High affinity [3H]imipramine and [3H]paroxetine binding sites in suicide brains

Specific binding of [3H]imipramine and [3H]paroxetine was simultaneously examined in human brains (frontal cortex, temporal cortex, cingulate cortex, hypothalamus, hippocampus and amygdala) from 11 controls and 11 depressed suicide victims. A single saturable high affinity site was obtained for both radioligands. Age was not related to significant changes in [3H]imipramine and [3H]paroxetine binding parameters, which indicates the stability of the brain serotonergic system with increasing age. A major finding of the present study concerns the existence of a significant decrease in the maximum number (Bmax) of [3H]imipramine binding sites in hippocampus from depressed suicides as compared with the control group, without changes in the binding affinity (Kd). In contrast, when [3H]paroxetine was used as radioligand, no changes in either Bmax or Kd were detected in any of the brain regions studied. These findings suggest that [3H]imipramine may be a better marker than [3H]paroxetine when alterations in the presynaptic serotonergic uptake site are to be detected.