Nitric oxide synthase in invertebrates

Apextrin from Ruditapes philippinarum functions as pattern recognition receptor and modulates NF-κB pathway

Apextrin belongs to ApeC-containing proteins (ACPs) and features a signal-peptide, an N-terminal membrane attack complex component/perforin (MACPF) domain, and a C-terminal ApeC domain. Recently, apextrin-like proteins were identified as pattern recognition receptor (PRR), which recognize the bacterial cell wall component and participate in innate immunity. Here, an apextrin (Rpape) was identified and characterized in Ruditapes philippinarum. Our results showed that Rpape mRNA was significantly induced under bacterial challenges. The Rpape recombinant protein exhibited a significant inhibitory effect on gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus) and bound with Vibrio anguillarum, S. aureus and B. subtilis. We found Rpape protein positively activated the NF-κB signaling cascade and increased the activity of Nitric oxide (NO). This study revealed the immunity role of apextrin in R. philippinarum and provided a reference for further study on the role of apextrin in bivalves.

Optimizing and Evaluating the Antihelminthic Activity of the Biocompatible Zinc Oxide Nanoparticles Against the Ascaridid Nematode, Parascaris equorum In Vitro

PURPOSE

In the present study, the effect of different biocompatible concentrations from ZnO nanoparticles (ZnO NPs) on the physiological state and surface topography of the nematode P. equorum was determined in vitro.

METHODS

Different concentrations of ZnO NPs (100, 200, 300 and 400 mg/l) synthesized using the egg white were prepared followed by the incubation of parasitic worms with these concentrations in vitro. The physiological state of treated worms such as oxidative stress markers, enzymatic activities and biochemical parameters in addition to the surface topography was determined and compared with control untreated worms.

RESULTS

In comparison to control worms, it was observed that at high concentrations of ZnO NPs, most of the treated worms showed an increase in the levels of ALT, AST and ALP (worm muscle damage, and gonad injury); enhancement of the total protein content (worm cellular dysfunction); significant increase in MDA level (free radical-mediated worm cell membrane damage); depletion in GST and GSH activities (reduced ability to clear toxic compounds like lipid peroxides); CAT depletion (superoxide dismutase and hydrogen peroxide toxicity) and NO increase (detoxification activity and stressful conditions on worms). SEM showed that there was a modified morphological appearance in the surface of treated worms; lips were wrinkled with irregularly arranged denticles, weathering of cuticle, bursts of cuticle layers, disruption of surface annulations and erosion of surface papillae of male around the cloacal opening.

CONCLUSION

ZnO NPs at environmentally relevant concentrations achieved a significant antihelminthic activity against P. equorum which represents a successful model used in parasite control experiments.

Modeling Renal Disease "On the Fly"

Detoxification is a fundamental function for all living organisms that need to excrete catabolites and toxins to maintain homeostasis. Kidneys are major organs of detoxification that maintain water and electrolyte balance to preserve physiological functions of vertebrates. In insects, the renal function is carried out by Malpighian tubules and nephrocytes. Due to differences in their circulation, the renal systems of mammalians and insects differ in their functional modalities, yet carry out similar biochemical and physiological functions and share extensive genetic and molecular similarities. Evolutionary conservation can be leveraged to model specific aspects of the complex mammalian kidney function in the genetic powerhouse Drosophila melanogaster to study how genes interact in diseased states. Here, we compare the human and Drosophila renal systems and present selected fly disease models.

Enzyme Histochemistry for Functional Histology in Invertebrates

In invertebrates, enzyme histochemistry has recently found a renaissance regarding its applications in morphology and ecology. Many enzyme activities are useful for the morphofunctional characterization of cells, as biomarkers of biological and pathologic processes, and as markers of the response to environmental stressors. Here, the adjustments to classic techniques, including the most common enzymes used for digestion, absorption, transport, and oxidation, as well as techniques for azo-coupling, metal salt substitution and oxidative coupling polymerization, are presented in detail for various terrestrial and aquatic invertebrates. This chapter also provides strategies to solve the problems regarding anesthesia, small body size, the presence of an exo- or endoskeleton and the search for the best fixative in relation to the internal fluid osmolarity. These techniques have the aim of obtaining good results for both the pre- and post-embedding labeling of specimens, tissue blocks, sections, and hemolymph smears using both light and transmission electron microscopy.

Characterization of NADPH Diaphorase- and Doublecortin-Positive Neurons in the Lizard Hippocampal Formation

The lizard cortex has remarkable similarities with the mammalian hippocampus. Both regions process memories, have similar cytoarchitectural properties, and are important neurogenic foci in adults. Lizards show striking levels of widespread neurogenesis in adulthood and can regenerate entire cortical areas after injury. Nitric oxide (NO) is an important regulatory factor of mammalian neurogenesis and hippocampal function. However, little is known about its role in nonmammalian neurogenesis. Here, we analyzed the distribution, morphology, and dendritic complexity (Neurolucida reconstructions) of NO-producing neurons through NADPH diaphorase (NADPHd) activity, and how they compare with the distribution of doublecortin-positive (DCX+) neurons in the hippocampal formation of the neotropical lizard Tropidurus hispidus. NADPHd-positive (NADPHd+) neurons in the dorsomedial cortex (DMC; putatively homologous to mammalian CA3) were more numerous and complex than the ones in the medial cortex (MC; putatively homologous to the dentate gyrus). We found that NADPHd+ DMC neurons send long projections into the MC. Interestingly, in the MC, NADPHd+ neurons existed in 2 patterns: small somata with low intensity of staining in the outer layer and large somata with high intensity of staining in the deep layer, a pattern similar to the mammalian cortex. Additionally, NADPHd+ neurons were absent in the granular cell layer of the MC. In contrast, DCX+ neurons were scarce in the DMC but highly numerous in the MC, particularly in the granular cell layer. We hypothesize that NO-producing neurons in the DMC provide important input to proliferating/migrating neurons in the highly neurogenic MC.

