Exam season is looming and stress levels are rising! Although a familiar feeling, and common, have you ever considered the biological factors associated with why we feel a certain way when stressed?
Most of us know when we get stressed, our brains release a ‘cocktail’ of neurotransmitters which in turn signal our sympathetic system to increase our heart rate, blood pressure, and overall awareness. Beyond this understanding, however, we are yet to fully grasp the ways in which our bodies respond to stress.
Interestingly, researchers from the University of Tsukuba in Japan have discovered a novel mechanism by which a specific area of the brain (the lateral habenula or LHb) regulates the cardiovascular system (CVS). The CVS is a unique system in the human body. It is able to function independently from the brain, as a person adapts to a new environment. Importantly, however, the brain does retain some regulatory control over this system through the autonomic system. Consequentially, our bodies have biological responses to stressful situations.
The LHb is located deep within the brain and is known to control behavioral responses to stressful events. As a result, it causes a strong CVS response. To observe how exactly the LHb elicits such a response, researchers electrically stimulated the LHb in rats by inserting an electrode through the skull.
Stimulation led to bradycardia (slowing of the heart rate) and increased mean arterial pressure (MAP), which is the average pressure in an individual during one cardiac cycle; also a good parameter for assessing blood pressure. In addition, researchers severed the vagal nerve which is the main nerve controlling the parasympathetic system to determine how the LHb interplays with the autonomic nervous system to regulate the CVS. Whilst this suppressed the LHb’s effect on heart rate, it did not affect the mean arterial pressure.
To understand the mechanism by which the LHb elicits the cardiovascular responses, researchers found the LHb acts on serotonin and increases MAP and heart rate. Notably, this is what we experience, when we are stressed: an increase in our heart rates and high blood pressure. They confirmed this by blocking the serotonin receptors to observe any changes in response. Interestingly, blocking the serotonin receptors significantly reduced the effect of LHb on MAP and heart rate, indicating that the stress we feel originates from a system that is somewhat dependent on serotonin.
Online Source: https://www.frontiersin.org/articles/10.3389/fnins.2021.655617/full
Original Source: “Lateral Habenula Regulates Cardiovascular Autonomic Responses via the Serotonergic System in Rats” by Tadachika Koganezawa et al. Frontiers in Neuroscience
Featured Photo Source: Alex Green, from Pexels.
Edited by Malavika