Neuroanatomy and control of the caudal lymphatic heart of the short-finned eel (Anguilla australis schmidtii)

Abstract

The caudal lymphatic heart of the short-finned eel is found in the most posterior segment of the tail. This organ pumps lymph from lateral, caudal, and caudal fin lymphatic vessels into the caudal vein. The anatomy of the heart was studied using light and electron microscopic techniques. Lymph heart muscle is typical of vertebrate fast-acting skeletal muscle. The muscles on each side are innervated by a spinal nerve from the penultimate vertebra. Neuromuscular junctions are of the "en plaque" type and contain spherical vesicles about 60 nm in diameter. Ablation experiments show that the lymph heart beat is neurogenic. It is suggested that action potentials from the penultimate segment of the spinal cord, which are transmitted to the lymph heart by spinal motor axons, initiate lymph heart contractions.