Innervation of the Systemic Heart of the California Hagfish

Abstract

Large nerves with myelinated fibers and ganglion cells were demonstrated in proximate relationship to the systemic heart of the California hagfish ( Eptatretus stouti ). A system of ganglion cells with fibers is distributed along the aorta, the epicardium, and the endocardium. The myocardium has a plexus of coarse and fine argyrophilic fibers and fibril branches similar to, if not as extensive as, that which occurs in the hearts of fish and amphibians. These details of anatomical structure contradict the original statement by Greene that the heart of the hagfish is aneural, a conclusion which he derived from his inability to obtain a change in the rate and force of cardiac contraction by electric stimulation of the vagus nerve. The high catecholamine content of the cardiac tissues of the California hagfish ( Eptatretus stouti ) is verified. Over 99% was determined to be epinephrine.