Comparative neurochemical features of the innervation patterns of the gut of the basal actinopterygian, <i><scp>L</scp>episosteus oculatus</i>, and the euteleost, <i><scp>C</scp>larias batrachus</i>

Abstract

Abstract The structure and physiology of enteric system are very similar in all classes of vertebrates, although they have been investigated only occasionally in non‐mammalian vertebrates. Very little is known about the distribution of the neurotransmitters in the gut of actinopterygian fishes. Anatomical and physiological studies of enteric nervous systems in the spotted gar ( L episosteus oculatus ) and airbreathing catfish ( C larias batrachus ), a non‐teleost and teleost actinopterygian, respectively, have not been undertaken. This study provides the first comprehensive characterization of the range of neurochemical coding in the enteric nervous system of these two species, including the chemical diversity of the mucosal endocrine cells in the pyloric stomach of C larias . Autonomic innervation of the secretory glands is also described and reported herein for the first time for fishes. We also report splanchnic (spinal) innervation of the stomach, submucosal ganglia (that also colocalize with nNOS ) and caudal intestine of C larias . In both fish species, numerous 5 HT , C h AT , n NOS and TH ‐positive nerve fibres have been observed. These discoveries demonstrate that much more physiological and pharmacological data are needed before a comprehensive model of enteric nervous system control in vertebrates can be developed.