Nitric oxide (NO) synthase immunoreactivity in the starfish Marthasterias glacialis

Ethical Considerations for Echinoderms: New Initiatives in Welfare

This paper explores the ethical considerations surrounding research on echinoderms, a group of invertebrates that has recently garnered attention in the scientific community. The importance of responsible animal handling and the need for an ethical framework that encompasses echinoderms are emphasized. The 3Rs principle, advocating for the replacement of conscious living vertebrates with non-sentient material in research, is discussed as a guiding tool in current animal research practices. As invertebrates are generally classified as non-sentient animals, the replacement dimension tends to favor them as prevalent models in experimental research. While it currently lacks the means to assess the mental states of invertebrates, there is undeniable evidence of social behavior in many species, suggesting that a lack of interactions with these organisms could potentially adversely affect their wellbeing. In the last few years, considerable progress has been made in developing an ethical framework that takes invertebrates into account, particularly cephalopods, crustaceans, and echinoderms. In this context, we discuss the development of a broader conceptual framework of 5Rs that includes responsibility and respect, which may guide practices ensuring welfare in echinoderms, even in the absence of any particular normative.

Enteroendocrine cells in the Echinodermata

Enteroendocrine cells are endocrine-like cells found in the luminal epithelia of the digestive tract. These cells have been described in most animal phyla. In echinoderms, the cells have been described mainly in organisms of the class Asteroidea (sea stars) and Holothuroidea (sea cucumbers). Here, we describe what is known about the enteroendocrine cells of the Echinodermata, including the cell types, their distribution in the digestive tract, their neuropeptide content and their regeneration and compare them to what has been found in other animal species, mainly in vertebrates. We also discuss the newly described view of enteroendocrine cells as chemical sensors of the intestinal lumen and provide some histological evidence that similar functions might be found within the echinoderms. Finally, we describe the temporal regeneration of the enteroendocrine cells in the holothurian intestine.

The known and unknown sources of reactive oxygen and nitrogen species in haemocytes of marine bivalve molluscs

Reactive oxygen and nitrogen species (ROS and RNS) are naturally produced in all cells and organisms. Modifications of standard conditions alter reactive species generation and may result in oxidative stress. Because of the degradation of marine ecosystems, massive aquaculture productions, global change and pathogenic infections, oxidative stress is highly prevalent in marine bivalve molluscs. Haemocytes of bivalve molluscs produce ROS and RNS as part of their basal metabolism as well as in response to endogenous and exogenous stimuli. However, sources and pathways of reactive species production are currently poorly deciphered in marine bivalves, potentially leading to misinterpretations. Although sources and pathways of ROS and RNS productions are highly conserved between vertebrates and invertebrates, some uncommon pathways seem to only exist in marine bivalves. To understand the biology and pathobiology of ROS and RNS in haemocytes of marine bivalves, it is necessary to characterise their sources and pathways of production. The aims of the present review are to discuss the currently known and unknown intracellular sources of reactive oxygen and nitrogen species in marine bivalve molluscs, in light of terrestrial vertebrates, and to expose principal pitfalls usually encountered.

Nitric oxide production and sequestration in the sinus gland of the green shore crab, Carcinus maneas

Molting in decapod crustaceans is regulated by molt-inhibiting hormone (MIH), a neuropeptide produced in the X-organ (XO)/sinus gland (SG) complex of the eyestalk ganglia (ESG). Pulsatile release of MIH from the SG suppresses ecdysteroidogenesis by the molting gland or Y-organ (YO). The hypothesis is that nitric oxide (NO), a neuromodulator that controls neurotransmitter release at presynaptic membranes, depresses the frequency and/or amount of MIH pulses to induce molting. NO synthase (NOS) mRNA was present in Carcinus maneas ESG and other tissues and NOS protein was present in the SG. A copper based ligand (CuFL), which reacts with NO to form a highly fluorescent product (NO-FL), was used to image NO in the ESG and SG and quantify the effects of NO scavenger (1 mM cPTIO), NOS inhibitor (1 mM L-NAME), and 1 mM sodium azide (NaN3) on NO production in the SG. Preincubation with cPTIO prior to CuFL loading decreased NO-FL fluorescence ~30%; including L-NAME had no additional effect. Incubating SG with L-NAME during preincubation and loading decreased NO-FL fluorescence ~40%, indicating that over half of the NO release was not directly dependent on NOS activity. Azide, which reacts with NO-binding metal groups in proteins, reduced NO-FL fluorescence to near background levels without extensive cell death. Spectral shift analysis showed that azide displaced NO from a soluble protein in SG extract. These data suggest that the SG contains NO-binding protein(s) that sequester NO and releases it over a prolonged period. This NO release may modulate neuropeptide secretion from the axon termini in the SG.

The early role of nitric oxide in evolution

Nitric oxide (NO), which today serves many different purposes in regulating complex cellular functions, must have played a crucial role in the early stages of the evolution of life. The formation of NO may have been a critical defence mechanism for primitive microorganisms at a time when life faced the problem of rising atmospheric levels of ozone (03) formed upon photolysis of oxygen (Oz), which occurred shortly after the development of respiration in cyanobacteria. The production of NO by organisms would have allowed neutralization of toxic 03 by chemical reaction outside the cell, thus acting as a protective mechanism against oxidative destruction, allowing evolutionary advantage. Later, NO production might have allowed the control of reactive OZ species within cells before the development of specific electron-accepting enzymes. The pathway of NO formation was then consequently developed further to serve other useful functions. Although mammalian cells produce NO from L-arginine, the origin of this ability might have arisen from the essential process of either nitrification or denitrification in prokaryotic cells.

Histological, histochemical and immunohistochemical study on the growing oocytes of the abyssal teleost Hoplostethus mediterraneus (V)

The oocytes of the abyssal Teleost, Hoplostethus mediterraneus were studied. Four stages of growth were observed and the oocytes of all the stages were surrounded by follicular cells and had several nucleoli in the nucleus. In the oocytes of the II degrees stage, vacuoles without contents, in oocytes of the III degrees stage several vacuoles with a basophilic contents and small yolk globules were identified. General and basic proteins, ribonucleoproteins, acid proteoglycans with -COOH groups were recognized in the cytoplasm, in the nucleoli of oocytes in the II degrees stage and in the vacuolar contents of oocytes in the III degrees stage. In the follicular cells, in the pellucid zone, in the yolk globules, from their beginning, glycoproteins were present. Positivity, for all lectins used, was revealed in the follicular cells and in the four stages of oocytes growth. alpha-D-glucose and alpha-D-mannose binding sites were in the pellucid zone and in the initial yolk globules. In the lather galactose and beta-N-acetyl glucosamine were present too. nNOS and VIP immunopositivity revealed at the periphery of the cytoplasm and at network of nerve fibres between oocytes, suggests NO is involved in a mechanism of regulation of the gametogenesis and of the spawning.

