Distribution of NADPH-diaphorase in the perioesophageal ganglia of the snail, Helix aspersa

Characterization of nitric oxide in Octopus maya nervous system and its potential role in sensory perception

The role of nitric oxide as a neurotransmitter in the olfactory and chemoreception systems of invertebrates has been well documented. This suggests an early and efficient sensory detection system that is evolutionarily preserved in various species, including vertebrates and invertebrates. Additionally, the presence of a nitric oxide neurotransmitter system has been reported in molluscs, particularly in octopus species. In this work, we present evidence for the existence of nitric oxide synthase in neurons and fibers, as well as its anatomical localization in various nuclei involved in chemosensory integration and the motor responses associated with these processes in Octopus maya.

A review of the actions of Nitric Oxide in development and neuronal function in major invertebrate model systems

Ever since the late-eighties when endothelium-derived relaxing factor was found to be the gas nitric oxide, endogenous nitric oxide production has been observed in virtually all animal groups tested and additionally in plants, diatoms, slime molds and bacteria. The fact that this new messenger was actually a gas and therefore didn't obey the established rules of neurotransmission made it even more intriguing. In just 30 years there is now too much information for useful comprehensive reviews even if limited to animals alone. Therefore this review attempts to survey the actions of nitric oxide on development and neuronal function in selected major invertebrate models only so allowing some detailed discussion but still covering most of the primary references. Invertebrate model systems have some very useful advantages over more expensive and demanding animal models such as large, easily identifiable neurons and simple circuits in tissues that are typically far easier to keep viable. A table summarizing this information along with the major relevant references has been included for convenience.

Initial studies on the direct and modulatory effects of nitric oxide on an identified central Helix aspersa neuron

The generation of the novel messenger molecule nitric oxide (NO) has been demonstrated in many tissues across phyla including nervous systems. It is produced on demand by the enzyme nitric oxide synthase often stimulated by intracellular calcium and typically affecting guanylate cyclase thought to be its principal target in an auto and/or paracrine fashion. This results in the generation of the secondary messenger cyclic guanosine monophosphate (cGMP). Nitric oxide synthase has been demonstrated in various mollusk brains and manipulation of NO levels has been shown to affect behavior in mollusks. Apart from modulation of the effect of the peptide GSPYFVamide, there appears little published on direct or modulatory effects of NO on Helix aspersa central neurons. We present here initial results to show that NO can be generated in the region around F1 in the right parietal ganglion and that NO and cGMP directly hyperpolarize this neuron. For example, application of the NO-donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP; 200 µM) can cause a mean hyperpolarization of 41.7 mV, while 2 mM 8-bromo-cyclic guanosine monophosphate (8-bromo-cGMP) produced a mean hyperpolarization of 33.4 mV. Additionally, pre-exposure to NO-donors or cGMP appears to significantly reduce or even eliminates the normal hyperpolarizing K(+)-mediated response to dopamine (DA) by this neuron; 200 µM SNAP abolishes a standard response to 0.5 µM DA while 1 mM 8-bromo-cGMP reduces it 62%.

The nociceptin/orphanin FQ-like opioid peptide in nervous periesophageal ganglia of land snail Helix aspersa

The neuropeptide nociceptin/orphanin FQ (N/OFQ) and its receptor are members of the endogenous opioid peptide family. In mammals N/OFQ modulates a variety of biological functions such as nociception, food intake, endocrine, control of neurotransmitter release, among others. In the molluscs Cepea nemoralis and Helix aspersa the administration of N/OFQ produces a thermopronociceptive effect. However, little is known about its existence and anatomic distribution in invertebrates. The aim of this study was to provide a detailed anatomical distribution of N/OFQ like peptide immunoreactivity (N/OFQ-IL), to quantify the tissue content of this peptide, as well as to demostrate molecular evidence of N/OFQ mRNA in the nervous tissue of periesophageal ganglia of the land snail H. aspersa. Immunohistochemical, immunocytochemical, radioimmunoanalysis (RIA) and reverse transcription-polymerase chain reaction (RT-PCR) techniques were used. With regard to RT-PCR, the primers to detect expression of mRNA transcripts from H. aspersa were derived from the rat N/OFQ opioid peptide. We show a wide distribution of N/OFQ-IL in neurons and fibers in all perioesophageal ganglia, fibers of the neuropile, nerves, periganglionar connective tissue, aortic wall and neurohemal sinuses. The total amount of N/OFQ-IL in the perioesophageal ganglia (7.75 ± 1.75 pmol/g of tissue) quantified by RIA was similar to that found in mouse hypothalamus (10.1 ± 1.6 pmol/g of tissue). In this study, we present molecular evidence of N/OFQ mRNA expression. Some N/OFQ-IL neurons have been identified as neuroendocrine or involved in olfaction, hydro-electrolyte regulation, feeding, and thermonociception. Therefore, we suggest that N/OFQ may participate in these snail functions.

