Brain Chemical Involved In Strokes Also Linked To Aggression In Mice

November 24, 1995|By New York Times News Service.

A brain chemical already infamous for its role in human strokes also holds sway over aggressive and sexual behavior, at least in male mice, scientists have reported.

Researchers at Johns Hopkins University in Baltimore have found that male mice specifically bred to lack a gene essential for the production of nitric oxide, a molecule that allows nerve cells to communicate, are relentlessly aggressive against their fellow males, often to the point of killing them.

The altered mice also pursue females monomaniacally, mounting them repeatedly even when the females are not in heat.

Dr. Solomon Snyder and his colleagues propose that nitric oxide may normally serve as a brake on excessive and potentially dangerous behaviors, and that a lack of the chemical leads to wild, impulsive activity. They suggest the findings may have implications for understanding some forms of human aggression, although they emphasize that studies to support such a claim remain to be done.

"This work certainly doesn't mean that the major or even any significant proportion of violent criminal behavior is due to abnormalities in nitric oxide," Snyder said. Nevertheless, he added, he has been impressed by how often "mouse behavior can predict human behavior."

The new report, which appeared Thursday in the journal Nature, is expected to stir the debate surrounding the contribution of genes to aggressive and criminal conduct.

Other researchers familiar with the latest work say that while the studies are well done and the findings provocative, they are disturbed by the haste with which the scientists extrapolate from rodents to humans.

"It's the first demonstration that nitric oxide has some effect on behavior, and it's valuable for that reason," said Evan Balaban of the Neurosciences Institute in San Diego. "But I'm disturbed by the extension of the claims to human beings."

The last paragraph of the paper, for example, says that nitric oxide "may be a major mediator of sexual and aggressive behavior, relevant for studies of their biological determination in humans as well as mice."

Dr. Joseph Coyle, chairman of the department of psychiatry at Harvard Medical School in Boston said, "The results are quite interesting, but we have to be very cautious about what this means in terms of human behavior."

Nitric oxide is a gaseous compound that scientists only recently have discovered can act in the human brain as a neurotransmitter, a chemical that transmits signals between nerve cells.

Scientists have also learned that during a stroke, the brain releases massive quantities of nitric oxide, which greatly increases damage to the neural tissue.

Animal experiments indicate that by blocking nitric oxide synthase, the enzyme responsible for making the gas, the incidence of stroke can be reduced by 70 percent.

The pharmaceutical industry is now seeking drugs that could safely impede the enzyme in humans and thus either prevent strokes or at least limit their severity.