Deciphering how the fruit fly brain works has been a significant branch of study in the biological sciences for several decades now. In this, a team of researchers from National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bengaluru (NCBS-TIFR), have figured out the neuronal circuitry that is involved in processing bitter taste.
Interneurons
While the neurons that sense the bitter taste have been identified, as have the motor neurons that innervate the physical reactions to having sensed bitter taste, the intermediate circuitry has remained unknown. In a collaborative work with researchers from University of California, Berkeley, USA, and University of Basel, Switzerland, the NCBS-TIFR team have identified a single pair of interneurons that are responsible for connecting the sensory and motor neurons involved in bitter taste processing. The work is published in Current Biology.
To identify these interneurons, genetic and imaging approaches are used. “We genetically activated and inactivated particular neurons to identify their role in bitter taste behavior. We then used imaging tools to record the activity of these neurons,” says Ali Asgar Bohra, the first author of the paper, then a PhD student at NCBS-TIFR.
Partly the reason for the interest in the workings of the Drosophila (fruit fly) brain is because it is a good proxy to approach the goal of knowing how the human brain itself works. There is also another reason: “Studying the bitter taste circuit helps in understanding how insecticides and pesticides work to repel insects,” says Dr Bohra, who is now a research associate with King’s College, London, in an email to The Hindu.
The reactions of fruit fly to bitter and sweet tasting material differ significantly. When it senses food cues, mainly sweet tasting, through the sensory neurons in its legs, or proboscis, it extends its proboscis for consuming the food. “If a fly senses a bitter, toxic or noxious substance, it won’t extend its proboscis,” explains Dr Bohra. “I used this assay [test] to screen and identify the neurons which are involved in bitter taste processing.” The team also used the live imaging technique developed by Benjamin R. Kallman, the collaborator in UC, Berkeley, to record the activity of the brain in live animals.
They plan to take forward the research, “by trying to identify the remaining neuronal type… thus completing the neural circuit for bitter taste. This will help understand the role of different neurons and molecules (present in the brain) in sensory information processing and behaviour,” he says.
