Biological complexity: breathing controls (Introduction)

by David Turell , Tuesday, May 09, 2017, 21:22 (2755 days ago) @ David Turell

The level of Carbon dioxide in the blood is one of the controls of the rate of breathing. The sensors for this control are in the brain stem. The vessels there constrict when the rest of the body dilates to wash out high CO2:

https://www.sciencedaily.com/releases/2017/05/170509121914.htm

"For more than a century, doctors and scientists have known that blood vessels dilate when cellular waste products like carbon dioxide build up. Widening the vessels allows fresh blood to flush through, carrying in oxygen and washing away the acidic carbon dioxide. This has been shown to be true throughout the body, and is standard dogma in undergraduate physiology classes.

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"He's shown in the past that RTN neurons respond to rising levels of carbon dioxide in the bloodstream by stimulating the lungs to breathe. But if the blood vessels in the RTN dilated in response to rising carbon dioxide the same way blood vessels do everywhere else, it would wash out that all-important signal, preventing cells in the RTN from doing their job driving us to breathe. It would be as if the drum major didn't notice the percussion section wandering off to left field.

"When Mulkey returned to the lab, he asked his team, including NIH postdoctoral fellow Virginia Hawkins, to see how blood vessels in thin slices of brainstem respond to carbon dioxide. And they saw it was indeed true -- RTN blood vessels constricted when carbon dioxide levels rose. But blood vessels from slices of cortex (the wrinkled top part of the brain) dilated in response to high carbon dioxide, just like the rest of the body.

"But how did the blood vessels know to act differently in the RTN? Mulkey guessed that RTN astrocytes had something to do with it. He suspected that the astrocytes were releasing adenosine triphosphate (ATP), a small molecule cells can use to signal one another. And that was causing the RTN blood vessels to constrict.

"When they tested it, they found the hypothesis was correct. The astrocytes in the RTN were behaving differently than astrocytes anywhere else in the body. When these brainstem astrocytes detected high levels of carbon dioxide, they released ATP signaling to the neurons and blood vessels.

"When the researchers induced the astrocytes artificially to release ATP, they got the same results. Bathing the RTN blood vessels directly in ATP also caused them to constrict. Blocking ATP receptors blocked the ability of blood vessels to respond to carbon dioxide. When the team did the same experiments in live animals, they got the same results. Perhaps most importantly, manipulating blood vessels in the RTN actually influenced how animals breathe, thus linking regulation of blood vessel diameter to behavior."

Comment: Obviously the vessels in the brain stem have to remain constricted to maintain the CO2 level there so the control neurons will continue to signal dilatation and more rapid breathing until the danger from CO2 is over. This is a highly complex coordinated activity, with similar astrocytes acting in different ways. How did evolution work this out? It requires design and planning. Only a thinking mind can do this.