Maladaptive activation of Nav1.9 channels by nitric oxide causes triptan-induced medication overuse headache

Medication-overuse headaches (MOH) occur with both over-the-counter and pain-relief medicines, including paracetamol, opioids and combination analgesics. The mechanisms that lead to MOH are still uncertain. Here, we show that abnormal activation of Nav1.9 channels by Nitric Oxide (NO) is responsible for MOH induced by triptan migraine medicine. Deletion of the Scn11a gene in MOH mice abrogates NO-mediated symptoms, including cephalic and extracephalic allodynia, photophobia and phonophobia. NO strongly activates Nav1.9 in dural afferent neurons from MOH but not normal mice. Abnormal activation of Nav1.9 triggers CGRP secretion, causing artery dilatation and degranulation of mast cells. In turn, released mast cell mediators potentiates Nav1.9 in meningeal nociceptors, exacerbating inflammation and pain signal. Analysis of signaling networks indicates that PKA is downregulated in trigeminal neurons from MOH mice, relieving its inhibitory action on NO-Nav1.9 coupling. Thus, anomalous activation of Nav1.9 channels by NO, as a result of chronic medication, promotes MOH.


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All studies must disclose on these points even when the disclosure is negative. We did not systematically performed calculation to justify sample size but our sample sizes are similar to those reported in previous publications. However, in some behavioral experiments we performed sample size calculations using the software G*Power (http:// www.gpower.hhu.de/). We found that sample sizes with a minimum of 8-13 animals were necessary in most experiments, hence our typical sample sizes of 10-15 animals in most tests. For electrophysiological experiments, more than 10 cells were typically analyzed, except for some technically challenging experiments.
No analyzed data were excluded. However, some (3) animals were discarded from the study because they developped a local inflammation following minipump implantation.
To verify reproducibility of the experimental findings, each tested condition was assessed in different experiments, elapsed by several weeks or months and always associated with its own control performed contemporaneously.
Randomization was used in behavioral experiments.
The behavioral experiments in which animals were treated with sumatriptan or saline solution chronically (with minipumps), and injected at day 21 with SNP or vehicle were made blind; i.e. the investigator was not aware of the content of the minipump and of the nature of the solution (SNP or vehicle) injected on day 21.
Our anti-Nav1.9 antibody has been validated using Nav1