Nitric Oxide-cyclic GMP Signaling Research Articles

Xylazole inhibits NO-cGMP pathway in fetal rat nerve cells.

BackgroundXylazole (Xyl) is a veterinary anesthetic that is structurally and functionally similar to xylazine. However, the effects of Xyl in vitro remain unknown.ObjectivesThis study aimed to investigate the anesthetic mechanism of Xyl using fetal rat nerve cells treated with Xyl.MethodsFetal rat nerve cells cultured for seven days were treated with 10, 20, 30, and 40 μg/ mL Xyl for 0, 5, 10, 15, 20, 25, 30, 45, 60, 90, and 120 min. Variations of amino acid neurotransmitters (AANTs), Nitric oxide-Cyclic GMP (NO-cGMP) signaling pathway, and ATPase were evaluated.ResultsXyl decreased the levels of cGMP and NO in nerve cells. Furthermore, Xyl affected the AANT content and Na+-K+-ATPase and Ca2+-Mg2+-ATPase activity in nerve cells. These findings suggested that Xyl inhibited the NO-cGMP signaling pathway in nerve cells in vitro.ConclusionsThis study provided new evidence that the anesthetic and analgesic effects of Xyl are related to the inhibition of the NO-cGMP signaling pathway.

Synaptic vesicle traffic is supported by transient actin filaments and regulated by PKA and NO

Synaptic vesicles (SVs) can be pooled across multiple synapses, prompting questions about their dynamic allocation for neurotransmission and plasticity. We find that the axonal traffic of recycling vesicles is not supported by ubiquitous microtubule-based motility but relies on actin instead. Vesicles freed from synaptic clusters undergo ~1 µm bouts of active transport, initiated by nearby elongation of actin filaments. Long distance translocation arises when successive bouts of active transport were linked by periods of free diffusion. The availability of SVs for active transport can be promptly increased by protein kinase A, a key player in neuromodulation. Vesicle motion is in turn impeded by shutting off axonal actin polymerization, mediated by nitric oxide-cyclic GMP signaling leading to inhibition of RhoA. These findings provide a potential framework for coordinating post-and pre-synaptic strength, using retrograde regulation of axonal actin dynamics to mobilize and recruit presynaptic SV resources.

Non-canonical chemical feedback self-limits nitric oxide-cyclic GMP signaling in health and disease

Nitric oxide (NO)-cyclic GMP (cGMP) signaling is a vasoprotective pathway therapeutically targeted, for example, in pulmonary hypertension. Its dysregulation in disease is incompletely understood. Here we show in pulmonary artery endothelial cells that feedback inhibition by NO of the NO receptor, the cGMP forming soluble guanylate cyclase (sGC), may contribute to this. Both endogenous NO from endothelial NO synthase and exogenous NO from NO donor compounds decreased sGC protein and activity. This effect was not mediated by cGMP as the NO-independent sGC stimulator, or direct activation of cGMP-dependent protein kinase did not mimic it. Thiol-sensitive mechanisms were also not involved as the thiol-reducing agent N-acetyl-L-cysteine did not prevent this feedback. Instead, both in-vitro and in-vivo and in health and acute respiratory lung disease, chronically elevated NO led to the inactivation and degradation of sGC while leaving the heme-free isoform, apo-sGC, intact or even increasing its levels. Thus, NO regulates sGC in a bimodal manner, acutely stimulating and chronically inhibiting, as part of self-limiting direct feedback that is cGMP independent. In high NO disease conditions, this is aggravated but can be functionally recovered in a mechanism-based manner by apo-sGC activators that re-establish cGMP formation.

