Question:
How strong is the evidence that people with clinical depression have lower-than-normal levels of Serotonin (or other neurotransmitters)?
Answer:
Clinical and research implications
A meta-analysis of molecular imaging studies demonstrated
significant reductions in serotonin reuptake sites (5-HTT) in the
midbrain and amygdala in depressed patients. However, due to the
unknown reliability of the studies included in the meta-analysis,
no definite clinical implications should be made from the current
evidence. In terms of research implications, the authors stated
that their results "may encourage imaging studies of the specific
role of serotonergic pathology in the striatum in the context of
geriatric depression." They also stated that larger, more
adequately powered studies are needed. The results from this
meta-analysis also demonstrated that age matching in molecular
imaging studies is critical, as even small differences in mean age
between groups effect the validity of results.