Mechanisms of vasodilation in the dorsal aorta of the elephant fish, Callorhinchus milii (Chimaeriformes: Holocephali)

This study investigated vasodilator mechanisms in the dorsal aorta of the elephant fish, Callorhinchus milii, using anatomical and physiological approaches. Nitric oxide synthase could only be located in the perivascular nerve fibres and not the endothelium of the dorsal aorta, using NADPH histochemistry and immunohistochemistry. In vitro organ bath experiments demonstrated that a NO/soluble guanylyl cyclase (GC) system appeared to be absent in the vascular smooth muscle, since the NO donors SNP (10(-4) mol l(-1)) and SIN-1 (10(-5) mol l(-1)) were without effect. Nicotine (3 x 10(-4) mol l(-1)) mediated a vasodilation that was not affected by ODQ (10(-5) mol l(-1)), L-NNA (10(-4) mol l(-1)), indomethacin (10(-5) mol l(-1)), or removal of the endothelium. In contrast, the voltage-gated sodium channel inhibitor, tetrodotoxin (10(-5) mol l(-1)), significantly decreased the dilation induced by nicotine, suggesting that it contained a neural component. Pre-incubation of the dorsal aorta with the calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP(8-37) (10(-6) mol l(-1)) also caused a significant decrease in the nicotine-induced dilation. We propose that nicotine is mediating a neurally-derived vasodilation in the dorsal aorta that is independent of NO, prostaglandins and the endothelium, and partly mediated by CGRP.

Nitric oxide in marine invertebrates: a comparative perspective

Since the discovery of the biological effects of nitric oxide (NO) more than two decades ago, NO has been identified as an important physiological modulator and a messenger molecule in mammals. Parallel to these studies, evidence that has accumulated in recent years has revealed that the NO signalling pathway is spread throughout the entire phylogenetic scale, being increasingly found in lower organisms, ranging from Chordata to Mollusca. The present review attempts to provide a survey of current knowledge of the genesis and possible roles of NO and the related signalling pathway in marine invertebrates, with special emphasis on Sepia, a choice dictated by the increasing appreciation of cephalopods as most valuable model systems for studies of NO biology and the present expectation for new exciting insights into as yet little explored segments of NO biology.

Immunohistochemical localization of nNOS and VIP in the mantle integument of the mussel, Mytilus galloprovincialis

The phylogeny and functional roles of many bioactive compounds in the invertebrate integument are still unclear. In order to deal with this issue, we performed an immunohistochemical investigation of the integument of the mussel, Mytilus galloprovincialis, to demonstrate the presence of nNOS- and VIP-positive nerve fibers in subepidermal connective tissue of the mantle. Positive nerve cell bodies were detected in this tissue as well as in cortex of sperm follicles, and adjacent to maturating oocytes and spermatocytes located in the thickness of the mantle. These results indicate involvement of a local inhibitory non-adrenergic-non-cholinergic (NANC) regulatory mechanism of epidermal functions, such as mucous secretion and ciliary beating. At the gonadic level, this mechanism probably regulates the cycle of maturation and release of the gametes in both sexes.

Postnatal changes in the nitric oxide system of the rat cerebral cortex after hypoxia during delivery

The impact of hypoxia in utero during delivery was correlated with the immunocytochemistry, expression and activity of the neuronal (nNOS) and inducible (iNOS) isoforms of the nitric oxide synthase enzyme as well as with the reactivity and expression of nitrotyrosine as a marker of protein nitration during early postnatal development of the cortex. The expression of nNOS in both normal and hypoxic animals increased during the first few postnatal days, reaching a peak at day P5, but a higher expression was consistently found in hypoxic brain. This expression decreased progressively from P7 to P20, but was more prominent in the hypoxic group. Immunoreactivity for iNOS was also higher in the cortex of the hypoxic rats and was more evident between days P0 and P5, decreasing dramatically between P10 and P20 in both groups of rats. Two nitrated proteins of 52 and 38 kDa, were also identified. Nitration of the 52-kDa protein was more intense in the hypoxic animals than in the controls, increasing from P0 to P7 and then decreasing progressively to P20. The 38-kDa nitrated protein was seen only from P10 to P20, and its expression was more intense in control than in the hypoxic group. These results suggest that the NO system may be involved in neuronal maturation and cortical plasticity over postnatal development. Overproduction of NO in the brain of hypoxic animals may constitute an effort to re-establish normal blood flow and may also trigger a cascade of free-radical reactions, leading to modifications in the cortical plasticity.

Expression of nitrergic system and protein nitration in adult rat brains submitted to acute hypobaric hypoxia

Changes in the nitric oxide (NO) system of the rat cerebral cortex were investigated by immunohistochemistry, immunoblotting, and NO synthase (NOS) activity assays in adult rats submitted for 30 min to hypoxia, in a hypobaric chamber at a simulated altitude of 38,000 ft (11000 m) (154.9 mm Hg). The cerebral cortex was studied after different survival times, 0 and 24 h, 5, 8, 15, and 30 days of reoxygenation. This situation led to morphological alterations in the large type I interneurons, as well as immunoreactive changes in the appearance and number of the small neurons (type II), both containing neuronal NOS (nNOS). Some of these small neurons showed immunoreactive cytoplasm and short processes; others, the more numerous during all reoxygenation periods, contained the immunoreactive product mainly related to a perinuclear ring. Ultrastructurally, these small neurons exhibited changes in nuclear structures as in the shape of the nuclear membrane, in the distribution of heterochromatin, and in the nucleolar morphology. The reaction product for nitrotyrosine, as a marker of protein nitration, showed modifications in distribution of the immunoreactive product. No expression was found for inducible NOS (iNOS). All these modifications were accompanied by increased nNOS and nitrotyrosine production as demonstrated by Western blotting and calcium-dependent activity, returning to control conditions after 30 days of reoxygenation, suggesting a reversible NO mechanism of action.

