Nitric oxide-sensitive guanylate cyclase activity is associated with the maturational phase of neuronal development in insects

Roles of 5-HT on phase transition of neurite outgrowth in the identified serotoninergic neuron C1, Helisoma trivolvis

Neurite outgrowth is a morphological marker of neuronal differentiation and neuroregeneration, and the process includes four essential phases, namely initiation, elongation, guidance and cessation. Intrinsic and extrinsic signaling molecules seem to involve morphological changes of neurite outgrowth via various cellular signaling cascades phase transition. Although mechanisms associated with neurite outgrowth have been studied extensively, little is known about how phase transition is regulated during neurite outgrowth. 5-HT has long been studied with regard to its relationship to neurite outgrowth in invertebrate and vertebrate culture systems, and many studies have suggested 5-HT inhibits neurite elongation and growth cone motility, in particular, at the growing parts of neurite such as growth cones and filopodia. However, the underlying mechanisms need to be investigated. In this study, we investigated roles of 5-HT on neurite outgrowth using single serotonergic neurons C1 isolated from Helisoma trivolvis. We observed that 5-HT delayed phase transitions from initiation to elongation of neurite outgrowth. This study for the first time demonstrated that 5-HT has a critical role in phase-controlling mechanisms of neurite outgrowth in neuronal cell cultures.

Implications for reactive oxygen species in schizophrenia pathogenesis

Oxidative stress is a well-recognized participant in the pathophysiology of multiple brain disorders, particularly neurodegenerative conditions such as Alzheimer's and Parkinson's diseases. While not a dementia, a wide body of evidence has also been accumulating for aberrant reactive oxygen species and inflammation in schizophrenia. Here we highlight roles for oxidative stress as a common mechanism by which varied genetic and epidemiologic risk factors impact upon neurodevelopmental processes that underlie the schizophrenia syndrome. While there is longstanding evidence that schizophrenia may not have a single causative lesion, a common pathway involving oxidative stress opens the possibility for intervention at susceptible phases.

Development of the Neurochemical Architecture of the Central Complex

The central complex represents one of the most conspicuous neuroarchitectures to be found in the insect brain and regulates a wide repertoire of behaviors including locomotion, stridulation, spatial orientation and spatial memory. In this review article, we show that in the grasshopper, a model insect system, the intricate wiring of the fan-shaped body (FB) begins early in embryogenesis when axons from the first progeny of four protocerebral stem cells (called W, X, Y, Z, respectively) in each brain hemisphere establish a set of tracts to the primary commissural system. Decussation of subsets of commissural neurons at stereotypic locations across the brain midline then establishes a columnar neuroarchitecture in the FB which is completed during embryogenesis. Examination of the expression patterns of various neurochemicals in the central complex including neuropeptides, a neurotransmitter and the gas nitric oxide (NO), show that these appear progressively and in a substance-specific manner during embryogenesis. Each neuroactive substance is expressed by neurons located at stereotypic locations in a given central complex lineage, confirming that the stem cells are biochemically multipotent. The organization of axons expressing the various neurochemicals within the central complex is topologically related to the location, and hence birthdate, of the neurons within the lineages. The neurochemical expression patterns within the FB are layered, and so reflect the temporal topology present in the lineages. This principle relates the neuroanatomical to the neurochemical architecture of the central complex and so may provide insights into the development of adaptive behaviors.

Developmental expression of neuromodulators in the central complex of the grasshopper Schistocerca gregaria

The central complex is a major integrative region within the insect brain with demonstrated roles in spatial orientation, the regulation of locomotor behavior, and sound production. In the hemimetabolous grasshopper, the central complex comprises the protocerebral bridge, central body (CB), ellipsoid body, noduli, and accessory lobes, and this modular organization develops entirely during embryogenesis. From a biochemical perspective, a range of neuroactive substances has been demonstrated in these modules of the adult central complex, but little is known about their developmental expression. In this study, we use matrix-assisted laser desorption/ionization-imaging mass spectrometry on single brain slices to confirm the presence of several peptide families (tachykinin, allatostatin, periviscerokinin/pyrokinin, FLRFamide, and neuropeptide F) in the adult central complex and then use immunohistochemistry and histology to examine their developmental expression, together with that of the indolamin serotonin, and the endogenous messenger nitric oxide (NO; via its synthesizing enzyme). We find that each neuromodulator is expressed according to a unique, stereotypic, pattern within the various modules making up the central complex. Neuropeptides such as tachykinin (55%) and allatostatin (65%), and the NO-synthesizing enzyme diaphorase (70%), are expressed earlier during embryonic development than the biogenic amine serotonin (80%), whereas periviscerokinin-like peptides and FLRFamide-like peptides begin to be expressed only postembryonically. Within the CB, these neuroactive substances are present in tangential projection neurons before they appear in columnar neurons. There is also no colocalization of serotonin-positive and peptide-positive projections up to the third larval instar during development, consistent with the clear dorsoventral layering of the neuropil we observe. Our results provide the first neurochemical fingerprint of the developing central complex in an hemimetabolous insect.

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.

Oxidative stress in schizophrenia: an integrated approach

Oxidative stress has been suggested to contribute to the pathophysiology of schizophrenia. In particular, oxidative damage to lipids, proteins, and DNA as observed in schizophrenia is known to impair cell viability and function, which may subsequently account for the deteriorating course of the illness. Currently available evidence points towards an alteration in the activities of enzymatic and nonenzymatic antioxidant systems in schizophrenia. In fact, experimental models have demonstrated that oxidative stress induces behavioral and molecular anomalies strikingly similar to those observed in schizophrenia. These findings suggest that oxidative stress is intimately linked to a variety of pathophysiological processes, such as inflammation, oligodendrocyte abnormalities, mitochondrial dysfunction, hypoactive N-methyl-d-aspartate receptors and the impairment of fast-spiking gamma-aminobutyric acid interneurons. Such self-sustaining mechanisms may progressively worsen producing the functional and structural consequences associated with schizophrenia. Recent clinical studies have shown antioxidant treatment to be effective in ameliorating schizophrenic symptoms. Hence, identifying viable therapeutic strategies to tackle oxidative stress and the resulting physiological disturbances provide an exciting opportunity for the treatment and ultimately prevention of schizophrenia.

Nitric oxide as a regulator of neuronal motility and regeneration in the locust embryo

Nitric oxide (NO) is known as a gaseous messenger in the nervous system. It plays a role in synaptic plasticity, but also in development and regeneration of nervous systems. We have studied the function of NO and its signaling cascade via cyclic GMP in the locust embryo. Its developing nervous system is well suited for pharmacological manipulations in tissue culture. The components of this signaling pathway are localized by histochemical and immunofluorescence techniques. We have analyzed cellular mechanisms of NO action in three examples: 1. in the peripheral nervous system during antennal pioneer axon outgrowth, 2. in the enteric nervous system during migration of neurons forming the midgut nerve plexus, and 3. in the central nervous system during axonal regeneration of serotonergic neurons after axotomy. In each case, internally released NO or NO-induced cGMP synthesis act as permissive signals for the developmental process. Carbon monoxide (CO), as a second gaseous messenger, modulates enteric neuron migration antagonistic to NO.

