Cerebroventricular sodium, regulated by Na,K,ATPase and endogenous ouabain, changes neuronal excitability in a rat migraine model
Authors: Gross Noah B. , Harrington Michael G. 
Published: November 2023

Migraine is among the most disabling neurological disorders. Hallmark features include hypersensitivity to external and/or internal stimuli, with a decreased pain threshold. Hyperexcitable neuronal pathways have been reported in migraine and preclinical models, but the pathophysiology is not fully understood.Leading candidates to alter neuronal excitability include ionic disturbances. Cations play important roles in regulating membrane potentials and deviations from their homeostasis have been implicated in the cortical spreading depression underlying migraine aura. Mutations in ion channels and transporters cause familial hemiplegic migraine, but these have not been found in migraine itself. Previously, our lab found cerebrospinal fluid (CSF) sodium concentration was higher during migraine, and rising extracellular sodium increased neuronal firing rates both in simulations and primary neuron cultures. Using sodium magnetic resonance imaging, we demonstrated that nitroglycerin (NTG) administration in a rodent migraine model of central sensitization (CS) increased total sodium in the brain and vitreous humor.Our hypothesis is that extracellular sodium increases in the CS model of migraine. A better understanding of this mechanism may help guide corrective treatments. To this end, we assessed 1) whether inhibiting Na,K,ATPase (NKA), the major regulator of brain sodium, modulates NTG‐triggered CS; 2) whether endogenous ouabain (EO) inhibition modulates the aversive threshold; and 3) whether direct increase of intracerebroventricular (ICV) sodium lowers the aversive pain threshold.Using standard stereotactic surgical methods, we implanted ICV cannulas in young adult, male, Sprague‐Dawley rats. Three experiments were carried out a week after surgery: 1) we infused the specific NKA inhibitor ouabain, or vehicle control, 10 minutes prior to NTG; 2) we infused anti‐digoxin immunoglobulin fragments, DigiFab®, to bind EO; 3) we infused hypertonic sodium or hyper‐osmolar control solutions ICV. For all studies, we determined the aversive threshold at hourly intervals, using Von Frey hairs. To measure activation in the central trigeminal system, we counted the number of nuclei expressing cFos in the trigeminal nucleus caudalis (TNC).ICV infusion of ouabain prior to intraperitoneal administration of NTG protected against NTG‐triggered aversive behavior and increasing cFos expression in the TNC. Conversely, unilateral ICV infusion of either hypertonic sodium or DigiFab® decreased the aversive threshold, while hyperosmolar controls or Fab control antibodies had no effect. ICV infusion of hypertonic sodium or DigiFab® also induced more cFos expression in the TNC compared to control infusions.This is the first demonstration that A) specific inhibition of central NKA protects against NTG‐triggered CS; B) EO in the rat central nervous system contributes to the baseline aversive threshold level; C) increasing ICV sodium concentration reduces the aversive pain threshold.Support or Funding Information5R01NS072497‐04, NIH (2011/08/01–2016/07/31)