Brain Serotonin Transporter Binding in Depressed Patients With Bipolar Disorder Using Positron Emission Tomography

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Abstract
Bipolar disorder is a brain disorder characterized by recurrent manic and major depressive episodes (MDEs), the latter being clinically indistinguishable from those observed in unipolar or major depressive disorder. Bipolar disorder ranks sixth in terms of disease burden worldwide,1 yet its neurobiological underpinnings have received scant attention, and most research has focused on functional abnormalities rather than on alterations in neurotransmission.2 However, pharmacotherapy development remains focused on testing molecules that target neuroreceptors, although the pathophysiologic mechanism of bipolar disorder is likely also to involve disturbances in second messenger systems and other subcellular abnormalities.3 Furthermore, treatments for bipolar depression show remission rates only modestly better than placebo.4 As a potential aid to rational drug development and to elucidate its pathophysiologic mechanism, neurotransmission deficits present in bipolar depression require attention.