Widely prescribed antidepressants such as Prozac, Paxil and Zoloft are thought to work by altering brain levels of serotonin, a chemical messenger that helps regulate mood. But new research suggests they may also work in another way, by stimulating production of sex hormones manufactured by cells in many brain regions.

The brain effects of hormones such as estrogen, progesterone and testosterone are a hot topic in neuroscience. Researchers began exploring possible hormonal effects of antidepressants several years ago, after they learned that Prozac helped women who suffered the effects of premenstrual dysphoric disorder--severe depression, anxiety or mood swings--in the week or so before their menstrual periods. They discovered that Prozac increases the brain's production of allopregnanolone, a hormone related to progesterone. Allopregnanolone, in turn, appears to reduce anxiety in a manner similar to Valium, by modifying the effects of a chemical messenger called GABA.

Progesterone and other sex hormones are made by chemical reactions in which a molecule is modified, step by step, to produce the hormone. Each step is catalyzed by an enzyme, a chemical that helps the reaction proceed faster. In the new study, Lisa D. Griffin and Synthia H. Mellon of the University of California at San Francisco tested various antidepressants to see how they affected a critical enzyme in the chain that produces allopregnanolone. They found that Prozac (fluoxetine), Paxil (paroxetine) and Zoloft (sertraline) all made the enzyme work more efficiently, thus enhancing brain levels of the anxiety-relieving hormone. In contrast, imipramine, an older antidepressant, had no effect on the enzyme's activity.

The researchers also found that Prozac and Paxil had a similar effect on male sex hormones, enhancing the brain's manufacture of the male sex hormone androstanediol. Such hormonal changes in the brain might underlie sexual side effects--such as reduced libido or difficulty reaching orgasm--experienced by some patients on antidepressants, Mellon suggested.

On the other hand, she added, the way the drugs alter the balance of various sex hormones in the brain may be just what's required to make some people feel better.

The study appears in the Nov. 9 issue of the journal Proceedings of the National Academy of Sciences.

--Susan Okie


A significant number of children aged 7 through 12 are riding up front in cars with passenger-side air bags, putting them at added risk in the event of a crash, according to a study by researchers from the Harvard School of Public Health.

In the study, researchers looked at 503 cars and light trucks that carried at least one child under the age of 13. The vehicles were stopped at restaurants, rest stops and other points in five New England states.

Nearly a quarter of the cars with children had at least one child in the front seat. More children were observed in the front seat in cars without air bags than in cars with them--suggesting that some parents have gotten the message about the potential danger of those air bags to young children. Yet cars with children from 7 to 12 years old were three times as likely as those with younger children to have a child in the front seat. That was true even when seats were available in the back; the researchers found that 91 percent of the time when a child was sitting up front, a seat in the rear was open.

Studies by the National Highway Traffic Safety Administration and numerous press reports have warned of the danger to youngsters from the high impact when air bags suddenly inflate.

Safety experts stress that children should be moved to the rear seats of the cars with passenger-side air bags. But they have also cautioned parents to put children in the rear even in cars without these features because it is generally safer for the child. That second message has received less attention.

Eve Wittenberg, lead author of the study, said the research suggests that public safety messages about the danger of putting young children, especially babies, near air bags has influenced parents' actions. "But the older children are less likely to be seated in the rear . . . ," she said. "What's not getting across is that these older kids are also at risk."

Safety experts have found, she added, that the best position for all children is in the rear seats because it is further from the forces of a frontal crash, which is generally the most dangerous type of accident.

The study is published in this month's edition of the journal Pediatrics.

--Lexie Verdon


The U.S. death rate reached a record low last year, led by declines in mortality from AIDS and homicides, while life expectancy hit an all-time high, according to an annual statistical report released this month.

In addition, the figures indicated that a steady, decade-long decline in birth and fertility rates had been reversed.

The report from the Johns Hopkins School of Hygiene and Public Health, in Baltimore, said the death rate during 1998 was 470.8 per 100,000 population, the lowest ever recorded in the United States. Average life expectancy reached a high of 76.7 years, an increase of 0.2 percent from the previous year.

The report said the U.S. population grew by more than 1.6 million during the year, exclusive of immigration, and total live births were up by 2 percent. Birth and fertility rates per 1,000 population were also up slightly.

Infant mortality during 1998 was 7.2 for every 1,000 live births, equaling the record low of the previous year. While U.S. infant mortality has declined by more than 40 percent since 1980, it still compares unfavorably with other developed nations, said the report, published in the journal Pediatrics.