Taste Sensing and Processing

Sensing of Taste Signals

• Taste papillae are found on the tongue and parts of the palate
• There is no taste map, and all flavors are sensed in different areas, although there are differences in abundance

Taste Buds

• There are different types of taste cells:
  • Type I: supporting, glial-like cells (50%)
  • Type II: sweet, bitter, umami (33%), express 1 class GPCR
  • Type III: sour, no GPCR
  • Type IV: precursors?

Transduction of Gustative Signals

• There are 5 basic tastes: salty, sour, bitter, sweet, and umami
• Sour/salty signals are processed via activation of ion channels
• Umami/bitter/sweet signals are processed via GPCR activation and transporters
• Sweet/Bitter/Umami taste signals are mediated by GPCRs
• There are 2 taste receptor families: T1R (Sweet/umami) and T2R (Bitter)

Salt and Sour Taste Signals

• Salty taste signals are mediated by ion channels (Amiloride-sensitive receptors)
• Sour taste signals are mediated by ion channels (PKD2L1, Otopetrin 1)

Taste Cell Transduction Mechanisms

• Type II Cells: Sweet/umami/bitter taste sensing, no vesicles or voltage-gated Ca2+ channels
• Type III Cells: Sour taste sensing, contain synaptic vesicles, may use multiple neurotransmitters

Processing of Sweet Taste

• Type II taste cells detect natural and artificial sweet compounds using different receptor combinations
• Activation of transporters may provide nutritional value

Interaction Between Tastes

• Salty and sweet foods interact, with salt perceived as sweet
• There is a complex interaction between different taste cell types

Cellular Sensing of Tastes

• Taste cells respond to one taste modality
• One individual taste cell can express several T2R, responding to different bitter molecules
• Taste perception involves the interaction between somatosensory, gustative, and olfactive signals

Role of Chemoreceptors

• Chemosensory intestinal cells possess taste receptors and other chemoreceptors
• There is a relationship between taste and nutritional/toxic value

The Combinatorial Model of Taste Coding

• Taste is needed to detect food sources and avoid spoiled/toxic substances
• Taste signals are relayed to higher-order neurons (CNS)

Gustative Processing Pathways

• Information reaches the CNS through VII, IX, X cranial nerves
• Relay on the NTS, with divergent pathways ensuing
• Concious and emotional taste processing pathways exist

Cortical Gustotopic Map

• A cortical gustotopic map (insular gustative cortex) was suggested for different tastes (other than sour)
• There is conflicting evidence on the existence of this map