Through the use of state-of-the-art brain imaging techniques and optogenetics, a team of researchers from the University of North Carolina School of Medicine was able to pinpoint a special kind of neurons responsible for triggering social attraction towards the opposite sex in mice.
The Medial Preoptic Area
Lead researchers Garret D. Stuber, PhD, and Jenna A. McHenry, PhD, discovered a hormone-sensitive circuit in the brain that regulates social attraction in female mice.
The scientists looked into the medial preoptic area (mPOA) of the brain, which earlier scientific works have associated to social and reproductive patterns in all vertebrate species, from fish to human.
They focused on one of its major pathways, the ventral tegmental area (VTA), which the mPOA use to transmit messages to other parts of the brain. VTA is also known to stimulate the release of dopamine, a neurotransmitter in the brain that helps control reward and pleasure receptors.
"These neurons essentially take sensory and hormonal signals and translate them into motivated social behavior," Stuber explained.
Male Attraction For Female Mice
Interestingly, the researchers also discovered that a huge group of the mPOA neurotensin neurons displayed greater activity when the female mice smelled the urine of a male mouse.
However, it did not have the same effect when the female mice were shown urine of another female mouse urine or enticing odors, like food. The activity of mPOA neurotensin neurons was more intense in female mice that had high estrogen levels or a mixture of estrogen and progesterone, which shoots up before they become fertile.
McHenry believes that their findings, which was published in the journal Nature Neuroscience, could only mean that some neurons in the brain are designed to favor social rewards as opposed to nonsocial rewards.
How Hormone Changes Affect Depression
McHenry, who is also a Fellow on the Postdoctoral Reproductive Mood Disorders Training Fellowship at UNC, suggested that their study can also provide valuable insights on the treatment of specific mental health disorders, such as anxiety, depression, and obsessive-compulsive disorder.
Anxiety disorders, the most common mental illness in the United States, affect at least 40 million adults — or 18 percent of the population.
She noted that these conditions may be worsened in the female population when hormone levels suddenly shift, just like what happens in postpartum depression.
According to the American Psychological Association, up to one in seven women experience postpartum depression. Aside from family history, previous diagnosis of depression or anxiety, and other stress-related factors, one of the most common risk factors for postpartum depression include the sudden change in a woman's hormone levels after childbirth.