Bullfrogs have a brain superpower
Popular Science...
The brain runs on glucose—a sugar in blood and the body’s main energy source. When that fuel runs out, neural activity falls apart very quickly. But American bullfrogs (Aquarana catesbeiana) have a surprising biological backup.
When glucose supplies dwindle, bullfrog brains can rely on another energy source to sustain important neural functions. This energy source is called ketone bodies, and most animals produce these energy molecules in the liver when fasting, starvation, or prolonged exercise cause glucose levels to drop.
When nutrients are scarce, the liver turns fatty acids into ketone bodies, which the blood then carries to organs such as the brain. However, bullfrogs can produce ketones directly in the brain without having to completely depend on the liver. This production can sustain brain activity, at least temporarily, without glucose, according to University of Missouri biologist Joseph Santin, the lead author of a study recently published in the journal PNAS .
“Scientists generally believe ketones are delivered to the brain from elsewhere in the body,” Santin said in a statement. “That’s what makes this discovery so exciting. It’s like finding a backup generator inside a building that everyone assumed had only one power source.”
These results also shed light on how these amphibians endure their yearly winter hibernation-like state, when their metabolism slows and their energy reserves are depleted. The brain’s local ketone bodies production may be one of the reasons why in the spring (when their oxygen and energy supplies are low) bullfrogs are able to reactivate key brain circuits that control bodily functions so quickly.
“Because a frog in the summer or fall typically is using glucose to fuel the brain, their ability to fully switch to brain derived energy sources like ketone bodies goes against dogma that the adult brain requires constant glucose delivery and metabolism,” Santin explains to Popular Science.
The team is now curious what causes bullfrogs to switch to this emergency energy supply, and how long they can depend on it. They don’t think the change is permanent—it appears to be a reliable backup system for the brain to continue operating when glucose isn’t cutting it anymore. And because bullfrogs and humans actually have many of the same fundamental biological processes, the research could also provide insight into the human brain.
“Many neurological disorders, such as ALS, Parkinson’s disease, and Alzheimer’s disease, each involve problems with metabolizing glucose, which means that while these diseases have different root causes, they all involve problems with the brain’s typical energy support system,” Santin says. “We believe that understanding the cellular and molecular biology that allows the brain to dial down its energy needs and still maintain performance could one day be useful for treating various neurological diseases, and we see this kind of result as the early phases of a road map that will help to figure it out.”
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