Reduced tyrosine hydroxylase immunoreactivity in locus coeruleus of suicide victims

Antibodies against tyrosine hydroxylase (TH, the rate-limiting enzyme in norepinephrine synthesis) and dopamine beta-hydroxylase (DBH, the last enzyme in the synthesis) were used for immunohistochemical staining of human brain locus coeruleus sections, obtained postmortem from suicide victims and matched controls. Stain density over individual cells was quantified by a computerized, video-camera-based image analysis system. Mean stain density for TH was significantly lower (by about 30%) in the locus coeruleus of suicide victims. There was no difference between suicides and controls in DBH immunoreactivity or in the number of TH immunoreactive cells. Reduced TH availability, either genetically or environmentally determined, may contribute to the noradrenergic insufficiency postulated to occur in depression and the increased beta-adrenergic receptor concentrations observed in prefrontal cortex of suicide victims.