Caudal neurosecretory system of the zebrafish: ultrastructural organization and immunocytochemical detection of urotensins

Abstract

The caudal neurosecretory system is described here for the first time in the zebrafish, one of the most important models used to study biological processes. Light- and electron-microscopical approaches have been employed to describe the structural organization of Dahlgren cells and the urophysis, together with the immunohistochemical localization of urotensin I and II (UI and UII) peptides. Two latero-ventral bands of neuronal perikarya in the caudal spinal cord project axons to the urophysis. The largest secretory neurons (approximately 20 microm) are located rostrally. UII-immunoreactive perikarya are much more numerous than those immunoreactive for UI. A few neurons are immunopositive for both peptides. Axons contain 75-nm to 180-nm dense-core vesicles comprising two populations distributed in two axonal types (A and B). Large dense vesicles predominate in type A axons and smaller ones in type B. Immunogold double-labelling has revealed that some fibres contain both UI and UII, sometimes even within the same neurosecretory granule. UII is apparently the major peptide present and predominates in type A axons, with UI predominating in type B. A surprising finding, not previously reported in other fish, is the presence of dense-core vesicles, similar to those in neurons, in astrocytes including their end-feet around capillaries. Secretory type vesicles are also evident in ependymocytes and cerebrospinal-fluid-contacting neurons in the terminal spinal cord. Thus, in addition to the urophysis, this region may possess further secretory systems whose products and associated targets remain to be established. These results provide the basis for further experimental, genetic and developmental studies of the urophysial system in the zebrafish.

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

“…The axon terminals releasing UII into the urophysis originate from Dahlgren cells, i.e., large cholinergic neurons that are located in the caudal region of the ventral horn of the spinal cord of teleosts (Enami, 1959). Immunohistochemical labeling has confirmed that UII is primarily located in neurosecretory cells of the ventral spinal cord (Owada et al, 1985;Oka et al, 1989;Parmentier et al, 2006). However, subsequent studies have shown that UII is also present in the fish brain (Waugh and Conlon, 1993), and the expression of UII mRNA in fish brain has been confirmed by reverse-transcription polymerase chain reaction (RT-PCR; Lu et al, 2006;Sun et al, 2014).…”

Loss of the Reissner Fiber and increased URP neuropeptide signaling underlie scoliosis in a zebrafish ciliopathy mutant

“…qPCR analysis in 5 control and 5 rpgrip1l ∆/∆ fish at the 3-4 wpf stage (0.8-0.9 cm) confirmed urp2 overexpression in rpgrip1l ∆/∆ fish and showed that this overexpression preceded scoliosis onset ( Figure 4A). To investigate the tissue specificity of this up-regulation, we performed immunofluorescence with an antibody to a conserved domain of the Urotensin II peptide family [24,25]. In the zebrafish spinal cord, urp1 and urp2 are expressed in ventral CSF-cNs while other genes of the family are expressed in the caudal neurosecretory system [23,25,26].…”

Dynamic Responses of the Caudal Neurosecretory System (CNSS) Under Thermal Stress in Olive Flounder (Paralichthys olivaceus)

“…Previous morphology and immunohistochemistry studies of the CNSS have found that CRH and UI were co-expressed (Cioni and Bordieri, 2003;Lu et al, 2004). Meanwhile, UI and UII could also be co-expressed in a fraction of Dahlgren cells (Parmentier et al, 2006). Therefore, the increased UI-positive cells might be recruited from the Dahlgren cells that expressed UII peptides.…”