The team that first recorded vagus nerve signals in humans has isolated the electrical activity of individual neurones responsible for cardiovascular regulation.
Published in The Journal of Physiology, the Monash University-led discovery paves the way for more research into how and why cardiovascular disease develops.
Monash University's Professor Vaughan Macefield was the first to record electrical signals from the vagus nerve in awake humans in 2020. Before that, our understanding of the physiology of this nerve – which supplies the heart, airways and other organs within the thorax and abdomen – came entirely from animal work.
Now, in another first, researchers from the Human Autonomic Neurophysiology Laboratory in Monash's School of Translational Medicine have isolated the activity of individual neurones within the vagus nerve. By looking specifically for neurones that fire in sync with the heartbeat, they could then identify those that are responsible for cardiovascular regulation.
"We have managed to isolate the activity of individual vagal neurones and identified those that are responsible for either informing the brain about cardiovascular function (afferent neurones) or controlling the rate of the heart beat (efferent neurones)," first author Dr David Farmer said.
The vagus nerves contain neurones that are crucial for the brain's ability to monitor organ function, as well as neurones that directly control organ function. This includes neurones that monitor or modify heart function.
Dr Farmer said that while animal studies over the past 150 years had provided great insights into the control of cardiovascular function by the brain, it was essential to study human neurones.
He said that while the new study's initial work was carried out in healthy individuals, the next logical step was to include people with cardiovascular diseases and learn how the behaviour of neurones that monitor or modify heart function was changed in those conditions.
"In cardiovascular disease states, the activity of vagal neurones that slow the heart appears to be reduced," he said. "Additionally, activation of the neurones that monitor heart function produce altered cardiovascular reflexes.
"We don't know precisely why that is or what neurones are responsible. The ability to isolate the activity of these neurones from vagal recordings in human participants may enable us to work this out, which is pretty cool."
Professor Macefield, who was senior author on the paper and is also a Professorial Fellow with the Baker Heart and Diabetes Institute, said the work provided proof of principle that the electrical activity of vagal neurones with cardiac function could be directly studied in human beings.
"Because the activity of these neurones is likely altered in cardiovascular disease, it is crucial to understand how and why." Professor Macefield said. "This technique will enable these investigations."
This work was a collaboration with Università Politecnica delle Marche in Italy, the Baker Heart and Diabetes Institute in Melbourne, the University of Split's School of Medicine in Croatia, the University of Windsor's Faculty of Human Kinetics in Canada, and the University of Novi Sad's Department of Physiology in Serbia.
