Taste Flashcards
how many taste buds in a taste cell?
contain 50-100 taste cells
three types of papillae
Fungiform, foliate, circumvallate
Morphology of three types of papillae
Fungiform: simple, 1-5 taste buds
Foliate: Small invagination, 50-100 taste buds
Circumvallate: Deep invagination, 250 taste buds
Length of taste cell life span
1 week
Taste cranial nerves and where they get info from
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
Where do the 3 cranial nerves for taste terminate?
Rostral part of the nucleus of the solitary tract
Salt channel for taste
Amiloride-sensitive epithelial sodium channels (ENaCs), straightforward sodium ion channel
Acid channel for taste
H+ sensitive TRP channel (PKD variant), use H+ ions as driving force for depolarization
Taste transducer for sweet
G-protein coupled heterodimer receptor made of T1R2 & T1R3
Taste transducer for umami
G-protein coupled heterodimer receptor made of T1R1 & T1R3
Mechanism for umami taste
- Amino acids bind to G-protein coupled receptor (T1R1 & T1R3)
- Alpha subunit acts on PLC beta 2
- IP3 is used as a second messenger to signal release of Ca2+ from endoplasmic reticulum
- Ca2+ activates TRPM5 channel for depolarization
Mechanism for bitter taste
- Bitter compounds bind to G-protein coupled receptor Gustducin (T2R5)
- Alpha subunit acts on PLC beta 2
- IP3 is used as a second messenger to signal release of Ca2+ from endoplasmic reticulum
- Ca2+ activates TRPM5 channel for depolarization
Two choice test for mice with different taste receptors KOed
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).
How are different taste receptors distributed on the tongue?
Each receptor type is present in all papillae of the tongue, not like the diagram where tastes are localized to one area each
Type I taste bud cells
Responsible for detecting salt, looks like a glial cell, specialized ROMK channel allows for K+ to be extruded at apical tip
Type II taste bud cells
For sweet, umami and bitter. Do not contain vesicles, instead bulk release ATP through CALHM1/3 pore
Type III taste bud cells
For sour, have vesicles containing serotonin that activate downstream serotonergic neurons, have inhibitory receptors for neighbouring cells (think center surround inhibition)
Geniculate ganglion cells response to taste
Most neurons are selective for one taste, but some sour and bitter overlap
microendoscopy
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)
responses of ganglion cells to basic taste qualities
found that each cell responds selectively to 1 tastant and no other
- argues against signal being mixed at synapse
gustotopic maps
shows activity segregated in different parts of gustatory cortex
- becomes spatially segregated (not combinatorial like smell)
photostimulation of bitter and sweet corticies
drives aversive and appetitive behavior
- expressed channel rhodopsin in cortex and saw perception of sweet and bitter even though they cannot detect
Tasting the light experiment
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.
