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3.2.9 Taste transduction-II
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From the course by Peking University
Advanced Neurobiology II
55 ratings
From the lesson
Chemosensory system
Meet the Instructors
Chenjian LiProfessor
School of Life Sciences
Donggen LuoResearch Fellow
School of Life Sciences
Yan ZhangProfessor
School of Life Sciences, Peking University
And these cell are responsible for the sour taste.
And they release.
That's a neurotransmitter.
And this guy, for the type two cells,
they don't have direct synapse formations there.
But actually, those axons around
the ganglion will wrap that quite closely.
[FOREIGN] synapse.
And for these cell propose that they also release neurotransmitter, ATP.
But if they don't have a synapse.
So the ATP release, then you have some trouble.
You release all, it don't have a synapse.
Then the ATP will diffuse to here to type 3 cells.
And also maybe will act on these bundles or
have some kind of effect on itself.
Okay, so take a look.
If some company came to a signal transmission,
how can you study that system, so
clearly like it's a vision system or olfactory system?
It's really challenging.
For example, we know this cell responding to the sour taste.
But if you stimulate the tongue with the sweet stuff,
this cell maybe also can detect, have the similar response to the sweet stuff.
Because this cell releases ATP.
We have some effect on the other cell.
Yet these actually cause the big trouble, okay?
About the taste of the coding.
Let's take a look about the taste of coding.
Okay, so we know this is a taste receptor cell seated here on the tongue.
And then you have those ganglion sends axons in the way to the tongue,
but only synapse onto the type 3, the sour taste cell.
And then they will further send the information to the brain stem.
We talk about NST.
This is the brain stem.
And then we'll further send to the PPM here.
And then to the thalamus with PPM.
And then to the cortex.
This is a signal process along this neurocircuitry.
We talk about here is already quite complicated.
The information transmission.
If you recall these cells.
These taste receptor cells.
Then you will have maybe each cell will respond to,
see it is sodium chloride then uses it salty taste.
And then, this is the [INAUDIBLE] of the sour taste, right?
And the sucrose.
So essentially, if you recall from these axons.
These axons from the axons.
This is the gastric ganglion cells axon.
And then, if you cut from this one, and
then they have detect the salt and sour,
and in from this neuron, also similar.
And this neuron then is a sucrose.
The history in the field is actually when people record from these bundles,
these axons use the single-unit recording.
Or extracellular recording.
[FOREIGN].
They found actually, these axons actually not only
detect one single modality, that is the bottom line.
They detect a lot of chemical given the modalities.
So then, what it tells you.
The taste system actually is not like olfactory system.
Those specific line go to the brain.
They are mixed signals.
They're already mixed actually at this region.
And then this is actually some kind of theory about the taste coding.
This is kind of three models, actually two.
One is actually they call it actually [INAUDIBLE] model.
That means actually one cell each offer the taste receptor cell,
only detect one type of modalities, sweet things sweet, bitter's bitter.
And sour then sour.
And also, the neuro-connection,
the ganglion cell, that axon, only in the specific to each type of cell.
And then this you see there is label the line.
One signal directly go to the brain.
But then these two, then it's different.
These two, one is like this.
One cell can detect all kinds of modalities.
You'll see these five they can detect.
Of course, then the axons, the signal was mixed.
And then another version will be
each individual one still detect only one modality.
But because over the synaptic connection, they mix again the signal.
Okay so there are two types of coding.
One is to labelled line, one is actually cross fiber.
This cross fiber actually is similar as maybe
in the brain you need to detect that information, whether it's sweet or bitter.
Then you really need to compare many different kind of axons.
The signal not based on single one.
Signal one based on this one is fine.
You'll know this is sweet or bitter, right?
Okay, so this is, we finished this slide, the last one.
They did a beautiful study.
So we know in the human,
we have this receptor, hT2R16.
This is a bitter receptor.
T2 family.
And then this receptor is supposed to detect this bitter stuff.
Okay, this human receptor, taste receptor.
But actually in the mouth actually this bitter stuff mouth does not care.
[FOREIGN].
Okay did a beautiful work, is actually,
they express this receptor in the mouth.
Use the promoter of the T1 and 2 promoter.
[FOREIGN] and also to express use T2R promoter.
[FOREIGN] Beautiful.
Now this one is actually the bitter stuff you put in the water,
let the mouth to drink.
Of course if the mouth don't like the water, they will reject,
they will not drink okay.
Now this is actually a consumption of the water.
And this one, if you express, this is control, control animal.
They don't care about this bitter stuff.
But if you express this bitter receptor in
the sweet neuron, receptor cell not neuron.
And then this mouth actually drink a lot of this bitter water.
Why?
And then if you put this receptor into the bitter
receptor cell then the mouth reject the water.
Okay, think about how this system works.
And based on these results group believe this is actually a labelled line.
That means, actually the taste system, the coding of the taste signal,
really actually they are kind of hard wired.
That means, actually, this sweet neuron carries information direct to the brain.
Tell the mouth this is sweet stuff.
You need to drink a lot.
It does not matter you express a bitter receptor or sweet receptor.
This is a key message.
But still, you can argue this may not be the only explanation.
This is a nature paper, actually conclusion.
Yeah, so the taste coding still a lot of debating there.
As we mentioned,
when people did the recording they found the signals mixed together.
And the data from this genetic study looks very clear.
Is it labeled or not?
But the people argue, this interpretation, it's not the only one.
You can have different explanation with the same results.
Yeah, you can think about some explanation.
Okay, that's it, yep.
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