Neurotransmitters in the Sympathetic Nervous System: Developmental Aspects
Authors: P.M. Masliukov
Abstract: Sympathetic ganglia consist of neurochemically and functionally distinct populations of neurons, characterized by a specific projection pattern and a set of neutransmitters including classical neutransmitters (catecholamines and acetylcholine), neuropeptides and small molecules such as NO, H2S, CO. The majority of the principal ganglionic sympathetic neurons is noradrenergic and expresses tyrosine hydroxylase (TH), i.e., a key enzyme in catecholamine synthesis. In mammals, two third of catecholaminergic neurons also co-localizes NPY. A small number of postganglionic sympathetic neurons contains enzyme of acetylcholine synthesis (ChAT) and some neuropeptides, such as somatostatin (SOM), vasoactive intestinal (poly)peptide (VIP), calcitonin gene-related peptide (CGRP). Acetylcholine-containing sympathetic neurons in most cases colocalize VIP and/or CGRP. Phenotype of autonomicneurons is regulated by both target-independent and target-dependent mechanisms. The most of transmitters are expressed during embryogenesis. TH appears during embryonic development and the percentage of TH-positive neurons remains virtually identical during ontogenesis. After birth, cholinergic neurons initially express catecholamine synthesising enzymes and exhibit a noradrenergicphenotype. Expression of different neuropeptides changes in pre- and postnatal development. Neurotransmitter expression in sympathetic neurons is influenced by soluble growth factor signaling via innervated target tissues. Multiple growth factors including bone morphogenetic proteins, neurotrophins, glialcellline-derived neurotrophic factor family ligands and neuropoietic cytokines play instructive role at different stages of neurotransmitter development.