新しい感覚器官の発見
Hello everyone, welcome to SCIEN-SPOT, the podcast that shines the spotlights on the latest scientific discoveries from Japan.
I'm your host, REN.
Now, how much thought do you usually give to something like coughing or swallowing?
These actions which we do automatically every day are actually super important defense mechanisms for our bodies.
They are absolutely essential for our daily well-being.
Today, we are going to dive deep into a groundbreaking discovery.
A joint research team, including Kyoto Prefectural University of Medicine,
has found brand new sensory organs hidden deep inside your throat that actually control both coughing and swallowing.
First, let's talk about why this research is so important.
Our throat is a critical crossroads.
It's where the food pathway, which is your esophagus, and the air pathway, which is your trachea, meet.
To prevent something called aspiration, that's when food or liquids accidentally go into your lungs,
our bodies have developed very sophisticated air protective reflexes like coughing and swallowing.
However, if these reflexes don't work properly, or if they become too sensitive, they can lead to serious health problems.
For example, coughing is one of the most common reasons people go to the doctor.
It's estimated that about 10% of people worldwide suffer from chronic cough,
which means a cough that lasts for more than 8 weeks.
Many of these cases have no clear cause, or they are intractable,
meaning they are rarely hard to treat with current methods.
On the other hand, if your swallowing function is impaired, it can lead to serious conditions like aspiration phenomena.
新しい神経伝達機構の発見
While we knew that certain chemical changes in the throat could trigger a cough or swallowing,
the detailed biological mechanisms behind it were still a big mystery.
And that's exactly what this research team tackled.
This group had actually discovered a special way cells and nerves communicate called channel synapse.
They had already shown its role in how we taste things on our tongue.
Unlike typical nerve communication, where substances were released from little sacs,
this unique way of transferring information involves releasing a chemical called ATP through tiny channels or pores
in certain voltage-dependent channels called CLHM13.
Until now, we didn't know if these channel synapses existed or worked anywhere else in the body besides the tongue.
But this discovery really opened up the possibility of uncovering new sensory functions throughout our bodies.
And now, through experiments done on mice, those hidden functions have been revealed.
The research team found these incredibly rare chemo-sensory cells that have channeled synapses
within the lining of the voice box, or larynx, and the back of the throat, or pharynx.
Specifically, in the larynx, these cells were tuft cells which look like they have little brushes on them.
And in the pharynx, they found type II taste cells which are typically found within the taste buds.
Through careful analysis, including detailed microscope observation and recording of nerve activity,
they confirmed that these cells form these special channel synapses with the vagus nerve and send information.
Even more amazing, they figured out what kind of stimuli these cells actually respond to.
新たな嗅覚器官の発見
Using a fancy technique called single-cell transcriptomic analysis, which looks at the gene expression in individual cells,
they found that the tuft cells in the larynx and the type II taste cells in the pharynx both have a group of receptors called T2R.
This T2R receptor group responded to literally countless types of harmful chemical substances.
Think beta-toxins from plants, tobacco smoke, air pollutants, and even materials related to germs.
Let me give you an analogy here.
The T2R receptors are like a universal keyhole that can recognize a wide variety of dangerous keys.
Before this research, we thought only a limited number of chemical substances could trigger a cough or swallowing.
But this research has shown us that countless harmful chemical substances can actually trigger these reflexes through this T2R receptor.
So how exactly do they trigger coughing and swallowing?
When this universal keyhole, the T2R receptor, is activated by these various dangerous keys, an electrical signal is generated inside the cells.
This signal then causes the release of that chemical, ATP, outside the cells through the channel synapse we just talked about.
By activating the vagus nerve, which has a specific ATP receptor called P2X3, the tough cells in the larynx then trigger the cough reflex.
And the type II taste cells in the pharynx trigger the swallowing reflex.
It's like we have a cough switch and a swallowing switch hidden in our throats that can sense different dangers in the environment and respond appropriately.
To confirm this mechanism, the research team did some really cool experiments.
They used genetically modified mice where the channel synapse function was turned off.
咳と飲み込みのメカニズム
In these mice, T2R stimulation no longer caused coughing or swallowing reactions.
However, coughs and swallowing triggers by more traditional things like acid were not affected.
This clearly shows that this channel synapse-mediated mechanism is especially for T2R-related stimuli.
Plus, using an advanced technique called optogenetics, which lets them activate specific cells with light,
they clearly showed that the tough cells in the larynx are indeed the triggers for the cough reflex.
And the type II taste cells in the pharynx are the triggers for the swallowing reflex.
What's more, they looked into how these cells might be involved in cough-related illness.
When they made mice have allergic cough hypersensitivity by giving them a specific mold antigen in their trachea,
the cough reflex to T2R stimulation became stronger.
But in the mice where the channel synapse function was turned off,
this enhancing effect of mold antigen on the cough reflex disappeared.
This strongly suggests that these laryngeal tough cells and the channel synapse
are deeply involved in cough symptoms related to illness like allergic cough hypersensitivity.
The results of this research have really opened up our understanding of the intricate defense system in our throats at the molecular level.
The potential of this discovery is huge.
Right now, a drug called gefapixant is used to treat chronic cough.
It works by blocking the P2X3 receptor.
But before this research, we didn't know exactly where the ATP that triggers this was coming from.
And there are side effects like taste disturbance.
However, with this new discovery, we've identified the laryngeal tough cells that release ATP.
新たな感覚器官の発見
This paves the way for developing more personalized treatments for chronic cough in the future.
Treatments that specifically target these cells potentially with fewer side effects.
And here's another fascinating tidbit.
It's been known that bitterness is important for that sensation we often describe as nodogoshi,
that smooth feeling when you drink something like beer.
But the scientific reason behind it was unclear until now.
By showing that bitter substances, which are T2R activators, actually promote swallowing,
this research also suggests a possible scientific explanation for part of that nodogoshi sensation we get from the bitterness in beer.
It's truly a fascinating outcome that shines a scientific light on our everyday sensory experiences.
That's all today SciencePod.
This podcast is broadcast daily on weekday morning in both Japanese and English.
I hope today's discovery has changed how you view your throat, even just a little.
I'd love for you to listen to the podcast and share your thoughts and notes with hashtag SciencePod.
See you next time.