Distribution of NADPH-diaphorase activity in the central nervous system of the young and adult land snail Megalobulimus abbreviatus

Nitric oxide (NO) is a gas produced through the action of nitric oxide synthase that acts as a neurotransmitter in the central nervous system (CNS) of adult gastropod mollusks. There are no known reports of the presence of NOS-containing neurons and glial cells in young and adult Megalobulimus abbreviatus. Therefore, NADPH-d histochemistry was employed to map the nitrergic distribution in the CNS of young and adult snails in an attempt to identify any transient enzymatic activity in the developing CNS. Reaction was observed in neurons and fibers in all CNS ganglia of both age groups, but in the pedal and cerebral ganglia, positive neurons were more intense than in other ganglia, forming clusters symmetrically located in both paired ganglia. However, neuronal NADPH-d activity in the mesocerebrum and pleural ganglia decreased from young to adult animals. In both age groups, positive glial cells were located beneath the ganglionic capsule, forming a network and surrounding the neuronal somata. The trophospongium of large and giant neurons was only visualized in young animals. Our results indicate the presence of a nitrergic signaling system in young and adult M. abbreviatus, and the probable involvement of glial cells in NO production.

Nitric oxide production and nitric oxide synthase immunoreactivity in Naegleria fowleri

Free-living ameba Naegleria fowleri produces an acute and fatal infectious disease called primary amebic meningoencephalitis (PAM), whose pathophysiological mechanism is largely unknown. The aim of this study was to investigate the role of nitric oxide (NO) in PAM. Although NO has a cytotoxic effect on various parasites, it is produced by others as part of the pathology, as is the case with Entamoeba histolytica. To test for the production of NO, we analyzed whether antibodies against mammalian NO synthase isoforms (neuronal, inducible, and endothelial) presented immunoreactivity to N. fowleri proteins. We found that the trophozoites produced NO in vitro. The Western blot results, which showed N. fowleri trophozoites, contained proteins that share epitopes with the three described mammalian NOS, but have relative molecular weights different than those described in the literature, suggesting that N. fowleri may contain undescribed NOS isoforms. Moreover, we found that trophozoites reacted to the NOS2 antibody, in amebic cultures as well as in the mouse brain infected with N. fowleri, suggesting that nitric oxide may participate in the pathogenesis of PAM. Further research aimed at determining whether N. fowleri contains active novel NOS isoforms could lead to the design of new therapies against this parasite.

A Possible Stimulatory Effect of FMRFamide on Neural Nitric Oxide Production in the Central Nervous System of Helix lucorum L

The anatomical and functional relationship between neurons expressing nitric oxide (NO) synthase and molluscan cardioexcitatory (FMRFamide)-like neuropeptides was studied in the central ganglia of Helix lucorum (Pulmonata, Gastropoda), applying NADPHdiaphorase (NADPHd) histochemistry to visualize NO synthase and immunocytochemistry to demonstrate FMRFamide (FMRFa) at the light microscopic level. The NO production of the ganglia was detected by the colorimetric Griess determination of nitrite, a breakdown product of NO. Effects of the NO synthase substrate amino acid L-arginine, the NO synthase inhibitor Nomega-nitro-L-arginine (NOARG), synthetic FMRFa and the FMRFa sensitive ion channel blocker amiloride hydrochloride on nitrite production were also tested. NADPHd reaction labeled nerve cells and fibers in the procerebra, mesocerebra and metacerebra within the cerebral ganglia, and cell clusters in the postcerebral ganglia. FMRFa immunolabeling could be observed within subpopulations of NADPHd positive cells and in pericellular varicose fibers surrounding NADPHd stained neurons. Nitrite production of the ganglia was stimulated by L-arginine (10- 20 mM) but was decreased by NOARG (1-2 mM). Synthetic FMRFa (0.830-3.340 mM) increased the nitrite production in a dose dependent manner, but was ineffective in the presence of NOARG. Amiloride hydrochloride (7.890 mM) reduced the FMRFa evoked nitrite production in all ganglia. This is the first description of an anatomical relationship between putative NO producing and FMRFa containing cells, suggesting a possible regulatory role of FMRFa in the NO mediated signaling in an invertebrate nervous system.

