Shorter Winter Days Triggers Agression Hormones Differently in Male and Female Hamsters

 

A recent study at Indiana University shows a hormonal mechanism in hamsters that connects short winter days with agression in females, and differs from the mechanism that controls this in males.

 

A quote from a psychologist who was part of the research states "The results show for the first time that melatonin acts directly on the adrenal glands in females to trigger a 'seasonal aggression switch' from hormones in the gonads to hormones in the adrenal glands -- a major contrast to how this mechanism works in males."

 

It was originally thought that the aggression came from sex hormones in the gonads.

 

Melatonin is a hormone that rises in the body during darkness and lowers during daylight. The hormone from the adrenal gland is dehydroepiandrosterone, or DHEA, a sex steroid shown to affect aggression levels in mammals and birds, and possibly humans. In another previous study, Demas' lab found that melatonin, in concert with a hormone secreted by the brain's pituitary gland called adrenocorticotropic increases the output and enhances the effects of DHEA from adrenal glands in males.

 

In contrast, Rendon and colleagues' new study reveals that melatonin acts directly on the adrenal glands in females to trigger the release of DHEA, without the need for the pituitary hormone.

 

DHEA can be converted into estrogen or androgens, which affects aggression. In female hamsters it compensates for low amounts of estradiol that occurs in the winter.

The research was conducted in Siberian hamsters, or Phodopus sungorus, a species with a similar adrenal system to humans. About 130 hamsters were exposed to long days for a week, after which 45 were exposed to shorter days for 10 weeks.

Strength of brain connectivity varies with fitness level in older adults

A new study led by Michelle Voss shows that there is a relationship between fitness levels of adults and strength of connections between different parts of the brain. The findings suggest that adults with a greater cardiovascular fitness level have stronger brain connections, and this is suggested to improve long term memory. 

Using functional magnetic resonance imaging, Voss and colleagues measured the strength of these connections throughout the brain in younger and older adults at rest. As expected, the team confirmed that most connections were weaker for older adults when compared with younger adults.They decided to build on these findings and test the role that cardiovascular fitness has on resting brain connectivity. 

A quote from Voss states "An encouraging pattern in the data from our study and others is that the benefits of fitness seem to occur within the low-to-moderate range of endurance, suggesting that the benefits of fitness for the brain may not depend on being extremely fit."

This study suggests that there is a positive relationship between fitness and brain connectivity as people age. This study can be extremely beneficial as it may be able to prevent/reduce the amount of people who suffer from brain problems related to forgetting by regularly exercising, such as dementia.