Effects of ectoine on behavioural, physiological and biochemical parameters of Daphnia magna

Ectoine (ECT) is a compatible solute produced by soil, marine and freshwater bacteria in response to stressful factors. The purpose of our study was to determine the possible toxic influence of ECT on Daphnia magna. We determined the following endpoints: survival rate during exposure and recovery, swimming performance, heart rate, thoracic limb movement determined by image analysis, haemoglobin level by ELISA assay, catalase and nitric oxide species (NOx) by spectrophotometric methods. The results showed 80% survival of daphnids exposed to 50mg/L of ECT after 24h and 10% after 90h, however lower concentrations of ECT were well tolerated. A concentration-dependent reduction of swimming velocity was noted at 24 and 48h of the exposure. ECT (at 2.5 and 4mg/L) induced an increase of heart rate and thoracic limb movement (at 2.5, 4 and 20mg/L) after 24h. After 10h of the exposure to ECT daphnids showed a concentration-dependent increase of haemoglobin level synthesized and accumulated in the epipodite epithelia. After 24h we noted a concentration-dependent decrease of haemoglobin level and its lowest value was found after 48h of the exposure. ECT at a concentration of 20 and 25mg/L slightly stimulated catalase activity after 24h. NOx level was also increased after 10h of the exposure to 20 and 25mg/L of ECT reaching maximal activity after 24h. Our results suggest that ECT possesses some modulatory potential on the behaviour, physiology and biochemical parameters in daphnids.

A kinetic approach to assess oxidative metabolism related features in the bivalve Mya arenaria

Electron paramagnetic resonance uses the resonant microwave radiation absorption of paramagnetic substances to detect highly reactive and, therefore, short-lived oxygen and nitrogen centered radicals. Previously, steady state concentrations of nitric oxide, ascorbyl radical (A·) and the labile iron pool (LIP) were determined in digestive gland of freshly collected animals from the North Sea bivalve Mya arenaria. The application of a simple kinetic analysis of these data based on elemental reactions allowed us to estimate the steady state concentrations of superoxide anion, the rate of A· disappearance and the content of unsaturated lipids. This analysis applied to a marine invertebrate opens the possibility of a mechanistic understanding of the complexity of free radical and LIP interactions in a metabolically slow, cold water organism under unstressed conditions. This data can be further used as a basis to assess the cellular response to stress in a simple system as the bivalve M. arenaria that can then be compared to cells of higher organisms.

Nitric oxide pathway in lower metazoans

The presence of nitric oxide (NO) pathway has been well demonstrated in the main invertebrate groups, showing parallel findings on the role of NO in vertebrates and invertebrates. Noteworthy is the example of the role played by the nitrergic pathway in the sensorial functions, mainly in olfactory-like systems. On the other hand, the emerging molecular information about NOSs from lower metazoans (Porifera, cnidarians up to higher invertebrates) suggests that NO pathways might represent examples of a parallel evolution of the NOS prototypes in different animal lineages. Nevertheless, increasing evidence suggests that NO is one of the earliest and most widespread signaling molecules in living organisms. Here, we attempt to provide a survey of current knowledge of the synthesis and possible roles of NO and the related signaling pathway in lower metazoans (i.e., Porifera and Cnidaria), two phyla forming a crucial bridge spanning the evolutionary gap between the protozoans and higher metazoans. From the literature data here reported, it emerges that future research on the biological roles of NO in basal metazoans is likely to be very important for understanding the evolution of signaling systems.

Hypothermia translocates nitric oxide synthase from cytosol to membrane in snail neurons

Neuronal nitric oxide (NO) levels are modulated through the control of catalytic activity of NO synthase (NOS). Although signals limiting excess NO synthesis are being extensively studied in the vertebrate nervous system, our knowledge is rather limited on the control of NOS in neurons of invertebrates. We have previously reported a transient inactivation of NOS in hibernating snails. In the present study, we aimed to understand the mechanism leading to blocked NO production during hypothermic periods of Helix pomatia. We have found that hypothermic challenge translocated NOS from the cytosol to the perinuclear endoplasmic reticulum, and that this cytosol to membrane trafficking was essential for inhibition of NO synthesis. Cold stress also downregulated NOS mRNA levels in snail neurons, although the amount of NOS protein remained unaffected in response to hypothermia. Our studies with cultured neurons and glia cells revealed that glia-neuron signaling may inhibit membrane binding and inactivation of NOS. We provide evidence that hypothermia keeps NO synthesis "hibernated" through subcellular redistribution of NOS.

Nitric oxide and respiratory helminthic diseases

Nitric oxide (NO) is a very simple molecule that displays very important functions both in helminths (mainly those involved in respiratory pathology) and in mammalian hosts. In this paper we review four issues related to interaction of NO and lung helminthic diseases. Firstly, we evaluated data available on the NO synthesis and release by helminths and their biological role. Next, we summarized the effect of antigens obtained from different phases of the biological cycle on NO production by host mammalian cells (mainly from human sources). Thirdly, we revised the evaluation of NO on the biological activities and/or the viability of respiratory helminths. Lastly, the deleterious consequences of increased production of NO during helminthic human infection are detailed.

Cyclic guanosine monophosphate signaling cascade mediates pigment aggregation in freshwater shrimp chromatophores

