Aggression genes in men and rhesus monkeys, testosterone rises in female soccer players and male hockey players with a home ice advantage, and a "love hormone" that might take the edge off of marital spats were some of the topics discussed yesterday at an international conference.

The sixth International Congress of Neuroendocrinology, organized by the International Neuroendocrine Federation, opened Monday at the David L. Lawrence Convention Center, Downtown. According to federation President John A. Russell, more than 800 scientists from 29 countries will be attending the event, which happens every four years and will end tomorrow.

At a press briefing, Stephen Manuck, a psychology professor at the University of Pittsburgh, said men who had a low-activity variation of a gene called monoamine oxidase-A, or MAOA, which breaks down the neurotransmitter serotonin, were more likely to be aggressive than those who carried another version of the gene, but only if they were maltreated as children.

In his study of 531 American men of European ancestry, those with the MAOA gene were more likely to fight, get into conflicts with authority or break things when angry if they lacked affection from their parents in childhood or their fathers had less than a high school education.

About a third of Caucasians of European descent carry the MAOA variant, Dr. Manuck said.

The findings were similar for a variation in another gene called the serotonin 2A receptor, where childhood physical abuse was also a factor in later aggressive behaviors, he added.

A study of rhesus monkeys echoed the Pitt findings. Animals that carried gene variants that altered serotonin metabolism were more impulsive and aggressive, "but only if they have a history of early neglect and abuse," said Stephen Suomi, chief of the comparative ethology lab at the National Institute of Child Health and Development.

"We view this as a buffering effect of good mothering," he said. "Good mothering can be protective."

Daughters copied their mother's parenting techniques when they had their own offspring.

Rhesus monkeys and humans are "an evolutionary success story," Dr. Suomi said, because "unlike virtually all other primate species, [they] can live just about anyplace."

Curiously, he added, they both have variants for MAOA, serotonin transporter and other genes, suggesting that the secret to success is not genetic specialization but genetic variability.

In other projects, Justin Carre, a doctoral student at Brock University in St. Catharines, Ontario, tracked hormones in young hockey players to see the impact of home-rink advantage. In general, testosterone levels rose more after wins than losses, and levels before home games were even higher, he said.

But along with self-confidence, levels of cortisol, a stress hormone, also went up at home, which may be due to the pressure of performing in front of friends and family in the stands, Mr. Carre said.

Similarly, Rui Oliveira, an associate professor at the Institute of Applied Psychology in Lisbon, Portugal, found that women soccer players produced more testosterone before a soccer match, which has also been found among male players. Testosterone stayed high among the women who won the match, but dropped in those who lost.

Researchers from Emory University, the University of Fribourg and the University of Zurich asked 50 couples to argue after half of them took an intranasal spray of the hormone oxytocin. The others got a placebo.

Those that got the hormone had much lower levels of cortisol, although they didn't report feeling any different, said Beate Ditzen, of Emory.