Immunohistochemical localization of nNOS in the skin and nerve fibers of the earthworm Lumbricus terrestris L. (Annelida Oligochaeta)

The epidermis of the earthworm Lumbricus terrestris is a multifunctional tissue. It is composed of supporting, mucous, neuroendocrine-like, sensory and basal cells. NO is considered to be a molecule that regulates numerous functional activities (also in non-neuronal cells) in vertebrates. In the earthworm epidermis, we found neuronal NO synthase immunopositivity in orthochromatic and metachromatic mucous cells, neuroendocrine-like cells and in epidermal and subepidermal nerve fibers and striated muscle fibers. It is suggested that NO has a multitude of biological actions, affecting functional activities of the epidermis such as tissue homeostasis, control of secretion, proliferation, respiration, defense, water-salt balance, as well as regulation of tonus in vascular and striated muscles.

Comparative analysis of nitric oxide and SALMFamide neuropeptides as general muscle relaxants in starfish

Previous studies have established that the gaseous signalling molecule nitric oxide (NO) and the SALMFamide neuropeptides S1 and S2 cause cardiac stomach relaxation in the starfish Asterias rubens. Here we show that S1, S2 and the NO donor SNAP also cause relaxation of two other preparations from Asterias - tube feet and the apical muscle of the body wall. The rank order of effectiveness as muscle relaxants when tested at a concentration of 10 micro mol l(-1) was SNAP>S2>S1 for both tube feet and apical muscle whereas for cardiac stomach it was S2>S1>SNAP. Significantly, these data indicate that NO and SALMFamide neuropeptides function as general muscle relaxants in starfish but vary in their relative importance in different organ systems. The molecular mechanisms by which NO and SALMFamides cause muscle relaxation in starfish are not known, but previous pharmacological studies on the cardiac stomach using the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazol[4,3-a]quinoxalin-1-one (ODQ) indicate that the cyclic nucleotide second messenger cGMP may mediate effects of NO. Consistent with this hypothesis, here we report that ODQ also causes partial inhibition of the relaxing effect of SNAP on tube foot and apical muscle preparations. To further investigate the involvement of cyclic nucleotides as mediators of the effects of NO and SALMFamides on starfish muscle, we have measured both cGMP and cAMP in cardiac stomach and in apical muscle after treatment with S1, S2 or SNAP. However, no significant changes in cyclic nucleotide content were observed compared with controls. Further experiments were performed on apical muscle tissue in the presence of the cyclic-nucleotide-phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX), a drug that also causes cardiac stomach relaxation in starfish. Treatment with IBMX caused a 2-3-fold increase above basal levels for cGMP and cAMP, but co-treatment with IBMX and S1 or S2 or SNAP resulted in no significant further increase above the level observed with IBMX alone. We conclude from these data that the relaxing action of NO on starfish muscle may be mediated by both cGMP-dependent and cGMP-independent pathways. However, the mechanisms by which SALMFamides cause muscle relaxation in starfish remain unknown and, although our results do not rule out the involvement of cGMP or cAMP, other signalling pathways may now need to be investigated.

The biochemical substrate of nitric oxide signaling is present in primitive non-cognitive organisms

Nitric oxide has been shown to have diverse actions in the mammalian nervous, immune and vascular systems. These include antimicrobial and antiviral activities as well as the modulation of cell adherence. In the nervous system, nitric oxide modulates neurotransmitter release, neurosecretion and behavioral activities such as feeding. In the present review, we discuss the finding that invertebrate organisms also contain nitric oxide and that they appear to use this multidimensional molecule in a similar manner as noted for mammals. Therefore, nitric oxide signaling appears to have emerged first in these primitive non-cognitive organisms. We conclude that basal nitric oxide functioning was established in these organisms and that this molecule was later employed in man, including its involvement in cognitive neural processes.

Regeneration neurohormones and growth factors in echinoderms

There has been much recent interest in the presence and biological functions of growth regulators in invertebrates. In spite of the different distribution patterns of these molecules in different phyla (from molluscs, insects, and annelids to echinoderms and tunicates), they seem always to be extensively involved in developmental processes, both embryonic and regenerative. Echinoderms are well known for their striking regenerative potential and many can completely regenerate arms that, for example, are lost following self-induced or traumatic amputation. Thus, they provide a valuable experimental model for the study of regenerative processes from the macroscopic to the molecular level. In crinoids as well as probably all ophiuroids, regeneration is rapid and occurs by means of a mechanism that involves blastema formation, known as epimorphosis, where the new tissues arise from undifferentiated cells. In asteroids, morphallaxis is the mechanism employed, replacement cells being derived from existing tissues following differentiation and (or) transdifferentiation. This paper focuses on the possible contribution of neurohormones and growth factors during both repair and regenerative processes. Three different classes of regulatory molecules are proposed as plausible candidates for growth-promoting factors in regeneration: neurotransmitters (monoamines), neuropeptides (substance P, SALMFamides 1 and 2), and growth-factor-like molecules (TGF-β (transforming growth factor β), NGF (nerve growth factor), RGF-2 (basic fibroblast growth factor)).

The enteric nervous system of echinoderms: unexpected complexity revealed by neurochemical analysis

Echinoderms are one of the most important groups of metazoans from the point of view of evolution, ecology and abundance. Nevertheless, their nervous system has been little studied. Particularly unexplored have been the components of the nervous system that lie outside the ectoneural and hyponeural divisions of the main nerve ring and radial nerve cords. We have gathered information on the nervous components of the digestive tract of echinoderms and demonstrate an unexpected level of complexity in terms of neurons, nerve plexi, their location and neurochemistry. The nervous elements within the digestive system consist of a distinct component of the echinoderm nervous system, termed the enteric nervous system. However, the association between the enteric nervous system and the ectoneural and hyponeural components of the nervous system is not well established. Our findings also emphasize the importance of the large lacunae in the neurobiology of echinoderms, a feature that should be addressed in future studies.

