Retinal plasma extravasation in animals but not in humans: implications for the pathophysiology of migraine

High-intensity electrical stimulation of the trigeminal ganglion is accompanied by mast cell degranulation, vasodilatation, increased endothelial permeability and leakage of albumin from postcapillary venules within the dura mater. Overall, the histological appearance suggests an evolving sterile inflammatory response. This neurogenic inflammation within the meninges has been suggested as a model to explain the pain in migraine and cluster headache, and has been used to characterize the pharmacology of anti-migraine compounds. Using the rat model of neurogenic inflammation, the albumin extravasation ratio (stimulated : unstimulated side) in vehicle-treated animals in the dura and retina was 1.60 +/- 0.11 and 1.76 +/- 0.18, respectively (n = 10; values are mean +/- SEM). Pretreatment with sumatriptan (n = 9) produced a highly significant reduction in the ratio of extravasation within the dura to 1.10 +/- 0.06 (P = 0.002) and in the retina to 0.96 +/- 0.06 (P = 0.001), as did the neurokinin-1 receptor antagonist RP 67580 (n = 12) in the dura (1.04 +/- 0.11, P = 0.002) and retina (1.08 +/- 0.06, P = 0.001). These data demonstrate increased endothelial permeability and leakage of albumin not only in the dura but also in the retina. In a second stage we investigated possible extravasation in the human retina in acute migraine (n = 8) and cluster headache (n = 5) using fluorescein or indocyanine angiography. No increased endothelial permeability or leakage of dye could be found in the human retinal or choroidal vessels during headache attacks or in the headache-free interval in persons suffering from both migraine and cluster headache. These data raise the possibility that neurogenic inflammation is not a major factor in headache attacks in migraine or cluster headache.