Abstract
Zinc ions in the synaptic vesicles of zinc-enriched neurons (ZEN) seem to have an important role in normal physiological and pathophysiological processes in target organ innervation. The factor directly responsible for the transport of zinc ions into synaptic vesicles is zinc transporter 3 (ZnT3), a member of the divalent cation zinc transporters and an excellent marker of ZEN neurons. As data concerning the existence of ZEN neurons in the small intestine is lacking, this study was designed to disclose the presence and neurochemical coding of such neurons in the porcine jejunum. Cryostat sections (10 mμ thick) of porcine jejunum were processed for routine double- and triple-immunofluorescence labeling for ZnT3 in various combinations with immunolabeling for other neurochemicals including pan-neuronal marker (PGP9.5), substance P (SP), somatostatin (SOM), vasoactive intestinal peptide (VIP), nitric oxide synthase (NOS), leu-enkephalin (LENK), vesicular acetylcholine transporter (VAChT), neuropeptide Y (NPY), galanin (GAL), and calcitonin-gene related peptide (CGRP). Immunohistochemistry revealed that approximately 39%, 49%, and 45% of all PGP9.5- positive neurons in the jejunal myenteric (MP), outer submucous (OSP), and inner submucous (ISP) plexuses, respectively, were simultaneously ZnT3+. The majority of ZnT3+ neurons in all plexuses were also VAChT-positive. Both VAChT-positive and VAChT-negative ZnT3+ neurons co-expressed a variety of active substances with diverse patterns of co-localization depending on the plexus studied. In the MP, the largest populations among both VAChT-positive and VAChT-negative ZnT3+ neurons were NOS-positive cells. In the OSP and ISP, substantial subpopulations of ZnT3+ neurons were VAChT-positive cells co-expressing SOM and GAL, respectively. The broad-spectrum of active substances that co-localize with the ZnT3+ neurons in the porcine jejunum suggests that ZnT3 takes part in the regulation of various processes in the gut, both in normal physiological and during pathophysiological processes.
Highlights
Recent studies on the chemical coding of the enteric nervous system (ENS) have identified a subpopulation of neuronsCell Tissue Res (2012) 350:215–223 that express the zinc transporter 3 (ZnT3; Gonkowski et al 2009; Gonkowski 2011)
The considerable quantity of ZnT3+ cells, namely more than 35% of all enteric neurons in each plexus, and the broadspectrum of active substances that co-localize with this peptide in each plexus suggest that ZnT3 and Zn are important factors within the digestive tract, and that both might be involved in the regulation of various processes in the gut
The precise function(s) of ZnT3 neurons and Zn are currently unknown, their presence in the enteric ganglia and in the adrenergic and cholinergic sympathetic neurons of the murine peripheral nervous system (Wang et al 2001a, 2003; Wang and Dahlstrom 2008) suggest that they play an integral role in the function of the gut
Summary
Recent studies on the chemical coding of the enteric nervous system (ENS) have identified a subpopulation of neuronsCell Tissue Res (2012) 350:215–223 that express the zinc transporter 3 (ZnT3; Gonkowski et al 2009; Gonkowski 2011). The ZnT3-mediated transport of zinc into synaptic vesicles serves to modulate neuron activity (Palmiter et al 1996) and plays an important role in the normal physiological and pathophysiological changes of the nervous system (Frederickson et al 2000, 2005; Smart et al 2004). Since previous studies on the central nervous system (CNS) have suggested that ZnT3 is present in neurons that use Zn as neuromodulator (Cousins et al 2006; Danscher et al 2003; Kim et al 2000; Wang et al 2003; Wenzel et al 1997), ZnT3 can be used as a marker for tracing ZEN structures. The presence of Zn in the ENS might suggest a similar modulatory role
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