Nitric Oxide and the Neuroendocrine Control of the Osmotic Stress Response in Teleosts

Abstract

The involvement of nitric oxide (NO) in the modulation of teleost osmoresponsive circuits is suggested by the facts that NO synthase enzymes are expressed in the neurosecretory systems and may be regulated by osmotic stimuli. The present paper is an overview on the research suggesting a role for NO in the central modulation of hormone release in the hypothalamo-neurohypophysial and the caudal neurosecretory systems of teleosts during the osmotic stress response. Active NOS enzymes are constitutively expressed by the magnocellular and parvocellular hypophysiotropic neurons and the caudal neurosecretory neurons of teleosts. Moreover, their expression may be regulated in response to the osmotic challenge. Available data suggests that the regulatory role of NO appeared early during vertebrate phylogeny and the neuroendocrine modulation by NO is conservative. Nonetheless, NO seems to have opposite effects in fish compared to mammals. Indeed, NO exerts excitatory effects on the electrical activity of the caudal neurosecretory neurons, influencing the amount of peptides released from the urophysis, while it inhibits hormone release from the magnocellular neurons in mammals.

Expression Pattern of nos1 in the Developing Nervous System of Ray-Finned Fish

“…In fish, a crosstalk between thyroid hormones and nitric oxide signaling pathways was demonstrated [48], although a direct role of NO has not yet been described in thyroid development. Analogously, the expression of nos genes in adult teleost liver was recently reported (reviewed in [49]), but the functions of nos1 in liver development remain to be established. These findings raise questions about specific roles NO might play in the growth, specialization, and physiology of these organs.…”

Nitric oxide synthase (NOS) inhibitor L‐NAME activates inducible NOS/NO system and drives multidimensional regulation of Na+/K+‐ATPase in ionocyte epithelia of immersion‐stressed air‐breathing fish (Anabas testudineus Bloch)

“…As a short‐lived free radical, nitric oxide (NO) acts as gasotransmitter and performs autocrine/paracrine function to impose physiological actions in mammals and fishes (Ally et al, 2020; Althaus, 2012; Cioni et al, 2019; Jensen et al, 2015; Hasan et al, 2020). The enzymatic actions of nitric oxide synthases (NOS) on l ‐arginine release NO in the presence of molecular oxygen and NADPH (Griffith & Stuehr, 1995).…”

“…The enzymatic actions of nitric oxide synthases (NOS) on l ‐arginine release NO in the presence of molecular oxygen and NADPH (Griffith & Stuehr, 1995). Among three NOS isoforms, constitutive neuronal NOS (nNOS) and inducible NOS (iNOS) are more active in teleost fishes (Andreakis et al, 2011; Cioni et al, 2019; Jensen et al, 2015). Generally, a small amount of NO is formed from l ‐arginine by nNOS, but during stress large amount of NO are released from inducible calcium‐independent iNOS in many cell types for a long period of time (Althaus, 2012; Choudhury & Saha, 2015).…”

“…Likewise, cortisol has been shown to modify the NO production and the pattern of nNOS and iNOS expression in the osmoregulatory tissues of rainbow trout (Gerber et al, 2017). Modulation of osmoresponsive circuits in the central nervous system in response to NO has also been demonstrated in many teleost fishes (Cioni et al, 2019). Despite this information, a role for iNOS/NO system in hypoxemia resistance has not yet delineated in air‐breathing fishes.…”

Endothelial nitric oxide synthase limits host immunity to control disseminated Candida albicans infections in mice

“…Nitric oxide (NO) is an endogenous signaling molecule produced in mammals by three isoforms of NO synthase (NOS). Neuronal NOS (nNOS/ NOS1 ) is synthesized by neuronal tissues and regulates the hypothalamo-neurohypophysical system [1]. Inducible NOS (iNOS/ NOS2 ) expressed predominantly by macrophages and neutrophils in response to LPS and IFNγ signaling produces high (μM) concentrations of NO that mediate cytotoxic effects [2].…”