Localized decrease in serotonin transporter-immunoreactive axons in the prefrontal cortex of depressed subjects...

A variety of postmortem brain studies and clinical investigations have provided evidence that reduced serotonin neurotransmission is associated with suicidal behavior and depression, and several serotonergic parameters have been found to be altered in the prefrontal cortex of suicide victims. However, the integrity of the serotonin innervation of the prefrontal cortex in mood disorders has not been directly investigated. The present study used immunocytochemical methods and an antibody against the serotonin transporter to examine the relative density of serotonin axons in the dorsolateral prefrontal cortex of suicide victims with a diagnosis of major depression. The mean total length of serotonin transporter-immunoreactive axons per unit area was unchanged in layers 2 and 4 of area 46 in the depressed suicide subjects compared to controls, but was significantly (P < 0.01) decreased by 24% in layer 6 in the depressed suicide group. The total length of serotonin transporter-positive axons in layer 6 was reduced in eight of the 12 depressed suicide subjects compared to their matched control subjects. These findings reveal that depressed subjects who have committed suicide exhibit a lamina-specific reduction in a marker of serotonin axons in the dorsolateral prefrontal cortex that may reflect an alteration in cortical serotonin neurotransmission.