Brain Energy Signals Concept

A rare phenomenon of reversible cerebral shrinkage

Brain energy signals concept

European moles shrink their brains by 11% before winter and enlarge them by 4% before summer.

Researchers discover another brain-shrinking mammal.

European moles face an existential crisis in the dead of winter. Their high-limit mammalian metabolisms require more food than is available during the colder months. Instead of migrating or hibernating to cope with the seasonal challenge, the moles have come up with an unexpected energy-saving strategy: shrinking their brains.

In a recent study, a group from the Max Planck Institute for Animal Behavior led by Dina Dechmann found that European moles shrink their brains by 11% before winter and grow them back by 4% in summer. This is a new group of mammals known to reversibly shrink their brains through a process known as the Dehnel phenomenon.

european mole

European moles are the latest known mammal species to reversibly shrink their brains before winter. Credit: Javier Lazaro

The research, however, does more than just add another species to the bizarre repertoire of brain-shrinking animals; it delves into the evolving puzzle of what drives them down this perilous path. When researchers compare moles from different regions, they find that Dehnel’s phenomenon is caused by cold conditions rather than lack of food alone. The reduction in brain tissue helps animals use less energy and therefore resist the cold.

Dehnel’s phenomenon was first described in shrew skulls, which were found to be smaller in winter and larger in summer. Dechmann and colleagues reported the first evidence that these atypical changes in shrew skulls occurred throughout an individual’s lifetime in 2018. Dechmann and colleagues have since shown that Dehnel’s phenomenon occurs in stoats and weasels. What these mammals have in common is a way of life that puts them on the energetic razor’s edge.

Comparison of mole skulls

The skulls of European moles shrink before winter and regrow in the spring in a process known as the Dehnel phenomenon. Credit: Lara Keicher / Max Planck Institute for Animal Behavior

“They have extremely high metabolisms and year-round activity in cold climates,” says Dechmann. “Their tiny bodies are like turbocharged Porsche engines that burn through energy reserves within hours.”

It was clear to the scientists that shrinking energy-expensive tissues, such as the brain, allows animals to reduce their energy needs. “We understood that the Dehnel phenomenon helps these animals to survive when times are tough. But we still didn’t understand what the real pressure points, the exact environmental triggers, were driving this process.

Now the team has answered that by studying a new mammal with metabolic extremes. Measuring skulls in museum collections, the researchers documented how two species of moles – the European mole and the Spanish mole – change with the seasons. They found that the European mole’s skulls had shrunk by 11% in November and regained by 4% in the spring, but those of the Spanish mole had not changed throughout the year.

Because the species live in very different climates, the researchers were able to determine that weather, not food availability, was responsible for the brain changes. “If it were just a matter of food, we should see European moles decline in the winter when food is scarce and Spanish moles decline in the summer when the sweltering heat makes food scarce,” says Dechmann. .

The study findings go beyond answering evolutionary questions, offering insight into how our bodies can regenerate after sustaining significant damage. “The fact that three distant mammalian groups can shrink and then regrow bone and brain tissue has huge implications for research into diseases such as

Alzheimer’s disease is a disease that attacks the brain, causing a decline in mental abilities that worsens over time. It is the most common form of dementia and accounts for 60-80% of dementia cases. There is currently no cure for Alzheimer’s disease, but there are medications that can help relieve symptoms.

” data-gt-translate-attributes=”[{” attribute=””>Alzheimer’s and osteoporosis,” says Dechmann. “The more mammals we discover with Dehnel’s, the more relevant the biological insights become to other mammals, and perhaps even to us.”

Reference: “Winter conditions, not resource availability alone, may drive reversible seasonal skull size changes in moles” by Lucie Nováková, Javier Lázaro, Marion Muturi, Christian Dullin and Dina K. N. Dechmann, 7 September 2022, Royal Society Open Science.
DOI: 10.1098/rsos.220652

#rare #phenomenon #reversible #cerebral #shrinkage

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