Q. My mother seems more prone to depression than my father. Do you know of research on depression rates by gender?

A. A study reported in the proceedings of the National Academy of Sciences may help to explain depression rates that differ by gender. Using Positron Emission Tomography, researchers at the Montreal Neurological Institute found that, while men and women normally have similar levels of serotonin in the brain, the male brain is able to produce the neurotransmitter faster.

Women’s slower serotonin production may make them more vulnerable to crashes in serotonin levels. (Earlier research has linked depression with low levels of serotonin.) The researchers also compared serotonin levels between men and women when given a laboratory test that mimicked stress, The stress test had four times more impact on serotonin levels in the female brains.