Serotonin Regulates Lactation

A new study reports that the neurotransmitter serotonin, which is produced in the brain and intestinal tract, is also produced in human mammary glands, where it controls milk production and secretion (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.0708136104).

Studies with human mammary cells and with mice show that the concentration of serotonin builds up in mammary glands as they fill with milk. The increase in serotonin inhibits further milk synthesis and secretion by suppressing expression of milk protein genes, according to Nelson D. Horseman, professor of molecular and cellular physiology at the University of Cincinnati, and colleagues. After nursing, the cycle of milk and serotonin production begins again.

The researchers note that the presence of so-called serotonin reuptake proteins in mammary cells "raises the possibility that selective serotonin reuptake inhibitors," which are used to treat depression, "could have effects on the breast or milk."

The researchers add that their findings could be used to develop new methods to enhance milk production in the dairy industry.