Neural control of muscle relaxation in echinoderms

Smooth muscle relaxation in vertebrates is regulated by a variety of neuronal signalling molecules, including neuropeptides and nitric oxide (NO). The physiology of muscle relaxation in echinoderms is of particular interest because these animals are evolutionarily more closely related to the vertebrates than to the majority of invertebrate phyla. However, whilst in vertebrates there is a clear structural and functional distinction between visceral smooth muscle and skeletal striated muscle, this does not apply to echinoderms, in which the majority of muscles, whether associated with the body wall skeleton and its appendages or with visceral organs, are made up of non-striated fibres. The mechanisms by which the nervous system controls muscle relaxation in echinoderms were, until recently, unknown. Using the cardiac stomach of the starfish Asterias rubens as a model, it has been established that the NO-cGMP signalling pathway mediates relaxation. NO also causes relaxation of sea urchin tube feet, and NO may therefore function as a ‘universal’ muscle relaxant in echinoderms. The first neuropeptides to be identified in echinoderms were two related peptides isolated from Asterias rubens known as SALMFamide-1 (S1) and SALMFamide-2 (S2). Both S1 and S2 cause relaxation of the starfish cardiac stomach, but with S2 being approximately ten times more potent than S1. SALMFamide neuropeptides have also been isolated from sea cucumbers, in which they cause relaxation of both gut and body wall muscle. Therefore, like NO, SALMFamides may also function as ‘universal’ muscle relaxants in echinoderms. The mechanisms by which SALMFamides cause relaxation of echinoderm muscle are not known, but several candidate signal transduction pathways are discussed here. The SALMFamides do not, however, appear to act by promoting release of NO, and muscle relaxation in echinoderms is therefore probably regulated by at least two neuronal signalling systems acting in parallel. Recently, other neuropeptides that influence muscle tone have been isolated from the sea cucumber Stichopus japonicus using body wall muscle as a bioassay, but at present SALMFamide peptides are the only ones that have been found to have a direct relaxing action on echinoderm muscle. One of the Stichopus japonicus peptides (holothurin 1), however, causes a reduction in the magnitude of electrically evoked muscle contraction in Stichopus japonicus and also causes ‘softening’ of the body wall dermis, a ‘mutable connective tissue’. It seems most likely that this effect of holothurin 1 on body wall dermis is mediated by constituent muscle cells, and the concept of ‘mutable connective tissue’ in echinoderms may therefore need to be re-evaluated to incorporate the involvement of muscle, as proposed recently for the spine ligament in sea urchins.

Nitric oxide production by coelomocytes of Asterias forbesi

Vertebrate mononuclear phagocytes produce a plethora of molecules involved in host defense. Among the most potent are the reactive oxygen and nitrogen intermediates. Coelomocytes from invertebrates subserve many of the same functions. In order to determine whether invertebrate phagocytes employ reactive nitrogen intermediates, we investigated the effect of various nonspecific stimulators and invertebrate interleukin (IL)-1alpha- and beta-like molecules on nitric oxide (NO) production. Elevated NO release by stimulated coelomocytes was seen after 24 h. Incubation of stimulated coelomocytes in the presence of arginine analogs inhibited NO release. When invertebrate IL-1-like molecules were added to the coelomocytes, they stimulated the release of NO. Western blot analysis using a polyclonal rabbit antiserum to murine NO synthase detected a band at approximately 125 kDa. These data indicate that coelomocytes are capable of producing and releasing NO and that NO is a chemical mediator that has been conserved as a host defense weapon of phagocytes through evolutionary time.

Giant identified NO-releasing neurons and comparative histochemistry of putative nitrergic systems in gastropod molluscs

Gastropod molluscs provide attractive model systems for behavioral and cellular analyses of the action of nitric oxide (NO), specifically due to the presence of many relatively giant identified nitrergic neurons in their CNS. This paper reviews the data relating to the presence and distribution of NO as well as its synthetic enzyme NO synthase (NOS) in the CNS and peripheral tissues in ecologically and systematically different genera representing main groups of gastropod molluscs. Several species (Lymnaea, Pleurobranchaea, and Aplysia) have been analyzed in greater detail with respect to immunohistochemical, biochemical, biophysical, and physiological studies to further clarify the functional role of NO in these animals.

Neuronal nitric oxide synthase (nNOS) expression in the epithelial neuroendocrine cell system and nerve fibers in the gill of the catfish, Heteropneustes fossilis

We studied immunohistochemically the localization of neuronal nitric oxide synthase (nNOS) in gills of an Indian catfish species, Heteropneustes fossilis. It is shown that most of the epithelial neuroendocrine cells that are present in gill filaments and lamellae stained positively. Co-localization of nNOS and endothelin was also shown in neuroendocrine cells. A dense plexus of nNOS-containing nerve fibers was present beneath the gill epithelium, associated with efferent filament arteries and the basal side of neuroendocrine cells. nNOS immunopositive neurons were not found in gill areas. nNOS immunopositive neuroendocrine cells appeared to differ from neuroepithelial cells in gills of various teleost species, which are considered as oxygen-sensitive receptors and are present in the distal halves of gill filaments. Other types of neuroendocrine cells have been identified previously in other areas of gills using antibodies to serotonin and endothelin peptides. These cell types are likely to be involved in chemical regulation of the physiology of gill cells. In relation to the function of the other cell types, our data on nNOS localization suggest that NO is a wide-spread transmitter in the gill of the Indian catfish. It may play a role both in the local regulation of vascular tone and in inhibitory innervation of the gill.

Inhibition of macrophage activity by mitogen-induced goldfish leukocyte deactivating factor

Macrophage activating and deactivating cytokines have been characterized in mammalian systems but little is known about these immunoregulatory molecules in fish. Using gel permeation and chromatofocusing fast performance liquid chromatography (GP-FPLC and C-FPLC) we partially purified a macrophage deactivating factor (MDF) from mitogen-induced goldfish kidney leukocytes. Inhibition of the macrophage-derived nitric oxide (NO) response induced by this MDF was time-, dose- and temperature-dependent. Macrophages pre-treated for 6 or 24 h with MDF before activation with macrophage activating factors (MAF) and/or bacterial lipopolysaccharide (LPS) exhibited a down-regulation in their NO response, while those treated with MDF 24 h after activation with MAF and LPS did not. MDF treatment also impaired the NO response of goldfish macrophages infected with the mammalian protozoan parasite Leishmania major. These results suggest that MDF exhibits its inhibitory effect downstream of the converging intracellular pathways induced by LPS and/or L. major. The novel teleost MDF has an approximate Mr of 15 kD and a pI < 4, and is the first endogenous molecule of teleosts known to down regulate macrophage antimicrobial responses.

