Male mice not as sex obsessed as you might expect

In a somewhat interesting article, it seems that they have identified a, shall we say,  one stop "horny centre" in the brains of male mice:

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 recognize the sex of another mouse—"Aha, this is a female, maybe I can mate if she's willing," Shah said. 

More details:

For their 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 would not have been shaped by social influences. 

Well, as long as there is no risk that lack of knowledge of female mice doesn't encourage mice to try mounting other males, I suppose?   To continue:

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 could turn on 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 specific signals came from a part of the amygdala called the bed nucleus of the stria terminalis, or BNST.

"We had no reason to believe that this POA region would not only control the act of mating, but also regulate the desire to mate or regulate the pleasurable feelings elicited by mating," Shah said.

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

There is more detail in the article (including speculation that humans might have a similar centre, but apparently it hasn't been investigated much).   But the most amusing bit about the study is this:

In this new 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 another small set of neurons in the POA that carried receptors for Substance P, essentially forming a connection with the BNST neurons.

The POA neurons ramped up their activity when stimulated by the Substance P-secreting BNST neurons. And about 10 to 15 minutes after that happened, male mice would go through their full sequence of mating behavior—mounting, penetration and ejaculation. 

I'm starting to feel sorry for the mice now:

Directly infusing the peptide to the POA accelerated mating behavior; in 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. 

Any guess what the refractory period for your average male mouse is?:

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

"It took one second or less for them to resume sexual activity," Shah said in a news release. "That's a more than 400,000-fold reduction in the refractory period."

Well, give the reputation of mice to reproduce at fantastic rate, I'm surprised that the males take five whole days to get interested in sex again.  

The article does not the obvious thought:  if there is anything like the same system in adult men, and a way to deliver Substance P to the right spot in the brain, it sounds like it'll make Viagra seem a relatively primate attempt at enhancing performance...