One of the main functions of the neural system is to coordinate movements of the body. In order to understand how brain controls adaptive motor behaviours, scientists have long been trying to decipher the neural circuit map down to the muscles.
Now researchers have connected the neurons from the fruit fly nerve cord, similar to the vertebrate spinal cord, with the muscles controlling the legs and wings. This sheds light on how the fly senses and controls movements of the legs and wings. Whilst connectomes in small animals have been mapped before, it is the first time that scientists find the synapse-level wiring diagram of motor circuits for a limbed animal.
Why the fruit fly? Drosophila melanogaster has a compact nervous system with sophisticated genetic tools and identified neurons with stereotyped function across individuals. “They are marvelously skilled at motor control, including walking and flying, despite their tiny nervous system”, explains John Tuthill, researcher at the University of Washington and corresponding author of the publication. Indeed, each of the flies’ legs is controlled only by 70 motor neurons (compared to 600 in a cat’s calf muscle) and only 29 motor neurons controlling each wing.
The fly has specialised muscles for power and steering in the wings. These wing muscles attach to different body parts: power muscles to the thorax and steering muscles to the wing hinge.
The team has now determined which pre-motor neurons in the fly’s version of the spinal cord, known as ventral nerve cord (VNC), coordinate motor neurons controlling the leg and wing. To achieve this, they used several techniques: electron microscopy, sparse genetic labelling, and X-ray holographic nanotomography (XNH) at the ESRF.
Read more on ESRF website
Image: The circuits controlling the wing steering (left) and the wing power (right) of the fruit fly.
Credit: Azevedo et al., Nature 2024