Gustation Flashcards
Do taste cells have neurons which project to higher brain regions?
Sort of: don’t have their own nerves, but are connected to cranial nerve terminals
Describe the volatility of gustatory compounds. How does this different from olfactory compounds?
Non volatile, as opposed to olfactory molecules, which are volatile
How many circumvallate papillae are there?
3-13
How many taste buds are contained in the circumvallate papillae?
252 taste buds per papillae
How many foliate papillae are there?
10-12
How many taste buds are there contained in a foliate papilla?
117
How many fungiform papillae are there?
200
How many taste buds are there in a fungiform papilla?
1-18
Which cranial nerve terminates in the circumvallae and foliate papillae?
Glossopharyngeal (IX)
Which cranial nerve terminates in the fungiform papillae?
Chorda tympani (VII)
Which other sensory systems contribute input to gustation? (2)
Visual system
Olfactory system
True or False: The modified epithelial cells of the taste buds generate APs
True
What kind of tissue are taste receptor cells?
Epithelial
Taste receptor cells are replaced this often
Every 2 weeks
Which taste modalities use GPCRs?
Bitter, sweet, and umami
Describe the 2 possible taste receptors for sweet
Can be homo or heterodimer of T1R2 and T1R3
Why don’t cats have a sweet taste?
Because they have a knock out in the T1R2 receptor gene
Describe the receptor for umami
Heterodimer of T1R1 and T1R3
What is the specific taste of umami detecting?
L-amino acids: aspartate and glutamate
What is common between the sweet and umami taste receptors?
T1R3
What is the name of the receptor family of bitter taste receptors?
T2Rs
How many genes make up the T2R (bitter) receptor family?
30
Why might there be more T2Rs in mice than in humans?
Humans are more visual: might need to rely on taste less
Describe human TRP channels (4)
6TM domains
Nonselective cation channels
Many thermosensitive (capsaicin/menthol)
Many associated with GPCRs
When PLC is knocked out, which taste modalities are also knocked out?
Umami, sweet, and bitter
When TRMP5 channels are knocked out, which taste modalities are knocked out?
Umami, sweet, bitter
Are bitter receptors expressed alone, or coexpressed with other bitter receptors?
Coexpressed: just need cells to respond to initiate aversive reaction
What does it mean for a cell to be “broadly tuned”
It is able to respond to a wide variety of ligands
Are sweet and umami receptors coexpressed with bitter receptors?
No
What is PKD2L1?
Polycystronic kidney disease channel: a TRP-like channel which was thought to be the sour channel but is NOT!
What is the channel which mediates sour taste?
OTOP1
What is OTOP1?
A H+-gated ion channel, entry of H+ into the cell causes depolarization
What are 2 possible modes of tasting carbonation?
- Activates mechanoreceptors in taste cells
- Carbon dioxide of sparkling water interacts with water to make bicarbonate, releases H+ and activates OTOP1
What is the sodium taste receptor? (Name of receptor)
ENaC
Describe ENaC
Epithelial sodium channel: not very well understood – unknown mechanism
ENaC is a (1)-sensitive ion channel
Amiloride
ENaC allows the passage of (1) ions
Na+
What are the 3 families of chemosensors in drosophila
Odorant receptors
Ionotropic receptors
Gustatory receptors
Olfactory receptors in drosophila are present on this body part
Antennae
Flies injest their food through this structure
Probiscis
Where are the 3 locations drosophila have gustatory receptors?
Wings
Legs
Mouthparts
Describe the labelled line model
Within a taste bud, different cells respond to a different taste modality
Describe the across-fiber model
Every cell has taste receptors for different taste modalities
Given that the GPCR taste modalities all use PLC and TRPM5, how is this evidence for the labelled line model?
Evidence because if they were in the same cell we would not be able to discriminate between bitter/sweet/umami
What are the 2 pieces of evidence in support of the labelled line hypothesis
- Some pathways use the same downstream cascade but we can discriminate between them
- Sour receptors are found in different cells than sweet/umami/bitter
Are sweet and umami expressed in the same cells?
No
Why are TRCs arranged in that ball-like shape?
Not confirmed: but possible that this is for lateral inhibition
Are human taste preferences innate?
Yes, but they can be affected by learning and memory
How did they test the question that sweet perception was due to the receptors or the cell?
What receptor was used?
What was the result?
Express an exogenous, unrelated receptor in a sweet-responsive cell and see if the ligand for that receptor can activate sweet perception
Receptor: RASSL, ligand: spiradoline
Preference for spiradoline water: seems to mediate sweet response! Therefore the cell is dependent on the response: even more evidence for the labelled line theory! Did the same for bitter cells and found spiradoline mediated avoidance
