Regular aerobic exercise does more than improve cardiovascular endurance. It physically alters the structure of the nerves that regulate heart function, according to new research published in Autonomic Neuroscience. Scientists at the University of Bristol discovered that moderate training changes the nerve clusters responsible for controlling heart rate, creating an unexpected imbalance between the left and right sides of the body.
Left-Right Nerve Imbalance in Trained Rats
The study examined rats that underwent 10 weeks of moderate aerobic training. Researchers used stereology, a three-dimensional analysis technique, to measure the number, size, and distribution of nerve cells within the stellate ganglia. These small clusters of nerve cells are located on both sides of the lower neck and upper chest. They act as hubs that send signals to influence heart rate and other aspects of cardiac function.
The results showed a striking difference between the two sides of the body in the trained animals. The cardiovascular nerve cluster on the right side contained roughly four times as many neurons as the cluster on the left. This pattern was not observed in untrained rats. The nerve cells also changed in size, but in opposite directions. Neurons on the left side nearly doubled in size, while those on the right side became slightly smaller.
Dr. Augusto Coppi, Senior Lecturer in Veterinary Anatomy at the University of Bristol and lead author of the study, described the stellate ganglia as the heart’s dimmer switch. He noted that regular, moderate exercise remodels this switch in a side-specific way. This discovery points to a previously hidden left-right pattern in the body’s autonomic nervous system, which automatically manages essential functions like heartbeat and breathing.
Potential for Targeted Cardiac Treatments
These findings could eventually help doctors develop more precise treatments for irregular heartbeats, chest pain, angina, and stress-induced broken-heart syndrome. In some patients, physicians treat these conditions by reducing excessive nerve signals reaching the heart. Procedures such as stellate ganglion nerve blocks temporarily interrupt nerve activity, while denervation involves disrupting certain nerve pathways.
Understanding how exercise changes these ganglia on each side offers clues that could one day fine-tune these procedures. By mapping the structural changes, doctors might determine which side of the body should be targeted for the greatest benefit. Dr. Coppi explained that irregular heart rhythms and certain types of chest pain are often treated by dialing down overactive stellate ganglia. The study suggests that future therapies could be tailored to the side most likely to help.
The research involved collaborators from University College London, the University of Sao Paulo, and the Federal University of Sao Paulo. While the structural changes were substantial, scientists still need to establish exactly how they affect heart function. The team plans to investigate whether the differences between the left and right nerve clusters influence how the heart behaves during rest and physical activity.
The findings are based on animal models, so further research is needed to determine whether the same changes occur in humans. For human studies, the researchers hope to use noninvasive markers to provide information about nerve activity without requiring surgery or tissue removal. If similar patterns appear in larger animals and humans, the discovery could help guide more personalized treatments for heart rhythm disorders and angina.
Source: ScienceDaily
