Abnormal neurovascular coupling as a cause of excess cerebral vasodilation in familial migraine

Acute migraine attack in familial hemiplegic migraine type 2 (FHM2) patients is characterized by sequential hypo- and hyperperfusion. FHM2 is associated with mutations in the Na, K-ATPase α2 isoform. Heterozygous mice bearing one of these mutations (α2^+/G301R mice) were shown to have elevated cerebrovascular tone and, thus, hypoperfusion that might lead to elevated concentrations of local metabolites. We hypothesize that these α2^+/G301R mice also have increased cerebrovascular hyperaemic responses to these local metabolites leading to hyperperfusion in the affected part of the brain.

Neurovascular coupling was compared in α2^+/G301R and matching wild-type (WT) mice using Laser Speckle Contrast Imaging. In brain slices, parenchymal arteriole diameter and intracellular calcium changes in neuronal tissue, astrocytic endfeet, and smooth muscle cells in response to neuronal excitation were assessed. Wall tension and smooth muscle membrane potential were measured in isolated middle cerebral arteries. Quantitative polymerase chain reaction, western blot, and immunohistochemistry were used to assess the molecular background underlying the functional changes. Whisker stimulation induced larger increase in blood perfusion, i.e. hyperaemic response, of the somatosensory cortex of α2^+/G301R than WT mice. Neuronal excitation was associated with larger parenchymal arteriole dilation in brain slices from α2^+/G301R than WT mice. These hyperaemic responses in vivo and ex vivo were inhibited by BaCl₂, suggesting involvement of inward-rectifying K⁺ channels (K_ir). Relaxation to elevated bath K⁺ was larger in arteries from α2^+/G301R compared to WT mice. This difference was endothelium-dependent. Endothelial K_ir2.1 channel expression was higher in arteries from α2^+/G301R mice. No sex difference in functional responses and K_ir2.1 expression was found.

This study suggests that an abnormally high cerebrovascular hyperaemic response in α2^+/G301R mice is a result of increased endothelial K_ir2.1 channel expression. This may be initiated by vasospasm-induced accumulation of local metabolites and underlie the hyperperfusion seen in FHM2 patients during migraine attack.