Nitric oxide synthase in the guinea pig preoptic area and hypothalamus: distribution, effect of estrogen, and colocalization with progesterone receptor

Nitric oxide (NO) may function as an intercellular messenger in the hypothalamus and may play a role in the control of gonadotropin-releasing hormone (GnRH) secretion and sexual behavior. Progesterone also plays an important role in the regulation of reproductive functions. Recent experiments have shown that progesterone-induced sexual behavior in ovariectomized, estrogen-primed rats was caused by the release of NO from nitric oxide synthase (NOS)-containing neurons and the subsequent stimulation of the release of GnRH. To provide further neuroanatomical support for the role of NO in these gonadal steroid-dependent behavioral and physiological processes, we determined (1) the distribution of the nicotinamide-adenosine-dinucleotide phosphate-diaphorase (NADPHd) and NOS enzymes in the guinea pig preoptic area and hypothalamus, regions that contain steroid receptors; (2) the effect of estrogen on NADPHd activity in these regions; and (3) the neuroanatomical relationship between NOS and the progesterone receptor (PR). For this purpose, single-(NADPHd) and double- (NADPHd with NOS or NADPHd with PR or NOS with PR) staining techniques were applied to sections of brains of guinea pigs. The studies showed scattered NADPHd-positive neurons in most parts of the preoptic area and heavily stained cells in the hypothalamus. In these regions, the pattern and density of NOS immunoreactivity closely corresponded to the pattern of NADPHd staining. Quantitative analysis showed an increase in the number of NADPHd-positive neurons in the ventrolateral nucleus of ovariectomized animals primed with estradiol. Approximately 16% of the NOS-immunoreactive (IR) cells in the rostral preoptic area and 55% of NOS-IR cells in the ventrolateral nucleus displayed PR immunoreactivity. These results suggest that NOS may be regulated by gonadal steroids and provide neuroanatomical evidence that progesterone may exert its effect directly on more than half of NOS-synthesizing cells in the ventrolateral nucleus, a key region in the control of sexual behavior.

Nitric oxide: discovery and impact on clinical medicine

Images

Single-cell analyses of nitrergic neurons in simple nervous systems

Understanding the role of the gaseous messenger nitric oxide (NO) in the nervous system is complicated by the heterogeneity of its nerve cells; analyses carried out at the single cell level are therefore important, if not critical. Some invertebrate preparations, most especially those from the gastropod molluscs, provide large, hardy and identified neurons that are useful both for the development of analytical methodologies and for cellular analyses of NO metabolism and its actions. Recent modifications of capillary electrophoresis (CE) allow the use of a small fraction of an individual neuron to perform direct, quantitative and simultaneous assays of the major metabolites of the NO-citrulline cycle and associated biochemical pathways. These chemical species include the products of NO oxidation (NO2-/NO3-), l-arginine, l-citrulline, l-ornithine, l-argininosuccinate, as well as selected NO synthase inhibitors and cofactors such as NADPH, biopterin, FMN and FAD. Diverse cotransmitters can also be identified in the same nitrergic neuron. The sensitivity of CE methods is in the femtomole to attomole range, depending on the species analysed and on the specific detector used. CE analysis can be combined with prior in vivo electrophysiological and pharmacological manipulations and measurements to yield multiple physiological and biochemical values from single cells. The methodologies and instrumentation developed and tested using the convenient molluscan cell model can be adapted to the smaller and more delicate neurons of other invertebrates and chordates.

Expression of an inducible nitric oxide synthase gene in rainbow trout Oncorhynchus mykiss

Using oligonucleotide primers based on mammalian nitric oxide synthases (NOS), expression of an inducible NOS (iNOS) gene was detected in head kidney and gill tissue of bacterially-challenged rainbow trout. Three overlapping fragments were amplified by RT-PCR and used to construct a contiguous sequence of 1410bp, with high nucleotide homology to iNOS in birds (61%) and mammals (57-59%). The nucleotide sequence translated in one reading frame to produce a partial peptide containing 470 amino acids, with 69-71% amino acid homology with mammalian iNOS, 81% homology with chicken iNOS and 85% homology with a partial (492bp) goldfish iNOS sequence. In vitro stimulation of head kidney macrophages with LPS also induced expression of the trout iNOS RNA, with optimal expression seen using 20-50 microg/ml LPS at 2h to 6h post-stimulation. The evolutionary and functional significance of the trout iNOS sequence are discussed.

Evidence for the involvement of nitric oxide in the inhibitory effect of GSPYFVamide on Helix aspersa central neurones

Intracellular recordings were made from neurones E-8, E-16 and E-13a in the visceral ganglion of Helix aspersa. GSPYFVamide inhibits the activity of these neurones and the role of a second messenger system in this inhibition was investigated. 8-Bromo-cGMP, 100 microM was found to potentiate this inhibition while ODQ, 100 microM, an inhibitor of guanylyl cyclase, almost completely blocked GSPYFVamide-induced inhibition. Four NO donors sodium nitroprusside, 100 microM, sodium nitrite, 1 mM, SNOG, 50 microM, and SNAP, 10-50 microM, all potentiated the GSPYFVamide-induced inhibition. L-NAME, 100-1000 microM, a competitive inhibitor of NOS, blocked the GSPYFVamide-induced inhibition. In some cases recovery was only partial. The possible role of NO in modulating the inhibitory response to GSPYFVamide is discussed.

Nitric oxide in invertebrates

Nitric oxide (NO) is considered an important signaling molecule implied in different physiological processes, including nervous transmission, vascular regulation, immune defense, and in the pathogenesis of several diseases. The presence of NO is well demonstrated in all vertebrates. The recent data on the presence and roles of NO in the main invertebrate groups are reviewed here, showing the widespread diffusion of this signaling molecule throughout the animal kingdom, from higher invertebrates down to coelenterates and even to prokaryotic cells. In invertebrates, the main functional roles described for mammals have been demonstrated, whereas experimental evidence suggests the presence of new NOS isoforms different from those known for higher organisms. Noteworthy is the early appearance of NO throughout evolution and striking is the role played by the nitrergic pathway in the sensorial functions, from coelenterates up to mammals, mainly in olfactory-like systems. All literature data here reported suggest that future research on the biological roles of early signaling molecules in lower living forms could be important for the understanding of the nervous-system evolution.