Molecular cloning and characterization of the nitric oxide synthase gene from kuruma shrimp, Marsupenaeus japonicus

Nitric oxide (NO) signaling is involved in many physiological processes in vertebrates and invertebrates. In crustaceans, nitric oxide synthase (NOS) plays a significant role in the regulation of the nervous system and in innate immunity. Here, we describe the entire cDNA sequence (4616 bp) of the kuruma shrimp Marsupenaeus japonicus NOS (Mj NOS) generated using the reverse transcriptase-polymerase chain reaction (RT-PCR) and 5'- and 3'- rapid amplification PCRs of cDNA ends from brain and gill mRNAs. The open reading frame of Mj NOS encoded a protein of 1187 amino acids with an estimated mass of 134 kDa, and had an 82.3% sequence homology with the NOS gene of the land crab Gecarcinus lateralis. Highly conserved amino acid sequences in heme and tetrahydrobiopterin were observed in the oxygenase domain. FMN, FAD and NADPH were found in the reductase domain. Mj NOS mRNA was constitutively expressed in the brain, gill, intestine, thoracic ganglion and testis of the kuruma shrimp. When Vibrio penaeicida was injected into the kuruma shrimp, Mj NOS was expressed in the brain, gill, heart, lymphoid organ, intestine and thoracic ganglion. Mj NOS expression in the gill reached its peak 12 h and decreased to its normal level 24 h after V. penaeicida injection.

A developmental study of enteric neuron migration in the grasshopper using immunological probes

Motility of enteric plexus neurons in the grasshopper Locusta migratoria depends critically on the NO/cGMP signaling cascade. This is reflected in a strong NO-dependent cGMP staining in migrating enteric midgut neurons. In contrast, first cGMP immunoreactivity (cGMP-IR) in the foregut enteric ganglia was detected clearly after the main migratory processes have taken place. Thus, expression of cGMP-IR in migrating neurons is a distinct phenomenon restricted to neurons forming midgut and foregut plexus, that does not occur during convergence of neurons forming the enteric ganglia. Analysis of time lapse video microscopy of migrating midgut neurons together with an immunofluorescence study of midgut cellular structures suggests a contribution of the midgut musculature to enteric neuron guidance. Additionally, during midgut plexus formation a fasciculating signal for enteric neuron neurites appears to be provided by the cell adhesion molecule Fasciclin I.

Involvement of nitric oxide in the head regeneration of Hydra vulgaris

Recent data have shown that a functional NO-cGMP signalling system plays an important role during development and seems to be operative early during the differentiation of embryonic stem cells. The intriguing possibility exists that this role can be evolutionarily conserved between vertebrates and invertebrates. In this paper, we have analyzed the effect of NO-cGMP pathway on the regeneration process in Hydra vulgaris, the most primitive invertebrate possessing a nervous system. Our results indicate that NO production increased during Hydra regeneration. The NOS inhibitor L-NAME reduced the regenerative process and the same effect was obtained by treatment with either the specific guanylate cyclase inhibitor ODQ or the protein kinase G (PKG) inhibitor KT-5823. In contrast, the regeneration process was increased by treating decapitated Hydra with the NO donor NOC-18. Furthermore, we found that cell proliferation was also increased by treating decapitated Hydra with the NO donor NOC-18 and reduced by treatment with the NOS inhibitor L-NAME. Our results strongly suggest that the NO-cGMP-PKG pathway is involved in the control of the proliferative-differentiative patterns of developing and regenerating structures in cnidarians as well as bilaterians.

Nitric oxide donor up-regulation of SDF1/CXCR4 and Ang1/Tie2 promotes neuroblast cell migration after stroke

We tested the hypothesis that a nitric oxide donor, DETA-NONOate, up-regulates stromal cell-derived factor-1 (SDF1) and angiopoietin 1 (Ang1) in the ischemic brain and their respective receptors chemokine CXC motif receptor 4 (CXCR4) and Tie2 in the subventricular zone (SVZ) and thereby promote SVZ neuroblast cell migration after stroke. C57BL/6J mice were subjected to middle cerebral artery occlusion (MCAo), and 24 hr later DETA-NONOate (0.4 mg/kg) or phosphate-buffered solution was intravenously administered. Mice were sacrificed at 14 days for histological assessment or sacrificed at 3 days for analysis by real-time polymerase chain reaction and migration after MCAo. To elucidate whether SDF1/CXCR4 and Ang1/Tie2 pathways mediate DETA-NONOate-induced SVZ migration after stroke, SDF1alpha, Ang1 peptide, a specific antagonist of CXCR4 (AMD3100), and a neutralizing antibody of Tie2 (anti-Tie2) were used in vitro. DETA-NONOate significantly increased the percentage area of doublecortin (DCX, a marker of migrating neuroblasts)-immunoreactive cells in the SVZ and ischemic boundary zone. DETA-NONOate significantly increased the expression of SDF1 and Ang1 in the ischemic border and up-regulated CXCR4 and Tie2 in the SVZ compared with MCAo control. DCX-positive cell migration from SVZ explants was significantly increased in the DETA-NONOate treatment group compared with MCAo-alone animals. In vitro, SDF1alpha and Ang1 significantly increased SVZ explants cell migration. In addition, inhibition of CXCR4 or Tie2 significantly attenuated DETA-NONOate-induced SVZ cell migration. Our data indicate that treatment of stroke with a nitric oxide donor up-regulates SDF1/CXCR4 and Ang1/Tie2 pathways and thereby likely increases SVZ neuroblast cell migration.

Decreased serum Ou/Zn sOD in children with Autism

Aim

To assess serum Cu/Zn SOD (Superoxide Dismutase) concentration in autistic children and evaluate its possible relationship to GI Symptoms.

Subjects and Methods

Serum from 50 autistic children (31 with chronic digestive disease (most with ileo-colonic lymphoid nodular hyperplasia (LNH) and inflammation of the colorectal, small bowel and/or stomach) and 19 autistic children without GI disease), and 29 non autistic controls (20 age matched non autistic children with no GI disease and 9 age matched non autistic children with GI disease) were tested for Cu/Zn SOD using ELISAs.

Results

Serum Cu/Zn SOD levels of autistic children were significantly lower than all non autistic controls (p < 0.0001). Serum Cu/Zn SOD of autistic children with severe GI disease was significantly lower than autistic children with no GI disease (p < 0.0001), non autistic children without GI disease (<0.0001) and non autistic children with GI disease (p = 0.0003).

Discussion

These results suggest an association between Cu/Zn SOD serum levels and autism, particularly autistic children with GI disease, and that the concentration of serum Cu/Zn SOD may be a useful biomarker for autistic children with severe GI disease.

Nitric oxide regulates axonal regeneration in an insect embryonic CNS

In higher vertebrates, the central nervous system (CNS) is unable to regenerate after injury, at least partially because of growth-inhibiting factors. Invertebrates lack many of these negative regulators, allowing us to study the positive factors in isolation. One possible molecular player in neuronal regeneration is the nitric oxide (NO)-cyclic guanosine-monophosphate (cGMP) transduction pathway which is known to regulate axonal growth and neural migration. Here, we present an experimental model in which we study the effect of NO on CNS regeneration in flat-fillet locust embryo preparations in culture after crushing the connectives between abdominal ganglia. Using whole-mount immunofluorescence, we examine the morphology of identified serotonergic neurons, which send a total of four axons through these connectives. After injury, these axons grow out again and reach the neighboring ganglion within 4 days in culture. We quantify the number of regenerating axons within this period and test the effect of drugs that interfere with NO action. Application of exogenous NO or cGMP promotes axonal regeneration, whereas scavenging NO or inhibition of soluble guanylyl cyclase delays regeneration, an effect that can be rescued by application of external cGMP. NO-induced cGMP immunostaining confirms the serotonergic neurons as direct targets for NO. Putative sources of NO are resolved using the NADPH-diaphorase technique. We conclude that NO/cGMP promotes outgrowth of regenerating axons in an insect embryo, and that such embryo-culture systems are useful tools for studying CNS regeneration.

