Exercise hormone irisin prevents physical inactivity-induced cognitive decline in mice, 2022, Park et al

Highlights

• Physical inactivity induced anxiety, depressive states, & working memory decline.
• Regular exercise raised plasma irisin and skeletal muscle FNDC5 and PGC-1α activity.
• Irisin-neutralizing antibody administration compromised the benefits of exercise.
• Plasma irisin released by skeletal muscles is vital for cognitive function even in PI.

Abstract

We previously reported that physical inactivity (PI) induces cognitive decline and depressive states, which were ameliorated by regular exercise. However, the mechanism underlying the preventive effect of exercise remains unelucidated. Irisin has recently been identified as an exercise-inducible myokine that improves cognitive impairment. Plasma irisin levels increase during physical exercise; therefore, PI could lead to a decline in cognitive function by reducing plasma irisin. Therefore, this study aimed to examine whether irisin is associated with cognitive decline and mental deterioration altered by PI and exercise. The mice were housed for eight weeks in the PI cage, whose living space was one-sixth that of a standard cage. Simultaneously, the mice were subjected to regular exercise in the presence or absence of an irisin-neutralizing antibody.

PI increased the epididymal fat mass without increasing body weight, muscle mass, or plasma corticosterone levels. Additionally, PI induced anxiety, depressive states, and a decline in working memory. In contrast, regular exercise after PI elevated irisin levels in plasma and increased fibronectin type III domain-containing 5 (FNDC5) and peroxisome proliferator-activated receptor gammacoactivator 1α expression in skeletal muscle. Regular exercise also increased hippocampal brain-derived neurotrophic factor (BDNF) expression and BrdU-positive cells, alleviating cognitive decline and mental deterioration induced by PI. The beneficial effects of exercise were compromised by the administration of an irisin-neutralizing antibody. Moreover, plasma irisin level was positively correlated with working memory, hippocampal BDNF levels, and hippocampal cell proliferation. These findings suggest that exercise-inducible irisin is critical for maintaining cognitive function in the PI state.

Open access, https://www.sciencedirect.com/science/article/pii/S0166432822002765

 

So, evolution has decided that inactive mice, possibly inactive due to lack of food, should get stupider, and therefor decrease their chances of survival in a low food environment?

 

Good grief. Not to be insulting to mice, but small animals do not have a rich cognitive life, do not have television, books, music or anything like that. They don't even have friendly conversations around a good meal. 100% of their activity will be physical, so any limitation of activity will also impact their cognition since it's pretty much their only mental activity. It seems expected that mice who have less cognitive stimulation, by way of activity in their case as it's all they have, will do poorer than those who do.

Whatever. However, again, the words they use simply don't mean anything, they are simply placeholders for ideas:

"Anxiety":

The OFT was performed to assess anxiety-like behavior in mice. The black box used in the test (length × width × height: 40 cm × 40 cm × 50 cm) was divided into 16 square grids. At the start of each trial, the mice were placed in the right-hand corner of the field and allowed to explore the arena freely, and their locomotor activity was recorded videographically for 10 min. The equipment was cleaned with 70% ethanol after each test. The animals’ behavior was scored using SMART® ver. 3.0 software (Panlab Inc., Spain), and the parameters scored included the center-staying duration, rearing, and distance traveled.
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"Depression":

The SPT was used to assess anhedonia depression-like behavior in mice. On the first day, two bottles containing tap water were placed on either side of the cage to acclimatize the mice for two days. The next day, one of the bottles was replaced with 1% sucrose solution, and the mice were allowed to choose freely during the night (19:00–09:00 h). The position of the two bottles was reversed on the next day to avoid the mice’s preference for any one position, which was conducted four times. The sucrose preference ratio (%) was derived by dividing the volume of sucrose intake by the total volume of sucrose and water intake, which was multiplied by 100.​

If someone wants to interpret that as meaning anything like the so-called "psychosocial" "thoughts and beliefs" with rumination, neuroticism or whatever, the complex made-up nonsense invented to explain those simplistic labels in humans, that's their choice. But this is silly nonsense. Frankly every bit as ridiculous as the most famous bad psychological experiments.

Because those "tests" here are basically put alongside questionnaires that ask people about symptoms and are interpreted to mean the same thing. This is completely delusional, comparing apples and oranges isn't even a fair comparison, it's so much worse than this. In the end all mental health medicine did is basically the medical equivalent of Meyers-Brigg, the rest is all up to interpretation, politics and public relations.

And this is especially problematic with vulnerable, uh, beings. Whether mice or children, they have little input or say into what they do. And it's in pediatric Long Covid that I see the worst obsession with mental health, it's all they talk about, even worse than with adults, probably because the power imbalance is so much greater, in addition to difficulty with communication, made even worse by the nonsensical use of labels devoid of any real meaning.