An important clue about the sex-hormone-sensitive neurons responsible for triggering a person's attraction to the opposite sex has been discovered by a new study from the from the University of North Carolina School of Medicine.

Using advanced deep brain imaging techniques and optogenetics, UNC scientists found that a small cluster of sex-hormone-sensitive neurons in the mouse hypothalamus are specialized for inducing mice to pay more attention to the opposite sex and triggering an attraction.

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This study identified a hormone-sensitive circuit in the brain that controls social motivation in female mice. It was led by Garret D. Stuber, PhD, associate professor of psychiatry and cell biology and physiology, and Jenna A. McHenry, PhD, a postdoctoral research associate in Stuber's lab.

The findings reported in Nature Neuroscience illuminate the neural roots of opposite-sex social behavior in mammals. They might also be relevant to certain psychiatric illnesses.

"These neurons essentially take sensory and hormonal signals and translate them into motivated social behavior," said Stuber, who is also a member of the UNC Neuroscience Center.

"These neural circuits that bridge social and reward processing should also provide important insights for disorders that impair social motivation," said McHenry, first author of the paper.

In the study, Stuber and colleagues examined the medial preoptic area (mPOA) of the brain. This clump of neurons sits within the hypothalamus, an evolutionarily ancient structure at the bottom-center of the brain.

Prior research showed that the mPOA is important for social and reproductive behavior in all vertebrate species studied from fish to human. But it's been unclear whether this area drives social motivation through circuit connections with reward systems in the brain.

Researchers focused on one of the mPOA's major connections through which it sends neural signals to another brain structure called the ventral tegmental area (VTA), which is known to be a powerful contributor in motivating behavior and the release of the neurotransmitter dopamine.

"On the whole, the data suggest that these mPOA neurons help drive social attraction toward a potential mate," said Stuber.

Stuber's team plans to follow up by applying similar imaging and optogenetics methods to the workings of the VTA neurons downstream from the mPOA.

Aside from its basic neuroscience impact, the research has implications for anxiety, depression and related disorders, which can be triggered or worsened in some women by shifts in hormone levels.

"While hormone-related changes in motivation are important for mating or maternal behavior in female mice, some atypical hormonal changes in women appear to underlie reproductive mood disorders, such as postpartum depression," said McHenry, who is also a Fellow on the Postdoctoral Reproductive Mood Disorders Training Fellowship at UNC.

Tagssex-hormone-sensitive neurons, University of North Carolina School of MedicineUniversity of North Carolina School of Medicine, Garret D. Stuber, Jenna A. McHenry, neurons, medial preoptic area, hypothalamus, mPOA, ventral tegmental area, optogenetics