Does Migraine Transiently Open the Blood–Brain Barrier?

In murine models of migraine, Evans blue leaked into the CNS after noninvasive induction of CSD. No leakage was observed in control animals that underwent a sham induction. Other controlled experiments that included objective measures of brain edema after CSD corroborated the association between CSD and BBB disruption.

“The opening of the BBB starts sometime between three and six hours [after induction of CSD], reaches a peak at six to 12 hours, and then gradually declines over the next 24 hours or so,” said Dr. Ayata. The BBB is completely restored at 48 hours, he added.

The Potential Role of Transcytosis

The BBB consists of astrocytes, pericytes, and endothelial cells with tight junctions that prevent most blood-borne substances from crossing into the CNS. Various processes can breach the BBB, and Dr. Ayata’s group is focusing on transcytosis. They hypothesize that ion pumps and other transporters cannot explain their observations that molecules as large as 70 kDa can pass through the BBB.

Transcytosis permits macromolecules from the luminal side of the endothelial cell to be brought into the cell by pinocytotic vesicles and to be released on the other side. It is a plausible mechanism for passage through the BBB, according to Dr. Ayata. Electron microscopy studies of BBB tissue from murine models strongly support this hypothesis.

“We found a significant increase in pinocytotic vesicles starting between three and six hours, but then a gradual decline to normal levels over the next 48 hours. This time course is exactly what we found in terms of leakage,” said Dr. Ayata. There was no evident change in endothelial tight junctions or in any other structure likely to provide an alternative mechanism for the observed BBB disruption, he added.

Although BBB disruption in an animal model of migraine is not proof of the same phenomenon in humans, Dr. Ayata suggested that the results are consistent with clinical observations. For example, a series of papers from 1985 to the present, including studies undertaken with gadolinium enhancement, found an association between severe migraine and documented edema. A twin study and studies of familial hemiplegic migraine also showed that CSD contributes to migraine pathogenesis and causes disruption of the BBB, he said.