In the event of blood loss, the human body has defense mechanisms that kick into gear to protect it from the worst outcomes, but they can only keep up the fight for so long. Scientists have pinpointed a set of neurons that regulate this process, which they were able to manipulate in rats suffering severe blood loss to prevent cardiovascular collapse.
The research was carried out by scientists at the University of Virginia who were investigating how the body deals with severe blood loss, which can lead to a sudden and dangerous loss of blood pressure. This is known as cardiovascular collapse or “decompensated hemorrhage,” and by using advanced imaging techniques the team was able to identify a set of cells in the brainstem that help the body avoid this fate.
Known as adrenergic C1 neurons, this cluster of cells were shown to monitor blood pressure in rats and then become hyperactive when blood loss was detected. Likened to a natural alarm for blood loss, the neurons then boost nerve activity to constrict blood vessels as a way of maintaining proper blood pressure. And the way they do this is quite clever, prioritizing the body's most important parts.
“During blood loss, the brain coordinates a cardiovascular response that supports blood flow to critical organs, like the heart and brain,” said study author George Souza. “Our study shows that the cardiovascular response to blood loss depends on changes in the activity of a few hundred neurons in the brainstem.”
While the neurons were seen to kick into overdrive in the event of blood loss, when that blood loss becomes severe they instead become inactive, which is what leads to cardiovascular collapse. This is a precursor to hemorrhagic shock, in which the entire body shuts down. But the team found that by using a technique called optogenetics to remotely control neurons using light, they could reactive the neurons, which restored the blood pressure and heart rate in rats suffering severe blood loss.
“Our study indicates that reactivating the brain pathways controlling blood pressure during decompensated hemorrhage effectively reverses cardiovascular collapse," said study author Stephen Abbott. "We think this indicates that neuromodulation of the pathways described by our study could be a beneficial adjunct therapy for low blood pressure following blood loss."
The scientists conclude that these C1 neurons are therefore a "nodal point for the sympathetic response to blood loss," but there is much still to learn. They say more research is needed to uncover the reasons why they become inactive in response to severe blood loss, but believe they've now got a solid foundation to pursue answers to these questions.
“These findings illuminate the importance of the brain-body interactions during blood loss and provide a new perspective for the underlying cause of cardiovascular collapse,” Abbott said.
The research was published in the journal Cell Reports.
Source: University of Nevada