Nitric oxide in the crustacean brain: regulation of neurogenesis and morphogenesis in the developing olfactory pathway

Nitric oxide (NO) plays major roles during development and in adult organisms. We examined the temporal and spatial patterns of nitric oxide synthase (NOS) appearance in the embryonic lobster brain to localize sources of NO activity; potential NO targets were identified by defining the distribution of NO-induced cGMP. Staining patterns are compared with NOS and cyclic 3,5 guanosine monophosphate (cGMP) distribution in adult lobster brains. Manipulation of NO levels influences olfactory glomerular formation and stabilization, as well as levels of neurogenesis among the olfactory projection neurons. In the first 2 days following ablation of the lateral antennular flagella in juvenile lobsters, a wave of increased NOS immunoreactivity and a reduction in neurogenesis occur. These studies implicate nitric oxide as a developmental architect and also support a role for this molecule in the neural response to injury in the olfactory pathway.

How to innervate a simple gut: familiar themes and unique aspects in the formation of the insect enteric nervous system

Like the vertebrate enteric nervous system (ENS), the insect ENS consists of interconnected ganglia and nerve plexuses that control gut motility. However, the insect ENS lies superficially on the gut musculature, and its component cells can be individually imaged and manipulated within cultured embryos. Enteric neurons and glial precursors arise via epithelial-to-mesenchymal transitions that resemble the generation of neural crest cells and sensory placodes in vertebrates; most cells then migrate extensive distances before differentiating. A balance of proneural and neurogenic genes regulates the morphogenetic programs that produce distinct structures within the insect ENS. In vivo studies have also begun to decipher the mechanisms by which enteric neurons integrate multiple guidance cues to select their pathways. Despite important differences between the ENS of vertebrates and invertebrates, common features in their programs of neurogenesis, migration, and differentiation suggest that these relatively simple preparations may provide insights into similar developmental processes in more complex systems.

Characterization of NO/cGMP-mediated responses in identified motoneurons

1. Nitric oxide (NO) is thought to play a neuromodulatory role in the nervous system of vertebrate and invertebrate species. In the hornworm Manduca sexta, NO-mediated signaling has been implicated in behavioral and developmental processes, but its exact function in neurons is unknown. In this study, we identify specific neurons in the CNS of Manduca larvae that accumulate cGMP in response to treatment with NO donors in the presence of cGMP-phosphodiesterase inhibitors. Subsets of these neurons were identified as motoneuron-12 (MN12) and intersegmental motoneurons (ISMs), which innervate dorsal oblique muscles of the larvae. 2. To investigate the physiological role of NO-evoked increases in cGMP in these motoneurons we performed intracellular recordings; we found that application of NO donors caused an increase in neuronal excitability that was characterized by an increase in the spontaneous firing frequency. When action potentials and EPSPs were blocked, NO treatment evoked a depolarization of the resting membrane potential and a decrease in the measured input resistance in both MN12 and the ISMs. 3. Additional experiments with MN12 showed that treatment with the cGMP analogue, 8-Br-cGMP mimicked the NO effect on the resting potential and the input resistance. Furthermore, MN12 incubation with the NOS inhibitor, L-NNA, resulted in a small hyperpolarization of the resting potential and an increase in the input resistance, and incubation with the sGC inhibitor, ODQ blocked the NO-evoked depolarization of MN12. Finally, NO treatment during voltage clamping of MN12 evoked an inward positive current. 4. Taken together, these results suggest that NO can act as a "gain control" of neuronal excitability, which might have an important role in insect behavior.

Pharmacological approaches to nitric oxide signalling during neural development of locusts and other model insects

A novel aspect of cellular signalling during the formation of the nervous system is the involvement of the messenger molecule nitric oxide (NO), which has been discovered in the mammalian vascular system as mediator of smooth muscle relaxation. NO is a membrane-permeant molecule, which activates soluble guanylyl cyclase (sGC) and leads to the formation of cyclic GMP (cGMP) in target cells. The analysis of specific cell types in model insects such as Locusta, Schistocerca, Acheta, Manduca, and Drosophila shows that the NO/cGMP pathway is required for the stabilization of photoreceptor growth cones at the start of synaptic assembly in the optic lobe, for regulation of cell proliferation, and for correct outgrowth of pioneer neurons. Inhibition of the NOS and sGC enzymes combined with rescue experiments show that NO, and potentially also another atypical messenger, carbon monoxide (CO), orchestrate cell migration of enteric neurons. Cultured insect embryos are accessible model systems in which the molecular pathways linking cytoskeletal rearrangement to directed cell movements can be analyzed in natural settings. Based on the results obtained from the insect models, I discuss current evidence for NO and cGMP as essential signalling molecules for the development of vertebrate brains.

Neonatal caffeine administration causes a permanent increase in the dendritic length of prefrontal cortical neurons of rats

We studied the morphological changes of the dendritic length of the pyramidal neurons of the prefrontal cortex (PFC) induced by the effect of chronic administration of caffeine in the neonatal rat. The caffeine (50 mg/kg, s.c.) was injected from day 1 after birth (P1) to day 12 (P12). The morphology of the pyramidal neurons of layer 3 of the PFC was investigated in these animals at two different ages, before puberty (P35) and after puberty (P70). Before the animals were sacrificed by using overdoses of sodium pentobarbital and being perfused intracardially with 0.9% saline, the locomotor activity in a novel environment was measured. The brains were then removed, processed by the Golgi-Cox stain, and analyzed by the Sholl method. The dendritic morphology clearly showed that the neonatal animals administered caffeine showed an increase in the dendritic length of the pyramidal neurons of the PFC when compared with the control animals at both ages. The present results suggest that neonatal administration of caffeine may in part affect the dendritic morphology of the pyramidal cells of this limbic structure and this effect persists after puberty and may be implicated in several brain processes.

Oxidative stress in autism

Autism is a severe developmental disorder with poorly understood etiology. Oxidative stress in autism has been studied at the membrane level and also by measuring products of lipid peroxidation, detoxifying agents (such as glutathione), and antioxidants involved in the defense system against reactive oxygen species (ROS). Lipid peroxidation markers are elevated in autism, indicating that oxidative stress is increased in this disease. Levels of major antioxidant serum proteins, namely transferrin (iron-binding protein) and ceruloplasmin (copper-binding protein), are decreased in children with autism. There is a positive correlation between reduced levels of these proteins and loss of previously acquired language skills in children with autism. The alterations in ceruloplasmin and transferrin levels may lead to abnormal iron and copper metabolism in autism. The membrane phospholipids, the prime target of ROS, are also altered in autism. The levels of phosphatidylethanolamine (PE) are decreased, and phosphatidylserine (PS) levels are increased in the erythrocyte membrane of children with autism as compared to their unaffected siblings. Several studies have suggested alterations in the activities of antioxidant enzymes such as superoxide dismutase, glutathione peroxidase, and catalase in autism. Additionally, altered glutathione levels and homocysteine/methionine metabolism, increased inflammation, excitotoxicity, as well as mitochondrial and immune dysfunction have been suggested in autism. Furthermore, environmental and genetic factors may increase vulnerability to oxidative stress in autism. Taken together, these studies suggest increased oxidative stress in autism that may contribute to the development of this disease. A mechanism linking oxidative stress with membrane lipid abnormalities, inflammation, aberrant immune response, impaired energy metabolism and excitotoxicity, leading to clinical symptoms and pathogenesis of autism is proposed.

