Morphology, innervation and its phylogenetic step in the heart of the longnose gar Lepisosteus Osseus

Abstract

Zaccone, D., Grimes, A.C., Farrell, A.P., Dabrowski, K. and Marino, F. 2011. Morphology, innervation and its phylogenetic step in the heart of the longnose gar Lepisosteus Osseus. —Acta Zoologica (Stockholm) 93: 381–389.AbstractAnatomical and physiological studies of cardiovascular control in garfish are scarce. The combination of muscle labelling and neurochemical identification of extrinsic and intrinsic nerves in the heart of Lepisosteus osseus reveals a well‐developed system of adrenergic, cholinergic, substance P (SP)‐ and neuronal nitric oxide synthase (nNOS)‐containing nerve terminals in the walls of the conus arteriosus, the sinus venosus and the atrium. Double labelling showed that nNOS‐immunoreactive terminals do not co‐label for tyrosine hydroxylase (TH) and choline acetyl transferase (ChAt). Coronary blood vessels running in the epicardium of the conus arteriosus and ventricle receive a rich supply of nNOS‐positive nerve fibres. The main intracardial localization of nervous tissue is in a sinoatrial plexus corresponding to the pacemaker region of the heart. This plexus is a network of SP‐, vasoactive intestinal polypeptide (VIP)‐ and pituitary adenylate cyclase‐activating polypeptide (PACAP)‐positive nerve fibres and nerve cell bodies, but its function in fish cardiac regulation remains to be elucidated. This study provides morphological data on distinct nitrergic, peptidergic, ChAT and TH nerve terminals thus pertaining to the neurochemical content of the vagal motor and adrenergic, and intrinsic innervation revealing a complexity of the neuronal control of the garfish heart. The neurochemical features of the innervation patterns of the heart put Lepisosteus with teleosts and among the more apical actinopterygians.