Neurochemical Features of Metasympathetic System Ganglia in the Course of Ontogenesis

Abstract

The neurochemical composition of the metasympathetic nervous system is characterized by large variation. The majority of ganglionic neurons in metasympathetic system is cholinergic. Along with cholinergic neurons, there are neurons detected in the intramural ganglia containing serotonin, histamine, GABA, and several peptides: cholecystokinin, dynorphin, enkephalins, galanin, gastrin-releasing peptide (bombesin in mammals), neuropeptide Y, neurotensin, somatostatin, tachykinins, neurokinin A, vasoactive intestinal polypeptide, and calcitonin gene-related peptide. Gas molecules such as NO, CO, and H₂S also act as neurotransmitters. Separate groups of neurons differ in the content of neuronal calcium-binding proteins, such as calbindin, calretinin and parvalbumin, and of neurofilaments: those of low, medium, and high molecular weight. Neurons of the gastrointestinal ganglia are the most diverse in their neurochemistry. There is species specificity: there are more combinations of chemical mediators in the ganglia of large animals and humans. The synthesis of main neurotransmitters takes place already in embryonic period, and most neurons contain acetylcholine by the time of birth. In postnatal ontogenesis in intramural gastrointestinal and cardiac ganglia, the fraction of neurons expressing NO-synthase decreases. The functional meaning of such changes remains unclear.