Nerve growth factor and ATP excite different neck muscle nociceptors in anaesthetized mice

Neck muscle nociception probably plays a major role in the pathophysiology of tension-type headache. Recent studies have demonstrated sustained facilitation of brainstem nociception due to noxious neck muscle input evoked by nerve growth factor (NGF) or alpha,beta-methylene ATP (ATP) in mice. Hypothesized different afferent pathways in NGF and ATP models were addressed by local application of tetrodotoxin (TTX) in neck muscles. Brainstem nociception was monitored in 55 anaesthetized mice by the jaw-opening reflex elicited by electrical tongue stimulation. Sole administration of 100 nmol/l ATP or 0.8 micromol/l NGF evoked sustained reflex facilitation for at least 95 min. Preceding TTX administration prevented ATP-induced facilitation, but was without effect on NGF. Subsequent administration of 100 nmol/l TTX reversed ATP-evoked facilitation, but was ineffective on NGF. Divergent effects of TTX suggest preferential excitation of group III muscle afferents by ATP and group IV by NGF. Thus, both models address different pathways in pericranial pain.