Taste

Question 1

how many taste buds in a taste cell?

Answer 1

contain 50-100 taste cells

Question 2

three types of papillae

Answer 2

Fungiform, foliate, circumvallate

Question 3

Morphology of three types of papillae

Answer 3

Fungiform: simple, 1-5 taste buds
Foliate: Small invagination, 50-100 taste buds
Circumvallate: Deep invagination, 250 taste buds

Question 4

Length of taste cell life span

Answer 4

1 week

Question 5

Taste cranial nerves and where they get info from

Answer 5

VII facial nerve:Anterior part of tongue and palate (branched), greater petrosal & chorda tympani
IX glossopharyngeal: Posterior third of tongue
X vagus: inferior ganglion cells from the epiglottis

Question 6

Where do the 3 cranial nerves for taste terminate?

Answer 6

Rostral part of the nucleus of the solitary tract

Question 7

Salt channel for taste

Answer 7

Amiloride-sensitive epithelial sodium channels (ENaCs), straightforward sodium ion channel

Question 8

Acid channel for taste

Answer 8

H+ sensitive TRP channel (PKD variant), use H+ ions as driving force for depolarization

Question 9

Taste transducer for sweet

Answer 9

G-protein coupled heterodimer receptor made of T1R2 & T1R3

Question 10

Taste transducer for umami

Answer 10

G-protein coupled heterodimer receptor made of T1R1 & T1R3

Question 11

Mechanism for umami taste

Answer 11

1. Amino acids bind to G-protein coupled receptor (T1R1 & T1R3)
2. Alpha subunit acts on PLC beta 2
3. IP3 is used as a second messenger to signal release of Ca2+ from endoplasmic reticulum
4. Ca2+ activates TRPM5 channel for depolarization

Question 12

Mechanism for bitter taste

Answer 12

1. Bitter compounds bind to G-protein coupled receptor Gustducin (T2R5)
2. Alpha subunit acts on PLC beta 2
3. IP3 is used as a second messenger to signal release of Ca2+ from endoplasmic reticulum
4. Ca2+ activates TRPM5 channel for depolarization

Question 13

Two choice test for mice with different taste receptors KOed

Answer 13

Had a water spout and a sucrose spout, mouse did not care between which one they drank from when TRPM5 was KOed, similar response to umami (glutamate in water), and bitter (quinine in water).

Question 14

How are different taste receptors distributed on the tongue?

Answer 14

Each receptor type is present in all papillae of the tongue, not like the diagram where tastes are localized to one area each

Question 15

Type I taste bud cells

Answer 15

Responsible for detecting salt, looks like a glial cell, specialized ROMK channel allows for K+ to be extruded at apical tip

Question 16

Type II taste bud cells

Answer 16

For sweet, umami and bitter. Do not contain vesicles, instead bulk release ATP through CALHM1/3 pore

Question 17

Type III taste bud cells

Answer 17

For sour, have vesicles containing serotonin that activate downstream serotonergic neurons, have inhibitory receptors for neighbouring cells (think center surround inhibition)

Question 18

Geniculate ganglion cells response to taste

Answer 18

Most neurons are selective for one taste, but some sour and bitter overlap

Question 19

microendoscopy

Answer 19

two photon imaging - lens to image deep areas of brain

imaged geniculate ganglion and visualized different populations of neurons
expressed Ca sensory (cAMP and GFP)

Question 20

responses of ganglion cells to basic taste qualities

Answer 20

found that each cell responds selectively to 1 tastant and no other
- argues against signal being mixed at synapse

Question 21

gustotopic maps

Answer 21

shows activity segregated in different parts of gustatory cortex
- becomes spatially segregated (not combinatorial like smell)

Question 22

photostimulation of bitter and sweet corticies

Answer 22

drives aversive and appetitive behavior

• expressed channel rhodopsin in cortex and saw perception of sweet and bitter even though they cannot detect

Question 23

Tasting the light experiment

Answer 23

Used optogenetics to stimulate specific parts of the gustatory cortex, put the mouse in a box with two chambers (one lit and one dark). If the light stimulates the sweet part of the cortex, it will spend more time in that chamber. If the light stimulates the bitter part of the cortex, it will stay in the dark chamber.