Our thirsty urge for a drink before bedtime? Why?
For many, a glass of milk or a herbal tea is the last thing they have before sleeping. And if you’ve ever put kids to sleep, you’ll know the request for “a last glass of water” all too well.
But the question has remained, is bedtime thirst just about routine and habits, or is there be an underlying biological explanation?
A study recently published in the journal Nature suggests the latter – that our circadian clocks may be responsible for triggering our pre-bedtime thirstiness.
But night-time thirstiness is different and occurs even when none of the above symptoms exist.
In the new study, the researchers found during the day, rats would seek out water only when their bodies needed it.
But in the hours before they slept, they would typically show increased thirst, despite exhibiting any of the typical reasons for being thirsty.
They found that water-deprived rats showed clear signs of dehydration towards the end of the sleep period.
This suggests that the rats were instinctively drinking more water at night to provide adequate hydration during the long hours of sleep.
Applying cutting-edge research utilizing laser light to manipulate the neurons in the brains of rats, they found that there was indeed some communication between the sleep and thirst centers of the brain.
They identified a dialogue between regions of the brain known as suprachiasmatic nucleus (SCN) which manages our circadian rhythms, and the OVLT, which controls the balance of fluids in our body. The vascular organ of lamina terminalis (VOLT), organum vasculosum of the lamina terminalis (OVLT), or supraoptic crest[1] is one of the four sensory circumventricular organs of the brain, the others being the subfornical organ, the median eminence, and the area postrema in the brainstem.
When the researchers activated the SCN of the rats to make the brain think it was preparing for sleep, they found that this led to a release of vasopressin – a peptide (protein chain) that affects thirst.
For example, shift workers often go against their circadian rhythms and tend to have disrupted sleep/wake schedules. Thus, sleeping at irregular times may not provide the necessary biological cues to drink the necessary amount of water – resulting in dehydration.
Commenting on their results, senior researcher Charles Bourque said “Although this study was performed in rodents, it points toward an explanation as to why we often experience thirst and ingest liquids such as water or milk before bedtime,”
He added “more importantly, this advance in our understanding of how the clock executes a circadian rhythm has applications in situations such as jet lag and shift work. All our organs follow a circadian rhythm, which helps optimize how they function. Shift work forces people out of their natural rhythms, which can have repercussions on health. Knowing how the clock works gives us more potential to actually do something about it.”
Based on the findings of this research, scientists may soon recommend that people drink water before sleeping even if they don’t feel thirsty. This will ensure adequate hydration during their sleep phase – resulting in better sleep as well as better overall health.
Thirsty before bed. Connection between ‘body clock’ brain area and ‘thirst’ area creates thirst before sleep, to maintain water balance overnight.
Do you drink a glass of water before going to bed? Then, hate to break it to you, but you have something in common with a mouse.
Overview
A new paper suggests that a mouse’s biological clock increases its thirst shortly before it sleeps.1 Why? The study’s authors suggest this increased drive to drink, allows a mouse to drink a little bit of extra water, which will help maintain the mouse’s balance of water and salt throughout the night as it loses fluid through for example through sweat.
The study shows the mouse’s brain is hard-wired to anticipate fluid will be lost throughout the night. The part of the brain that keeps track of the biological clock, the SCN, sends a connection that signals to the part of the brain that regulates thirst, the OVLT,2 and this connection releases Vasopressin as a neurotransmitter.
Brain Slices: Scientists anesthetize the mouse and remove it’s brain keeping it in an oxygenated fluid with nutrients, so the cells stay alive. In this case, they cut the brain at a 34 degree angle to obtain a slice that contains the OVLT, SNC, and connection between them.
Then experimenters looked at a ‘slice’ of the mouse’s brain, a thin strip of brain tissue that maintained the connection between the SCN and OVLT. They showed that the OVLT neurons that respond to vasopressin, increased in the time shortly before the animal would sleep.
When scientists stimulated the SCN they could increase activity in the vasopressin-detecting neurons in the OLVT. Crucially, however, when the scientists stimulated the SCN, while simultaneously blocking the receptors that sense Vasopressin, the OVLT showed no increase in activity.
These experiments suggest that the SCN’s releases of vasopressin increases the activity of OVLT neurons, and the activity of OVLT neurons has been shown to correlate with drinking behavior in other experiments.
