A higher flow of dopamine

Feb 5, 2007 12:19 GMT  ·  By

Easy lovers can understand why they are not motivated for a long relationship or why their partners aren’t either.

But if studies on humans could seem somehow biased, the fact seems to be true also for animals. Animal sex has been regarded for a long time as following this pattern: the male wants above all else to ejaculate quickly, and once he has done its “job” with one female, he is eager to seed new partners. The female, meanwhile, wants to extend the sex encounter through "pacing".

A recent research on rats has discovered that if pacing is slow enough, the male will prefer to mate only with the familiar female, rejecting new partners. It was found that the more waited for the female is, the more attractive she is. "It's an awful lot like what we were taught in high school," says Concordia University psychologist James Pfaus.

The experiment used newly developed pacing chambers, cages with dividers possessing either one or four holes large enough to let a female rat through but too tiny for the larger male. The female could join or leave the male, being able to significantly prolong her arousal and her chance of pregnancy, as proven by previous studies. But the mating rituals lasted more in the one-hole chambers, as the eager males stick their big heads in the hole, blocking the passage and delaying her return.

When the researchers reunited each couple, along with a new female, in a larger cage, half of the males from four-hole chambers preferred their familiar mates, but for males in the one-hole chamber the percentage was 80 %.

The researchers believe there must be some neurochemical reward behind this behavior. "Sexual preferences come from chemical rewards, and we can be sure there are some here", said Boston University biologist Mary Erskine.

During the sexual peak, the brain expels dopamines (pleasure-producing hormones). The researchers believe that the higher level of excitement provoked by the longer wait triggers a higher release and a more substantial reward. "Whether it's simply a stronger dose of the usual chemical rewards or some in addition, we don't know," Pfaus says. "But something is making this sort of mating more rewarding to the male or rewarding in a different way."