Colocalization of NADPH-diaphorase and GABA-immunoreactivity in the olfactory and visual system of the locust

Nitric oxide synthesizing neurons of the locust CNS have been identified by NADPH-diaphorase staining. However, the conventional transmitters of these neurons are unknown. Here we use double labelling for NADPH-diaphorase and GABA-immunofluorescence on sections of the brain to investigate a potential coexpression of both markers. The antennal lobe is innervated by a cluster of about 45-50 NADPH-diaphorase positive local interneurons which express GABA-immunofluorescence. The mushroom bodies are a higher order olfactory center which receive an extrinsic innervation from GABA-immunoreactive and NADPH-diaphorase positive fiber systems. Each optic lobe contains about 4500 GABA-immunoreactive cell bodies. In the visual system, identifiable GABA-immunoreactive neurons arborize in the external plexiform layer of the lamina, in several strata of the medulla, and in the lobula complex. A survey of all NADPH-diaphorase positive cell groups detected a colocalization of GABA-immunoreactivity in a small subpopulation of somata along the anterior rim of the medulla. These cytochemical findings suggest that nitric oxide may be a characteristic cotransmitter of GABAergic circuits of the antennal lobe, while in mushroom bodies and the visual system the majority of nitric oxide and GABA releasing neurons are distinct populations.

Subcellular localization of nitric oxide synthase in the cerebral ventricular system, subfornical organ, area postrema, and blood vessels of the rat brain

The distribution of neuronal nitric oxide synthase (nNOS) has been studied in the more rostral portion of the lateral ventricle, subfornical organ, area postrema and blood vessels of the rat central nervous system. nNOS was located by means of a specific polyclonal antibody, by using light and electron microscopy. Light microscopy showed immunoreactive varicose nerve fibers and terminal boutons-like structures in the lateral ventricle, positioned in supra- and subependimal areas. The spatial relationships between immunoreactive neuronal processes and the wall of the intracerebral blood vessels were studied. Electron microscopy showed numerous nerve fibers in the wall of the lateral ventricle; many were nNos-immunoreactive and established very close contact with ependymal cells. Immunoreactive neurons and processes were found in the subependymal plate of the ventricular wall, the subfornical organ, the area postrema, and the circularis nucleus of the hypothalamus. In these last three areas, the immunoreactive neurons were found close to the perivascular space of fenestrated and nonfenestrated blood vessels. The nNOS immunoreactivity was localized to the endoplasmic reticulum, cisterns, ribosomes, neurotubules, and in the inner part of the external membrane. In the terminal boutons, the reaction product was found surrounding the vesicle membranes. This distribution showed nNOS as a predominantly membrane-bound protein. The nitrergic nerve fibers present in the wall of the ventricular system might regulate metabolic functions as well as neurotransmission in the subfornical organ, area postrema and circularis nucleus of the hypothalamus.

Pro-opiomelanocortin-derived peptides, cytokines, and nitric oxide in immune responses and stress: an evolutionary approach

In vertebrates, including man, the study of stress has contributed substantially to unravelling the complex relationship between immune-neuroendocrine interactions and the systems involved. On the basis of data on the presence and distribution of the main actors (POMC products, cytokines, biogenic amines, and steroid hormones) in different species and taxa from invertebrates to vertebrates, we argue that these responses have been deeply connected and interrelated since the beginning of life. Moreover, the study of nitric oxide suggests that the inflammatory reaction is located precisely between the immune and stress responses, sharing the same fundamental evolutionary roots. The major argument in favor of this hypothesis is that the immune, stress, and inflammation responses appear to be mediated by a common pool of molecules that have been conserved throughout evolution and that from a network of adaptive mechanisms. One cell type, the macrophage, appears to emerge as that most capable of supporting this network critical for survival; it was probably a major target of selective pressure. All these data fit the unitarian hypothesis we propose, by which evolution favors what has been conserved, rather than what has changed, as far as both molecules and functions are concerned.

A partial sequence for nitric oxide synthase from a goldfish (Carassius auratus) macrophage cell line

Expression of inducible nitric oxide synthase (iNOS) mRNA was detected in a recently developed goldfish macrophage cell line by RT-PCR, using degenerate primers designed against conserved nucleotide motifs within the different mammalian isoforms of NOS. Increased expression of iNOS poststimulation with LPS was found, and suggests that it is a functional enzyme in goldfish macrophages, supporting the view that iNOS regulation is pretranslational. The nucleotide sequence translated in one reading frame with no stop codons to produce a partial peptide containing 164 amino acids, with highest homology (85%) to a recently identified rainbow trout iNOS sequence. The peptide translation also gave an insight into the conservation of binding motifs, since two cofactor binding sites were present in the amplified PCR product (FMN and calmodulin). In addition, a 42 aa motif present in the region just upstream of the FMN binding motif of mammalian endothelial and neuronal NOS isoforms was absent in the translation, in agreement with every published sequence for iNOS. Finally, the translation was used to construct an unrooted phylogenetic tree.

Nitric oxide synthase in the brain of a urodele amphibian (Pleurodeles waltl) and its relation to catecholaminergic neuronal structures

The neuronal structures with NADPH-diaphorase activity and nitric oxide synthase (NOS) immunoreactivity have been studied in the brain of the urodele amphibian Pleurodeles waltl by means of histochemical and immunocytochemical techniques. Both approaches resulted in the selective labeling of the same neurons and fiber tracts in the brain, except for the primary olfactory fibers that did not stain for NOS but were positive for NADPH-diaphorase. NOS-containing neurons were found in the olfactory bulbs, pallial regions, septum, caudal striatum, amygdala and preoptic area. Only a few diencephalic cells were labeled in the posterior tubercle and ventral hypothalamus. In the brainstem, abundant cells were labeled in the tectum, mesencephalic tegmentum and isthmic region. The most conspicuous cell population was found in the isthmic-pretrigeminal region. Particularly well stained cells were distributed throughout the rhombencephalon in areas related to the descending trigeminal tract, solitary tract, raphe nucleus and the mid-caudal reticular formation. In the cervical spinal cord, NOS-containing cells were present in the dorsal, intermediate and ventral grey fields. Cells in the preoptic, postotic and dorsal root ganglia were also labeled. Double labeling techniques revealed an extensive codistribution of neurons with NOS and catecholamines in the urodele brain but actual colocalization in the same cells was never observed. The organization of the central systems in urodeles with NOS appears to share many features not only with other anamniotes but also with amniotes.

