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.