The nitric oxide/cyclic GMP pathway in the olfactory processing system of the terrestrial slug Limax marginatus

To examine the distribution of nitric oxide (NO)-generative cells and NO-responsive cells in the tentacles and procerebral lobes (olfactory processing center) of terrestrial slugs, we applied NADPH diaphorase (NADPH-d) histochemistry and NO-induced cyclic GMP (cGMP)-like immunohistochemistry. We found that NADPH-d reactive cells/fibers and cGMP-like immunoreactive cells/fibers were different, but they were localized adjacent to each other, in both the tentacles and the procerebral lobes. Then, we measured the concentration of NO that was generated around the procerebral lobes using an NO sensitive electrode, when the olfactory nerve was electrically stimulated as a replacement for an odorant stimulus. Stimulation of the olfactory nerve evoked an increase in NO concentration at nanomolar levels, suggesting that binding of nanomolar concentrations of NO to the prosthetic heme group activates soluble guanylyl cyclase. Taken together with previously reported physiological data, our results, therefore, showed that the NO/cGMP pathways are involved in slug olfactory processing.

Histochemical and immunohistochemical localization of neuronal nitric oxide synthase in the olfactory epithelium of the axolotl, Ambystoma mexicanum

The aim of this study was to describe the anatomic distribution of neuronal nitric oxide synthase immunoreactivity (nNOS-IR) and nicotinamide-adenine dinucleotide phosphate-diaphorase (NADPH-d) staining in the olfactory epithelium of the axolotl, juvenile, and neotenic adult, Ambystoma mexicanum. Nitric oxide (NO, nitrogen monoxide) is a widespread molecule that has been identified both as a neuromodulator and as an intracellular messenger. In the olfactory system, NO has been proposed to play a role in olfactory transduction. Nitric oxide synthase (NOS) can be detected by histochemical (NADPH-d) and immunohistochemical techniques. NADPH-d staining has been described in olfactory receptor neurons (ORN) of several species; however, nNOS-IR has not always been found at ORN. Present results show intense NADPH-d staining and nNOS-IR in the dendrites and cell bodies of ORN in both the nasal cavity and the vomeronasal organ of axolotls. Unilateral olfactory axotomy was conducted to confirm that labels were at ORN. Two weeks after this procedure an important decrease in NADPH-d staining and nNOS-IR was observed. The remaining labels were mostly in basal cells. By 5 weeks postaxotomy both labels were almost totally absent. Thus, both NADPH-d staining and nNOS-IR were mainly localized in ORN. NADPH-d staining and nNOS-IR were also found in nerve fibers surrounding arterioles, as well as in secretory and duct cells of the Bowman's glands. This last anatomical localization suggests that in the A. mexicanum NO might be involved in functions other than only olfactory transduction, such as regulation of local blood flow, glandular secretion, and ORN development.

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.

Nitric oxide and carbon monoxide modulate oscillations of olfactory interneurons in a terrestrial mollusk

Spontaneous or odor-induced oscillations in local field potential are a general feature of olfactory processing centers in a large number of vertebrate and invertebrate species. The ubiquity of such oscillations in the olfactory bulb of vertebrates and analogous structures in arthropods and mollusks suggests that oscillations are fundamental to the computations performed during processing of odor stimuli. Diffusible intercellular messengers such as nitric oxide (NO) and carbon monoxide (CO) also are associated with central olfactory structures in a wide array of species. We use the procerebral (PC) lobe of the terrestrial mollusk Limax maximus to demonstrate a role for NO and CO in the oscillatory dynamics of the PC lobe: synthesizing enzymes for NO and CO are associated with the PC lobes of Limax, application of NO to the Limax PC lobe increases the local field potential oscillation frequency, whereas block of NO synthesis slows or stops the oscillation, the bursting cells of the PC lobe that drive the field potential oscillation are driven to higher burst frequency by application of NO, the nonbursting cells of the PC lobe receive trains of inhibitory postsynaptic potentials, presumably from bursting cells, due to application of NO, and application of CO to the PC lobe by photolysis of caged CO results in an increase in oscillation frequency proportional to CO dosage.

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.

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.

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.