Putative nitric oxide synthase (NOS)-containing cells in the central nervous system of the leech, Hirudo medicinalis: NADPH-diaphorase histochemistry

The presence and distribution of putative nitric oxide synthase (NOS)-containing cells in whole-mount preparations of the central nervous system of the leech, Hirudo medicinalis, were studied using NADPH-diaphorase (NADPH-d) histochemistry. Specific staining occurred mainly in somata of some central neurones but NADPH-d-reactive branches and terminals were found in peripheral nerves and connectives: neuropile areas were stained weakly or unstained. Intense staining was located in many neurones on the ventral side of the segmental ganglia, including primary sensory neurones, motoneurones and interneurones, and in the anterior root ganglion. The sex ganglia contained some extra NADPH-d-positive cells. Head and tail ganglia and the dorsal side of the segmental ganglia showed less staining. Specific activity was not detected in salivary glands, crop or intestine. Controls using beta-NADPH or nitro blue tetrazolium (NBT) alone or with NBT plus alpha-NADPH, beta-NAD+, beta-NADH or beta-NADP+ did not induce specific staining. A potential NOS inhibitor, 2,6-dichlorophenol-indophenol (DPiP) at 10(-3) M, totally abolished NADPH-d-positive staining. Long-term fixation did not change the pattern of distribution of NADPH-d-positive cells. We conclude that (i) fixative-resistant NADPH-diaphorase is a characteristic marker of 12-15% of neurones in the leech CNS, and (ii) the specific distribution of the putative NOS-containing neurones suggests that NO may be a natural signal molecule in leeches.

Morphine stimulates nitric oxide release from invertebrate microglia

Morphine stimulates nitric oxide (NO) release in human endothelial cells. To determine whether this mechanism also occurs in invertebrates, the mussel Mytilus edulis was studied. Exposure of excised ganglia to morphine for 24 h resulted in a significant dose-dependent decrease in microglial egress that was naloxone sensitive. In coincubating the excised ganglia with morphine and the nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME), an increase in microglial egress was observed, suggesting that morphine may stimulate microglia to release NO. Morphine exposure to these cells in vitro resulted in NO release (39.4 +/- 4.9 nM), a phenomenon found to be naloxone sensitive (10(-6) M; NO level = 5.9 +/- 2.6 nM) and L-NAME sensitive (10(-4) M; NO level = 2.8 +/- 1.8 nM). Opioid peptides did not stimulate NO release, indicating that the process was mediated by the opiate alkaloid selective mu 3 receptor. Coincubation of microglia with L-arginine or the superoxide scavenger, superoxide dismutase, resulted in significantly higher NO levels observed following morphine stimulation. Taken together, the data demonstrate that morphine can stimulate NO release in cells obtained from an invertebrate that represents an animal 500 million years divergent in evolution from man, underscoring the significance of this process and further substantiating the critical importance of morphine as a naturally occurring signal molecule.

NADPH-diaphorase localization in the CNS and peripheral tissues of the predatory sea-slug Pleurobranchaea californica

The distribution of putative nitric oxide synthase (NOS)-containing cells in the opisthobranch mollusc Pleurobranchaea californica was studied histochemically via NADPH-diaphorase (NADPH-d) reduction of Nitro Blue Tetrazolium (NTB). Whole mounts and cryostat sections were prepared from the central nervous system and peripheral organs, including the buccal muscles, esophagus, salivary glands, foot, mantle, and gills. NADPH-d-positive neurons were localized predominantly to the buccal and pedal ganglia as well as to distinct areas of the cerebropleural and visceral ganglia. A variety of identified neurons were positive for NADPH-diaphorase in various central ganglia, including the metacerebral cells of the cerebropleural ganglion, putative locomotor neurons of the pedal ganglia, and buccal motoneurons. Specific staining was observed only in somata of central neurons, whereas neuropil areas remained unstained. However, NADPH-d-reactive axons were dense in buccal ganglion nerves, whereas peripheral nerves and connectives of other ganglia had few or no NADPH-d positive terminals. In the periphery, NADPH-d activity was detected only in a few neurons of the rhinophore and tentacle ganglia. NADPH-d staining was marked in the salivary glands and gills, but there was no or very little staining in the esophagus, buccal mass, and foot. Histochemical stain production required the presence of both beta-NADPH and NBT; alpha-NADPH could not substitute for beta-NADPH. The inhibitor of NOS, 2,6-dichlorophenol-indophenol, at 10(-3) M, totally abolished NADPH-d-positive staining. The apparent high activity of central NADPH-d contrasts with much lower activity in the ganglia of the related gastropod Tritonia. These data suggest a role for nitric oxide as a signal molecule in the central nervous system of Pleurobranchaea.

Topographical distribution of NADPH-diaphorase activity in the central nervous system of the frog, Rana perezi

