A new study shows that hibernating ground squirrels are able to achieve rapid brain-wide recovery when they wake up after experiencing similar "brain damage" in winter. This amazing neuroplasticity is expected to provide new ideas for human recovery after stroke. Relevant results have been published in JNeurosci, a journal of the American Society for Neuroscience. The above findings confirm for the first time that changes in neuronal structure in the primary visual cortex of squirrels during hibernation are reversible.
Hendrikje Nienborg, author of the paper and a scientist at the US National Eye Institute, said that previous studies on the touch processing areas of the squirrel brain (including the hippocampus, somatosensory cortex and thalamus) have suggested the existence of similar neuroplasticity mechanisms, so the team speculated that the same "reshaping" process may also be taking place in the brain areas responsible for processing visual information. In this experiment, the research team focused on the hibernation state (deep hibernation period) and the short awakening period of 12 to 24 hours in order to compare the changes in the structure of the two types of neurons at different stages.
When a local squirrel enters hibernation, its body temperature drops significantly, its heart rate drops to just a few times per minute, its metabolism slows down significantly, its breathing is almost imperceptible, and its brain activity becomes extremely quiet, as if the entire animal has been switched to "flight mode." From a neurological perspective, this state is similar to the brains of human stroke patients, where brain cells receive significantly reduced supplies of oxygen and nutrients, but the key difference is that the squirrels' brain cells are able to resume normal function after hibernation ends. Researchers believe that understanding how squirrels "resurrect with full blood" from long-term low temperature and low oxygen supply is expected to provide important clues for human recovery after neuronal damage diseases such as stroke, and promote the exploration of the "Holy Grail" goal of "using the body's own mechanisms to repair damaged neurons" in stroke research.
In specific experiments, scientists dissected the brains of hibernating ground squirrels and observed the different responses of two types of neurons during deep hibernation and the awakening interval. It was found that one type of neurons underwent significant structural changes during deep hibernation, and that these changes had largely returned to their pre-hibernation state about 90 minutes after the squirrels were awakened. Even more strikingly, when the researchers reassessed six months later, it was almost impossible to tell from the neuronal structure that the squirrel had ever hibernated. Previous research has also found that hibernating squirrels have significantly increased binding levels of "small ubiquitin-like modification protein" (SUMO). This process is called SUMOylation and is thought to protect their brain cells from damage.
"We already know that these structural changes affect how neurons communicate with each other and are closely related to learning ability and recovery after conditions such as stroke," Nienborg said. She pointed out that it is exciting to see such a rapid and reversible brain structure change mechanism in hibernating animals, because once its molecular and functional basis is clarified, there may be an opportunity to "borrow" similar mechanisms to the human adult brain in the future, making it more "plastic" during critical stages such as stroke recovery.
Globally, stroke is currently the third leading cause of death and an important cause of long-term disability. About 80% of these strokes are ischemic strokes, in which blood clots block blood flow, preventing brain tissue from getting enough oxygen and triggering cell death. Human recovery after stroke mainly relies on the establishment of new neural connections and the reorganization of existing neural networks. This process helps patients gradually regain key functions such as swallowing, language and walking. Nienborg said that as this study further reveals the specific structural change paths of hibernating squirrel neurons, the scientific community will also have a better idea of which directions to focus on next.
"We already have a fairly in-depth understanding of how different brain regions support visual information processing," she said. "Therefore, continuing to explore the functional changes in the visual system during hibernation and awakening in the ground squirrel brain is likely to be an important research step in the next phase." This research has been officially published in JNeurosci and has been peer-reviewed and fact-checked, laying the foundation for future neural repair research using hibernating animals as models.