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

Abstract

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.

Origins of the sympathetic innervation to the nasal-associated lymphoid tissue (NALT): An anatomical substrate for a neuroimmune connection

“…2B). Similar findings but, constrained to rats, were previously reported Peter et al, 1995;Hou and Dahlström, 1996;Headley et al, 2007). The omission of VMAT2 primary and/or secondary antibodies during the incubation protocol resulted in the lack of immunoreactivity (data not shown).…”

“…Few VMAT2-ir nerve fibers and varicosities were seen however, many were certainly masked by the intense immunostaining of neurons. Similar results, but restricted to rats, were previously reported Peter et al, 1995;Hou and Dahlström, 1996;Headley et al, 2007). Although in hamsters SCG neurons exhibiting a robust immunostaining for VMAT2 are preponderant, few of them displayed variable intensities.…”

“…The basis for the differential intensity of VMAT2 immunostaining of neurons can only be speculated. It has been proposed that the expression of VMAT2 and the ensuing intensity of the immunostaining depend upon different functional subclasses of neurons reflecting diverse physiological states in the subcellular processing of the vesicular transporter (Headley et al, 2007). While out of the scope of our study, whether the variability in VMAT2 immunostaining reveals any physiological condition or are due to detection threshold of the immunochemical technique awaits further investigation.…”

“…VMAT1 is expressed solely in endocrine cells of the intestine, stomach, adrenal medulla and small intensely fluorescent cells in sympathetic ganglia . Contrastingly VMAT2 that is expressed in monoaminergic neurons, has been widely employed as a reliable immunocytochemical marker for sympathetic neurons and nerve fibers Peter et al, 1995;Erickson et al, 1996;Hou and Dahlström, 1996;Weihe and Eiden, 2000;Headley et al, 2007). Indeed, the coexistence of VMAT2 and tyrosine hydroxylase (TH) immunoreactivities was confirmed in neurons of both paravertebral and prevertebral sympathetic chains of rats (Weihe and Eiden, 2000).…”

Segregation of the classical transmitters norepinephrine and acetylcholine and the neuropeptide Y in sympathetic neurons: Modulation by ciliary neurotrophic factor or prolonged growth in culture

“…Consequently, these neurons express the proteins necessary to produce and use NE as a transmitter including the vesicular monoamine transporter 2 (VMAT2) in addition to neuropeptide Y (NPY; Romeo et al, 1994;Liu et al, 1996;Headley et al, 2007). However, sympathetic neurons demonstrate plasticity in regard to transmitter expression under certain circumstances.…”