Sample of a mouse brain showing blood vessels in blue. Leaky vessels are overlaid in green; tight vessels are in red. Image credit: Benz et al. (CC BY 4.0)
Infections and diseases in the brain and spine can be very damaging and debilitating. Indeed, the central nervous system also needs a carefully controlled biochemical environment to survive. As such, all animals with a backbone have barriers and defenses to protect and preserve this key system. One of these is the blood-brain barrier, a physical barrier between the brain and the outside world. Where most blood vessels allow relatively free exchange of chemicals between the blood and surrounding cells, the blood-brain barrier controls what can move between the bloodstream and the brain.
Yet, there are gaps in the blood-brain barrier, specifically within structures in the brain called the circumventricular organs. These leaky vessels allow the brain cells in these regions to monitor the blood and respond to changes, for example, by triggering sensations such as hunger, thirst or nausea. It is not clear what stops the blood-brain barrier from forming in these regions and what effect the presence of a barrier would have on the brains activity, or the health and behavior of the animal.
Benz et al. have now used mice and zebrafish to examine the development and structure of the blood-brain barrier. The investigation revealed that the signals that induce the blood-brain barrier throughout the brain are absent in the circumventricular organs of both species. Next, by artificially activating a protein involved in cell-cell interactions in mice, Benz et al. created blood-brain barrier-like structures in circumventricular organs by converting the leaky vessels into tight ones. This change meant that the brain cells in these regions did not respond properly to water deprivation, which potentially may have affected the regulation of thirst in these mice.
Understanding the blood-brain barrier could have a variety of impacts on how we treat diseases in the central nervous system. This includes stroke, brain tumors and Alzheimers disease. These findings could particularly help scientists to better understand conditions that affect basic needs like thirst and hunger.
