Sex-specific electrophysiological and behavioral responses to nitrous oxide in a murine model of neuropathic pain.

Nitrous oxide (N₂O) at 50% concentration for one hour produced sex-specific effects on behavior and brain activity in mice with chronic pain. In males with neuropathic pain, N₂O reduced pain sensitivity, while females showed no pain relief. The drug decreased movement in both sexes, with longer-lasting effects in males. Brain recordings showed N₂O reduced low-frequency electrical activity in all mice, with stronger effects in females. In animals without pain, N₂O dampened brain responses to stimulation, but in pain-model mice it restored prefrontal activity. No antidepressant-like effects appeared 24 hours after treatment in either sex. These results indicate that N₂O's effects depend on sex and pain state, emphasizing the need to consider sex in NMDA receptor-based treatments.

Study at a glance

Abstract

Chronic pain-depression comorbidity is characterized by sensory hypersensitivity and emotional dysregulation, and has been linked to alterations in prefrontal network connectivity. It represents a major therapeutic challenge due to its pronounced sex differences in symptom manifestation and increased treatment resistance. Nitrous oxide (N₂O), an inhalational anesthetic traditionally used for its analgesic properties, has recently emerged as a potential rapid-acting antidepressant, with evidence suggesting both rapid and sustained antidepressant effects. Here, we evaluated the behavioral and electrophysiological effects of N₂O (50%, 1 h) in adult male and female mice subjected to the chronic constriction injury (CCI) model of neuropathic pain, assessing its potential to simultaneously target nociceptive and affective symptoms, as well as locomotor behavior. N₂O reduced locomotor activity in both sexes, with longer-lasting effects in males. EEG recordings revealed decreased low-frequency spectral power in both sham and CCI animals, with more widespread effects in females. In the acetone test, N₂O produced analgesia in CCI males but no significant effect in females, while stimulus application increased oscillatory EEG activity across groups and sexes. Notably, CCI females showed an attenuated electrophysiological response compared with Sham-Air controls. In sham animals, N₂O reduced post-stimulus power, whereas in CCI mice it restored prefrontal EEG activity, enhancing the electrophysiological responses in both sexes. In the tail suspension test, only CCI males exhibited a prodepressive phenotype, while no antidepressant-like effects were observed in either sex 24 h post-treatment. These findings demonstrate sex-specific behavioral and neurophysiological responses to N₂O, highlighting the importance of incorporating sex as a biological variable in NMDA receptor-targeted interventions.