Your heart has its own brain – and it’s surprisingly complicated: ScienceAlert

Long before we are born, the tissues of our heart contract and convulse at a rate that does not stop until our final hour.

It’s such a mechanical function that one could be forgiven for overlooking its complexity. Yet each contraction is considered a musician’s note, played enthusiastically or gently under the direction of an architecture of nerves buried just beneath the outer layers of the heart.

Known as the intracardiac nervous system, these pathways were considered a simple stopping point for information transmitted from parts of the brain and spinal cord.

Scientists from Karolinska Institutet in Sweden and Columbia University in the United States have discovered a surprising level of complexity among the neurons surrounding the zebrafish heart, challenging existing theories about how this organ’s pulse is maintained in animals like us.

“This ‘little brain’ plays a key role in maintaining and controlling the heart rate, in the same way that the brain regulates rhythmic functions such as locomotion and breathing,” explains Konstantinos Ampatzis, neuroscientist at the Karolinska Institutet. , who led the study.

For much of history, the activity of the heart was thought to be autonomous, beating its own regular rhythm under the influence of its own animus, which many cultures considered to be the very essence of life itself. -even.

A new perspective on the independence of the heart was given by the 18th-century German anatomist Albrecht von Haller, who in his summary of physiology asserted that the heart possessed an “intrinsic irritability” triggered by blood entering it.

In the 19th century, bundles of nerves called ganglia were discovered in the hearts of frogs, and later in those of humans, which were quickly understood to act as the heart’s “pacemaker,” controlling the speed of muscle contractions.

It would be the start of centuries of study into the heart’s consistent ability to maintain its heartbeat, with scientists debating the extent to which the central nervous system controlled the pulse.

Today, the brain is thought to control heart function through its two branches: the sympathetic “fight or flight” system and the parasympathetic “rest and digest” system.

It achieves this through multiple neuronal pathways that connect nerve muscle fibers from the heart to peripheral ganglia, which in turn are connected to bundles of neurons in the central nervous system, changing the rhythm remotely in response to chemical stimuli and pressure.

Given the scrutiny of several generations of scientists, it is not only surprising that the debate over the influence of the brain continues, but also that there is still so much to discover about the structure of the heart.

Ampatzis and his team used a combination of immunolabeling, RNA profiling of single cells, and analysis of the electrical properties of neurons passing through heart tissue to develop a detailed map of the intracardiac nervous system of a zebrafish heart.

The researchers discovered a wide diversity of cell types, including a subset of nerves that resembled central pattern-generating neurons in the central nervous system, pathways that govern everything from chewing food to walking. passing through ejaculation.

Despite being separated by hundreds of millions of years of evolution, humans and zebrafish have strikingly similar cardiovascular physiology, implying that most vertebrates share these neural pathways.

Given existing knowledge, it seems likely that vertebrate hearts have a more sophisticated “brain” than anyone thought, consisting of a pacemaker that sets the heart into action and an intermediate regulatory manager that takes cues from of the central nervous system before deciding how the heart should respond.

“We were surprised to find how complex the nervous system of the heart is,” says Ampatzis. “A better understanding of this system could lead to new insights into heart disease and help develop new treatments for diseases such as arrhythmias.”

Far from drawing a clear line between heart and brain, the findings raise new questions about how these signals vary depending on disease, diet and activity, with future studies potentially revealing new targets for treatments that can keep the old ticker going for years. future.

This research was published in Natural communications.