By Jensen, Randy on June 6, 2020.
For many years, many scientific studies have focused on using only male subjects, in both human and animal experiments.
Now researchers like Jamshid Faraji and Gerlinde Metz at the University of Lethbridge’s Canadian Centre for Behavioural Neuroscience are shining a spotlight on biological sex differences and making them an integral part of their research.
“It’s a big issue,” says Faraji. “Researchers and scientist have to consider males and females, particularly in relation to stress. The results could be misleading if we don’t consider the psychological differences between males and females.”
In their recent study, published in Frontiers in Behavioural Neuroscience, Faraji and Metz developed an animal model that demonstrates sex differences in the thermal response to stress. While fever is typically produced as a result of an infection, a condition in humans called psychogenic hyperthermia results in increased body temperature due to chronic stress. The condition affects more females than males, as well as in adolescence.
“Young females are known to experience high raises in temperature in response to stress,” says Metz. “Their core body temperature can go up to 41 degrees. There’s not a good animal model and, if you want to understand the mechanisms, it’s helpful to see if this also works in animals. This study is the first observation of psychogenic regulation of temperature in mice. No one has shown that before.”
The researchers subjected male and female mice to two types of stress. In one condition, mice were individually placed into transparent Plexiglas tubes that mimicked a natural burrow of a mouse. The tunnel allowed the mice to move around freely, but prevented them from standing up. Mice engage in rearing behaviour, or standing on their hind limbs to explore their environment. Before the mice experienced any stress, the researchers monitored their behaviour during free exploration and found that females reared more often than males during active hours.
After both stress conditions, researchers took blood samples to measure levels of stress hormones. They then went a step further and used an infrared thermal imaging camera that detects changes in skin temperatures, and that is where the differences showed up.
“While we expected differences, both males and females showed the same flight or fight response to being deprived of some of their natural physical activity,” says Faraji. “Our results showed a significant difference between males and females only when they were deprived of rearing behaviour. Female mice showed an increase in temperature while males did not. This shows that males and females respond differently to certain kinds of stress.”
Having established an animal model will allow researchers to do further work on exploring the thermal regulation systems in males and females, which could one day lead to a better understanding of the same mechanisms in humans.
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