The distribution of NADPH-diaphorase (ND) activity was histochemically investigated in the brain of the frog Rana perezi. This technique provides a highly selective labeling of neurons and tracts. In the telencephalon, labeled cells are present in the olfactory bulb, pallial regions, septal area, nucleus of the diagonal band, striatum, and amygdala. Positive neurons surround the preoptic and infundibular recesses of the third ventricle. The magnocellular and suprachiasmatic hypothalamic nuclei contain stained cells. Numerous neurons are present in the anterior, lateral anterior, central, and lateral posteroventral thalamic nuclei. Positive terminal fields are organized in the same thalamic areas but most conspicuously in the visual recipient plexus of Bellonci, corpus geniculatum of the thalamus, and the superficial ventral thalamic nucleus. Labeled fibers and cell groups are observed in the pretectal area, the mesencephalic optic tectum, and the torus semicircularis. The nuclei of the mesencephalic tegmentum contain abundant labeled cells and a conspicuous cell population is localized medial and caudal to the isthmic nucleus. Numerous cells in the rhombencephalon are distributed in the octaval area, raphe nucleus, reticular nuclei, sensory trigeminal nuclei, nucleus of the solitary tract, and, at the obex levels, the dorsal column nucleus. Positive fibers are abundant in the superior olivary nucleus, the descending trigeminal, and the solitary tracts. In the spinal cord, a large population of intensely labeled neurons is present in all fields of the gray matter throughout its rostrocaudal extent. Several sensory pathways were heavily stained including part of the olfactory, visual, auditory, and somatosensory pathways. The distribution of ND-positive cells did not correspond to any single known neurotransmitter or neuroactive molecule system. In particular, abundant codistribution of ND and catecholamines is found in the anuran brain. Double labeling techniques have revealed restricted colocalization in the same neurons and only in the posterior tubercle and locus coeruleus. If ND is in amphibians a selective marker for neurons containing nitric oxide synthase, as generally proposed, with this method the neurons that may synthesize nitric oxide would be identified. This study provides evidence that nitric oxide may be involved in novel tasks, primarily related to forebrain functions, that are already present in amphibians.

NADPH diaphorase activity in peptidergic neurones of the parasitic nematode, Ascaris suum

The histochemical marker for nitric oxide synthase, NADPH diaphorase, is known to co-localize in mammalian neurones with various classical neurotransmitters and neuropeptides. The nervous system of the parasitic nematode Ascaris suum has previously been shown to contain both NADPH diaphorase activity and neuropeptide immunoreactivity. This study examined the possibility that NADPH diaphorase and neuropeptide immunoreactivity may co-exist in the same neurones. Two antisera were used, one raised to KYSALMFamide, a C-terminal synthetic analogue of SALMFamide 1 (GFNSALMFamide), and another that recognizes calcitonin-gene-related peptide (CGRP). We provide evidence that in a distinct subset of neurones in the ventral, dorsal and lateral ganglia NADPH diaphorase staining and SALMFamide-like immunoreactivity are co-localized, suggesting a possible role for nitric oxide in modulating neuropeptide activity in these regions. CGRP-like immunoreactivity was less widely distributed, and was not consistently co-localized with NADPH diaphorase.

Nitric oxide: a synchronizing chemical messenger

Nitric oxide (NO) has been recognized as a ubiquitous chemical messenger in a large number of different biological systems. Its chemical properties make it less specific and less controllable than practically any other neurotransmitter or hormone. In view of this, its extensive biological role as a chemical messenger seems surprising. It is suggested that the biological function of NO evolved early in the anaerobic stage of evolution. In view of its low molecular weight, limited interaction with water, and its electrical neutrality, which allow it to diffuse rapidly through the cytoplasm and biomembranes, it is suggested that the need for NO has been retained by and maintained in eukaryote cells because of its ability to affect many biochemical functions simultaneously, acting primarily as an intracellular synchronizing chemical messenger.

NO-synthase: what can research on invertebrates add to what is already known?

The present study attempts to review presently known data regarding the distribution of nitric oxide (NO) synthase and the function of NO in invertebrate species. NO is synthesized from L-arginine by the enzyme NO-synthase, and activates guanylate cyclase which in turn leads to an increase in levels of cGMP in target cells. Major contributions to the knowledge of NO as a messenger molecule in invertebrates have been made by NADPH-diaphorase histochemistry and biochemical assays. These techniques suggest the presence of a L-arginine/NO pathway in a variety of tissues, thus implicating multiple roles for NO in invertebrates.

Localization of nitric oxide synthase in the adult rat brain

The distribution of the immunoreactivity to nitric oxide synthase has been examined from rostral to caudal areas of the rat central nervous system using light microscopy. Endogenous nitric oxide synthase was located using a specific polyclonal antiserum, produced against affinity purified nitric oxide synthase from whole rat brain, following the avidin-biotin peroxidase procedure. Immunoreactive cell bodies and processes showed a widespread distribution in the brain. In the telencephalon, immunoreactive structures were distributed in all areas of the cerebral cortex, the ventral endopiriform nucleus and claustrum, the main and accessory olfactory bulb, the anterior and posterior olfactory nuclei, the precommisural hippocampus, the taenia tecta, the nucleus accumbens, the stria terminalis, the caudate putamen, the olfactory tubercle and islands of Calleja, septum, globus pallidus and substantia innominata, hippocampus and amygdala. In the diencephalon, the immunoreactivity was largely found in both the hypothalamus and thalamus. In the hypothalamus, immunoreactive cell bodies were characteristically located in the perivascular-neurosecretory systems and mamillary bodies. In addition, immunoreactive nerve fibres were detected in the median eminence of the infundibular stem. The mesencephalon showed nitric oxide synthase immunoreactivity in the ventral tegmental area, the interpeduncular nucleus, the rostral linear nucleus of the raphe and the dorsal raphe nucleus. Immunoreactive structures were also found in the nuclei of the central grey, the peripeduncular nucleus and substantia nigra pars lateralis, the geniculate nucleus and in the superior and inferior colliculi. The pons displayed immunoreactive structures principally in the pedunculopontine and laterodorsal tegmental nuclei, the ventral tegmental nucleus, the reticulotegmental pontine nucleus, the parabrachial nucleus and locus coeruleus. In the medulla oblongata, immunoreactive neurons and processes were detected in the principal sensory trigeminal nucleus, the trapezoid body, the raphe magnus, the pontine reticular nuclei, the supragenual nucleus, the prepositus hypoglossal nucleus, the medial and spinal vestibular nuclei, the dorsal cochlear nucleus, the medullary reticular field, the nucleus of the solitary tract, the gracile and cuneate nuclei, the dorsal nucleus of the vagus nerve and the oral, interpolar and caudal parts of the spinal trigeminal nucleus. In the cerebellum, the stellate and basket cells showed immunoreactivity, which was also seen in the basket terminal fibres of the Purkinje cell layer. Isolated immunoreactive Purkinje cells were found in the vermis and parafloccular regions of the cerebellum. In the granular layer of the cerebellum, the granular cells and glomeruli were also immunoreactive. Numerous positive varicose nerve fibres and occasional neurons were also found in the lateral and interposed cerebellar nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)