Lampreys look very primitive with their sharp circular mouth and teeth, but a new study shows they have nerve cells responsible for the 'fight or flight' response, similar to humans. This challenges the idea that this part of the nervous system came later in evolution, and it puts lampreys closer to complex vertebrates like humans.
Daniel Meulemans Medeiros, an evolutionary biologist at the University of Colorado Boulder who has worked with the research group before but was not involved in the new study, says the conclusions are groundbreaking.
Sea lampreys belong to a group of fish called jawless vertebrates. Scientists previously thought they lacked nervous system characteristics seen in jawed vertebrates, such as the sympathetic nervous system. This system is responsible for the 'fight or flight' response, and it activates the body by releasing hormones to control body temperature and cardiovascular function.Sea lampreys} belong to a group of fish called jawless vertebrates, which scientists thought lacked nervous system characteristics seen in jawed vertebrates, such as the sympathetic nervous system. This system is what’s behind the “fight or flight” response, and it activates the body by releasing hormones to control body temperature and cardiovascular function.
In previous work, Caltech neuroscientist Marianne Bronner had studied the lamprey nervous system in detail, particularly the peripheral nervous system, which lies outside of the brain and spinal cord, and the neurons in the gut.While examining and creating markers for these neurons, Brittany Edens, a researcher in Bronner’s lab and coauthor of the new study, observed peripheral neurons outside the lamprey’s intestine. Bronner’s team chose to investigate.
The team utilized a technique that tags and illuminates specific mRNA in individual cells of lamprey embryos. This allowed the researchers to analyze three or four genetic factors linked to sympathetic neurons at the same time. These genetic factors were found in a group of cells lining the heart and trunk of the embryonic lampreys, indicating that these cells were the sympathetic neurons observed in other vertebrates, as reported by the team on April 17 in the publication.The cells originated from the neural crest, a patch of stem cells that migrate during development and give rise to cells of the peripheral nervous system, as tracked by the team. The lamprey’s sympathetic neurons lit up with the dye, showing that the cells came from the neural crest, just like they do in more complex vertebrates. Nature.
The team also found that compared to other vertebrates, the lamprey’s sympathetic nervous system formed much later in development and the clusters of cells were smaller. Previous studies might have missed these cells by examining them at the wrong time during embryo development. Therefore, although the sympathetic system is present, it’s rudimentary compared to what it is in mammals, according to Bronner.
The findings suggest that the sympathetic nervous system was not an innovation of jawed vertebrates, but rather that the blueprint for it has been around since even before lampreys diverged from the main vertebrate line about half a billion years ago, says Shreyas Suryanarayana, a neuroscientist at Duke University who was not involved with the study.
“As you investigate further, it becomes evident that the fundamental components of these intricate systems found in humans are actually very ancient,” Suryanarayana states. In more intricate animals with spines, this system then became more varied, expanded, and grew in size, he states.
Previous research had already started to deconstruct the concept of a simple nervous system in lampreys. For instance, scientists had discovered that
connections and proteins in specific brain areas of the lamprey looked like those observed in other vertebrates . More recently, scientists discovered thatsignaling involved in how the lamprey’s brain arranges itself also applied to all vertebrates. Medeiros suggests that researchers should now delve even further back in evolutionary time to examine invertebrates and see if they also have sympathetic neurons, which could clarify how the vertebrate nervous system developed.
“That’s really one of the questions that has intrigued me for years: How did you go from invertebrates to vertebrates?” Bronner says. “I don’t have the answer, but I will keep trying to figure it out.”
The identification of sympathetic nervous system cells in lampreys strengthens the connection between the animal and complex vertebrates — such as humans.
