Inhibition of nitric oxide synthases prevents and reverses α,β-meATP-induced neck muscle nociception in mice:

Introduction: Tension-type headache (TTH) is associated with noxious input from neck muscles. Intravenous administration of the unspecific nitric oxide synthase inhibitor L-NMMA in chronic TTH patients caused analgesia and reduction of neck muscle tenderness.Methods: The unspecific nitric oxide synthase inhibitor L-NMMA was applied in an experimental model for neck muscle nociception in anesthetized mice (N = 25).Results: Local injection of α,β-meATP into semispinal neck muscles induced sustained facilitation of brainstem nociception as monitored by the jaw-opening reflex. Preceding intraperitoneal administration of L-NMMA (0.05, 0.1, 1 mg/kg) prevented reflex facilitation evoked by α,β-meATP in a dose-dependent manner. Intraperitoneal injection of L-NMMA subsequent to intramuscular α,β-meATP application reversed established brainstem reflex facilitation back to baseline values.Discussion: Both experiments with preceding and subsequent L-NMMA indicate the involvement of nitric oxide synthases in the induc...