Chromogranin A and vesicular monoamine transporter 2 immunolocalization in protein bodies of human locus coeruleus neurons.

ABSTRACT

Our previous histochemical and ultrastructural studies have identified, in human catecholamine neurons, abundant spherical acidophilic protein bodies (pb), which originate from regular mitochondria, retaining their double membrane. In locus coeruleus (LC) neurons, pb have somatodendritic distribution and are unequivocal storage vesicles for noradrenaline, as demonstrated by immunolocalization of Dopamine-ß-Hydroxylase. In the present study, in order to reinforce the identity of pb as monoamine storage sites in human LC, and to assess their potential of somatodendritic release, we studied the subcellular immunolocalization of chromogranin A (CgA) and vesicular monoamine transporter 2 (VMAT2), given the fact that their localization defines the vesicles capacity of filling with monoamine and hence exocytotic release. The data provided in the present study, demonstrate the novel ultrastructural immunolocalization of both CgA and VMAT2 in protein bodies, supporting their involvement in somatodendritic storage and release of noradrenaline in human LC. Since the molecular mechanism of LC somatodendritic exocytosis remains largely elusive, the present study may shed light to a better understanding of this mechanism.