To prove that this effect was real in the context of the whole brain, the experimenters bred mutant mice that express optogenetic proteins only in Vasopressin releasing neurons. These optogenetic proteins allowed the researchers to shine a light into the mouses brain and inhibit or excite the Vasopressin-releasing neurons that project from the SCN to the OVLT.3 When they inhibited this connection during the pre-sleep period, they could decrease animals pre-sleep drinking behavior. When they activated this connection outside of the pre-sleep period the animals increased the amount they drunk.
Importantly, this study was performed in mice. Although circadian rhythms are similar and many hypothalamic processes are conserved throughout evolution, they are not exactly the same–mice are for example nocturnal. Therefore, it is still unclear whether this exact mechanism occurs in other animals such as humans. (So maybe I was premature in comparing you to a mouse, my apologies.)
—-
I’m curious about your own experience. I’ve found I always wake up from naps extremely thirsty (and I don’t think it’s just from the drool). I wonder if that too might relate to an interplay between circadian rhythm, sleep, and thirst.
What’s your experience–do you feel you get thirsty right before bed? Do you sleep with a glass of water on your nightstand?
Some nerdy comments for those who care and References:
Additionally, while this experiment showed statistically significant effects and makes an extremely strong case for the existence of this pathway and its role in modulating pre-sleep thirst, other pathways may also play roles. For example vasopressin levels into the blood also follow circadian rhythms and may have effects on OVLT neurons.4
New research suggests the circadian clock may be responsible for our thirsty urge for a drink before bedtime.
Why is it that just as we’re getting ready to sleep, we often get an inexplicable thirsty urge?For many, a glass of milk or a herbal tea is the last thing they have before sleeping. And if you’ve ever put kids to sleep, you’ll know the request for “a last glass of water” all too well.
But the question has remained, is bedtime thirst just about routine and habits, or is there be an underlying biological explanation?
A study recently published in the journal Nature suggests the latter – that our circadian clocks may be responsible for triggering our pre-bedtime thirstiness.
Non-thirst drinking
Mostly, our thirst response is activated when we’re at risk of of becoming dehydrated. This could happen for instance if our body temperature increases, or if blood plasma volume decreases. In general we experience thirstiness when the ratio of fluid in the body is lower than normal.But night-time thirstiness is different and occurs even when none of the above symptoms exist.
In the new study, the researchers found during the day, rats would seek out water only when their bodies needed it.
But in the hours before they slept, they would typically show increased thirst, despite exhibiting any of the typical reasons for being thirsty.
Stocking – up on fluids
To investigate, researchers Claire Gizowski and her team restricted the rats’ access to water just before sleep time.They found that water-deprived rats showed clear signs of dehydration towards the end of the sleep period.
This suggests that the rats were instinctively drinking more water at night to provide adequate hydration during the long hours of sleep.
This makes sense because during sleep, rats (and most mammals – including humans) keep on using up fluids as the body goes about digesting foods and repairing tissue.
The brain mechanism
The researchers at McGill University wanted to verify whether the parts of the brain that control thirst and sleep were in any way communicating.Applying cutting-edge research utilizing laser light to manipulate the neurons in the brains of rats, they found that there was indeed some communication between the sleep and thirst centers of the brain.
They identified a dialogue between regions of the brain known as suprachiasmatic nucleus (SCN) which manages our circadian rhythms, and the OVLT, which controls the balance of fluids in our body. The vascular organ of lamina terminalis (VOLT), organum vasculosum of the lamina terminalis (OVLT), or supraoptic crest[1] is one of the four sensory circumventricular organs of the brain, the others being the subfornical organ, the median eminence, and the area postrema in the brainstem.
When the researchers activated the SCN of the rats to make the brain think it was preparing for sleep, they found that this led to a release of vasopressin – a peptide (protein chain) that affects thirst.
Implications
Although the findings are preliminary, they could have important implications for our everyday lives. Understanding the reasons and mechanisms for our biological drives could lead to major improvements in health-care and lifestyle.For example, shift workers often go against their circadian rhythms and tend to have disrupted sleep/wake schedules. Thus, sleeping at irregular times may not provide the necessary biological cues to drink the necessary amount of water – resulting in dehydration.
