There's an old joke in the gay community: What does a lesbian bring on the second date? A U-Haul. What does a gay guy bring? A friend.

Gay women, according to the stereotype, are all too ready to move from fiery romance to feathering the nest. And what follows is Lesbian Bed Death, a warm, cuddly, committed but asexual relationship.

Of course, this is a stereotype. Throngs of old-married lesbians have sizzling sex lives, while scads of gay men enjoy monogamous relationships that Ward Cleaver would envy. Still, there is some neurochemical truth to this joke.

Certainly, gay men and lesbian women love and bond the same way as straight people do: During sex and orgasm, their brains produce spurts of oxytocin and exciting rushes of dopamine. Oxytocin is the neurochemical of generosity, trust and social memory. The interaction of oxytocin and dopamine in the brain's reward system ties the pleasure of sex to that particular partner, creating the bond we call love.

In gay love, however, the lovers' systems are more alike than those of a heterosexual pair. Most important, estrogen enhances the bonding effects of oxytocin, while testosterone mutes them. While the effects of orgasm's oxytocin surge may last for hours in a woman's body, they may clear from a man's body in just a half hour.

When two women have sex, the oxytocin surge can induce cuddling that lasts for days. Two male lovers, under the heavier influence of testosterone, may quickly feel ready to move on physically and emotionally after love-making.

In addition to the match in brain chemistry in same-sex couples, there's evidence that one partner -- gay or straight -- can absorb the other's sex and bonding chemicals; in a same-sex couple, this could heap on an extra helping of estrogen or testosterone.

Most mammals have a special area in the nose called the vomeronasal organ. This sensitive tissue, located in the nasal passages, sends molecules that the animal inhales directly to the brain, where they can influence behavior. This organ reacts to pheromones, the chemical signaling substances put out by animals from insects to apes. It's the organ that draws a female elephant to the musth secreted by a bull in his prime.

Human fetuses have a vomeronasal organ, and for a long time biologists thought that it was a vestigial structure that disappeared by birth. But recently, researchers have found evidence that the human response to pheromones is alive and well in adults. This is the organ that seems to be responsible, for example, for the tendency of women living together to synchronize their menstrual cycles. More sex and bonding chemicals may be exchanged via lovers' sweat and saliva, according to preliminary research by Cameron Muir of Brock University. How we react to the chemicals coming off another person's skin seems to be related to our sexual orientation. These studies certainly do not prove anything about neural differences in gays and straights, but they make it clear that people of all sexual flavors do react to the neurochemicals they swap when they kanoodle.

This effect in a gay couple may reinforce their neurochemical states. With every nuzzle, taste and touch, a same-sex pair creates a neurochemical feedback loop that reinforces the tendencies of their sex.

When two women engage in intimate behavior, from hanging out with a friend to wild love-making, it's likely that, with every breath, they take in molecules of estrogen and oxytocin emitted by the other's body -- as well as the testosterone women produce. Two men enjoying the same behaviors likely inhale each other's testosterone and oxytocin -- along with some estrogen, which is part of the male hormonal mix. Overall, two women may experience more oxytocin in their relationship than a man and a woman; two men may experience less.

It's crucial to note here that the wide range of temperaments and tendencies in men and women certainly extends to gays and lesbians. Men gay and straight may find it extremely easy to bond, while women of all sexual persuasions run the gamut from runaround to stay-at-home. All of us, gay and straight, bond the same way. And every relationship is bathed in a unique neurochemical soup.

But be aware that the neurochemistry of a lesbian love may nudge the relationship further toward the sedate. You can counteract this tendency by building some -- safe -- danger into your life. An adrenaline rush counters that oxytocin calm nicely. So, if you feel your relationship becoming a little too comfortable, grab some chocolate and wine and head for an exciting getaway. It's never too late.

References:

Smith, Timothy D. and Bhatnagar, Kunwar P., The human vomeronasal organ. Part II: prenatal development Journal of Anatomy (2000), 197: 421-436

Holland, Giles, Hot Sweaty Sex: Investigating the ins and outs of human chemical communication (Research Reporter No. 27, March 2006

Savic, Ivanka; Berglund, Hans;and Lindström, Per, Brain response to putative pheromones in homosexual men (Neuroscience May 9, 2005, 10.1073/PNAS.0407998102

Berglund, Hans; Lindström, Per; and Savic, Ivanka, Brain response to putative pheromones in lesbian women (Proceedings of the National Academy of Sciences, May 23, 2006, Vol. 103, No. 21, pp. 8269–8274

Wysocki, Charles, Gender and Sexual Orientation Influence Preference for Human Body Odors, Monell Chemical Senses Center press release, May 9 2005

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