2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
The ancient impulse that pushes an animal to reproduce is necessary for survival, so it must be "sewn" directly into the brain, according to scientists from the University of North Carolina. Using neuroimaging and optogenetics - a technique in which light is used to activate and deactivate certain areas of the brain - they were able to detect in the hypothalamus of mice a small cluster of neurons that are sensitive to sex hormones and arouse interest in the opposite sex. The discovery was published in the journal Nature Neuroscience.
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“These neurons primarily receive signals from hormones and senses and translate them into motivated social behavior,” explains Garrett Stuber, assistant professor of psychiatry, cell biology and physiology.
According to the researchers, the findings shed light on the social behavior of animals in relation to the opposite sex and, in addition, may be useful in the treatment of certain mental illnesses.
“These neural circuits serve as a bridge between social processes and the reward system, as well as provide insight into disorders associated with impaired social motivation,” said lead author Jenna McHenry, a researcher at Stuber's lab.
In the study, Stuber and colleagues worked with the medial preoptic region, a part of the hypothalamus that is important for social and reproductive behavior in all vertebrate species studied, from fish to humans. The scientists wanted to find out if this area is related to the body's reward system.
The researchers focused on the ventral tegmental area, the area where one of the dopamine pathways begins. They injected female mice into this area with fluorescent molecules, which moved upward along the neural connections. Having reached the medial preoptic region, they “illuminated” the neurons responsible for the production of neurotensin, a protein involved in the regulation of hormones necessary for the normal functioning of the reproductive system and the reward system.
In addition, these neurons were found to be sensitive to the female sex hormones estrogens and, therefore, could respond to hormonal changes during estrus. When the female mouse smelled the male's urine, the detected neurons were activated. At the same time, they did not react to the smell of urine of females or the smell of food. The reaction was most pronounced just before ovulation, when estrogen levels rose in the female's body.
“This suggests that some neurons in the brain can adapt to social reward bypassing any other, and that social signal processing is sensitive to hormone circulation,” concludes McHenry.
Artificial stimulation of neurons caused the release of dopamine. Both males and females after stimulation preferred to stay closer to individuals of the opposite sex.
“Overall, the findings suggest that these neurons help shape the mechanism of social attraction to a potential mate,” says Stuber.
Hormonal changes can cause depression and anxiety, so in the field of psychotherapy, the new discovery may also come in handy.
"Since hormonal changes associated with motivation are important for mating or maternal behavior in female mice, some hormonal disturbances in females may underlie disorders such as postpartum depression," McHenry explains.
So exploring the hormone-sensitive circuits that control motivation could open up entirely new targets for drugs to treat these kinds of disorders.