When are females most open to sex? A female in heat, as any unspayed dog owner will tell you, indiscriminately encourages every male she encounters... but how exactly does that translate into hormonal activity within the brain? A new animal study has identified an exact group of oxytocin-receptive brain cells located within the cerebral cortex that perform a very specific job — regulating sexual desire while a female is in heat. In fact, the researchers believe this circuit of cells may be key to many social behaviors inspired by oxytocin, the so-called love hormone.

Oxytocin, a hormone which functions as a neurotransmitter in the brain, plays an important role in social behaviors. The hormone increases trust, generosity, and even your ability to identify the emotion appearing on other people's faces. Neuroscientists know that oxytocin-responsive neurons can be found in many brain regions, which suggests the hormone is important to a wide variety of social behaviors. However, they do not understand which cells are targeted by oxytocin, or how exactly the hormone affects whole circuits or systems of brain cells.

For the current study, the researchers, led by Dr. Nathaniel Heintz of the Rockefeller University, began with their discovery of a population of neurons in the medial prefrontal cortex; they observed how these brain cells expressed an oxytocin receptor. From there, the researchers designed an experiment using mice. The researchers began by disrupting the activity of these oxytocin-receptive brain cells — silencing the neurons — in male mice, and saw how their social behavior remained unchanged.

Next, the researchers silenced the same neurons in female mice who were in heat. Surprisingly, the female mice lost all interest in male mice and invested about the same amount of time with the boys as they spent with a plastic Lego block. At the same time, these females retained a normal level of social interest in other females. However, when the researchers silenced the brain cells of females who were no longer in heat, the female mice acted in their usual manner.

Taken together, the findings show that these oxytocin-responsive neurons in the medial prefrontal cortex regulate one crucial aspect of female behavior: their desire to mate. Yet, the researchers believe this system of brain cells is not limited to one role and may come into play during other social behaviors. "Our findings suggest that social interactions that stimulate oxytocin production will recruit this newly identified circuit to help coordinate the complex behavioral responses elicited by changing social situations in all mammals, including humans," Heintz said. Going forward, Heintz and his co-authors plan to investigate how this circuit is activated in humans with the hope of gaining insights into autism spectrum disorder and other social behavioral disorders.

Source: Nakajima M, Gorlich A, Heintz N. Oxytocin modulates female sociosexual behavior through a specific class of prefrontal cortical interneurons. Cell. 2014.