Unraveling the coordination between neurons

A new research paper published in the journal iScience provides insight into how the rhythms of neurons function in the brain
of the fly Drosophila melanogaster.

An interdisciplinary team from IBioBA, formed by neuroscientists and physicists from the Institute, published a research paper in the journal iScience, in which they studied the rhythms of neurons in the brain of the fruit fly (Drosophila melanogaster), especially those involved in sleep and circadian cycles, that is, those that function as the internal clock that regulates when we sleep and when we are awake.

“It was already known that neurons in the mammalian brain have a rhythmic behavior, but there was no knowledge about what happens in insects, and in this work we could see that neurons in the fly brain also have an oscillatory activity: they go up and down repeatedly and regularly”, says Nara Muraro, head of the ‘Neurobiology of sleep’ group.

“We investigated a group of neurons in the brain of this fly, called LNvs, which are linked to the internal biological clock (the one that regulates sleep-wake cycles). We knew that these neurons can generate electrical oscillations, but it was not clear whether they did so collectively or each one separately”, adds Luis Morelli, head of the ‘Information processing in cells and tissues’ group.

Florencia Fernández Chiappe received her PhD under Muraro’s direction at the Institute and is now a postdoctoral fellow at Boston University. She is also one of the first authors of the paper in which she used a very precise technique called “patch clamp” to record the electrical activity of LNvs neurons. “We were able to see that the oscillations disappear if we block a molecule called acetylcholine, which neurons use to communicate. This suggests that the oscillations are not generated in isolation, but depend on external signals”, explains Florencia.

In addition, they found that when a neuron was perturbed, it quickly returned to its rhythm without altering the overall phase of the group, indicating that they are being “guided” from outside. According to their theoretical description to explain what they had seen, neurons act like ‘forced oscillators’: they receive an external push that synchronizes them.

“A key prediction of this model is that neurons of the same type should oscillate together, while neurons of different types may have a small phase lag between them”, says Marcos Wappner, a recent PhD in physical sciences in Morelli’s group. What the theoretical description proposed by the team, and carried forward by Wappner, then, suggests is that both follow the beat, but with a slight delay.

Finally, to test their theory, they recorded the activity in pairs of neurons at the same time, and indeed saw that some oscillate slightly ahead of others, but follow a joint rhythm. They also saw that other nearby neurons, which were not LNvs, showed similar, synchronized oscillations.

In summary, the results of this work serve to understand how neurons are organized to generate collective rhythms in the fly brain, which could provide clues about how brains are organized to perform complex functions in both insects and mammals.

Studying these processes in simple models such as the fly helps us understand general principles of brain function, and how the collective activity of neurons gives rise to complex behaviors and functions.