FRIDAY, Aug. 11, 2023 (HealthDay News) — A single hardwired brain circuit is likely to be accountable for male sexual drive, a brand new mouse study reports.

Researchers have singled out in lab mice a brain region that controls sexual interest, libido, mating behavior and pleasure, said senior researcher Dr. Nirao Shah, a professor of psychiatry and neurobiology at Stanford University School of Medicine, in California.

This region uses sensory input from the environment to acknowledge the sex of one other mouse — “Aha, it is a female, perhaps I can mate if she’s willing,” Shah said.

“That recognition is then transformed into the need to mate and the act of mating by this circuit,” he added. “Also, the circuit enables the behavior to be pleasurable so animals will seek to do it again, which may be very necessary, because for a species to survive, animals need to breed.”

While this study was in mice, Shah said similar brain structures have been present in other mammals — and even perhaps humans.

“There are analogous anatomical counterparts we predict within the human brain, but after all their function within the human brain stays to be determined,” he noted.

For his or her experiments, Shah’s team used adult virgin male mice that had not seen a female mouse after being weaned at about 3 weeks of age. That way, the brain activity and behavior they observed wouldn’t have been shaped by social influences.

The researchers meticulously mapped the brain cells and connections that compose this particular circuit, called the preoptic area of the hypothalamus (POA).

Earlier work by the research team had found they might activate and off male mice’s recognition of an unfamiliar female mouse by manipulating neurons that communicate to the POA from the amygdala, which is the seat of human emotion.

The particular signals got here from an element of the amygdala called the bed nucleus of the stria terminalis, or BNST.

“We had no reason to imagine that this POA region wouldn’t only control the act of mating, but additionally regulate the need to mate or regulate the pleasurable feelings elicited by mating,” Shah said.

“In principle, those three elements of sexual behavior — the act of mating, the physical act itself, the urge to mate and the pleasure that accompanies it — those might be embodied in numerous brain regions,” he added. “But what we found is that the POA has these attributes.”

On this latest study, the researchers zeroed in on a small set of genetically distinct BNST neurons that secrete a slow-acting signaling protein, or peptide, called Substance P.

The scientists also found one other small set of neurons within the POA that carried receptors for Substance P, essentially forming a reference to the BNST neurons.

The POA neurons ramped up their activity when stimulated by the Substance P-secreting BNST neurons. And about 10 to quarter-hour after that happened, male mice would undergo their full sequence of mating behavior — mounting, penetration and ejaculation.

Substance P sensitizes the POA neurons so that they turn out to be increasingly lively, the researchers concluded.

Directly infusing the peptide to the POA accelerated mating behavior; in actual fact, direct activation of the circuit even led to mating with inanimate objects, the findings showed.

Stimulation of the POA also cut short the mice’s refractory period, or the stretch of recovery time required before full sexual drive and capability is restored after ejaculation.

For the mice utilized in this study, the conventional refractory period is five days. But directly stimulating the POA with Substance P prompted male mice that had just ejaculated to right away repeat their sexual mating routine.

“It took one second or less for them to resume sexual intercourse,” Shah said in a news release. “That’s a greater than 400,000-fold reduction within the refractory period.”

Then again, blocking the POA completely eliminated the mating urge in male mice, Shah said.

“After we switch off the middle, the POA within the male mouse, he simply stops mating,” Shah said. “Even when he has a willing female in his cage. Even when there’s no danger. Even when there’s ample food. He just stops mating.”

There appear to be no other effects researchers can see, he said.

“He walks about normally. There’s no problems in other behaviors like aggression. He’ll still fight with males, because they’re competitors. He simply doesn’t mate,” Shah said.

Further, Substance P receptor-containing neurons within the POA hook up with two downstream brain centers which are known to be critical to voluntary movement and experiencing or anticipating pleasure.

“Importantly, similar structures exist in creatures less complex than mice comparable to birds, that usually are not even mammals,” Shah said.

“In monkeys, studies done some years ago showed that switching on certainly one of the centers that we worked on within the mouse actually does elicit male mating behavior, suggesting a functional correspondence between the mouse and the monkey counterpart within the brain,” he added.

“So there appears to be anatomical correspondences between birds, mice, monkeys, humans and these brain regions, and there appears to be functional correspondence as well between mice and monkeys,” Shah said.

The findings may lead to drugs that tamp down the sex circuitry within the brains of men with hyperactive sex drives. Alternatively, latest treatments might boost sex drive in men who are suffering from an absence of desire.

“If these centers exist in humans — and now we all know where to look — it needs to be possible to design small molecules that will be used to manage these circuits,” Shah said

“But whether this is possible is unknown because first we would wish to discover these centers within the human brain and, furthermore, regulating libido is enormously complex in humans with a lot of social, political, ethical and other considerations that have to be addressed prior to enthusiastic about any such approach,” he added.

A sex-stimulating drug geared toward the human equivalent of the POA would act very otherwise than erectile dysfunction drugs like Viagra, Shah said.

As an alternative of stimulating blood flow within the small blood vessels, such drugs would directly act upon the particular brain area that controls the male libido, he explained.

Shah’s group can be trying to seek out equivalent brain circuits in females.

The brand new study was published online Aug. 11 within the journal Cell.

More information

The Cleveland Clinic has more concerning the sexual response cycle.

SOURCES: Nirao Shah, MBBS, PhD, professor, psychiatry and neurobiology, Stanford University School of Medicine, Palo Alto, Calif.; Cell, Aug. 11, 2023, online