N-cadherin mediates nitric oxide-induced neurogenesis in young and retired breeder neurospheres

Neurogenesis may contribute to functional recovery after neural injury. Nitric oxide donors such as DETA-NONOate promote functional recovery after stroke. However, the mechanisms underlying functional improvement have not been ascertained. We therefore investigated the effects of DETA-NONOate on neural progenitor/stem cell neurospheres derived from the subventricular zone from young and retired breeder rat brain. Subventricular zone cells were dissociated from normal young adult male Wistar rats (2-3 months old) and retired breeder rats (14 months old), treated with or without DETA-NONOate. Subventricular zone neurosphere formation, proliferation, telomerase activity, and Neurogenin 1 mRNA expression were significantly decreased and glial fibrillary acidic protein expression was significantly increased in subventricular zone neurospheres from retired breeder rats compared with young rats. Treatment of neurospheres with DETA-NONOate significantly decreased neurosphere formation and telomerase activity, and promoted neuronal differentiation and neurite outgrowth concomitantly with increased N-cadherin and beta-catenin mRNA expression in both young and old neurospheres. DETA-NONOate selectively increased Neurogenin 1 and decreased glial fibrillary acidic protein mRNA expression in retired breeder neurospheres. N-cadherin significantly increased Neurogenin 1 mRNA expression in young and old neurospheres. Anti-N-cadherin reversed DETA-NONOate-induced neurosphere adhesion, neuronal differentiation, neurite outgrowth, and beta-catenin mRNA expression. Our data indicate that age has a potent effect on the characteristics of subventricular zone neurospheres; neurospheres from young rats show significantly higher formation, proliferation and telomerase activity than older neurospheres. In contrast, older neurospheres exhibit significantly increased glial differentiation than young neurospheres. DETA-NONOate promotes neuronal differentiation and neurite outgrowth in both young and older neurospheres. The molecular mechanisms associated with the DETA-NONOate modulation of neurospheres from young and older animals as well age dependent effects of neurospheres appear to be controlled by N-cadherin and beta-catenin gene expression, which subsequently regulates the neuronal differentiating factor Neurogenin expression in both young and old neural progenitor cells.

Local activation of the nitric oxide/cyclic guanosine monophosphate pathway in growth cones regulates filopodial length via protein kinase G, cyclic ADP ribose and intracellular Ca2+ release

Nitric oxide (NO) is a gaseous messenger that has been shown to affect growth cone motility and neurite outgrowth in several model systems, but how NO brings about its effects is not understood. We have previously demonstrated that global and long-term application of NO to Helisoma trivolvis B5 neurons results in a transient increase in filopodial length, decrease in filopodial number and decrease in neurite outgrowth, all of which are mediated via soluble guanylyl cyclase (sGC) and involve an increase in the intracellular Ca2+ concentration [S. Van Wagenen & V. Rehder (1999)Journal of Neurobiology, 39, 168-185; K.R. Trimm & V. Rehder (2004) European Journal of Neuroscience, 19, 809-818]. The goal of the current study was twofold: to investigate the effects of short-term NO exposure on individual growth cones and to further elucidate the downstream pathway through which NO exerts its effects. Local application of the NO donor NOC-7 for 10-20 ms via puffer micropipette resulted in a transient increase in filopodial length and a small decrease in filopodial number. We show evidence that these effects of NO are mediated via sGC, protein kinase G and cyclic ADP ribose, resulting in the release of Ca2+ from intracellular stores, probably of the ryanodine-sensitive type. These results suggest that growth cones expressing sGC are highly sensitive to local and short-term exposure to NO, which they may experience during pathfinding, and that the stereotyped response of transient filopodial elongation seen in B5 neurons in response to NO requires intracellular Ca2+ release.

Enhanced locomotor activity in adult rats with neonatal administration ofN-omega-nitro-L-arginine

Nitric oxide (NO) is a neuronal messenger molecule that plays important roles in the development, maintenance, and functional modifications of brain circuits. We investigated whether the NO levels at different postnatal day (P) periods of the brain develop interference with the locomotion in a novel environment during the postpuberal age (P60). First, using the determination of the nitrite accumulation, we evaluated whether treatment with the NO-synthase inhibitor N-nitro-L-arginine (L-NNA) during different neonatal ages (P1 to P3, P4 to P6, and P7 to P9) affected the levels of NO activity in different regions in the neonatal brain of the rat. We then evaluated whether the locomotor activity in the adult rat (P60) is affected by the blocking of the neonatal NO-activity during a specific period of the development of the nervous system. Neonatal rats with L-NNA administration at P4 to P6 and P7 to P9 show a significant decrease in the levels of NO activity in all the brain regions. However, the blocking of NO synthesis during the neonatal period between P4 to P6 produced an increase in the locomotion after puberty. These data suggest that during a specific step in the development of the brain, the NO levels may play a critical role in the structures that control the spontaneous locomotion in a novel environment after puberty.

Drosophila soluble guanylyl cyclase mutants exhibit increased foraging locomotion: behavioral and genomic investigations

Genetic variation in the gene foraging (for) is associated with a natural behavioral dimorphism in the fruit fly, Drosophila melanogaster. Some larvae, called 'rovers', have increased foraging locomotion compared to others, called 'sitters', and this difference is directly related to for-encoded cGMP-dependent protein kinase (PKG) activity. Here we report that larvae with mutations in the gene dgcalpha1, which encodes a soluble guanylyl cyclase (sGC) subunit, have increases in both PKG activity and foraging locomotion. This is contrary to our original prediction that, based on the role of sGC in the synthesis of cGMP, dgcalpha1 mutant larvae would have deficient cGMP production leading to decreased PKG activation and thus reduced larval foraging locomotion. We performed DNA microarray analyses to compare transcriptional changes induced by a dgcalpha1 mutation in both rover and sitter wildtype genetic backgrounds. In either background, we identified many genes that are differentially transcribed, and interestingly, relatively few are affected in both backgrounds. Furthermore, several of these commonly affected genes are enhanced or suppressed in a background-dependent manner. Thus, genetic background has a critical influence on the molecular effects of this mutation. These findings will support future investigations of Drosophila foraging behavior.

