Scientists have found a potential way to control lust in men

These findings could further lead to the development of medicines that can adjust a person's sex drive. For instance, such drugs could either be used to reduce excessive sexual urges in men with hyperactive sex drives or boost libido in men who lack interest in sex.

Shah claims, “Such drugs would be quite different from today’s phosphodiesterase inhibitors which counter erectile dysfunction. Instead of generally enhancing blood flow in small vasculature throughout the body, they would directly amplify or tamp down a specific brain area that controls male sexual desire.”

So, which part of the brain controls libido in mice

During their study, Shah and his team mapped different neuronal circuits that make up the mice's brain (or any mammal's brain). 

They selected three to four-week-old male mice who had never seen a female except their mothers and studied how the various neuronal circuits in these mice affected the functioning of their different brain cells.

From their previous research work, Shah and his team realized that a male mouse turns on and off when a group of genetically distinct neurons found in its brain's amygdala, called the BNST (bed nucleus of the stria terminalis), interact with another brain area called the preoptic hypothalamus.

In the current study, they examined a specific group of BNST neurons that secrete a slow-acting protein called Substance P. They discovered that these neurons interact with another small group of neurons in the preoptic hypothalamus that have receptors for Substance P.

When the researchers stimulated the tract comprising Substance P-secreting BNST neurons in their mice subjects, it activated neurons in the mice’s preoptic hypothalamus with Substance P receptors. This increased activity lasted for 90 seconds and, after 10 to 15 minutes, resulted in a series of male mating behaviors, including mounting, penetration, and ejaculation.

The researchers found that mice experience sexual urges and engage in mating behavior when Substance P from their BNST neurons binds with receptors in their preoptic hypothalamus. 

They further suggest that a mouse’s sex drive can be suddenly increased by injecting Substance P in the area near its receptors. Moreover, direct activation of neurons containing the Substance P receptors could result in mice mating with non-living objects. 

Sexual behavior can be manipulated

After ejaculation, nearly all male mammals can’t immediately engage in more mating behavior. They need some time to fully regain their sexual desire before they can ejaculate again. This resting time is called the refractory period. 

Surprisingly, the current study suggests that by manipulating neurons that contain Substance P and Substance P receptors, they can not only increase or decrease the libido but can also reduce the refractory period to less than a second in mice.   

For instance, the mice used in the study had a refractive period of five days. However, when the scientists directly activated the receptor neuron in their preoptic hypothalamus region, the mice were able to mate and ejaculate without needing rest.

“It took one second or less for them to resume sexual activity. That’s a more than 400,000-fold reduction in the refractory period. In contrast, “if you silence just this set of preoptic hypothalamus neurons, the males don’t mate,” Shah said.

“It’s very likely there are similar sets of neurons in the human hypothalamus that regulate sexual reward, behavior, and gratification, and they’re probably quite similar to the ones we’ve observed in mice,” he added. 

Therefore, it is quite possible that drugs targeting these neurons could help doctors regulate sexual behavior in men having libido-linked disorders.

The study is published in the journal Cell. 

Study Abstract:

Male sexual behavior is innate and rewarding. Despite its centrality to reproduction, a molecularly specified neural circuit governing innate male sexual behavior and reward remains to be characterized. We have discovered a developmentally wired neural circuit necessary and sufficient for male mating. This circuit connects chemosensory input to BNSTprTac1 neurons, which innervate POATacr1 neurons that project to centers regulating motor output and reward. Epistasis studies demonstrate that BNSTprTac1 neurons are upstream of POATacr1 neurons, and BNSTprTac1-released substance P following mate recognition potentiates activation of POATacr1 neurons through Tacr1 to initiate mating. Experimental activation of POATacr1 neurons triggers mating, even in sexually satiated males, and it is rewarding, eliciting dopamine release and self-stimulation of these cells. Together, we have uncovered a neural circuit that governs the key aspects of innate male sexual behavior: motor displays, drive, and reward.