Inhibition of the Met-enkephalin-induced K+ current in B-cluster neurons of Aplysia by nitric oxide donor

The effects of sodium nitroprusside (SNP), a nitric oxide (NO) donor, on a methionine-enkephalin (Met-E)-induced K+ current recorded from B-cluster neurons in Aplysia cerebral ganglion were investigated with voltage-clamp and pressure ejection techniques. Bath-applied SNP (10-25 microM) reduced the Met-E-induced K+ current in the neurons without affecting the resting membrane conductance and holding current. The inhibitory effects of SNP were reversible. Pretreatment with methylene blue (10 microM), a non-specific inhibitor of guanylate cyclase, and hemoglobin (50 microM), a NO scavenger, decreased the SNP-induced inhibition of the Met-E-induced current. Intracellular injection of 1 mM guanosine 3',5'-cyclic monophosphate (cGMP) or bath-applied 3-isobutyl-1-methylxanthine (IBMX; 50 microM), a nonspecific phosphodiesterase inhibitor, inhibited the Met-E-induced current. Furthermore, 1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 1 microM), a more specific inhibitor of NO-stimulated guanylate cyclase, decreased the SNP-induced inhibition of the Met-E-induced current. These results suggest that SNP induces suppression of the Met-E-induced K+ current recorded from B-cluster neurons of Aplysia cerebral ganglion via stimulation of cGMP formation.

NADPH-diaphorase activity changes during gangliogenesis and metamorphosis in the gastropod mollusc Ilyanassa obsoleta

Gaseous nitric oxide (NO) is produced through the action of the enzyme nitric oxide synthase (NOS) and acts as a neurotransmitter (Jacklet and Gruhn, 1994b. Elphick et al., 1995a; Jacklet, 1995) in the nervous systems of adult gastropod molluses. By comparison, little or no information appears to exist about the ontogeny of molluscan NOS-containing neurons. NADPH-diaphorase (NADPHd) has been determined biochemically and histochemically to colocalize with NOS immunoreactivity in neurons; NOS is an isoform of NADPHd (Dawson et al., 1991; Hope et al., 1991). We used NADPHd histochemistry to map the distribution of NOS activity in the nervous systems of larvae, including metamorphosing individuals, and juveniles of the marine snail Ilyanassa absoieta. Several ganglionic neuropils displayed reaction product throughout development. The most intense NADPHd staining occurred in the neuropil of the apical ganglion, a specialized larval structure. Intermediate staining levels occurred in neuropils of the cerebral, pedal, and pleural ganglia. Larval buccal and intestinal ganglia showed little reaction product, with slight increases arising in metamorphically competent larvae. NADPHd activity conspicuously decreased in the central nervous systems of metamorphosing larvae. The osphradial ganglion, which was present in young larvae, showed only weak NADPHd activity. Our results provide evidence for the existence of a nitrergic signalling system in molluscan larvae and juveniles.

Oscillations and gaseous oxides in invertebrate olfaction

Olfactory systems combine an extraordinary molecular sensitivity with robust synaptic plasticity. Central neuronal circuits that perform pattern recognition in olfaction typically discriminate between hundreds of molecular species and form associations between odor onsets and behavioral contingencies that can last a lifetime. Two design features in the olfactory system of the terrestrial mollusk Limax maximus may be common elements of olfactory systems that display the twin features of broad molecular sensitivity and rapid odor learning: spatially coherent oscillations in the second-order circuitry that receives sensory input; and involvement of the interneuronal messengers nitric oxide (NO) and carbon monoxide (CO) in sensory responses and circuit dynamics of the oscillating olfactory network. The principal odor processing center in Limax, the procerebrum (PC) of the cerebral ganglion, contains on the order of 10(5) local interneurons and receives both direct and processed input from olfactory receptors. Field potential recordings in the PC show an oscillation at approximately 0.7 Hz that is altered by odor input. Optical recordings of voltage changes in local regions of the PC show waves of depolarization that originate at the distal pole and propagate to the base of the PC. Weak odor stimulation transiently switches PC activity from a propagating mode to a spatially uniform mode. The field potential oscillation in the PC lobe depends on intercellular communication via NO, based on opposing effects of reagents that decrease or increase NO levels in the PC. Inhibition of NO synthase slows the field potential oscillation, while application of exogenous NO increases the oscillation frequency. A role for CO in PC dynamics is suggested by experiments in which CO liberation increases the PC oscillation frequency. These design features of the Limax PC lobe odor processing circuitry may relate to synaptic plasticity that subserves both connection of new receptors throughout the life of the slug and its highly developed odor learning ability.