Commenting on their results, senior researcher Charles Bourque said “Although this study was performed in rodents, it points toward an explanation as to why we often experience thirst and ingest liquids such as water or milk before bedtime,”
He added “more importantly, this advance in our understanding of how the clock executes a circadian rhythm has applications in situations such as jet lag and shift work. All our organs follow a circadian rhythm, which helps optimize how they function. Shift work forces people out of their natural rhythms, which can have repercussions on health. Knowing how the clock works gives us more potential to actually do something about it.”
Based on the findings of this research, scientists may soon recommend that people drink water before sleeping even if they don’t feel thirsty. This will ensure adequate hydration during their sleep phase – resulting in better sleep as well as better overall health.
Thirsty before bed. Connection between ‘body clock’ brain area and ‘thirst’ area creates thirst before sleep, to maintain water balance overnight.
Do you drink a glass of water before going to bed? Then, hate to break it to you, but you have something in common with a mouse.
Overview
A new paper suggests that a mouse’s biological clock increases its thirst shortly before it sleeps.1 Why? The study’s authors suggest this increased drive to drink, allows a mouse to drink a little bit of extra water, which will help maintain the mouse’s balance of water and salt throughout the night as it loses fluid through for example through sweat.
The study shows the mouse’s brain is hard-wired to anticipate fluid will be lost throughout the night. The part of the brain that keeps track of the biological clock, the SCN, sends a connection that signals to the part of the brain that regulates thirst, the OVLT,2 and this connection releases Vasopressin as a neurotransmitter.
Brain Slices: Scientists anesthetize the mouse and remove it’s brain keeping it in an oxygenated fluid with nutrients, so the cells stay alive. In this case, they cut the brain at a 34 degree angle to obtain a slice that contains the OVLT, SNC, and connection between them.
Then experimenters looked at a ‘slice’ of the mouse’s brain, a thin strip of brain tissue that maintained the connection between the SCN and OVLT. They showed that the OVLT neurons that respond to vasopressin, increased in the time shortly before the animal would sleep.
When scientists stimulated the SCN they could increase activity in the vasopressin-detecting neurons in the OLVT. Crucially, however, when the scientists stimulated the SCN, while simultaneously blocking the receptors that sense Vasopressin, the OVLT showed no increase in activity.
These experiments suggest that the SCN’s releases of vasopressin increases the activity of OVLT neurons, and the activity of OVLT neurons has been shown to correlate with drinking behavior in other experiments.
To prove that this effect was real in the context of the whole brain, the experimenters bred mutant mice that express optogenetic proteins only in Vasopressin releasing neurons. These optogenetic proteins allowed the researchers to shine a light into the mouses brain and inhibit or excite the Vasopressin-releasing neurons that project from the SCN to the OVLT.3 When they inhibited this connection during the pre-sleep period, they could decrease animals pre-sleep drinking behavior. When they activated this connection outside of the pre-sleep period the animals increased the amount they drunk.
Importantly, this study was performed in mice. Although circadian rhythms are similar and many hypothalamic processes are conserved throughout evolution, they are not exactly the same–mice are for example nocturnal. Therefore, it is still unclear whether this exact mechanism occurs in other animals such as humans. (So maybe I was premature in comparing you to a mouse, my apologies.)
—-
I’m curious about your own experience. I’ve found I always wake up from naps extremely thirsty (and I don’t think it’s just from the drool). I wonder if that too might relate to an interplay between circadian rhythm, sleep, and thirst.
What’s your experience–do you feel you get thirsty right before bed? Do you sleep with a glass of water on your nightstand?
Some nerdy comments for those who care and References:
Additionally, while this experiment showed statistically significant effects and makes an extremely strong case for the existence of this pathway and its role in modulating pre-sleep thirst, other pathways may also play roles. For example vasopressin levels into the blood also follow circadian rhythms and may have effects on OVLT neurons.4
- Gizowski, C., Zaelzer, C. & Bourque, C. W. Nature 537, 685–688 (2016).
- Both of these regions are within the hypothalamus, an area which regulates maintains homeostatic balance of things like body temperature, food intake, etc.
- Though technically back-propagating action potentials could lead to other brain areas being affected as well, especially if the SCN neurons have branching connections.
- Trudle, E. & Bourque, C. W. Nature Neurosci. doi:10.1038/nn.2503 (2010).
No comments:
Post a Comment