Have you ever wondered why candies taste so good and pills so bitter? It seems the secret lies in one pair of brain cells. At least this is the case in fruit flies, which serve as a model for understanding human genetics. Insects don’t open their mouth to avoid poisonous or toxic substances. Understanding why this happens may provide clues about taste buds and their link to the brain.

Scientists at the National Centre for Biological Sciences (NCBS) have discovered a single neuron – interneuron – which enables fruit flies to avoid eating toxic substances. They have shown how only a set of brain cells react to unpleasant substances. Insects have sensors for bitter substances and the moment they come in contact with bitter substances, these cells are activated. Interestingly, insects learn this quickly and show a peculiar response of not opening their mouths. It is similar to how toddlers react to bitter medical syrups.

National Centre for Biological Sciences (NCBS)

It has been found that interneurons are involved in communicating a bitter taste response from sensory neurons using small thread-like connections. The results of the study have been published in the journal Current Biology .

These findings can help understand how humans learn about food and the environment. Interneurons create neural circuits to enable communication between sensory neurons and the central nervous system. They also play an important role in functions such as reflexes, neuronal oscillations, and neurogenesis in the adult mammalian brain.

The group at NCBS is focused on the study of the progressive development of sensory and locomotory organs of the fruit fly, especially muscles, nerves, neural circuits and their behaviours. “This timely addition of information would help researchers understand whether flies use different neurons for different types of taste substances or it has a common circuit for all,” said Ali Asgar Bohra, a member of the research team.

“Even sugar fails to entice insects when these brain cells are active. These cells are on the top of the hierarchy that decides whether to eat or starve. In many insects, they have an extensible tubular sucking mouthpart or organ which is known as proboscis. In fruit flies these bitter-sensitive interneurons can essentially suppress proboscis extension reflex to appetitive stimuli, such as sugar and water,” Bohra explained.

The study, he said, will let scientists decipher the fly brain circuit of bitter/ toxic taste processing. Since the taste perception has similar modalities in flies and mammals including humans, it could help understand how the human brain differentiates between sweet and bitter taste. It may also be useful in understanding how mosquitoes sense environment particularly chemical substances, and control them using better repellents.

The research team included Ali Asgar Bohra, K. VijayRaghavan (both NCBS), Benjamin R. Kallman (University of California, USA), and Heinrich Reichert (University of Basel, Switzerland). This work was supported by the Department of Science and Technology (DST).

(India Science Wire)

Twitter handle: @ratnesh_thakur

Keywords: Brain cells, neurons, fruit fly, taste, NCBS, TIFR, DST

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