Nitric oxide/cyclic guanosine monophosphate signaling in the central complex of the grasshopper brain inhibits singing behavior

Grasshopper sound production, in the context of mate finding, courtship, and rivalry, is controlled by the central body complex in the protocerebrum. Stimulation of muscarinic acetylcholine receptors in the central complex has been demonstrated to stimulate specific singing in various grasshoppers including the species Chorthippus biguttulus. Sound production elicited by stimulation of muscarinic acetylcholine receptors in the central complex is inhibited by co-applications of various drugs activating the nitric oxide/cyclic guanosine monophosphate (cGMP) signaling pathway. The nitric oxide-donor sodium nitroprusside caused a reversible suppression of muscarine-stimulated sound production that could be blocked by 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxaline-1-one (ODQ), which prevents the formation of cGMP by specifically inhibiting soluble guanylyl cyclase. Furthermore, injections of both the membrane-permeable cGMP analog 8-Br-cGMP and the specific inhibitor of the cGMP-degrading phosphodiesterase Zaprinast reversibly inhibited singing. To identify putative sources of nitric oxide, brains of Ch. biguttulus were subjected to both nitric oxide synthase immunocytochemistry and NADPH-diaphorase staining. Among other areas known to express nitric oxide synthase, both procedures consistently labeled peripheral layers in the upper division of the central body complex, suggesting that neurons supplying this neuropil contain nitric oxide synthase and may generate nitric oxide upon activation. Exposure of dissected brains to nitric oxide and 3-(5'hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1) induced cGMP-associated immunoreactivity in both the upper and lower division. Therefore, both the morphological and pharmacological data presented in this study strongly suggest a contribution of the nitric oxide/cGMP signaling pathway to the central control of grasshopper sound production.

STOP and GO with NO: nitric oxide as a regulator of cell motility in simple brains

During the formation of the brain, neuronal cell migration and neurite extension are controlled by extracellular guidance cues. Here, I discuss experiments showing that the messenger nitric oxide (NO) is an additional regulator of cell motility. NO is a membrane permeant molecule, which activates soluble guanylyl cyclase (sGC) and leads to the formation of cyclic GMP (cGMP) in target cells. The analysis of specific cells types in invertebrate models such as molluscs, insects and the medicinal leech provides insight how NO and cyclic nucleotides affect the wiring of nervous systems by regulating cell and growth-cone motility. Inhibition of the NOS and sGC enzymes combined with rescue experiments show that NO signalling orchestrates neurite outgrowth and filopodial dynamics, cell migration of enteric neurons, glial migration and axonogenesis of pioneer fibers. Cultured insect embryos are accessible model systems in which cellular mechanisms of NO-induced cytoskeletal reorganizations can be analyzed in natural settings. Finally, I will outline some indications that NO may also regulate cell motility in the developing and regenerating vertebrate nervous system.

Functional recovery in aged and young rats after embolic stroke: treatment with a phosphodiesterase type 5 inhibitor

BACKGROUND AND PURPOSE

Advanced age is associated with a decrease in brain plasticity compared with the young adult. Sildenafil, a phosphodiesterase type 5 (PDE5) inhibitor promotes brain plasticity and improves functional outcome after stroke in the young animal. Here, we test the hypothesis that sildenafil provides restorative therapeutic benefit to the aged animal.

METHODS

Male Wistar rats (aged, 18-month old; young, 3-month old) were subjected to embolic stroke. Saline or sildenafil was administered daily at a dose of 2 mg/kg orally or 10 mg/kg subcutaneously for 7 consecutive days starting 24 hour after stroke onset.

RESULTS

Aged rats exhibited significant impairment of functional recovery and reductions of vascular density, and endothelial cell proliferation compared with young rats. Aged rats treated with sildenafil at a dose of 10 mg/kg but not 2 mg/kg, showed significant improvements of functional recovery and concomitant increases in cortical cyclic guanosine 3',5'-cyclic monophosphate (cGMP) level, vascular density, endothelial cell proliferation, and synaptogenesis compared with aged rats treated with saline. In young rats, treatment with sildenafil at a dose of 2 or 10 mg/kg significantly enhanced functional recovery and amplified brain plasticity compared with young rats treated with saline.

CONCLUSIONS

Age is associated with reduction of angiogenesis, and poor neurological functional recovery after stroke. However, treatment of aged stroke rats with sildenafil improves functional recovery that is likely fostered by enhancement of angiogenesis and synaptogenesis.

The localization of neuronal nitric oxide synthase may influence its role in neuronal precursor proliferation and synaptic maintenance

Neuronal nitric oxide synthase (nNOS) is implicated in some developmental processes, including neuronal survival, differentiation, and precursor proliferation. To define the roles of nNOS in neuronal development, we utilized the olfactory system as a model. We hypothesized that the role of nNOS may be influenced by its localization. nNOS expression was developmentally regulated in the olfactory system. During early postnatal development, nNOS was expressed in developing neurons in the olfactory epithelium (OE), while in the adult its expression was restricted to periglomerular (PG) cells in the olfactory bulb (OB). At postnatal week 1 (P1W), loss of nNOS due to targeted gene deletion resulted in a decrease in immature neurons in the OE due to decreased proliferation of neuronal precursors. While the pool of neuronal precursors and neurogenesis normalized in the nNOS null mouse by P6W, there was an overgrowth of mitral or tufted cells dendrites and a decreased number of active synapses in the OB. Cyclic GMP (cGMP) immunostaining was reduced in the OE and in the glomeruli of the OB at early postnatal and adult ages, respectively. Our results suggest that nNOS appears necessary for neurogenesis in the OE during early postnatal development and for glomerular organization in the OB in the adult. Thus, the location of nNOS, either within cell bodies or perisynaptically, may influence its developmental role.

Nitric oxide acts as a slow-down and search signal in developing neurites

Nitric oxide (NO) has been demonstrated to act as a signaling molecule during neuronal development, but its precise function is unclear. Here we investigate whether NO might function at the neuronal growth cone to affect growth cone motility. We have previously demonstrated that growth cones of identified neurons from the snail Helisoma trivolvis show a rapid and transient increase in filopodial length in response to NO, which was regulated by soluble guanylyl cyclase (sGC) [S. Van Wagenen and V. Rehder (1999) J. Neurobiol., 39, 168-185]. Because in vivo studies have demonstrated that growth cones have longer filopodia and advance more slowly in regions where pathfinding decisions are being made, this study aimed to establish whether NO could function as a combined 'slow-down and search signal' for growth cones by decreasing neurite outgrowth. In the presence of the NO donor NOC-7, neurites of B5 neurons showed a concentration-dependent effect on neurite outgrowth, ranging from slowing at low, stopping at intermediate and collapsing at high concentrations. The effects of the NO donor were mimicked by directly activating sGC with YC-1, or by increasing its product with 8-bromo-cGMP. In addition, blocking sGC in the presence of NO with NS2028 blocked the effect of NO, suggesting that NO affected outgrowth via sGC. Ca2+ imaging of growth cones with Fura-2 indicated that [Ca2+]i increased transiently in the presence of NOC-7. These results support the hypothesis that NO can function as a potent slow/stop signal for developing neurites. When coupled with transient filopodia elongation, this phenomenon emulates growth cone searching behavior.

High nitric oxide production in autistic disorder: a possible role for interferon-gamma

BACKGROUND

Neuroimmune regulation abnormalities have been implicated in the pathophysiology of autistic disorder. Nitric oxide (NO) is involved in immune reactivity and is known to affect brain neurodevelopmental processes. Recent evidence indicates that NO, and cytokines involved in NO production, may be high in children with autism. The purpose of this study was to verify that plasma NO is high in children with autism and determine whether this elevation is related to plasma levels of cytokines involved in NO production.

METHODS

The metabolites of NO, nitrite, and nitrate (NOx), along with the cytokines interferon-gamma (IFN-gamma), tumor necrosis factor-alpha, and interleukin-1beta, were measured in plasma of 29 children with autism (mean age +/- SD = 6.1 +/- 2.8 years) and 27 age- and gender-matched healthy comparison subjects using commercially available assay kits.

