New Delhi: “It was actually quite unbelievable,” said Anna Andreasen, a PhD student at the Norwegian University of Science and Technology. “The whole mind lit up.” Living species, whether fish or humans, tend to perform poorly as the temperature rises. This one This is something that many people have certainly experienced on a very hot summer day, but what happens inside the body when the temperature gets too high?
To find the solution, researchers from NTNU’s Department of Biology used genetic techniques combined with neurophysiological methods.
“We were interested in the factors that restrict the heat tolerance of organisms.” Which organisms will thrive when the Earth’s temperature rises as a result of climate change, and why? “We decided to look at the brain,” Andreasson explains.
Climate change due to heat waves
Heat waves blowing across continents are becoming more common, and living organisms are facing dangerously high temperatures. Understanding what limits survival at extremely high temperatures is important for predicting how organisms will respond to climate change.
“Thermal tolerance has been studied for decades and the idea that temperature affects brain activity is not new. What is different is that we can now analyze the phenomenon using genetic techniques and neurophysiology,” says Andreasson. telling.
Researchers at NTNU in Trondheim studied the brain activity of newly hatched zebrafish larvae as the temperature around the larval fish progressively increased.
“These fish have been genetically engineered in such a way that when neurons in the brain are activated, they emit fluorescent light.” While the larvae swim, we can see this light through a microscope. These larval fish have the added benefit of being translucent. “We peer directly into the brains of living larvae,” Andreasen explains.
lose the ability to react
Researchers can then monitor brain activity while gradually increasing the temperature of the water in which the fish are swimming.
“We’ll see how the larvae react when the weather is warm. When it gets too hot, they lose their balance and start swimming in circles, belly up.”
The researchers incinerated the fish larvae to see how they responded. They suppress the tail of the larvae, which usually causes them to swim.
But something strange happened when they raised the temperature.
“At a certain point, the fish stopped responding to the jokes.” They were still alive, but in an ecological sense, they were dead. “They wouldn’t be able to swim away from predators or make their way to cold water in that situation in nature,” Andreasen says, adding that the condition is only temporary in small experimental fish.
“Once we put them back in the cold water, they’ll be completely fine,” Andreassen says.
heat shuts down the mind
So far, the experiments have gone as expected. They could also test whether the brain was perceiving visual stimuli by shining a light in front of the fish’s eyes. As the temperature rose, the brain stopped responding to the input and became completely inactive. But something strange happened when they raised the temperature.
“My whole head lit up.” “What we saw is the closest we can describe,” explains Andreassen.
Normally, brain activity is seen only as small spots of light in certain areas of the brain. Under the microscope, the researchers could see how the fluorescent light spread in a matter of seconds and covered the entire brain of the microscopic fish larvae.
“We know that the zebrafish brain has a lot in common with the human brain – 70% of the genetic material is identical,” Andreasson explains.
After that, the researchers intend to examine glial cells, a type of brain cell.
“We are particularly interested in the activity of glial cells during heating.” These cells are important for oxygen delivery to the brain as they both measure oxygen levels and control blood flow and oxygen supply. Because we can see that oxygen levels affect temperature tolerance, one theory is that the brain shuts down because glial cells no longer have the ability to control oxygen levels.”
Differences drive development
To get a better understanding of what happened, the Trondheim researchers began adjusting the amount of oxygen in the fish’s swimming water as the temperature changed.
“We were surprised to see that oxygen levels played a role in modulating heat tolerance.” When we introduced more oxygen, larval fish performed better at higher temperatures, had higher brain activity, and recovered faster from exposure to upper thermal limits than fish with less oxygen.
When evaluating the effect of oxygen content on temperature tolerance in different animals, the researchers found conflicting results.
Being “insensitive” to changes in oxygen levels could potentially provide an evolutionary advantage as Earth’s temperature rises.
“The data suggest that temperature tolerance varies between species.” This can be a trait that determines whether a species can adapt to climate change or will perish as temperatures rise. Many species live in oxygen-deficient conditions where temperatures can rise faster than normal. “They will be extremely vulnerable,” Andreasen predicts.
She uses species living in shallow freshwater environments, rivers, or the intertidal zone as an example.
“These are habitats where substantial changes in oxygen levels can occur, often accompanied by temperature fluctuations.” In these settings, fish whose heat tolerance is limited by oxygen levels are more likely to struggle than fish that are not.
Being “insensitive” to changes in oxygen levels could potentially provide an evolutionary advantage as Earth’s temperature rises.
“Animals that can maintain nerve function under low oxygen levels may be best at withstanding high temperatures,” Andreasen says.