The cell signaling cascades that mediate pigment movements in crustacean chromatophores are not yet well established, although Ca(2+) and cyclic nucleotide second messengers are involved. Here, we examine the participation of cyclic guanosine monophosphate (cGMP) in pigment aggregation triggered by red pigment concentrating hormone (RPCH) in the red ovarian chromatophores of freshwater shrimp. In Ca(2+)-containing (5.5 mmol l(-1)) saline, 10 micromol l(-1) dibutyryl cGMP alone produced complete pigment aggregation with the same time course ( approximately 20 min) and peak velocity ( approximately 17 microm/min) as 10(-8) mol l(-1) RPCH; however, in Ca(2+)-free saline (9 x 10(-11) mol l(-1) Ca(2+)), db-cGMP was without effect. The soluble guanylyl cyclase (GC-S) activators sodium nitroprusside (SNP, 0.5 micromol l(-1)) and 3-morpholinosydnonimine (SIN-1, 100 micromol l(-1)) induced moderate aggregation by themselves ( approximately 35%-40%) but did not affect RPCH-triggered aggregation. The GC-S inhibitors zinc protoporphyrin IX (ZnPP-XI, 30 micromol l(-1)) and 6-anilino-5,8-quinolinedione (LY83583, 10 micromol l(-1)) partially inhibited RPCH-triggered aggregation by approximately 35%. Escherichia coli heat-stable enterotoxin (STa, 1 micromol l(-1)), a membrane-receptor guanylyl cyclase stimulator, did not induce or affect RPCH-triggered aggregation. We propose that the binding of RPCH to an unknown membrane-receptor type activates a Ca(2+)-dependent signaling cascade coupled via cytosolic guanylyl cyclase and cGMP to protein kinase G-phosphorylated proteins that regulate aggregation-associated, cytoskeletal molecular motor activity. This is a further example of a cGMP signaling cascade mediating the effect of a crustacean X-organ neurosecretory peptide.

Seawater Ca2+ concentration influences solar orientation in Talitrus saltator (Crustacea, Amphipoda)

The role of salinity in the ecophysiology of many intertidal invertebrates has been extensively investigated. Calcium (Ca2+), magnesium(Mg2+), potassium (K+) and sodium (Na+) are the major constituents of seawater and it has been demonstrated that sandhoppers tested under the sun in diluted seawater (3.5‰) head seaward, instead of going landward as expected. Therefore, the variation in seawater salinity (from 35‰ to 3.5‰) influences their directional choice. This paper investigates the contribution of different cations to the sea–land directional choice of Talitrus saltator(Crustacea, Amphipoda) by the sun compass orientation mechanism. Results of releases carried out in basic seawater selectively deprived of Ca2+, Mg2+ or K+ and containing the same concentration of Na+ indicate that only the reduction in Ca2+ concentration affects the capacity of solar orientation. The pH does not influence the directional choice of sandhoppers and nor do small variations in salinity in the range 32–39‰. Moreover, the clear photopositive tendency registered in experiments of phototaxis in Ca2+-deprived seawater indicates that the absence of Ca2+ does not affect the normal functioning of the visual cells. Therefore, our results show that Ca2+ seawater concentration is important for the correct functioning of one of the principal mechanisms of orientation in supralittoral amphipods and it could affect their survival in the field.

Changes in the expression pattern of the nitrergic system of ovine cerebellum affected by scrapie

The constitutive and inducible isoforms of nitric oxide synthase (NOS) and the end-product of nitration, nitrotyrosine, were analyzed by immunohistochemistry, Western blotting, and enzymatic activity in sheep at different stages of the prion disease, scrapie. Four groups were studied: 1) nonaffected (control), 2) preclinical, 3) clinical, and 4) terminal. Constitutive neuronal NOS (nNOS) was the most abundant isoform present in cerebellar neurons of the sheep. Expression of nNOS increased in preclinical animals but diminished in the late stages of the disease. The Purkinje cells that usually are not immunoreactive for this protein became immunopositive in the clinical phase. In unaffected sheep, the inducible isoform (iNOS) was slightly positive in the Purkinje cells. As the disease progressed, the immunoreactivity of Purkinje neurons for iNOS increased. At the final stages, numerous iNOS-positive microglial cells were found in the molecular layer. There was a basal level of protein nitration in the cerebellum of unaffected sheep, especially in the molecular layer. As the disease progressed, the distal prolongations of the Purkinje cells and the astroglia became immunoreactive for nitrotyrosine. Our results suggest that the nitrergic system reacts to the progression of spongiform diseases and may be part of their pathogenesis mechanism.

Distribution and expression pattern of the nitrergic system in the cerebellum of the sheep

The nitrergic system produces nitric oxide as an atypical neurotransmitter in the nervous system. Nitric oxide is produced from l-arginine through specific enzymes known as nitric oxide synthases. Of these, the more abundant form in neurons is the constitutive neuronal nitric oxide synthase, although the inducible isoform can be expressed as well, especially following stress or other injuries. The excessive formation of nitric oxide results in protein nitration, particularly at tyrosine residues, thus the presence of nitrotyrosine can be used as a marker of nitric oxide production. In previous studies we have shown the distribution of the components of the nitrergic system in the cerebellum of rodents, where neuronal nitric oxide synthase immunoreactivity was present in stellate and basket cells, and occasionally in granule cells. Here, we present evidence that in the sheep, as a model of larger mammals, most cerebellar neurons display an intense immunostaining for neuronal nitric oxide synthase, including unipolar brush cells, and Lugaro and Golgi neurons, which are not immunoreactive in rodents. In addition, weak immunoreactivity for inducible nitric oxide synthase and nitrotyrosine was found in particular cell types, indicating a basal expression for these markers. Our results suggest a larger dependence on the nitrergic system for the cerebella of larger mammals. Since this increase happens in both activating and inhibitory neurons of the cerebellar circuitry, we propose that in these animals there is a higher steady-state regulation of the cerebellum based on nitric oxide.

Nitric oxide production in blowfly hemolymph after yeast inoculation

Although insects lack the adaptive immune response of the mammalians, they manifest effective innate immune responses that include both cellular and humoral components. Cellular responses are mediated by hemocytes and humoral responses include the activation of proteolytic cascades that initiate many events, including NO production. In this work, we determined NO production in Chrysomya megacephala hemolymph and hemocytes after yeast inoculation. Assays were performed with non-infected controls (NIL), saline-injected larvae (SIL) or larvae injected with Saccharomyces cerevisiae (YIL). The hemolymph of injected groups was collected 0.5, 1, 2, 4, 12, 24 or 48h post-injection. NO levels in SIL were comparable to those measured in NIL until 12h, which might be considered the basal production, increasing at 24 and 48h post-injection, probably in response to the increased larval fragility after cuticle rupture. YIL exhibited significantly higher levels of NO than were found in other groups, peaking at 24h. l-NAME and EDTA caused a significant reduction of NO production in YIL at this time, suggesting the activity of a Ca(2+)-dependent NOS. Plasmatocytes and granular cells phagocytosed the yeasts. Plasmatocytes initiated the nodule formation and granular cells were the only hemocyte type to produce NO. These results permit us to conclude that yeasts induced augmented NO production in C. megacephala hemolymph and granular cells are the hemocyte type involved with the generation of this molecule.