RESULTS

Plasma levels of NOx were significantly higher in the autistic subjects (p =.006); plasma levels of the cytokines did not differ between groups. NOx and IFN-gamma levels were positively correlated in the autistic subjects (r =.51; p =.005).

CONCLUSIONS

These results confirm that plasma NO is high in some children with autism and suggest that this elevation may be related to IFN-gamma activity.

mRNA expression patterns of the cGMP-hydrolyzing phosphodiesterases types 2, 5, and 9 during development of the rat brain

Recent evidence indicates that cGMP plays an important role in neural development and neurotransmission. Since cGMP levels depend critically on the activities of phosphodiesterase (PDE) enzymes, mRNA expression patterns were examined for several key cGMP-hydrolyzing PDEs (type 2 [PDE2], 5 [PDE5], and 9 [PDE9]) in rat brain at defined developmental stages. Riboprobes were used for nonradioactive in situ hybridization on sections derived from embryonic animals at 15 days gestation (E15) and several postnatal stages (P0, P5, P10, P21) until adulthood (3 months). At all stages PDE9 mRNA was present throughout the whole central nervous system, with highest levels observed in cerebellar Purkinje cells, whereas PDE2 and PDE5 mRNA expression was more restricted. Like PDE9, PDE5 mRNA was abundant in cerebellar Purkinje cells, although it was observed only on and after postnatal day 10 in these cells. In other brain regions, PDE5 mRNA expression was minimal, detected in olfactory bulb, cortical layers, and in hippocampus. PDE2 mRNA was distributed more widely, with highest levels in medial habenula, and abundant expression in olfactory bulb, olfactory tubercle, cortex, amygdala, striatum, and hippocampus. Double immunostaining of PDE2, PDE5, or PDE9 mRNAs with the neuronal marker NeuN and the glial cell marker glial fibrillary acidic protein revealed that these mRNAs were predominantly expressed in neuronal cell bodies. Our data indicate that three cGMP-hydrolyzing PDE families have distinct expression patterns, although specific cell types coexpress mRNAs for all three enzymes. Thus, it appears that differential expression of PDE isoforms may provide a mechanism to match cGMP hydrolysis to the functional demands of individual brain regions.

Statins induce angiogenesis, neurogenesis, and synaptogenesis after stroke

We demonstrate that the 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitors atorvastatin and simvastatin enhance functional outcome and induce brain plasticity when administered after stroke to rats. With atorvastatin treatment initiated 1 day after stroke, animals exhibited significant increases in vascular endothelial growth factor, cyclic guanosine monophosphate, angiogenesis, endogenous cell proliferation and neurogenesis, and an increase in the synaptic protein, synaptophysin. Atorvastatin-induced angiogenesis in a tube formation assay was reduced by an antibody against the vascular endothelial growth factor receptor 2 (FIK-1) and by the nitric oxide synthase inhibitor, N-mono-methyl-L-arginine (L-NAME). Atorvastatin also induced phosphorylation of Akt and Erk in cultured primary cortical neurons. These data indicate that atorvastatin induced brain plasticity and has neurorestorative activity after experimental stroke.

The distribution of putative nitric oxide releasing neurones in the locust abdominal nervous system: a comparison of NADPHd histochemistry and NOS-immunocytochemistry

Nitric oxide is well established as a signalling molecule in the nervous system of vertebrates and invertebrates. In this study we evaluate the usefulness of NADPHdiaphorase histochemistry and immunocytochemistry for detecting the presence of nitric oxide synthase in locusts. We describe the distribution of putative nitric oxide releasing neurones and stained neuropiles in the locust ventral nerve cord, in particular the abdominal ganglia and abdominal neuromeres. NADPHdiaphorase histochemistry revealed prominent staining in all neuropilar regions and a specific distribution pattern of stained cell bodies in all examined ganglia. Nitric oxide synthase immunocytochemistry, using a commercially available universal antibody, labelled cells in corresponding positions within the ganglia. This was confirmed by double labelling of alternate sections. Western blot analysis demonstrated that in locusts this universal NOS-antibody binds to a protein of similar size to nitric oxide synthase identified in other insect species. The antibody also labelled axons in most peripheral nerves of all examined ganglia, whereas NADPHdiaphorase histochemistry only revealed such stained fibres within peripheral nerves in some preparations, because they may have been masked by intense background staining. We therefore conclude that nitric oxide synthase-immunocytochemistry and NADPHd histochemistry are both good markers for the presence of nitric oxide synthase in the locust ventral nerve cord, and that nitric oxide may be used as a signalling molecule by efferent neurones in locusts.

Developmental expression of nitric oxide/cyclic GMP signaling pathways in the brain of the embryonic grasshopper

Biochemical, cytochemical, and physiological investigations have demonstrated the presence of the nitric oxide/cyclic GMP signaling system in the brain of the adult locust, Schistocerca gregaria. Here, we characterize nitric oxide (NO) releasing neurons and neurons that synthesize cyclic GMP (cGMP) in response to a NO stimulus in the brain of the embryonic grasshopper. Using NADPH-diaphorase histochemistry to detect NO synthesizing cells we describe the appearance of several individually identifiable neurons. At embryonic stage 50% four NADPH-diaphorase positive neurons can be detected in each brain hemisphere. In addition to the labeling of differentiating neurons, NADPH-diaphorase staining appears also in distinct proliferative cell clusters. At embryonic stage 70% the general organization of NADPH-diaphorase activity starts to resemble the adult brain. The immunocytochemical detection of NO-induced accumulation of cGMP starts at embryonic stage 45% resulting in the staining of large neuronal populations in all brain areas. During embryonic stages 50-70%, the number of cGMP-immunoreactive cells increases from 200 to several hundred in each brain hemisphere. Since all NADPH-diaphorase positive local interneurons of the adult antennal lobe express GABA-immunoreactivity, we also report on the earliest appearance of GABA-immunoreactivity in the embryonic antennal lobe. Thus, we present a first developmental investigation of nitrergic and GABAergic transmitter phenotypes in the brain of the embryonic grasshopper.

Neuropeptides in the nervous system of Drosophila and other insects: multiple roles as neuromodulators and neurohormones

Neuropeptides in insects act as neuromodulators in the central and peripheral nervous system and as regulatory hormones released into the circulation. The functional roles of insect neuropeptides encompass regulation of homeostasis, organization of behaviors, initiation and coordination of developmental processes and modulation of neuronal and muscular activity. With the completion of the sequencing of the Drosophila genome we have obtained a fairly good estimate of the total number of genes encoding neuropeptide precursors and thus the total number of neuropeptides in an insect. At present there are 23 identified genes that encode predicted neuropeptides and an additional seven encoding insulin-like peptides in Drosophila. Since the number of G-protein-coupled neuropeptide receptors in Drosophila is estimated to be around 40, the total number of neuropeptide genes in this insect will probably not exceed three dozen. The neuropeptides can be grouped into families, and it is suggested here that related peptides encoded on a Drosophila gene constitute a family and that peptides from related genes (orthologs) in other species belong to the same family. Some peptides are encoded as multiple related isoforms on a precursor and it is possible that many of these isoforms are functionally redundant. The distribution and possible functions of members of the 23 neuropeptide families and the insulin-like peptides are discussed. It is clear that each of the distinct neuropeptides are present in specific small sets of neurons and/or neurosecretory cells and in some cases in cells of the intestine or certain peripheral sites. The distribution patterns vary extensively between types of neuropeptides. Another feature emerging for many insect neuropeptides is that they appear to be multifunctional. One and the same peptide may act both in the CNS and as a circulating hormone and play different functional roles at different central and peripheral targets. A neuropeptide can, for instance, act as a coreleased signal that modulates the action of a classical transmitter and the peptide action depends on the cotransmitter and the specific circuit where it is released. Some peptides, however, may work as molecular switches and trigger specific global responses at a given time. Drosophila, in spite of its small size, is now emerging as a very favorable organism for the studies of neuropeptide function due to the arsenal of molecular genetics methods available.

