Application of antibodies to the vesicular transporter of acetylcholine and acetylcholinesterase in the studies of prenatal development of parasympathetic innervation of the human pancreas

Abstract

Introduction. Parasympathetic fibers innervating the pancreas are involved in the regulation of both exo-crine and endocrine function, in the regulation of endocrine cell proliferation, and are also implicated in the pathogenesis of type 1 diabetes. Nonetheless, data concerning the distribution of parasympathetic fibers within the human pancreas in prenatal development are absent in the literature. Our aim was to evaluate the possibility of using the markers of cholinergic neurons and nerve fibers, namely vesicular acetylcholine transporter (VAChT) and acetylcholinesterase (AChE) in studies of prenatal develop-ment of parasympathetic innervation of the human pancreas. Materials and methods. The study was performed on 10 autopsies of the fetal pancreas (gestational age 10-34 weeks) using immunoperoxidase labeling with antibodies to VAChT and AChE. Results. Immunopositive reaction to AChE was detected in bundles of nerve fibers of various diameters, networks of thin nerve fibers as well as in individual neurons of the intramural ganglia. The structures of the nervous system were immunonegative to VAChT. In the exocrine pancreas, that is, in the interlobular connective tissue, near the ducts and inside the forming lobules, thin cholinergic fibers prevailed on the studied developmental periods. In pancreatic islets, cholinergic fibers were detected less frequently and were located at the periphery.Immunopositive reaction with antibodies to AChE and mouse monoclonal antibodies to VAChT was also detected in some endocrine cells in the pancreatic islets. Conclusion. We have shown that antibodies to AChE detect cholinergic neurons and nerve fibers in the developing human pancreas. We have also demonstrated that in the fetal pancreas thin cholinergic fibers prevail in the exocrine part and rarely are detected in the pancreatic islets, which is typical in adults. The results showing the VAChT and AChE immunoreactivity in the endocrine cells of fetal pancreatic islets are in agreement with data obtained in the adult human pancreas and suggest that the endocrine cells can be a source of acetylcholine. Keywords: pancreas, human development, parasympathetic innervation, VAChT, AChE