To investigate if MAO-A levels may explain the mood changes during perimenopause, his research team conducted brain scans of three groups of women using a brain imaging technique called positron emission tomography (PET).

Among the three groups of women, 19 were of reproductive age, 27 were in perimenopause, and 12 were in menopause.

On average, levels of MAO-A were 34 percent higher in women with perimenopause than in the younger women, and 16 percent higher than those in menopause, the team said.

The women in perimenopause also reported a higher tendency to cry, based on a questionnaire called the Adult Crying Inventory, and this was associated with high MAO-A levels in the front part of the brain, the prefrontal cortex, it said.

The researchers had also predicted that MAO-A levels would drop during menopause, once fluctuating levels of estrogen stabilized, and this also proved to be the case.

The results suggested new opportunities for prevention. "Using PET imaging, we can test treatments to see if they can prevent this elevation of MAO-A, and potentially prevent clinical depression," Meyer said.

One approach may be a dietary supplement, which he is currently investigating in another study of women after childbirth, to prevent post-partum depression.

Another approach may be to offer hormone replacement therapy at an earlier stage to prevent the fluctuation of estrogen levels, which is also linked to higher amounts of MAO-A, he added.