Summary: A new population of taste cells that can detect multiple types of stimuli has been identified. Researchers say taste cells can either be selective or generally responsive to stimuli, and the presence of the new cells provides insight into how taste information is sent to the brain for processing.
Our mouths may be home to a newly discovered set of multi-tasking taste cells that, unlike most known taste cells, which detect individual tastes, are capable of detecting sour, sweet, bitter and umami stimuli. A research team led by Kathryn Medler at the University at Buffalo reports this discovery in a study published 13th August in PLOS Genetics.
Taste buds in the mouth are critical to our survival and help us to decide whether a food is a good source of nutrients or a potential poison. Taste buds employ three types of taste cells: Type I cells acts as support cells; Type II cells detect bitter, sweet and umami tastes; and Type III cells detect sour and salty flavors. To better understand how taste cells detect and signal the presence of different tastes, the researchers used an engineered mouse model to investigate the signaling pathways that the animals use to relay taste information to the brain. They discovered a previously unknown subset of Type III cells that were “broadly responsive” and could announce sour stimuli using one signaling pathway, and sweet, bitter and umami stimuli using another.
The idea that mammals might possess broadly responsive taste cells has been put forth by multiple lab groups, but previously, no one had isolated and identified these cells. The researchers suspect that broadly responsive cells make a significant contribution to our ability to taste. Their discovery provides new insight into how taste information is sent to the brain for processing, and suggests that taste buds are far more complex than we currently appreciate.
“Taste cells can be either selective or generally responsive to stimuli which is similar to the cells in the brain that process taste information,” commented author Kathryn Medler. “Future experiments will be focused on understanding how broadly responsive taste cells contribute to taste coding.”
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A subset of broadly responsive Type III taste cells contribute to the detection of bitter, sweet and umami stimuli
Taste receptor cells use multiple signaling pathways to detect chemicals in potential food items. These cells are functionally grouped into different types: Type I cells act as support cells and have glial-like properties; Type II cells detect bitter, sweet, and umami taste stimuli; and Type III cells detect sour and salty stimuli. We have identified a new population of taste cells that are broadly tuned to multiple taste stimuli including bitter, sweet, sour, and umami. The goal of this study was to characterize these broadly responsive (BR) taste cells. We used an IP3R3-KO mouse (does not release calcium (Ca2+) from internal stores in Type II cells when stimulated with bitter, sweet, or umami stimuli) to characterize the BR cells without any potentially confounding input from Type II cells. Using live cell Ca2+ imaging in isolated taste cells from the IP3R3-KO mouse, we found that BR cells are a subset of Type III cells that respond to sour stimuli but also use a PLCβ signaling pathway to respond to bitter, sweet, and umami stimuli. Unlike Type II cells, individual BR cells are broadly tuned and respond to multiple stimuli across different taste modalities. Live cell imaging in a PLCβ3-KO mouse confirmed that BR cells use this signaling pathway to respond to bitter, sweet, and umami stimuli. Short term behavioral assays revealed that BR cells make significant contributions to taste driven behaviors and found that loss of either PLCβ3 in BR cells or IP3R3 in Type II cells caused similar behavioral deficits to bitter, sweet, and umami stimuli. Analysis of c-Fos activity in the nucleus of the solitary tract (NTS) also demonstrated that functional Type II and BR cells are required for normal stimulus induced expression.