Researchers Begin to Solve Mystery of Taste’s Journey to the Brain
We are all familiar with our ability to distinguish among different taste characteristics — sweet, sour, salty, etc. — but the way in which that information is encoded and transmitted from our taste buds to our brain is still an open question. In large part, this is because the molecular “fingerprints” of gustatory neurons have remained a mystery.
Now, researchers at the University of Miami Miller School of Medicine have uncovered the molecular identities of the sensory neurons in taste’s gateway to the brain. Their findings appeared in an article published October 2 in the journal Nature Communications.
“Consider the neurons that sense heat, pain, cold, gentle touch or pressure. Neuroscientists have been able to identify each type of neuron and track where they send their information in the brain because molecular markers have been available,” said senior author Nirupa Chaudhari, Ph.D., who wrote the journal article with long-time research collaborator Stephen D. Roper, Ph.D. Both have dual appointments in the Department of Physiology and Biophysics and the Department of Otolaryngology. Other University of Miami co-authors include Gennady Dvoriantchikov, Ph.D., and two graduate students, Damian Hernandez and Jennifer Roebber.
“Now we can do the same for taste. Our report defines the molecular identities of the sensory neurons for taste,” Chaudhari said. “These neurons reside in the geniculate ganglion, a tiny cluster of neurons near the base of the skull. Using sophisticated single-cell isolation and RNA sequencing — technology only recently made available at the Miller School — to obtain the complete transcriptome of taste neurons, we show that these neurons fall into several distinct subpopulations. Unexpectedly, they include a novel type of neuron that may sense both taste and mechanosensations such as touch and texture.”
Now that the catalog of genes used by taste neurons has been revealed, say the authors, it will be possible to identify molecular markers to track where the different taste neurons enter the brain and the diverse pathways to which they connect in the brain.
“The next step will be to engineer additional strains of mice with genetically encoded anatomical and functional markers (typically fluorescent proteins) in specific subpopulations of taste neurons,” said Chaudhari.
It will then be possible to use sophisticated confocal imaging in living mice to monitor their responses to taste stimuli to decode how tastes and other oral sensations are transmitted to the brain. Having these molecular tags on different neurons will also enable the investigators to understand how taste circuits are regulated.
“The role of taste is to help ensure adequate and balanced nutrient consumption,” Chaudhari said. “After a meal, food becomes less palatable, and we stop eating. This may occur, in part, through regulation of taste circuits, but that is just a hypothesis, because we have lacked the tools to see taste circuits clearly. If the taste circuits are mis-regulated, however, that could be an underlying cause for eating disorders. We hope our continuing research will enable us to find the answer and explore ways to correct mis-regulation.”