Sex and violence

They are connected in the male brain, but not in the female brain

Ksenia Malysheva, Naked Science

Neuroscientists have discovered a difference in the structure of the brain of a female and a male laboratory mouse. It turned out that the neurons involved in the formation of sexual and aggressive behavior in males are woven into one tangle, and in females they are separated into two separate groups.

Aggression is an important type of behavior in animals: it helps to defend oneself, occupy and maintain high positions in the group, get food and successfully fight for sexual partners. In many animals, from crocodiles to monkeys, males are more likely than females to behave aggressively, so aggression studies traditionally consider male mechanisms of such behavior. However, females can also attack and intimidate – for example, protecting offspring. A group of American, Chinese and Korean neuroscientists led by Dayu Lin found out how aggressive behavior is formed in female mice, and found a number of significant differences with the formation of similar reactions in males. In particular, it was found that aggression and sexual behavior in males are inseparable from each other, and in females they "turn on" and "turn off" independently.

In male mice, the neurons responsible for argession and sexual behavior are connected in a tight tangle in the ventromedial hypothalamus (VMHvl). A 2011 study (Lyn et al.) showed that VMHvl cells can only be activated and deactivated simultaneously. By "turning off" the genes encoding estrogen receptors, scientists suppressed aggression, and with it sexual behavior; male mice did not bite, did not scratch and did not show interest in females.

Neurons of the ventromedial hypothalamus also participate in the formation of aggressive behavior in females, carrying receptors for the hormones estrogen and progesterone (VMHvlEsr1+PR+), however, in the brain of a female, the populations of VMHvlEsr1+PR+ and cells involved in the formation of sexual behavior are separated. Thanks to this, the authors of the article published in Nature Neuroscience managed to stimulate VMHvlEsr1+PR+ cells and cause aggression without stimulating sexual behavior in females, and vice versa: to suppress the activity of neurons and get very docile, but still sexually active mice.

There were also some other nuances of aggressive behavior in female mice. To provoke aggressive behavior, unfamiliar individuals (always females) were launched into cages with experimental mice. Depending on the breed, the experimental mice showed two types of aggressive reaction: an attack and an attempt to cover a new female. Optogenetic activation of VMHvl neurons has always enhanced the reaction characteristic under normal conditions for each breed, from which scientists concluded that this part of the hypothalamus in females is responsible for aggression, regardless of how it manifests itself.

Some behaviors differ quantitatively in male and female individuals, while others differ qualitatively, the authors note. The same groups of neurons may be responsible for those behavioral reactions that differ only quantitatively (aggression). Sexual behavior implies qualitatively different actions in males (active movement, erection, ejaculation) and females (passivity, caring for offspring), therefore, the brain regions responsible for them may have morphological differences. The authors note that the structure of the hypothalamus in humans and mice is similar, but it is impossible to extend the conclusions about the relationship of aggression and sexual behavior in male and female mice to our species: sexual and aggressive behavior in mice is difficult to regulate, and in humans it is even more difficult.

Portal "Eternal youth" http://vechnayamolodost.ru  19.09.2017