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.

Formation of reactive species and induction of antioxidant defence systems in polar and temperate marine invertebrates and fish

High oxygen solubility at cold-water temperature is frequently considered to be responsible for an apparently elevated level of antioxidant protection in marine ectotherms from polar environments. However, tissue oxidative stress is in most cases a function of elevated or variable pO2, rather than of an elevated tissue oxygen concentration. This review summarizes current knowledge on pro- and antioxidant processes in marine invertebrates and fish, and relates reactive oxygen species (ROS) formation in polar ectotherms to homeoviscous adaptations of membrane and storage lipids, as well as to tissue hypoxia and re-oxygenation during physiological stress.

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.

Evidence for a possible role for nitric oxide in the modulation of heart activity in Achatina fulica and Helix aspersa

The effects of nitric oxide (NO) donors, S-nitroso-N-acetylpenicillamine, S-nitroso-l-glutathione, sodium nitroprusside and sodium nitrite were investigated on the activity of the isolated hearts of Achatina fulica and Helix aspersa. NO donors inhibited heart activity in a concentration-dependent manner. The only exception was sodium nitroprusside, which excited H. aspersa heart. The inhibitory effects of these NO donors were reduced by the NO scavenger, methylene blue, the guanylyl cyclase inhibitor, 1H-(1,2,4) Oxadiazolo(4,3-a)quinoxalin-1-one (ODQ), and potentiated by 8-Br-cGMP and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). Acetylcholine also inhibited the heart activity, and this inhibition was reduced by methylene blue and ODQ. Positive NADPH-diaphorase staining was located in the outer pericardial layer of the heart of A. fulica. The present results provide evidence that NO may modulate the activity of gastropod hearts, and this modulation may modify the inhibitory action of acetylcholine on heart activity.

Methylene blue blocks cGMP production and disrupts directed migration of microglia to nerve lesions in the leech CNS

Migration and accumulation of microglial cells at sites of injury are important for nerve repair. Recent studies on the leech central nervous system (CNS), in which synapse regeneration is successful, have shown that nitric oxide (NO) generated immediately after injury by endothelial nitric oxide synthase (eNOS) stops migrating microglia at the lesion. The present study obtained results indicating that NO may act earlier, on microglia migration, and aimed to determine mechanisms underlying NO's effects. Injury induced cGMP immunoreactivity at the lesion in a pattern similar to that of eNOS activity, immunoreactivity, and microglial cell accumulation, which were all focused there. The soluble guanylate cyclase (sGC) inhibitor methylene blue (MB) at 60 microM abolished cGMP immunoreactivity at lesions and blocked microglial cell migration and accumulation without interfering with axon conduction. Time-lapse video microscopy of microglia in living nerve cords showed MB did not reduce cell movement but reduced directed movement, with significantly more cells moving away from the lesion or reversing direction and fewer cells moving toward the lesion. The results indicate a new role for NO, directing the microglial cell migration as well as stopping it, and show that NO's action may be mediated by cGMP.

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.

Regulation of early embryonic behavior by nitric oxide in the pond snail Helisoma trivolvis

Helisoma trivolvis embryos display a cilia-driven rotational behavior that is regulated by a pair of serotonergic neurons named ENC1s. As these cilio-excitatory motor neurons contain an apical dendrite ending in a chemosensory dendritic knob at the embryonic surface, they probably function as sensorimotor neurons. Given that nitric oxide (NO) is often associated with sensory neurons in invertebrates, and has also been implicated in the control of ciliary activity, we examined the expression of NO synthase (NOS) activity and possible function of NO in regulating the rotational behavior in H. trivolvis embryos. NADPH diaphorase histochemistry on stage E25-E30 embryos revealed NOS expression in the protonephridia, buccal mass,dorsolateral ciliary cells and the sensory dendritic knobs of ENC1. At stages E35-40, the pedal ciliary cells and ENC1's soma, apical dendrite and proximal descending axon were also stained. In stage E25 embryos, optimal doses of the NO donors SNAP and SNP increased the rate of embryonic rotation by twofold, in contrast to the fourfold increase caused by 100 μmol l-1serotonin. The NOS inhibitors L-NAME (10 mmol l-1) and 7-NI (100μmol l-1) decreased the rotation rate by approximately 50%,whereas co-addition of L-NAME and SNAP caused a twofold increase. In an analysis of the surge and inter-surge subcomponents of the rotational behavior, the NO donors increased the inter-surge rotation rate and the surge amplitude. In contrast, the NO inhibitors decreased the inter-surge rotation rate and the frequency of surges. These data suggest that the embryonic rotational behavior depends in part on the constitutive excitatory actions of NO on ENC1 and ciliary cells.

Nicotinic-acetylcholine receptors are functionally coupled to the nitric oxide/cGMP-pathway in insect neurons

In addition to their ionotropic role, neuronal nicotinic acetylcholine receptors (nAChRs) can influence second messenger levels, transmitter release and gene transcription. In this study, we show that nAChRs in an insect CNS control cGMP levels by coupling to NO production. In conditions that inhibit spiking, nicotine induced cGMP synthesis. This increase in cGMP was blocked by nicotinic antagonists, and by inhibitors of both nitric oxide synthase and soluble guanylyl cyclase. The nicotinic-evoked increase in cGMP was localized to specific NO-sensitive neurons in the CNS, several of which are identified motoneurons. Because NO production requires Ca2+, we investigated the effect of nicotinic stimulation on [Ca2+]i in cultured neurons. We found that activation of nAChRs increased [Ca2+]i, which was blocked by nAChR antagonists. Nicotinic stimulation of neurons in the isolated CNS in low-Na+, also evoked increases in [Ca2+]i independent of fast changes in voltage. In addition, approximately 10% of the nicotinic-evoked [Ca2+]i increase in cultured neurons persisted when voltage-gated Ca2+ channels were blocked by Ni2+. Under the same conditions, nicotinic stimulation of cGMP in the CNS was unaffected. These combined results suggest that nicotinic stimulation is coupled to NOS potentially by directly gating Ca2+.

