Insects are the largest group of animals on Earth with over a million species. Their success is due to their small body size and ability to fly, which allows access to untapped niches and rapid translocation.
However, aerodynamic and space constraints require high wing frequencies and miniaturization of central nervous controllers for flight.
Researchers from the Humboldt-Universität zu Berlin and Johannes Gutenberg University Mainz have collaborated to solve a mystery that has baffled experts for years.
They discovered the type of electrical activity in the nervous system that controls insect flight.
They describe a previously unreported role for the electrical synapses used by fruit flies during flight in research recently published in the journal Nature.
Fruit Flies Drosophila melanogaster needs about 200 wing beats per second to move forward, while other small insects can reach 1,000. The high frequency of wingbeats creates that annoying high-pitched buzzing sound we usually associate with mosquitoes.
Because of their small bodies, insects must beat their wings at a certain frequency to avoid getting “stuck” in the air, which acts as a viscous medium. To achieve this, they adopt a clever strategy common among insects.
Antagonistic muscles that lift and depress the wings are thus activated by mutual stretch. The high-frequency oscillation of the system can result in the rapid flapping speed of the wing necessary for propulsion.
Each motor neuron generates an electrical impulse that regulates the wing muscles approximately every 20th wing beat because they cannot keep up with the speed of the wings. These impulses perfectly match the activity of other neurons.
The motor neurons that control the frequency of wingbeats produce specific patterns of activity. Although they do not fire at the same time, all neurons fire at a constant rate. Each of them fires at regular, predetermined intervals. Although such patterns of fruit fly brain activity have been observed since the 1970s, the underlying regulatory mechanism has never been fully understood.
Researchers have found the answer to the mystery, which is controlled by a small circuit consisting of several synapses and neurons. This may apply to more species than fruit flies.
According to Karsten Duch, professor of biology at JGU, “A small circuit consisting of only a few neurons and synapses controls the movement of the wings of the fruit fly Drosophila melanogaster. And maybe it’s not just about fruit flies.”
The researchers estimate that the more than 600,000 known insect species that rely on a similar method of propulsion use similar neural circuits.
Drosophila melanogaster is an excellent subject for research in neurobiology because various components of its neural circuitry can be genetically manipulated.
Just two examples include the ability to directly influence the activity of individual neurons and to turn individual synapses on and off. In this case, the researchers combined different genetic methods to assess the electrical characteristics and activity of the neurons of the circuit.
As a result, they were able to identify the cells and synaptic connections in each brain circuit that contribute to flight patterns. As a result, they discovered that the neural network that controls flight consists of only a small number of neurons and uses only electrical synapses for communication.
Researchers have used a variety of genetic methods to assess the electrical characteristics and activity of neurons in a circuit. They discovered that the brain network that controls flight consists of a few neurons that can only connect through electrical synapses.
Scientists have shown that such a consistent distribution of impulse generation can occur even when brain activity is directly controlled electrically, without neurotransmitters.
The team, based in Mainz and Berlin, investigated the theoretical claim that electrical transmission between neurons leads to a consistent firing pattern. To test this theory, specific ion channels in the neurons of the network were modified and the activity pattern of the flywheel was synchronized.
The power generated in flight has changed significantly as a result of this experimental adjustment. The team’s findings are particularly surprising given that electrical synapses have previously been shown to cause neurons to fire synchronously.
The behavior of the electrical synapses discovered here suggests that the nervous system may process information in currently unknown ways.
A similar mechanism may operate in thousands of other insect species and in the human brain, where the function of electrical synapses is still unknown.
The study was funded by the German Research Foundation.
- Hurkey, S., Niemeyer, N., Schleimer, et al. Gaps synchronize neural circuitry to stabilize insect flight. Nature. DOI: 10.1038/s41586-023-06099-0
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