Nitric oxide donor sodium nitroprusside inhibits the acetylcholine-induced K+ current in identified Aplysia neurons

The effects of bath-applied sodium nitroprusside (SNP), a nitric oxide (NO) donor, on an acetylcholine ACh-induced K+ current recorded from identified neurons (R9 and R10) of Aplysia kurodai were investigated with conventional voltage-clamp and pressure ejection techniques. Bath-applied SNP (25-50 microM) reduced the ACh-induced K+ current in the neurons without affecting the resting membrane conductance and holding current. The suppressing effects of SNP on the current were completely reversible. Intracellular injection of 1 mM guanosine 3',5'-cyclic monophosphate (cGMP) or bath-applied 50 microM 3-isobutyl-1-methylxanthine (IBMX), a nonspecific phosphodiesterase (PDE) inhibitor, also inhibited the ACh-induced current, thus mimicking the effect of the NO donor on the ACh-induced current. In contrast, pretreatment with methylene blue (10 microM), an inhibitor of guanylate cyclase, and hemoglobin (50 microM), a nitric oxide scavenger, decreased the SNP-induced inhibition of the ACh-induced current. These results suggest that SNP, a NO donor, inhibits the ACh-induced K+ current, and that the mechanism of NO inhibition of the ACh-induced current recorded from identified Aplysia neurons involves cGMP-dependent protein kinase.

Nitric oxide, but not serotonin, is involved in acquisition of food-attraction conditioning in the snail Helix pomatia

The effects of inhibition of nitric oxide (NO) or serotonin (injection of nitro-L-arginine methyl ester (L-NAME) or 5,6-dihydroxytryptamine (5,6-DHT), respectively) on food-attraction conditioning was investigated in Helix. Blocking NO synthase (NOS) prior to conditioning significantly impaired the food-finding ability of the snails. Food-conditioned snails, after inhibition of NOS, remained able to locate the conditioned food. These results indicate that the acquisition of memory depends on NO, whereas memory recall and olfactory orientation are not dependent. Ablating the serotonergic system did not influence food-attraction conditioning, suggesting that food-attraction conditioning may be at variance with conventional associative conditioning procedures.

A nitric oxide synthase activity is involved in the modulation of acetylcholine release in Aplysia ganglion neurons: a histological, voltammetric and electrophysiological study

The role of nitric oxide or related molecules as neuromodulators was investigated in the buccal and the abdominal ganglia of the mollusc Aplysia californica. In a first step we showed that reduced nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry and specific nitric oxide synthase immunohistochemistry labelled the same neurons and fibres in both ganglia, pointing to the presence of a neuronal nitric oxide synthase. In a second step, we performed voltammetric detection of nitric oxide-related molecules using a microcarbon electrode in a reduction mode. A peak identified as N-nitroso-L-arginine was detected at -1.66 V in both ganglia. The identification of this compound as a product of endogenous nitric oxide synthase activity was reinforced by the fact that its peak amplitude was decreased in the presence of NG-monomethyl-L-arginine, an inhibitor of nitric oxide synthase, and increased with its substrate, L-arginine. An additional proof of a nitric oxide synthase activity was the detection of nitrites and nitrates in high concentrations (millimolar range) by capillary electrophoresis. We also showed that these nitric oxide-related molecules modulated acetylcholine release at two identified synapses in these ganglia. L-Arginine decreased acetylcholine release at the inhibitory synapse (buccal ganglion), whereas it increased acetylcholine release at the excitatory synapse (abdominal ganglion). The nitric oxide synthase inhibitors, N omega-nitro-L-arginine and NG-monomethyl-L-arginine, had opposite effects. Moreover, the exogenous nitric oxide donor, 3-morpholinosydnonimine hydrochloride mimicked the effects of L-arginine on both inhibitory and excitatory cholinergic synapses. The identification of two cholinergic synapses where nitric oxide affects acetylcholine release in opposite ways provides a useful tool to study the cellular mechanisms through which nitric oxide-related molecules modulate transmitter release.

Histochemical distribution of NADPH-diaphorase in the cerebral ganglion of the crayfish Cambarellus montezumae

The presence and localization of NADPH-diaphorase in the cerebral ganglion of the crayfish Cambarellus montezumae was shown. The reactivity of this enzyme was found in the deuterocerebrum, mainly in the commissure, in fibers of olfactory and accessory lobes, and in the laterodorsal group of cells. The presence of this enzyme in these cerebral regions suggests that nitric oxide is involved in primary sensory afferents in the crayfish.

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.