Researchers at the University of Tsukuba in Japan have discovered a novel mechanism by which the brain acts as the cardiovascular systemreaction to stressregulated. The cardiovascular system, and in particular the heart and blood vessels, has a certain independent activity. This way it can work independently of the brain. Nevertheless, the study shows that the brain has a certain protective function in stressful situations. The purpose is to adapt the cardiovascular system to the situation.
Cardiovascular system protected by the brain
What was supposed to serve as protection against other predators in earlier times now also occurs in other stressful situations. The brain, and more specifically the so-called lateral habenula (LHb), is given a certain regulatory power over the circulatory system. This is achieved by controlling the autonomic nervous system. This consists of the sympathetic and parasympathetic systems, with the former having a stimulating effect on the cardiovascular system and increasing heart rate and blood pressure. The latter in turn has the opposite effect.
The Study
In their study, the researchers focused on this LHb, which is located deep in the brain. They found that it controls behavioral responses to stressful events and produces strong cardiovascular responses. The researchers electrically stimulated the LHb in rats. Stimulation of the LHb resulted in bradycardia (low heart rate) and increased mean arterial pressure (MAP), which is a clinically useful parameter for assessing total blood pressure. To determine how the LHb interacts with the autonomic nervous system to regulate the cardiovascular system, the researchers turned off the parasympathetic system by cutting off the main parasympathetic nerve, the vagus nerve, or by suppressing it with a drug. While this suppressed the effect of LHb on heart rate, it did not change MAP. The suppression of the sympathetic system in turn had the opposite effect. It decreased MAP but did not change heart rate.
The researchers then focused on the neurotransmitter serotonin, which, among other things, determines the modulation of mood, cognition and memory. They found that blocking all serotonin receptors significantly reduced the effect of LHb on both MAP and heart rate. However, certain subtypes of serotonin receptors were particularly involved in the process. “These are remarkable results that demonstrate how the lateral habenula controls the cardiovascular system. Our results reveal the mechanism of a neural circuit that plays an important role in stress-induced behavioral responses,” says Masayuki Matsumoto, authorof the studyand professor at the University of Tsukuba.
