Immunohistochemical localization of urotensin I/corticotropin‐releasing factor, urotensin II, and serotonin immunoreactivities in the caudal spinal cord of nonteleost fishes

Abstract

Neurosecretory cells in the caudal spinal cord of fishes were first discovered in elasmobranches. However, most of the subsequent work on the caudal neurosecretory system has emphasized its morphology and function in teleosts. Two major peptides, urotensins I and II (UI and UII), have been isolated from this system in teleosts and their amino acid sequences have been determined. We have used immunohistochemical techniques to confirm and expand previous morphological and pharmacological findings regarding the phylogenetic occurrence and the anatomical organization of the caudal neurosecretory system and to localize putative neurohormonal products within its structural elements. UII-immunoreactive neuronal structures were found in the holocephalan, Hydrolagus collei; the elasmobranches, Squalus acanthias, Dasyatis sabina, and Raja binoculata; the dipnoan, Protopterus annectens; the brachiopterygian, Erpetoichthys calabaricus; the chondrostean, Polyodon spathula; and the holosteans Lepisosteus platyrhinchus and Amia calva. UI/corticotropin-releasing-factor immunoreactive elements were detected in the caudal spinal cords of Petromyzon marinus, Raja binoculata, Polydon spathula, Lepisosteus platyrhinchus, L. osseus, L. platostomus, and Amia calva. In addition, in several of these species, immunohistochemical techniques have provided evidence for serotoninergic input to the caudal neurosecretory system.

International Union of Basic and Clinical Pharmacology. XCII. Urotensin II, Urotensin II–Related Peptide, and Their Receptor: From Structure to Function

“…Although nonteleost fish do not possess an authentic urophysis, they do exhibit a neurohemal area apposed to the ventral spinal cord that extends along several spinal cord segments (Fridberg and Bern, 1968). UII-immunoreactive cell bodies actually occur in the caudal spinal cord of representative species of nonteleost fish, including chondrichthyes (cartilaginous fish) and dipnoans (lungfish) but not agnatha (jawless fish) (Onstott and Elde, 1986).…”

Ontogenetic Development of the Caudal Neurosecretory System in the Chum Salmon, Oncorhynchus keta, with Regard to Its Ultrastructural Changes and with Relation to Neuropeptide Y-immunoreactive Fibers

“…The chemical nature of the neuronal inputs to the caudal neurosecretory system has been analyzed by various techniques including electron microscopy (O'Brien and Kriebel, 1983;Miller and Kriebel, 1986a) and immunohistochemistry (Miller and Kriebel, 1986b;Onstott and Elde, 1986;Yulis et al, 1990;Oka et al, 1997). With respect to the peptidergic innervation, we reported that NPY-positive fibers made occasional contact with UI-and/or UII-positive cells and fibers in several fishes and cyclostomes, strongly suggesting NPYergic afferent innervation of the Dahlgren cells (Oka et al, 1997).…”

Seasonal morphological and biochemical changes of Dahlgren cells implies a potential role of the caudal neurosecretory system (CNSS) in the reproduction cycle of teleostean fish

“…The caudal neurosecretory system is a neuroendocrine system found in the posterior spinal cord of teleost and elasmobranch fishes. It has been identified in most teleostean fishes and in a few dipnoans (e.g., Kobayashi et al 1986;Onstott and Elde 1986). In 1914, Dahlgren described enlarged neurosecretory cells dispersed in the posterior region of the spinal cord in 11 species of skates (Dahlgren 1914), and subsequently Speidel named these enlarged neurosecretory cells after Dahlgren (Speidel 1922).…”