DENT 608 10 Taste buds
Taste stimuli associated sensory attributes
1) Sensory attributes: -Sweet -Umami -Salty -Sour -Bitter 2) Taste qualities also have different hedonic values
Major taste receptor subtypes/families
1) 2 major kinds of receptors: -T2Rs: bitter taste receptors -T1Rs: sweet taste receptors 2) Mammalian taste receptor families: a. T1R taste receptors consist of 2 genes (T1R1, T1R2, T1R3): -*T1R1+T1R3*: amino acid receptors (*umami*) -*T1R2+T1R3*: sugar receptors (*sweet*) b. T2R family of bitter receptors contains about 30 genes 3) Clinical sequelae: -Loss of function mutations to T1R3 gene would result in loss of sweet and umami taste
Dynamic properties of taste buds (study)
1) Experimental design: -Inject rats w/ radioactive precursor of DNA at time 0 -It gets incorporated into DNA -Sacrifice rates and remove their tongues -Cut sections of tongue and mount on microscope -Coat sections w/ photographic emulsion (tissue that had radioactive DNA) gets exposed: can see spots under microscope 2) Results: -After 24 hours: see grains in taste buds (most of the grains are in basal cells of taste bud) -100 hours after injection: grains are in various nuclei (meaning daughter cells came from division of base cells and moved up taste bud) -Half life of taste bud cells determined to be about 10.5 days
Innervation to taste buds
1) Superior laryngeal nerve: -Supplies epiglottis taste buds 2) Chorda tympani: -Supplies tongue taste buds 3) Distribution of taste buds: -Most are in posterior tongue -Relatively small number on anterior tongue 4) Taste buds need innervation to function: -W/o innervation they degrade -By 8 days there are no taste buds present in areas where afferent innervation is lost -Regeneration can occur (even after total loss); regneration only promoted by taste nerves
Taste bud general characteristics
1) Taste buds: contact chemoreceptors -Flavor perception (detection and recognition) -Detect chemicals in food and allow recognition of them -We can also tell concentration of chemicals 2) 3 forms of papillae where taste buds are situated: -Fungiform -Circumvellate -Foliate 3) Also taste buds on epiglottis but they have nothing to do w/ taste perception; -Detect chemicals in upper airway and initiate protective reflexes
Basic Steps in Taste Signal Transduction
1) Taste stimuli either bind to ion channels or GPCR's 2) Ligand bound receptors then couple to release of synaptic vesicles -Via intracellular signal pathways
Signal transduction involved in taste
1) Transduction: analog to digital conversion -We live in an analog world -Nervous system perceives digital information 2) Digital signal: -Consists of series of pulses of different frequency -Increasing stimulus only increases frequency but not amplitude 3) Analog signal: -Taste buds: amplitude is increased as stimulus is increased 4) Conversion from analog to digital occurs in receptor: -Via axon interaction 5) The greater the stimulus, the greater the amplitude in taste bud receptor -Generator potential causes conversion form analog to digital
Taste Bud Signal Transduction
1) Type 1 glial-like cell: degrades or absorbs NT's -May also clear EC K+ that accumulates after APs in receptor or presynaptic cells 2) Receptor cells (Type 2): activated by sweet, bitter, and umami taste compounds -Release ATP through Pannexin1 (Panx1) hemichannels -Extracellular ATP excites ATP receptors on sensory nerve fibers and taste cells 3) Presynaptic cells (Type 3): release serotonin, which inhibits receptor cells -Sour stimuli directly activates presynaptic cells -Only these cells form ultrastructurally identifiable synapses w/ nerves