A critical assessment of the neurodestructive and neuroprotective effects of nitric oxide

Whether nitric oxide is cytodestructive or cytoprotective is of obvious clinical importance. The debate on this subject in the past decade has generated much "heat and light". This paper focuses on the actions of NO on the nervous system and reexamines the controversial issue and the contribution of the authors and their colleagues in the light of recent findings. We also report new findings, critically assesses previous experimental data, and share perspectives on this important subject.

Nitric oxide synthase sequences in the marine fish Stenotomus chrysops and the sea urchin Arbacia punctulata, and phylogenetic analysis of nitric oxide synthase calmodulin-binding domains

The phylogenetic distribution and structural diversity of the nitric oxide synthases (NOS) remain important and issues that are little understood. We present sequence information, as well as phylogenetic analysis, for three NOS cDNAs identified in two non-mammalian species: the vertebrate marine teleost fish Stenotomus chrysops (scup) and the invertebrate echinoderm Arbacia punctulata (sea urchin). Partial gene sequences containing the well-conserved calmodulin (CaM)-binding domain were amplified by RT-PCR. Identical 375-bp cDNAs were amplified from scup brain, heart, liver and spleen; this sequence shares 82% nucleic acid and 91% predicted amino acid identity with the corresponding region of human neuronal NOS. A 387-bp cDNA was amplified from sea urchin ovary and testes; this sequence shares 72% nucleic acid identity and 65% deduced amino acid identity with human neuronal NOS. A second cDNA of 381 bp was amplified from sea urchin ovary and it shares 66% nucleic acid and 57% deduced amino acid identity with the first sea urchin sequence. Together with earlier reports of neuronal and inducible NOS sequences in fish, these data indicate that multiple NOS isoforms exist in non-mammalian species. Phylogenetic analysis of these sequences confirms the conserved nature of NOS, particularly of the calmodulin-binding domains.

Role of superoxide and reactive nitrogen intermediates in Rhodnius prolixus (Reduviidae)/Trypanosoma rangeli interactions

This study compares aspects of the superoxide, nitric oxide and prophenoloxidase pathways in Rhodnius prolixus hemolymph, measured in parallel, in response to Trypanosoma rangeli inoculation. Responses to two strains of T. rangeli, and two developmental forms, were studied, and the results obtained were correlated with the ability of the parasites to survive, multiply, and complete their life cycles in the hemolymph of the host. T. rangeli H14 strain parasites, which fail to complete their life cycle in Rhodnius by invading the salivary glands, stimulated high levels of superoxide and prophenoloxidase activity, which peaked 24 h after inoculation. Simultaneously, the concentration of hemolymph nitrites and nitrates increased, indicative of nitric oxide activity, but parasite numbers remained low. T. rangeli Choachi strain parasite inoculation also stimulated superoxide and prophenoloxidase activity, which, though significantly lower than the equivalent responses to the H14 strain, also peaked at 24 h. However, nitrate and nitrite levels in Choachi strain-inoculated hemolymph remained low, and this parasite strain multiplied rapidly, especially following peak superoxide activity, and eventually invaded the salivary glands for transmission to a vertebrate host. In both strains, short form epimastigotes stimulated greater superoxide and prophenoloxidase responses than long form epimastigotes. Injection of the NADPH oxidase inhibitor N-ethylmaleimide or the inducible nitric oxide synthase inhibitor S-methyl isothiourea sulfate caused significantly higher insect mortalities in groups of R. prolixus inoculated with either parasite strain compared with those of uninfected control insects. This indicates that both NADPH oxidase and nitric oxide synthase activity may be involved in the immune response of R. prolixus to infection by T. rangeli. Finally, Western blotting of R. prolixus hemocyte lysates revealed the presence of a protein immunologically related to the human NADPH oxidase complex, the initiator enzyme of the respiratory burst.

Nitric oxide synthase in filariae: demonstration of nitric oxide production by embryos in Brugia malayi and Acanthocheilonema viteae

The radical gas nitric oxide (NO) is synthesized by nitric oxide synthase (NOS) from l-arginine and molecular oxygen. Nitric oxide is an important signaling molecule in invertebrate and vertebrate systems. Previously we have shown that NOS is localized to more tissues in Brugia malayi than has been reported in Ascaris suum. In this paper, we analyze the distribution of NOS in Acanthocheilonema viteae, a filarial nematode that differs from B. malayi in that A. viteae females release microfilariae without a sheath. A. viteae is also one of a few filarial parasites without the Wolbachia intracellular endosymbiont. By use of a specific antibody, NOS was demonstrated in extracts of A. viteae and Dirofilaria immitis. The localization pattern of NOS in A. viteae was similar to that seen in B. malayi, with the enzyme localized to the body wall muscles of both sexes, developing spermatozoa, intrauterine sperm, and early embryos. By use of DAF-2, a fluorescent indicator specific for nitric oxide, the embryos of B. malayi and A. viteae were demonstrated to produce NO ex utero. The near identical staining patterns seen in A. viteae and B. malayi argue that NO is not produced by Wolbachia, nor is it produced by the nematodes in response to the infection. Localization of NOS to the sperm of filarial nematodes suggests a role for NO during fertilization as has been described for sea urchin and ascidian fertilization. Demonstration of the activity of embryonic NOS supports our earlier hypothesis that NO is a signaling molecule during embryogenesis in filarial nematodes.

