Distribution and neurotransmitter localization in the heart of the ray-finned fish, bichir (Polypterus bichir bichir Geoffroy St. Hilaire, 1802)

Abstract

Anatomical and physiological studies of cardiovascular control are lacking in the ray-finned fish, the bichirs. The present immunohistochemical studies on the bichir (Polypterus bichir bichir) demonstrated the occurrence of intracardiac neurons and nerve fibers in the heart. Immunoreactivity to tyrosine hydroxylase (TH) and acetylcholinesterase (AchE) and various neuropeptides (substance P, galanin, vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP)), including neuronal nitric oxide synthase (nNOS), was found in the nerve cell bodies lying close to the Sinus venosus and the sino-atrial region. The main intracardiac localization of the nervous tissue is a network of nerve fibers, presumably corresponding to the postganglionic outflow giving rise to nerve terminals and the nerve cell bodies. In addition, the heart is innervated by extrinsic monoamine-containing nerve fibers supplying the Conus arteriosus and Sinus venosus, and substance P and galanin immunopositive fibers probably originating from cranial and spinal ganglia. The adrenergic innervation of the heart of the bichir is similar to that of the teleosts, but further studies are required on nervous control of the heart.