When we have to face situations that generate anxiety, such as speaking in public, getting lost in a forest, or having to walk through dark and deserted streets late at night, we can experience dry mouth and throat, excessive sweating, and even feel the heart palpitations, but is it anxiety that makes the heart beat faster, or could it be that an increase in heart rate makes us anxious?
A team of scientists from Stanford University has now analyzed this link in mice and found that when their heart rate is increased, animals that would have remained calm under normal circumstances become more anxious, indicating that heart activity may affect to mental state and suggests that finding ways to slow the heart rate could be useful in treating mood disorders such as anxiety and depression. The results of the study have been published in Nature.
The new research is led by neuroscientist Karl Deisseroth, who during his psychiatric training observed that patients with panic disorder often also had heart problems. Tachycardia – or a heart rate of more than 100 beats per minute (bpm) – is a hallmark sign of anxiety and a panic attack. And at least one study found that people with anxiety had a 26% higher risk of developing coronary artery disease.
The maze test showed that “increasing heart rate worsened anxiety-like behaviors”
To carry out the experiment that would allow them to isolate the brain-heart connection, the researchers took advantage of a light-sensitive protein called ChRmine, which was originally found in algae and controls the flow of charged particles into cells, just as if they were of a gate, which is normally closed, but when the protein is exposed to light it opens and charged particles, mainly potassium ions, flow into the cells.
What they did was introduce ChRmine into heart muscle cells from live mice that had been fitted with a vest with a microlight-emitting diode bulb. The light from this bulb penetrated through the skin of the rodents to activate ChRmine within the heart cells and act as a small pacemaker that made their hearts beat faster. Since they could turn the light on and off, they were able to control the heart rate of the animals.
At rest, a mouse’s heart rate is typically around 600 bpm, and the team increased it to around 900 bpm to induce tachycardia. In addition, they placed the mice in a maze with one pathway open and one closed. Mice have a tendency to behave anxiously by avoiding open areas, and during the experiment, those with racing hearts preferred to stay in the closed area. The maze test showed that “increasing heart rate worsened anxiety-like behaviors,” Deisseroth said.
Manipulating the heart to treat anxiety or depression
The researchers then analyzed the brains of the mice to look for signals, such as gene activation or electrical activity, indicating that an area of the brain was activated by raising the heart rate, and found that increased heart rate activated regions involved in the analysis of physiological information from the body, particularly the insular cortex, a brain area known to maintain emotional regulation.
When these scientists used a similar light-sensitive protein to block nerve signals from the insular cortex, the mice began to explore the open area of the maze, suggesting that their mental state was calmer, despite lower heart rates. it was still high.
Deisseroth and his team plan to induce tachycardia in the mice for longer periods to see if increasing the heart rate for weeks or months can increase or worsen behaviors similar to anxiety or depression. If they can replicate their findings in other settings, especially in humans, they could have implications for the treatment of mental health problems, since available drugs don’t always work and can take months to take effect.
“Manipulating the heart is much easier than manipulating the brain,” said Nadine Gogolla, a neuroscientist at the Max Planck Institute for Psychiatry, who was not involved in the study. “In reality, we can unravel new treatment strategies for patients with anxiety or depressive disorder,” concludes this specialist.
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