Nitric oxide generation by hemocytes of the mussel Mytilus galloprovincialis

The phagocytic activity of Mytilus galloprovincialis hemocytes is thought to be associated with NADPH-oxidase activity of the plasma membrane, thus producing superoxide anions. Few studies, however, have been devoted to nitric oxide release by these haemocytes. We investigated NO generation in M. galloprovincialis in order to understand its role in the defensive mechanisms of these organisms. The presence of NO-synthase-like enzymatic activity in protein homogenates from M. galloprovincialis hemocytes was revealed by the conversion of radiolabelled L-arginine to L-citrulline. We observed partial inhibition of the luminol-dependent chemiluminescence of stimulated M. galloprovincialis hemocytes by both NO-synthase inhibitors and superoxide dismutase, indicating that peroxynitrite (which results from the reaction between nitric oxide and superoxide anions) partially mediated this chemiluminescence. Furthermore, we confirmed the production of nitric oxide by M. galloprovincialis by highlighting the nitric oxide-synthase-dependence of the nitrate and nitrite production of stimulated hemocytes.

Effects of nitric oxide donors on the afferent resting activity in the cephalopod statocyst

The effects of bath applications of the nitric oxide (NO) donors sodium nitroprusside (SNP), diethylamine sodium (DEA), 3-morpholinosydnonimine (SIN-1), and S-nitroso-N-acetyl-penicillamine (SNAP) on the resting activity (RA) of afferent crista fibers were studied in isolated statocysts of the cuttlefish Sepia officinalis. The NO donors had three different effects: inhibition, excitation, and excitation followed by an inhibition. The SNAP analog N-acetyl-DL-penicillamine (xSNAP; with no NO moiety) had no effect. When the preparation was pre-treated with the NO synthase inhibitor N(G)-nitric-L-arginine methyl ester HCl (L-NAME), the NO donors were still effective. When the preparation was pre-treated with the guanylate cyclase inhibitors methylene blue (M-BLU) or cystamine (CYS), NO donors had only excitatory effects, whereas their effects were inhibitory only when pre-treatment was with the adenylate cyclase inhibitors nicotinic acid (NIC-A), 2',3'-dideoxyadenosine (DDA), or MDL-12330A. When pre-treatment was with a guanylate and an adenylate cyclase inhibitor combined, NO donors had no effect; in that situation, the RA of the afferent fibers remained and the preparation still responded to bath applications of GABA. Selective experiments with statocysts from the squid Sepioteuthis lessoniana and the octopod Octopus vulgaris gave comparable results. These data indicate that in cephalopod statocysts an inhibitory NO-cGMP and an excitatory NO-cAMP signal transduction pathway exist, that these two pathways are the key pathways for the action of NO, and that they have only modulatory effects on, and are not essential for the generation of, the RA.

Nitric oxide synthase activity and immunoreactivity in the crayfish Procambarus clarkii

The presence, characteristics and localization of nitric oxide synthase (NOS) in the eyestalk ganglia of the crayfish (Procambarus clarkii) were investigated. Biochemical assay indicated that NOS activity was significantly inhibited by N(G)-nitro-L-arginine (a NOS inhibitor), fluphenazine-N-2-chloroethane (a calmodulin inhibitor) as well as by omitting beta-NADPH or Ca2+ from the incubations. Immunohistochemical studies localized NOS immunoreactivity (IR) to the first chiasma and the sinus gland. Finally, a NOS-immunoreactive protein (138 kDa) was detected by Western blot analysis. These data demonstrate for the first time the existence in crustacean eyestalk ganglia of NOS with biochemical characteristics similar to mammalian constitutive NOS. The localization of NOS-IR suggests that NO may be involved in regulating visual processes and neuroendocrine function in crustaceans.

Characterisation of nitric oxide synthase activity in the tropical sea anemone Aiptasia pallida

The presence of nitric oxide synthase (EC 1.14.23 NOS) activity is demonstrated in the tropical marine cnidarian Aiptasia pallida (Verrill). Enzyme activity was assayed by measuring the conversion of [3H]arginine to [3H]citrulline. Optimal NOS activity was found to require NADPH. Activity was inhibited by the competitive NOS inhibitor NG-methyl-L-arginine (L-NMA), but not the arginase inhibitors L-valine and L-ornithine. NOS activity was predominantly cytosolic, and was characterised by a Km for arginine of 19.05 microM and a Vmax of 2.96 pmol/min per microgram protein. Histochemical localisation of NOS activity using NADPH diaphorase staining showed the enzyme to be predominantly present in the epidermal cells and at the extremities of the mesoglea. These results provide a preliminary biochemical characterisation and histochemical localisation of NOS activity in A. pallida, an ecologically important sentinel species in tropical marine ecosystems.

Nitric oxide synthase and cGMP activity in the salivary glands of the American dog tick Dermacentor variabilis

We colocalized nitric oxide synthase (NOS) activity in epithelial cells that surround the salivary gland duct in female Dermacentor variabilis with NADPH diaphorase histochemistry and immunohistochemistry using a polyclonal anti-endothelial NOS. Using size-exclusion chromatography, a fraction with a molecular mass of about 185 kDa that had diaphorase activity was eluted from tick salivary gland homogenate. This fraction converted arginine to citrulline with the production of nitric oxide (NO), which was detected by using electron spin resonance spectroscopy. The complete activity of the diaphorase fraction was dependent on NADPH, FAD, tetrahydrobiopterin, calmodulin, (CaM), and Ca(2+), but was not dependent on dithiothreitol. The arginine analog N(G)-monomethyl-L-arginine inhibited the activity of this fraction. NO and arginine activated soluble guanylate cyclase to produce cGMP in dopamine-stimulated isolated salivary glands. Dopamine-stimulated isolated salivary glands treated with tick saline containing either EDTA, the NOS inhibitor N(G)-nitro-L-arginine methyl ester, or the calcium/CaM binding inhibitor W-7 showed no increase in cGMP. The NO donor sodium nitroprusside significantly increased cGMP levels in unstimulated isolated salivary glands. A possible function for NO in salivation by this ixodid tick is discussed.

