Precursors of Urotensins and Their Co-Expression in the Caudal Neurosecretory System

Abstract

An array of neurosecretory neurons in the posterior spinal cord and their associated neurohemal organ, the urophysis, comprise the caudal neurosecretory system (CNS) of fishes. The CNS is credited with the synthesis and release of at least 2 neurohormones, urotensins I and II (UI and UII). There is no clear evidence for the existence of urotensin III as a separate chemical entity. Urotensin IV appears to be chemically and pharmacologically indistinguishable from arginine vasotocin (Lacanilao, 1972a,b), which occurs in small amounts in the urophysis of only some teleost species (Lacanilao and Bern, 1972). Also present in the teleost urophysis are large amounts of acetylcholine of unknown significance (Kobayashi et al., 1963; Ichikawa, 1978; Ichikawa and Kobayashi, 1978) and putative carrier proteins analogous to the neurophysins, the urophysins (Berlind et al., 1972; Moore et al., 1975; Lederis et al., 1981).