Central and Peripheral Effects of Urotensin II and Urotensin II-Related Peptides on Cardiac Baroreflex Sensitivity in Trout

The Caudal Neurosecretory System: A Still Enigmatic Second Neuroendocrine Complex in Fish

The caudal neurosecretory system (CNSS) is a neuroendocrine complex, whose existence is specific to fishes. In teleosts, it consists of neurosecretory cells (Dahlgren cells) whose fibers are associated with a neurohemal terminal tissue (urophysis). In other actinopterygians as well as in chondrichthyes, the system is devoid of urophysis, so that Dahlgren cells end in a diffuse neurohemal region. Structurally, it has many similarities with the hypothalamic-neurohypophysial system. However, it differs regarding its position at the caudal end of the spinal cord and the nature of the hormones it secretes, the most notable ones being urotensins. The CNSS was first described more than 60 years ago, but its embryological origin is still hypothetical, and its role is poorly understood. Observations and experimental data gave some evidences of a possible involvement in osmoregulation, stress, and reproduction. But one may question the benefit for fish to possess this second neurosecretory system, while the central hypothalamic-pituitary complex already controls such functions. As an introduction of our review, a brief report on the discovery of the CNSS is given. A description of its organization follows, and our review then focuses on the neuroendocrinology of the CNSS with the different factors it produces and secretes. The current knowledge on the ontogenesis and developmental origin of the CNSS is also reported, as well as its evolution. A special focus is finally given on what is known on its potential physiological roles.

The Inhibitory Role of Hydrogen Sulfide in UII-Induced Cardiovascular Effects and the Underlying Signaling Pathways

Urotensin II (UII) could increase blood pressure and heart rate via increased central reactive oxygen species (ROS) levels. We reported previously that hydrogen sulfide (H2S) exerts an antihypertensive effect by suppressing ROS production. The aim of the current study is to further examine the effects of endogenous and exogenous H2S on UII-induced cardiovascular effects by using an integrated physiology approach. We also use cell culture and molecular biological techniques to explore the inhibitory role of H2S on UII-induced cardiovascular effects. In this study, we found that cystathionine-β-synthase (CBS), the main H2S synthesizing enzyme in CNS, was expressed in neuronal cells of the rostral ventrolateral medulla (RVLM) area. Cellular distribution of CBS and urotensin II receptor (UT) in SH-SY5Y cells that are confirmed as glutamatergic were identified by immunofluorescent and Western blots assay. In Sprague-Dawley rats, administration of UII into the RVLM resulted in an increase in mean arterial pressure (MAP), heart rate (HR), ROS production, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, and phosphorylation of p47phox, extracellular signal-regulated protein kinase (ERK)1/2 and p38MAPK, but not stress-activated protein kinase/Jun N-terminal kinase (SAPK/JNK). These effects of UII were attenuated by application into the RVLM of endogenous (L-cysteine, SAM) or exogenous (NaHS) H2S. These results were confirmed in SH-SY5Y cells. UII-induced cardiovascular effects were also significantly abolished by pretreatment with microinjection of Tempol, Apocynin, SB203580, or PD98059 into the RVLM. Preincubated SH-SY5Y cells with Apocynin before administration of UII followed by Western blots assay showed that ROS is in the upstream of p38MAPK/ERK1/2. Gao activation assay in SH-SY5Y cells suggested that H2S may exert an inhibitory role on UII-induced cardiovascular effects by inhibiting the activity of Gαo. These results suggest that both endogenous and exogenous H2S attenuate UII-induced cardiovascular effects via Gαo-ROS-p38MAPK/ERK1/2 pathway.