A high-dose of fentanyl induced delayed anxiety-like behavior in rats. Prevention by a NMDA receptor antagonist and nitrous oxide (N2O)

► Anxiety-like behavior was spontaneously increased 24-h after a high-dose of fentanyl. ► This anxiety-like behavior was prevented by a NMDA-R antagonist. ► Fentanyl induced anxiety-like behavior was also prevented by a 50% N2O exposure.