[A flow cytometric postmortem brain study for major depressive disorders: implication for oligodendroglial differentiation and functions].

The neuropathology of psychiatric disorders has long been of interest in psychiatry. Several abnormalities in the prefrontal cortex have been demonstrated in major depressive disorders; however, only a small number of quantitative studies have been conducted, partly because the stereological techniques often used for such investigations are hampered by intrinsically low throughput, typically requiring long periods of time to complete. Recently, we developed a quantitative cell-counting method for frozen unfixed postmortem brains using a flow cytometer. Anisotropic frozen brain tissue was transformed into an isotropic suspension of nuclei; the numbers and fluorescent intensities of 7-AAD(+), a DNA marker, were quantified; and the nuclei were immunolabeled for the neuronal and oligodendroglial nuclear markers, NeuN and olig2, respectively. Using this method, the frontopolar and inferior temporal cortical gray matter of major depressive disorder patients, as well as that of normal controls, was analyzed. We found that the densities of 7-AAD(+) and olig2(+) nuclei in the gray matter tissue of the frontopolar cortex from major depressive disorder subjects were significantly reduced when compared to those from controls, but not in the inferior temporal cortex. Our findings suggest that the pathogenesis of major depressive disorders may involve some abnormalities in cortical myelination in the adult frontopolar cortex.