Taste buds in the mouth are crucial for our survival, helping us to decide whether a certain food can be eaten or should be avoided. These mini warning systems contain 50–100 taste receptor cells and are located in the tongue and oral cavity. Taste receptors are specialized cells stimulated by the chemicals found in our food. Subsequently, this stimulation initiates the cascade of neurotransmitters onto nerve fibers attached to the bottom of each taste bud to relay information to the brain.
The sense of taste is thought to consist of three types of taste cells responsible for identifying different flavors. Firstly, there are Type I cells, which support nerve cells and possess glia-like properties. The second population is Type II cells which detect bitter, sweet, and umami/savory flavors. And finally, Type III cells which detect sour and salty flavors. Accordingly, these flavors are known as the five tastes, with each cell population only able to discern 1-2 different types of flavors.
Now, a study from researchers at the University at Buffalo identifies a new type of taste cell capable of identifying a ‘broad range’ of flavors. The team states their data shines more light on how flavor is transmitted to the brain for processing. In addition, their trial also suggests taste buds are far more complex than previously thought. The opensource study is published in the journal PLOS Genetics.
Past and current studies
Previous studies have indicated taste cells are highly selective. This is because they are only capable of discerning one or two types of the five flavors. For example, a taste cell may be tuned to identify only sweet flavors, whilst another only responds to salt or sour stimulus. Accordingly, signals derived from the recognition of these flavors form a taste code to send to the brain. However, it is unclear just how the coding of taste works.
The idea of broadly tuned taste cells in mammals has been put forth by multiple labs. However, these earlier studies used intact taste buds, which consist of different taste cell types. Therefore, Type III cells may have been interacting and receiving input from the neighboring Type II cells, marring results. The current study separates the cell types to identify which flavors stimulate them.
The current study engineers a mouse model whose Type II cells were turned off to avoid the interaction of Type II and Types III cells. Subsequently, the isolated Type III cells were then stimulated with the five known flavors. Results describe a previously unknown subset of Type III cells broadly responsive to sour, sweet, bitter, and umami stimuli. Data suggests the BR cells are a subset of Type III cells possessing the ability to respond to multiple flavors, except salt.
The lab states the mammalian PLCβ signaling pathway enables BR cells to identify sweet, bitter, and umami flavors. Meanwhile, sour stimulants are picked up by native Type III cell pathways also present in the BR cells. Experiments showed when BR taste cells are silenced, mice have trouble tasting multiple flavors. Some of the muted flavors identified are also detected by Type II cells. This means both Type II and BR cells may have to work together to send taste data to the brain.
The team surmises their study in mice identifies a new type of taste cell that responds to every flavor except salt. For the future, the researchers state experiments will focus on the relationship between Type II and BR cells in relation to flavor coding.
Source: University at Buffalo
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