Different subcellular distributions of the vesicular monoamine transporter, VMAT2, in subclasses of sympathetic neurons

A subpopulation of neurons in the rat superior cervical ganglion (SCG) was found to lack immunostaining for VMAT2, an isoform of the vesicular monoamine transporter that loads catecholamines into vesicles for release at the synapse. Double labeling with neuropeptide Y (NPY), a marker for vasomotor neurons, revealed selective cellular colocalization of NPY together with intense perinuclear staining for VMAT2. This implied that VMAT2-negative neurons were likely to have secretomotor and pilomotor phenotypes. We tested this by identifying peripheral noradrenergic axons by their expression of immunoreactivity for tyrosine hydroxylase (TH) and determining whether they also expressed NPY and VMAT2. This analysis revealed the presence of VMAT2-positive, non-vasomotor sympathetic axons in the submandibular gland and at the base of piloerector hairs. Together the results confirm earlier indications that virtually all sympathetic neurons in the rat SCG express VMAT2 and they show for the first time that functional subclasses of cells can be distinguished by different somatic levels of immunoreactivity for VMAT2.