antidepressant and NMDAR antagonist. In vivo local field potential recordings showed that IS increased CeA neuronal firing rates, which were markedly suppressed by N₂O exposure. Notably, N₂O reduced CeA neuronal firing more effectively than ketamine. Voltage-sensitive dye imaging demonstrated increased population-level neuronal activity in the CeA following stress, which was significantly attenuated during 30 min of N₂O exposure and partially recovered after washout.

Together, these results demonstrate that N₂O suppresses stress-induced hyperexcitability in the CeA across multiple electrophysiological measures, providing evidence for its anti-stress actions under sensitized conditions.

[National Research Foundation of Korea (NRF), funded by the Korea government (MSIT) (RS-2025-00555096, RS-2023-00262398)]