Keeping abreast of serotonin's roles.

Biologists studying mice have unexpectedly found that the well-known brain chemical serotonin also controls the secretion of milk within mammary glands.

Serotonin is one molecule that nerve cells use to communicate with each other. The drug fluoxetine, or Prozac, and related antidepressants appear to work by influencing serotonin chemistry in the brain.

Nelson Horseman of the University of Cincinnati and his colleagues stumbled upon serotonin's mammary role while looking for genes activated by the hormone prolactin as it stimulates milk production. Some of the triggered genes encode the enzymes needed to synthesize serotonin, the researchers report in the February Developmental Cell. The scientists also detected serotonin in mammary tissue and breast milk.

Experiments by Horseman's team indicate that serotonin offers a feedback signal that shuts down milk production once the mammary glands are full. The researchers speculate that drugs affecting serotonin chemistry, such as Prozac, might disturb milk production or alter the quality of the milk.--J.T.