Summary It is an experience so common that few of us give it a thought.
(Online)- A new study maps the brain circuits that tell us when we need to drink water, as well as when we have had enough. The research uncovered a neural hierarchy by stimulating and suppressing the urge to drink in mice.
We all need water, but how do our brains tell us it’s time to drink? Feeling thirsty is a sensation that everyone and every animal is familiar with.
It is an experience so common that few of us give it a thought. But neuroscientists are fascinated by it.
In relation to the survival of an organism, thirst is incredibly important. An animal that doesn’t take on fluids when it needs them will not be alive for long.
Without water, most of the processes within the body will seize up, and in humans, death follows in a short number of days.
Although the idea that our brains can detect water levels in the body and drive our desire to drink is not new, the exact neuroscience behind it is only slowly being fleshed out.
The most recent study to investigate the thirst mechanism was carried out by Yuki Oka, an assistant professor of biology at Caltech in Pasadena, CA. The findings were published this week in Nature.
The thirsty brain
Some work has already been done in this area. Studies have shown that a sheet-like structure in the forebrain, the lamina terminalis (LT), is important in thirst regulation. The LT comprises three parts: the organum vasculosum laminae terminalis (OVLT), the subfornical organ (SFO), and the median preoptic nucleus (MnPO).
The majority of the brain is separated from the bloodstream by the blood-brain barrier. Alongside other roles, this membrane protects the brain from pathogens, such as bacteria. But the SFO and OVLT are unusual; they are not protected by the blood-brain barrier and can directly contact the bloodstream.
Why is drinking water important?
Keeping hydrated is crucial for health and well-being, but many people do not consume enough water in a day.
This direct communication with the blood allows them to assess sodium concentration, so the "saltiness" of the blood is a good indication of how hydrated an animal is.
Earlier work has already shown that the LT contains excitatory neurons. When they are stimulated in a mouse, it elicits drinking behavior.
In this new study, the scientists found that the MnPO is particularly important, in that the nucleus receives excitatory input from the SFO but not vice versa.
They showed that when the MnPO’s "excitatory neurons are genetically silenced, stimulating the SFO or OVLT" no longer produces drinking behavior in the mice.