Brugia malayi: localization of nitric oxide synthase in a lymphatic filariid

Nitric oxide synthase converts L-arginine to citrulline and nitric oxide, a gaseous signaling molecule critical to multiple physiological responses. Nitric oxide synthase was detected by Western blot analysis of Brugia malayi extracts using an antibody raised against a peptide from murine brain nitric oxide synthase. Using NADPH diaphorase staining and immunohistochemistry, nitric oxide synthase was localized in the parasitic nematode B. malayi. As in Ascaris suum, nitric oxide synthase was detected in the body wall muscles of adult B. malayi. This localization pattern is in agreement with the role of nitric oxide in the control of muscle tone in other invertebrates and in vertebrates. A novel finding was the localization of nitric oxide synthase in the oocytes, in developing embryos, and in spermatozoa. B. malayi nitric oxide synthase may play a role in developmental signaling, as has been suggested for Drosophila and Ilyanassa, a marine mud snail.

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.

Effects of L-arginine on the afferent resting activity in the cephalopod statocyst

The effects of bath application of the nitric oxide (NO) precursor L-arginine (L-ARG) on the resting activity (RA) of afferent crista fibers were studied in isolated statocysts of the cuttlefish Sepia officinalis under various experimental conditions. L-ARG (threshold 10(-7) M) had three different effects: inhibition, excitation, and excitation followed by an inhibition; only the inhibitory effect of L-ARG was dose-dependent. D-Arginine (D-ARG) had no effect. When the preparation was pre-treated with NO synthase inhibitors (N(G)-Nitric-L-arginine methyl ester HCl (L-NAME), N(G)-Nitro-L-arginine (L-NOARG)), both the inhibitory and the excitatory effects of L-ARG significantly decreased at higher concentrations (10(-5 to -4) M), or were completely blocked at lower concentrations (10(-7 to -6) M), of L-ARG. When the preparation was pre-treated with guanylate cyclase inhibitors (1H-[1,2, 4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), methylene blue (M-BLU), cystamine (CYS)), L-ARG had only excitatory effects, whereas its effects were only inhibitory when the preparation was pre-treated with adenylate cyclase inhibitors 2',3'-dideoxyadenosine (DDA), MDL-12330A (MDL), nicotinic acid (NIC-A)). L-ARG had no effects when the pre-treatment was with a guanylate cyclase inhibitor and an adenylate cyclase inhibitor combined; in that situation, the RA of the afferent fibers remained. These data indicate that in cephalopod statocysts, a cGMP and a cAMP signal transduction pathway (presumably via the generation of NO) are responsible for the effects of L-ARG on the RA of crista afferent fibers. They also indicate that the L-ARG-cGMP pathway is the dominant pathway and is inhibitory, and that both pathways have only modulatory effects on, but are not essential for, the generation of the RA.

Mature and developing visual system of Ceratitis capitata (Diptera, Tephritidae): histochemical evidence of nitric oxide synthase in the wild type and the white eye mutant strains

Nitric oxide (NO) is acknowledged as a messenger molecule in the nervous system. It has a role in the modulation of the chemosensory information and seems implicated also in visual processes and visually guided behaviour of some insects. In the present study, we used two different strains of the medfly Ceratitis capitata (Diptera, Tephritidae), a wild type eye colour and a white eye mutant line, as models to clarify the involvement of NO in the mature and developing visual system. The comparison between the pattern of enzyme histochemical localization of NO synthase (NOS), through NADPH diaphorase (NADPHd) staining, in the optic lobes of the two strains revealed for adults a stronger intensity of reaction in all the neuropiles and the sub-retinic monopolar cell layer of the wild type flies, with respect to the white eye mutant correspondent areas. Anti-NOS immunocytochemistry correlated with these results, underlying reactivity both in fine fibres and varicosities and in cell bodies and supporting the idea of presence of NOS also in the retina of the medfly optic lobes. NADPHd reactivity was present in the first developmental stages of the white eye mutant also, but at lower intensity than wild type, and it decreased in some areas during the transition to adult fly stage both in the wild type and in the white eye mutant. All these observations together indicate that changes in the NO system of C. capitata could be related to the visual information processing, when the visual response or discrimination are altered. Furthermore, NO may be involved in the establishment of the retinal projection pattern and in the control of optic lobes morphogenesis.

Nitric oxide-containing neurons in the nervous ganglia of Helix aspersa during rest and activity: immunocytochemical and enzyme histochemical detection

Nitric oxide synthase (NOS) immunoreactivity and staining for nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-diaphorase) activity are two cytochemical markers for nitric oxide (NO)-containing neurons. The authors examined the changes in the distribution of NOS immunolabeling and NADPH-diaphorase reactivity in the cerebral and buccal ganglia of the terrestrial snail Helix aspersa during resting and active phases. During inactivity and after 1 day of activity, in the mesocerebrum and metacerebrum of the snails, there were several reactive neurons for both markers; after 7 days of activity, the number of reactive neurons was lower. Opposite results were obtained in the buccal ganglia, in which increased staining and numbers of reactive neurons were present in the active snails (after 1 day and 7 days of activity). Although the staining patterns for the two reactions were similar, colocalization was not always observed. The comparison between inactive and active animals provided a more precise survey of NOS-containing neurons in the snail cerebral ganglia than previously described. Moreover, it suggested that not only is NO involved in distinct nervous circuits, but, as a ubiquitous molecule, it also plays a role in neuroprotection and neuropeptide release.

Growth phase-dependent subcellular localization of nitric oxide synthase in maize cells

A protein band of approximately 166 kDa was detected in the soluble fraction of root tips and young leaves of maize seedlings, based on Western blot analysis using antibodies raised against mouse macrophage nitric oxide synthase (NOS) and rabbit brain NOS. NOS activity was present in these soluble fractions, as determined by L-[U-14C]citrulline synthesis from L[U-14]arginine. Immunofluorescence showed that the maize NOS protein is present in the cytosol of cells in the division zone and is translocated into the nucleus in cells in the elongation zone of maize root tips. These results indicate the existence of a NOS enzyme in maize tissues, with the localization of this protein depending on the phase of cell growth.

