Over the past 20 years, psychotropics affecting the serotonergic system have been used extensively in the treatment of
psychiatric disorders. Molecular imaging, in particular PET, has allowed for elucidation of the essential contribution of the
serotonin transporter to the pathophysiology of various
psychiatric disorders and their treatment. We review studies that use PET to measure cerebral
serotonin transporter activity in
psychiatric disorders, focusing on
major depressive disorder and
antidepressant treatment. We also discuss opportunities and limitations in the application of this neuroimaging method in clinical practice. Although results from individual studies diverge, meta-analysis indicates a trend towards reduced
serotonin transporter availability in patients with
major depressive disorder. Inconsistencies in results might suggest symptom heterogeneity in
major depressive disorder and might therefore be relevant for stratification of patients into clinical subsets. PET has enabled the elucidation of mechanisms of response to
selective serotonin reuptake inhibitors (
SSRIs) and hence provides a basis for rational pharmacological treatment of
major depressive disorder. Such imaging studies have also suggested that the pattern of
serotonin transporter binding before treatment might predict response to
antidepressant treatment, which could potentially be clinically useful in the future. Additionally, this Review discusses PET studies investigating the
serotonin transporter in anxiety,
obsessive-compulsive disorder, and
eating disorders. Few studies have shown changes in
serotonin transporter activity in
schizophrenia and
attention deficit hyperactivity disorder. By showing the scarcity of data in these
psychiatric disorders, we highlight the potential for further investigation in this field.