cDNA cloning, characterization and gene expression of nitric oxide synthase from the silkworm, Bombyx mori

Molecular cloning and nucleotide sequencing of cDNA encoding Bombyx mori nitric oxide synthase (BmNOS) was conducted to analyse its possible role in insect immunity. The amino acid sequence deduced from the BmNOS cDNA showed 84%, 54% and 53% identity with those of NOSs from Manduca sexta, Drosophila melanogaster and Rhodonius prolixus. Recombinant BmNOS produced in insect cells using baculovirus was found to require NADPH, Ca2+, calmodulin and tetrahydrobiopterin (BH4) for its activity. The BmNOS gene was constitutively expressed at a low level in the larval fat body, haemocyte, Malpighian tubule and midgut, and adult antenna, and induced strongly in the fat body by lipopolysaccharide (LPS), suggesting that the BmNOS gene plays different physiological roles in different tissues. Injection of NO donors that produce NO in vivo induced the gene expression of an antibacterial peptide, cecropin B, strongly suggesting that NO produced by BmNOS following LPS stimulation is involved in signal transduction as a signalling molecule for immune gene expression.

Neuron-glia communication via nitric oxide is essential in establishing antennal-lobe structure in Manduca sexta

Nitric oxide synthase recently has been shown to be present in olfactory receptor cells throughout development of the adult antennal (olfactory) lobe of the brain of the moth Manduca sexta. Here, we investigate the possible involvement of nitric oxide (NO) in antennal-lobe morphogenesis. Inhibition of NO signaling with a NO synthase inhibitor or a NO scavenger early in development results in abnormal antennal lobes in which neuropil-associated glia fail to migrate. A more subtle effect is seen in the arborization of dendrites of a serotonin-immunoreactive neuron, which grow beyond their normal range. The effects of NO signaling in these types of cells do not appear to be mediated by activation of soluble guanylyl cyclase to produce cGMP, as these cells do not exhibit cGMP immunoreactivity following NO stimulation and are not affected by infusion of a soluble guanylyl cyclase inhibitor. Treatment with Novobiocin, which blocks ADP-ribosylation of proteins, results in a phenotype similar to those seen with blockade of NO signaling. Thus, axons of olfactory receptor cells appear to trigger glial cell migration and limit arborization of serotonin-immunoreactive neurons via NO signaling. The NO effect may be mediated in part by ADP-ribosylation of target cell proteins.

The Drosophila nitric-oxide synthase gene (dNOS) encodes a family of proteins that can modulate NOS activity by acting as dominant negative regulators

Nitric oxide (NO) is involved in organ development, synaptogenesis, and response to hypoxia in Drosophila. We cloned and analyzed the only gene in the fly genome that encodes Drosophila nitric-oxide synthase (dNOS). It consists of 19 exons and is dispersed over 34 kilobases of genomic DNA. Alternative transcription start sites and alternative splice sites are used to generate a remarkable variety of mRNAs from the dNOS gene. We identified eight new transcripts that are widely expressed throughout Drosophila development and encode a family of DNOS-related proteins. Alternative splicing affects both the 5'-untranslated region and the coding region of the dNOS primary transcript. Most of the splicing alterations in the coding region of the gene lead to premature termination of the open reading frame. As a result, none of the alternative transcripts encode an enzymatically active protein. However, some of these shorter DNOS protein products can effectively inhibit enzymatic activity of the full-length DNOS1 protein when co-expressed in mammalian cells, thus acting as dominant negative regulators of NO synthesis. Using immunoprecipitation, we demonstrate that these short DNOS protein isoforms can form heterodimers with DNOS1, pointing to a physical basis for the dominant negative effect. Our results suggest a novel regulatory function for the family of proteins encoded by the Drosophila NOS gene.

Nitric oxide: an unconventional messenger in the nervous system of an orthopteroid insect

Nitric oxide (NO) is a membrane-permeant messenger molecule generated from the amino acid L-arginine. NO can activate soluble guanylyl cyclase leading to the formation of cyclic GMP (cGMP) in target cells. In the nervous system, NO/cGMP signalling is thought to play essential roles in synaptic plasticity during development and also in the mature animal. This paper examines biochemical, cell biological, and physiological investigations of NO/cGMP signalling in the nervous system of the locust, a commonly used neurobiological preparation. Biochemical investigations suggest that an identical enzyme is responsible for both NO synthase (NOS) and NADPH-diaphorase activity after tissue fixation. Immunocytochemical staining of an olfactory center in the locust brain shows that NOS-immunoreactivity colocalizes with NADPH-diaphorase at the cellular level. The cytochemical staining of NO donor and target cells in adult animals suggests functions in olfaction, vision, and sensorimotor integration. During development, NO is implicated in axonal outgrowth and synaptogenesis. The cellular distribution of NO-responsive cells in neural circuits reflects potential functions of NO as a retrograde synaptic messenger, as an intracellular messenger, and as a lateral diffusible messenger independent of conventional synaptic connectivity.

Opposing actions of nitric oxide on synaptic inputs of identified interneurones in the central nervous system of the crayfish

Little is known of the action of nitric oxide (NO) at the synaptic level on identified interneurones in local circuits that process mechanosensory signals. Here, we examine the action of NO in the terminal abdominal ganglion of the crayfish Pacifastacus leniusculus, where it has modulatory effects on the synaptic inputs of 17 identified ascending interneurones mediated by electrical stimulation of a sensory nerve. To analyse the role of NO in the processing of sensory signals, we bath-applied the NO donor SNAP, the NO scavenger PTIO, the nitric oxide synthase (NOS) inhibitor l-NAME, the NOS substrate l-arginine, a cyclic GMP (cGMP) analogue, 8-Br-cGMP, and the soluble guanylate cyclase (sGC) inhibitor ODQ. The effects of these chemicals on the synaptic inputs of the interneurones could be divided into two distinct classes. The NO donor SNAP enhanced the inputs to one class of interneurone (class 1) and depressed those to another (class 2). Neither the inactive isomer NAP nor degassed SNAP had any effect on the inputs to these same classes of interneurone. The NO scavenger PTIO caused the opposite effects to those of the NO donor SNAP, indicating that endogenous NO may have an action in local circuits. Preventing the synthesis of NO using l-NAME had the opposite effect to that of SNAP on each response class of interneurone. Increasing the synthesis of endogenous NO by applying l-arginine led to effects on both response classes of interneurone similar to those of SNAP. Taken together, these results suggested that NO was the active component in mediating the changes in amplitude of the excitatory postsynaptic potentials. Finally, the effects of 8-Br-cGMP were similar to those of the NO donor, indicating the possible involvement of a NO-sensitive guanylate cyclase. This was confirmed by preventing the synthesis of cGMP by sGC using ODQ, which caused the opposite effects to those of 8-Br-cGMP on the two response classes of interneurone. The results indicate that a NO-cGMP signal transduction pathway, in which NO regulates transmitter release from mechanosensory afferents onto intersegmental ascending interneurones, is probably present in the local circuits of the crayfish.

