Elevated platelet vesicular monoamine transporter density in untreated patients diagnosed with major depression

The intraneuronal uptake of monoamines into brain synaptic vesicles is mediated by the vesicular monoamine transporter (VMAT2). This transporter plays a major role in monoamine storage and quantal release. Recently we demonstrated a high degree of similarity between the pharmacodynamic characteristics of platelet and brain VMAT2. In the present study we measured the VMAT2 density, using [³H]dihydrotetrabenazine ([³H]TBZOH) as a ligand, in platelets of untreated patients diagnosed with major depressive disorder (MDD) (n=10; three with recurrent depression and seven with first episode depression) compared to sex- and age-matched healthy control subjects (n=23). A significant elevation in the VMAT2 density (B_max) was observed in the platelets of untreated MDD patients (+24%) compared to healthy control subjects. No significant change was found in the affinity constant (K_d). The increased platelet VMAT2 density may reflect depression-related enhancement of the capacity to accumulate monoamines in the vesicles in the presence of lower monoamine turnover.