Neuronal nitric oxide synthase is involved in the induction of NGF induced neck muscle nociception

BACKGROUND: Neck muscle nociception mediated by nitric oxide may play a role in the pathophysiology of tension-type headache.OBJECTIVE: The present study addresses the involvement of neuronal nitric oxide synthase (nNOS) in the facilitation of neck muscle nociception after local application of nerve growth factor (NGF).METHODS: After administration of NGF into semispinal neck muscles, the impact of neck muscle noxious input on brainstem processing was monitored by the jaw-opening reflex in anesthetized mice. The modulatory effect of preceding and subsequent administration of an inhibitor of neuronal nitric oxide synthase on central facilitation was addressed in a controlled study.RESULTS: With preceding i.p. application of saline or 0.096 mg/kg of the specific nNOS inhibitor Nw-propyl-L-arginine (NPLA), NGF induced a sustained reflex facilitation within 60 minutes. Preceding injection of 0.96 mg/kg or 1.92 mg/kg NPLA completely prevented the potentially facilitatory effect of NGF. Subsequent administration of 0.96 mg/kg NPLA did not affect established NGF-evoked reflex facilitation. Thus, NPLA prevents facilitation of brainstem processing by noxious myofascial input from neck muscles in a dose-dependent manner.CONCLUSION: These findings suggest that nNOS is involved in the induction but not the maintenance of NGF-evoked facilitation of nociception in the brainstem. These results from an experimental animal model may support the idea of NOS and nNOS as potential targets for pharmacological treatment of tension-type headache