It's been a long winter in northern Utah, and not just because we had that extra day in February.

We've had what you might call the Lawn Effect: so many days where our front yards were covered in snow that we've become extra antsy for spring to arrive.

At Highland High School in Salt Lake City, the students in Room D-201 have been wistfully staring out the window since late February, says biology and zoology teacher Doug Jorgensen. Perhaps because of all those days of gray skies, he says, cabin fever started earlier this year. The forecast this week is for yet more clouds, maybe even more snow.

But spring, technically, is only nine days away. The amount of daylight will be equal to the amount of darkness — and that means that, theoretically, there will now be enough sunlight to fire up your pro-opiomelanocortin gene. Pretty soon you'll be falling in love and/or wanting to sit outside when you should be inside typing something.

Not a very romantic word, pro-opiomelanocortin. Pretty hard to rhyme in a love poem. Still, when you deconstruct spring fever and that whole "when a young man's fancy" thing, it's all about brain chemicals, says University of Utah biology professor Erik Jorgensen.

The pro-opiomelanocortin gene, known more familiarly as POMC and pronounced pom-see, is activated by exposure to sunlight as the days get longer. That activation readjusts the body's chemistry, making a number of peptide hormones, including Melanocyte-stimulating hormone (MSH) and beta endorphin. When released in the brain, MSH stimulates sexual arousal and beta endorphin creates a sense of euphoria.

So, says Jorgensen, "essentially when spring arrives, everyone is on drugs."

Some people might think spring fever requires warm temperatures, but according to Jorgensen that's not technically the case. He concedes, though, that "warmth probably contributes to the whole response, since people tend to wear fewer clothes in warm weather, which has a ripple effect in the rest of the population."

Jorgensen, who is scientific director of the U.'s Brain Institute, says he was once witness to "one of the most vigorous spring fevers recorded in the U.S." After weeks and weeks of cloudy days, he recalls, when the sun finally came out in Seattle one June, "people went berserk."

"People were cavorting in the parks, throwing Frisbees for their dogs, making love on the lawns, and ecstatically smiling with their arms in the air like it was 1967 again. It was mass hysteria."

Back over at Highland High, Doug Jorgensen knows how spring fever makes his students "wander," both mentally and physically. That's one reason, in spring, he takes them on trips to Sugarhouse Park, where they study how the trees are coming out of their dormancy and the birds are behaving in the pond.

Speaking of which, spring has a knack for affecting everybody, from people to rodents. Research done by former University of Utah biology professor Norman Negus in the 1980s showed that a chemical in new shoots of grass, munched in early spring by lemmings and voles in the Arctic, affects their reproductive hormones. The result was earlier maturation and larger litters.

"Evolution has come up with a lot of interesting mechanisms to be sure that females get pregnant during the plentiful times," notes the U.'s Erik Jorgensen. "The Frisbee on a sunny day is just one of many."

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E-mail: jarvik@desnews.com