Mechanisms of Harmful Overhydration And Brain Swelling


Source: McGill University Health Centre

Summary: Researchers uncovered a key piece to the puzzle of how our brains detect hyponatremia and regulate overhydration.


We are all familiar with the drawbacks of dehydration, but we rarely hear about the harmful effects of overhydration. For one, the excess fluid accumulation can lead to dangerously low sodium levels in the blood or hyponatremia a life-threatening condition that can result in brain swelling. Similarly, more is known about the mechanisms in the body that detect and drive thirst while little is known about how the brain detects a state of overhydration. Hyponatremia occurs in common pathological conditions, including brain injury, sepsis, cardiac failure and in the use of drugs, such as MDMA (ecstasy). Researchers from the McGill University Health Centre uncovered a key piece to the puzzle of how our brains detect hyponatremia and regulate overhydration which unearths the fundamental mechanism of how hyponatremia is detected in the brain. The study findings were published in the journal Cell Reports.

Hydration sensing neurons

Image shows the hydration sensing neurons (red) and the glial cells (green) in a mouse brain. Credit: Charles Bourque’s lab

The research team is no strangers to studying the mechanisms of hydration in the body and made several key discoveries in the past on how the brain detects and prevents dehydration; how salt intake increases blood pressure; and how the brain’s biological clock stimulates thirst prior to sleep. In this instance, the team revealed that the brain’s hydration sensing neurons don’t detect overhydration in the same way that they detect dehydration. This new research shows that overhydration activates Trpv4, which is a cellular gatekeeper implicated in maintaining the balance of water in the body. Trpv4 is a calcium channel that can be found in glial cells, which are cells that act to surround hydration sensing neurons.

Dr. Charles Bourque said, “Our study shows that it is, in fact, glial cells that first detect the overhydrated state and then transfer this information to turn off the electrical activity of the [hydration sensing] neurons.”


More Information: Sorana Ciura et al, “Trpv4 Mediates Hypotonic Inhibition of Central Osmosensory Neurons via Taurine Gliotransmission, Cell Reports (2018). DOI: 10.1016/j.celrep.2018.04.090 


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