Injury-induced expression of endothelial nitric oxide synthase by glial and microglial cells in the leech central nervous system within minutes after injury

It is known that nitric oxide (NO) is produced by injured tissues of the mammalian central nervous system (CNS) within days of injury. The aim of the present experiments was to determine the cellular synthesis of NO in the CNS immediately after injury, using the CNS of the leech which is capable of synapse regeneration, as a step towards understanding the role of NO in nerve repair. We report that within minutes after crushing the nerve cord of the leech, the region of damage stained histochemically for NADPH diaphorase, which is indicative of nitric oxide synthase (NOS) activity, and was immunoreactive for endothelial NOS (eNOS). On immunoblots of leech CNS extract, the same antibody detected a band with a relative molecular mass of 140,000, which is approximately the size of vertebrate eNOS. Cells expressing eNOS immunoreactivity as a result of injury were identified after freezing nerve cords, a procedure that produced less tissue distortion than mechanical crushing. Immunoreactive cells included connective glia and some microglia. Calmodulin was necessary for the eNOS immunoreactivity: it was blocked by calmodulin antagonist W7 (25 microM), but not by similar concentrations of the less potent calmodulin antagonist W12. Thus in the leech CNS, in which axon and synapse regeneration is successful, an increase in NOS activity at lesions appears to be among the earliest responses to injury and may be important for repair of axons.

Malaria infection of the mosquito Anopheles gambiae activates immune-responsive genes during critical transition stages of the parasite life cycle

Six gene markers have been used to map the progress of the innate immune response of the mosquito vector, Anopheles gambiae, upon infection by the malaria parasite, Plasmodium berghei. In addition to four previously reported genes, the set of markers included NOS (a nitric oxide synthase gene fragment) and ICHIT (a gene encoding two putative chitin-binding domains separated by a polythreonine-rich mucin region). In the midgut, a robust response occurs at 24 h post-infection, at a time when malaria ookinetes traverse the midgut epithelium, but subsides at later phases of malaria development. In contrast, the salivary glands show no significant response at 24 h, but are activated in a prolonged late phase when sporozoites are released from the midgut into the haemolymph and invade the glands, between 10 and 25 days after blood feeding. Furthermore, the abdomen of the mosquito minus the midgut shows significant activation of immune markers, with complex kinetics that are distinct from those of both midgut and salivary glands. The parasite evidently elicits immune responses in multiple tissues of the mosquito, two of which are epithelia that the parasite must traverse to complete its development. The mechanisms of these responses and their significance for malaria transmission are discussed.

Histochemical study on the relation between NO-generative neurons and central circuitry for feeding in the pond snail, Lymnaea stagnalis

To examine whether nitric oxide (NO)-generative neurons are included in the central circuitry for generation of feeding pattern in the pond snail, Lymnaea stagnalis, two staining techniques for NADPH diaphorase and serotonin (5-HT) were applied for its central nervous system (CNS). The former technique is known to show localization of NO synthase; the latter is well employed as a marker for the feeding circuitry because 5-HT is a main transmitter in it. In the buccal ganglion, B2 motoneuron was found to be a putative NO-generative neuron. This motoneuron is not involved directly in the coordination of feeding pattern but is activated simultaneously with the feeding to control the oesophageal and gut tissues for the digestion. Taking account of the diffusion effects of NO, the NO released from B2 motoneuron, when the feeding is started, is thought to sufficiently modulate the feeding circuitry. In the cerebral ganglion, the superior lip nerve, the median lip nerve and the tentacle nerve included both putative NO-generative fibers and serotonergic fibers. These fibers are not identical, but the NO released in the nerves may activate the serotonergic fibers, resulting in the influence upon the initiation of the feeding. Therefore, our present findings clearly showed that NO is not involved in transmission within the central circuitry for the feeding, but suggested that NO can crucially affect the feeding behavior, such as initiation and modulation of the feeding pattern.

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.

NADPH-diaphorase containing cells and fibers in the central nervous system of squid, Loligo bleekeri keferstein

Distribution of NADPH-diaphorase in the central nervous system of squid was determined using histochemical technique. We found NADPH-diaphorase positive cell bodies and fibers both in the optic and the posterior anterior lobe and fibers in the peduncle lobe. These results clarify the biochemical similarity between two structurally similar organs of invertebrate and vertebrate, the peduncle lobe and the anterior basal lobe, and the cerebellum. NADPH-diaphorase positive fibers innervated the inner granule layer and the outer plexiform layer of the outer cortex of the optic lobe. This is in good agreement with avian centrifugal projection from isthmo-optic nucleus to retina where nitric oxide synthase is known to be contained. There may be at least two distinct neural systems, the motor control system and the visual information processing system, which use nitric oxide as a transmitter or modulator in the squid central nervous system.

Opiate signaling regulates microglia activities in the invertebrate nervous system

1. Evidence supporting the presence in the invertebrate nervous system of a class of glial cells resembling vertebrate microglia was obtained in the freshwater snail Planorbarius corneus. These cells are easily identified by their immunopositivity to anti-pro-opiomelanocortin (POMC)-derived peptide antibodies. 2. Invertebrate microglia, as in vertebrates, exhibit macrophage-like activity in vivo and in cell cultures. These cells respond to the trauma of ganglionic excision and their organotypic culture by leaving their location around neurons and moving to the lesion site from which they migrate in the culture dish. 3. In vitro, these microglia undergo conformational changes and show phagocytic properties in the presence of bacteria or lipopolysaccharide. The activated cells also express tumor necrosis factor-alpha-like material and an increase in nitric oxide synthase, as shown by immunocytochemistry. 4. The inhibitory effect of morphine on the mobility and phagocytic activity of invertebrate microglia provide additional functional evidence for a possible role of opiate-like compounds in downregulating immunoregulatory processes, as also observed in the circulating immunocytes.