With its suction-cup-like mouth, rings of sharp teeth, and toothed tongue, lampreys attach themselves to fish and feast on their blood and other bodily fluids, sometimes killing them in the process. It’s a strategy that has served them well, as they have remained relatively unchanged for over 300 million years. Described as one of the most primitive vertebrate species, this unique cartilaginous fish helps neuroscientists understand vertebrate locomotion and behavior.
Dennis Weingarten, a postdoctoral fellow at the Oregon Health and Science University, has long studied neural systems in mammals like mice, but he took an interest in lampreys and the research doors they open. The anatomy of their spinal cord and particularly large axons makes them an ideal candidate for electrophysiological recordings, Weingarten’s specialty.
He wondered if lampreys could be used to investigate the effects of carbon dioxide on marine animals’ neuronal function – a prescient question as carbon dioxide levels in our atmosphere continue to rise as humans burn fossil fuels. And as atmospheric CO2 dissolves into Earth’s oceans, it forms carbonic acid (which exists in solution as a balance of bicarbonate, carbonate, and hydrogen ions). Researchers have sounded the alarm about ocean acidification and its effects on organisms like corals and molluscs with calcium carbonate shells: the increase in acidity makes it difficult for animals to build their calcium carbonate shells in the first place, and it dissolves existing calcium carbonate structures as the acid reacts with it. With this backdrop, what is occurring among marine animal’s neural systems? How will neurons, circuits, systems, and behaviors be impacted by increased bicarbonate in Earth’s oceans?
Weingarten spent a summer at the Marine Biological Laboratory in Woods Hole, Massachusetts, to answer some of these questions. He participated in the Grass Fellowship as a 2024 Kavli-Grass Fellow, supported by a partnership between The Grass Foundation and The Kavli Foundation, as part of the latter’s Neurobiology and Changing Ecosystems program. Kavli-Grass Fellows investigate neuroscience questions within the context of a changing environment, such as the rising CO2 levels at the center of Weingarten’s project.
Weingarten considered how different concentrations of dissolved bicarbonate, as well as short-term and long-term exposure, affected nerve cell function as well as swimming behaviors in the lampreys. For the elevated bicarbonate amounts, Weingarten used estimates for future CO2 levels in the year 2100 and 2300 – 75 years and 275 into the future.
His data shows profound effects on these animals. The lampreys lose their ability to swim quickly, their muscle contractions weaken, and the action potentials of neurons decrease. “They lose function in these very high CO2 concentrations,” said Weingarten.
The data he collected is vital for understanding the thresholds for these creatures, with implications for how other vertebrates will fare, and confirms what Weingarten and others suspected. “I was in this weird position where I maybe didn’t want to be right,” Weingarten says.
While Weingarten found diminished activity in the neurons of lampreys, the exact pathway for bicarbonate exposure to weaken nerve cells is still unknown. He isolated effects on GABAA receptors in particular, finding their function diminished, but it’s not yet clear if bicarbonate is acting upon them directly or if perhaps a different transporter is the cause.
With this preliminary data in hand, Weingarten plans to collaborate further with Jennifer Morgan, Marine Biological Laboratory senior scientist and director of the Bell Center. “She’s one of the world’s leading experts on lamprey synaptic transmission and physiology,” said Weingarten. “She’s incredible at looking at their synapses in great detail with electron microscopy.”
A theme for research in the growing field of neurobiology and changing ecosystems is describing direct connections between environment, mechanisms, and behavior in order to discover the limits of resilience in these systems. In understanding the detailed pathways that affect creatures like lampreys, clues can emerge concerning how they and other animals could hopefully adjust to the “new normals” of environmental changes over time.
And much like their model systems, scientists like Weingarten will need to find avenues to thrive as the scientific research environment shifts and evolves. In that regard, Weingarten credits his experience as a Kavli-Grass Fellow with cementing his passion for a future of science: “I don’t look at science the same way, and I’m completely locked in. I always was very open to the idea to keep doing this, but now I’m dead certain. This is what I wanted to do for the rest of my days.”