2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
Biologists have shown that chilled sweets are less appetizing to fruit flies than room temperature sweets. It turned out that cooling by itself does not affect the "sweet" neurons, but activates the "bitter" ones, which indirectly suppress the attractiveness of sweet water for flies, write the authors of the article in Current Biology.
It is known that temperature affects the perception of sweet taste in both rodents and humans - for example, cold ice cream seems less sweet than melted ice cream. The mechanism of this phenomenon is not entirely clear - scientists have not yet come to a consensus whether a decrease in temperature affects taste adaptation, or directly on the pathway of signal transmission from sweet receptors.
Researchers from the University of California at Santa Barbara and the Okazaki National Institute of Physiology have found that similar thermal sensitivity is observed in fruit flies, fruit flies, and even manifests itself when the sweet water is cooled by two degrees. The flies were offered a drop of water with sugar, touching their main organ of taste - labellum ("lips"). In response, the flies either signaled their readiness to eat by extending their proboscis, or they did not. It turned out that sweet water at room temperature (23 degrees Celsius) attracts flies in one hundred percent of cases, however, even lowering its temperature to 21 degrees reduces the percentage of cases of stretching the proboscis, and cooling to 17 degrees reduces the attractiveness of the treat by half or three times. The effect persisted even after the flies were forced to fast for 20 hours.
The percentage of stretching the proboscis when treating with sweet water, depending on its temperature, water was offered three times in a row with a difference per minute
The receptors for sweet, bitter, and mechanoreceptors in flies are located at the end of individual sensory neurons. To investigate which neurons are affected by temperature (sweet or not), scientists isolated a fluorescent calcium-dependent sensor in them. When a neuron is activated, a calcium current occurs in the cell, which makes the protein glow. It turned out that when in contact with cold liquid or air, sweet-tasting neurons are silent (do not glow), but cooling activates bitter-tasting neurons and mechanosensitive neurons.
In addition, the researchers found that a protein from the rhodopsin family Rh6 is the direct sensor of temperature in bitter-tasting neurons. Usually rhodopsins are responsible for the perception of light, and they can do this thanks to the "built-in" retinal molecule, the change in conformation of which leads to a change in the conformation of the entire protein. In this case, the retinal was needed for thermal perception, and regardless of the presence of light.
The activation of bitter taste neurons, in turn, can indirectly suppress the perception of sweetness - both by suppressing "sweet" neurons through intermediate GABAergic neurons, and by reducing appetite in general.