Hypoxia and nitric oxide induce a rapid, reversible cell cycle arrest of the Drosophila syncytial divisions

Cells can respond to reductions in oxygen (hypoxia) by metabolic adaptations, quiescence or cell death. The nuclear division cycles of syncytial stage Drosophila melanogaster embryos reversibly arrest upon hypoxia. We examined this rapid arrest in real time using a fusion of green fluorescent protein and histone 2A. In addition to an interphase arrest, mitosis was specifically blocked in metaphase, much like a checkpoint arrest. Nitric oxide, recently proposed as a hypoxia signal in Drosophila, induced a reversible arrest of the nuclear divisions comparable with that induced by hypoxia. Syncytial stage embryos die during prolonged hypoxia, whereas post-gastrulation embryos (cellularized) survive. We examined ATP levels and morphology of syncytial and cellularized embryos arrested by hypoxia, nitric oxide, or cyanide. Upon oxygen deprivation, the ATP levels declined only slightly in cellularized embryos and more substantially in syncytial embryos. Reversal of hypoxia restored ATP levels and relieved the cell cycle and developmental arrests. However, morphological abnormalities suggested that syncytial embryos suffered irreversible disruption of developmental programs. Our results suggest that nitric oxide plays a role in the response of the syncytial embryo to hypoxia but that it is not the sole mediator of these responses.

Feeding-related motor patterns of the locust suboesophageal ganglion induced by pilocarpine and IBMX

The mandibular motor pattern induced by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) in isolated locust suboesophageal ganglia (SOG) was investigated and compared with the motor pattern induced by pilocarpine in an already established preparation of the SOG. Motor patterns occurring after bath application of IBMX or pilocarpine were recorded extracellularly from suitable nerves of isolated SOG. For a quantitative evaluation of long (15 min) sequences of rhythmic neural activity containing several hundred cycles, spectral analysis of spike trains was applied. Using a set of characteristic parameters extracted from spectra computed for each individual preparation, quantitative comparisons of the rhythms induced by IBMX and pilocarpine were made. Significant differences in regularity, frequency of oscillation, and intra-burst frequency were found whereas the phase relationships of different motor pools were similar. Differences in the effect of the drugs on the activity recorded extracellularly from mandibular closer motoneurones were investigated further using intracellular recordings. Our findings imply that the IBMX-induced motor pattern is a suitable in vitro model of mandibular central motor control like the pilocarpine induced pattern. The better regularity is an advantageous feature for further experiments on central pattern generation. Information on second messengers involved in central pattern generation provided by the pharmacological profile of IBMX forms a basis for pharmacological and histological investigations on the mandibular central pattern generating network.

Whole brain spheroid cultures as a model to study the development of nitric oxide synthase-guanylate cyclase signal transduction

Whole brain spheroids provide a suitable model to study neurodevelopment. In the literature a role for the nitric oxide (NO)-cyclic guanosine 3',5'-monophosphate (cGMP) signalling pathway during development has frequently been suggested. In this study we investigated whether functional cGMP pathways were present in differentiated spheroids. In 3-week-old spheroids soluble guanylate cyclase was stimulated with N-methyl D-aspartic acid or sodium nitroprusside (NO donor). The results showed that the NO synthase-cGMP pathway is present in the culture system. Soluble guanylate cyclase-dependent cGMP formation was found in NO synthase containing neurons, in neurons of the GABAergic, glutamatergic and cholinergic system, and in astroglia and oligodendroglia. Activation of particulate guanylate cyclase by atrial natriuretic peptide also triggered an increase in cGMP production. Particulate guanylate cyclase was found in astroglia and in microglia as well as in glutamic acid decarboxylase and calbindin containing structures and neuronal NO synthase containing neurons. Chronic inhibition of NO synthase during culture development had no effect on soluble or particulate guanylate cyclase functioning. Similarly, inhibition of soluble guanylate cyclase during culture development did not have any effect on NO synthase and particulate guanylate cyclase functioning. It is concluded that NO synthase and both soluble and particulate guanylate cyclase are present in whole brain spheroid cultures and that their activity can be influenced by several stimuli. The spheroid culture system constitutes a suitable model to study the NO-cGMP pathway during brain development in mammals.

Nitric oxide and cGMP influence axonogenesis of antennal pioneer neurons

The grasshopper embryo has been used as a convenient system with which to investigate mechanisms of axonal navigation and pathway formation at the level of individual nerve cells. Here, we focus on the developing antenna of the grasshopper embryo (Schistocerca gregaria) where two siblings of pioneer neurons establish the first two axonal pathways to the CNS. Using immunocytochemistry we detected nitric oxide (NO)-induced synthesis of cGMP in the pioneer neurons of the embryonic antenna. A potential source of NO are NADPH-diaphorase-stained epithelial cells close to the basal lamina. To investigate the role of the NO/cGMP signaling system during pathfinding, we examined the pattern of outgrowing pioneer neurons in embryo culture. Pharmacological inhibition of soluble guanylyl cyclase (sGC) and of NO synthase (NOS) resulted in an abnormal pattern of pathway formation in the antenna. Axonogenesis of both pairs of pioneers was inhibited when specific NOS or sGC inhibitors were added to the culture medium; the observed effects include the loss axon emergence as well as retardation of outgrowth, such that growth cones do not reach the CNS. The addition of membrane-permeant cGMP or a direct activator of the sGC enzyme to the culture medium completely rescued the phenotype resulting from the block of NO/cGMP signaling. These results indicate that NO/cGMP signaling is involved in axonal elongation of pioneer neurons in the antenna of the grasshopper.

Roles of NMDA receptor activity and nitric oxide production in brain development

The concept that neural activity is important for brain maturation has focused much research interest on the developmental role of the NMDA receptor, a key mediator of experience-dependent synaptic plasticity. However, a mechanism able to link spatial and temporal parameters of synaptic activity during development emerged as a necessary condition to explain how axons segregate into a common brain region and make specific synapses on neuronal sub-populations. To comply with this developmental constraint, it was proposed that nitric oxide (NO), or other substances having similar chemical and biological characteristics, could act as short-lived, activity-dependent spatial signals, able to stabilize active synapses by diffusing through a local volume of tissue. The present article addresses this issue, by reviewing the experimental evidence for a correlated role of the activity of the NMDA receptor and the production of NO in key steps of neural development. Evidence for such a functional coupling emerges not only concerning synaptogenesis and formation of neural maps, for which it was originally proposed, but also for some earlier phases of neurogenesis, such as neural cell proliferation and migration. Regarding synaptogenesis and neural map formation in some cases, there is so far no conclusive experimental evidence for a coupled functional role of NMDA receptor activation and NO production. Some technical problems related to the use of inhibitors of NO formation and of gene knockout animals are discussed. It is also suggested that other substances, known to act as spatial signals in adult synaptic plasticity, could have a role in developmental plasticity. Concerning the crucial developmental phase of neuronal survival or elimination through programmed cell death, the well-documented survival role related to NMDA receptor activation also starts to find evidence for a concomitant requirement of downstream NO production. On the basis of the reviewed literature, some of the major controversial issues are addressed and, in some cases, suggestions for possible future experiments are proposed.