WASHINGTON: What is desire? What triggers it? Some think oysters, and chocolate-among other mythical things-are aphrodisiacs. They are rich in nutrients and give energy, but no one has proven they give you passion.

Even the "little blue pill" Viagra just works on, shall we say, the plumbing-it keeps the blood flowing in the right direction.

Now there's a drug in the pipeline that its makers say really will restore lost libido. It's being tested and developed, in part, in a laboratory at Concordia University in Montreal by neuroscientist Jim Pfaus.

Professor and part-time punk rocker, Pfaus is using rats to test id the new substance, bremelanotide triggers desire.

Rats stand in for humans, because, like people, they're social and they have a similar hypothalamus, the part of the brain that controls desire.

Pfaus says he's finding that bremelanotide seems to put rats in the mood. Given the peptide, female rats, he says, initiate sex four times more often than those who do not receive it.

And bremelanotide's makers are betting it will work the same way on both men and women. "It brings back your libido,"Pfaus said. "It doesn't make it something that it wasn't. It brings it back to where it probably was when you were having good sex."

Carl Spana, chief executive officer of Palatin Tech, which holds the patent on bremelanotide, said it activates parts of the brain that are involved in regulating sexual function.

He says other products on the market, such as Viagra, Cialis and Levitra, "work by affecting peripheral blood flow, rather than the nervous system."

Palatin Technologies hopes to have bremelanotide on the market for men within a couple of years-and for women shortly after that.

Bremelanotide didn't start out as a drug for sexual dysfunction. In fact, it was being developed as a tanning enhancer.

"All treatments for sexual dysfunction, especially erectile dysfunction, have colorful stories about how they started,"said Spana in a statement on Saturday.