Toward elucidating diversity of neural mechanisms underlying insect learning

Insects are widely used as models to study neural mechanisms of learning and memory. Our recent studies on crickets, together with reports on other insect species, suggest that some fundamental differences exist in neural and molecular mechanisms of learning and memory among different species of insects, particularly between crickets and fruit flies. First, we suggested that in crickets octopamine (OA) and dopamine (DA) neurons convey reward and punishment signals, respectively, in associated learning. On the other hand, it has been reported that in fruit flies different sets of DA neurons convey reward or punishment signals. Secondly, we have suggested that in crickets OA and DA neurons participate in the retrieval of appetitive and aversive memories, respectively, while this is not the case in fruit flies. Thirdly, cyclic AMP signaling is critical for short-term memory formation in fruit flies, but not in crickets. Finally, nitric oxide-cyclic GMP signaling and calcium-calmodulin signaling are critical for long-term memory (LTM) formation in crickets, but such roles have not been reported in fruit flies. Not all of these differences can be ascribed to different experimental methods used in studies. We thus suggest that there are unexpected diversities in basic mechanisms of learning and memory among different insect species, especially between crickets and fruit flies. Studies on a larger number of insect species will help clarify the diversity of learning and memory mechanisms in relation to functional adaptation to the environment and evolutionary history.

Modulation of glycinergic synaptic transmission in the trigeminal and hypoglossal motor nuclei by the nitric oxide–cyclicGMP signaling pathway

In a previous work we found that nitric oxide (NO) and cyclicGMP (cGMP) inhibit glutamatergic synaptic transmission in trigeminal motoneurons (MnV). Here we study the actions of the NO/cGMP signaling pathway on glycinergic synaptic transmission in trigeminal and hypoglossal motoneurons (MnXII) in brain stem slices of neonatal rats. Glycinergic inhibitory postsynaptic currents (IPSCs) were recorded in MnV by stimulation of the supratrigeminal nucleus (SuV) and in MnXII by stimulation of the nucleus of Roller. The NO donor DETA/NONOate (DETA/NO) reduced the amplitude of the IPSC to 58.1±4.2% of control values in MnV. In the presence of YC-1, a modulator of guanylate cyclase that acts as a NO sensitizer, lower and otherwise ineffective concentrations of DETA/NO induced a reduction of the IPSC to 47.2±15.6%. NO effects were mimicked by 8 bromo cyclicGMP (8BrcGMP). They were accompanied by an increase in the paired pulse facilitation (PPF) and in the failure rate of evoked IPSCs. 8BrcGMP did not modify the glycinergic currents elicited by exogenous glycine. In MnXII the IPSCs were also reduced by NO donors and 8BrcGMP to 52.9±6.3% and 45.9±4% of control values, respectively. In these neurons, but not in MnV, we also observed excitatory postsynaptic actions of NO donors. We propose that the differences between the two motor pools may be due to a differential development of the nitrergic system in the two nuclei. Our data show that NO, through its second messenger cGMP, reduces inhibitory glycinergic synaptic transmission in both MnV and MnXII. For MnV, evidence in favor of presynaptic inhibition of glycine release is presented. Given our previous data together with the current results, we propose that the NO/cGMP signaling pathway participates pre- and postsynaptically in the combined regulation of MnV and MnXII activities in motor acts in which they participate.

Soluble Guanylate Cyclase Generation of cGMP Regulates Migration of MGE Neurons

Here we have provided evidence that nitric oxide-cyclic GMP (NO-cGMP) signaling regulates neurite length and migration of immature neurons derived from the medial ganglionic eminence (MGE). Dlx1/2(-/-) and Lhx6(-/-) mouse mutants, which exhibit MGE interneuron migration defects, have reduced expression of the gene encoding the α subunit of a soluble guanylate cyclase (Gucy1A3). Furthermore, Dlx1/2(-/-) mouse mutants have reduced expression of NO synthase 1 (NOS1). Gucy1A3(-/-) mice have a transient reduction in cortical interneuron number. Pharmacological inhibition of soluble guanylate cyclase and NOS activity rapidly induces neurite retraction of MGE cells in vitro and in slice culture and robustly inhibits cell migration from the MGE and caudal ganglionic eminence. We provide evidence that these cellular phenotypes are mediated by activation of the Rho signaling pathway and inhibition of myosin light chain phosphatase activity.

Abstract 386: Compound 21 Induces Natriuresis via Renal AT2 Receptor Activation in Male and Female Rats

Endogenous renal des-aspartyl 1 -angiotensin II (angiotensin III) activates renal proximal tubule AT 2 receptors (AT 2 Rs) and induces natriuresis via a nitric oxide-cyclic GMP signaling pathway. The present study explores the ability of highly selective non-peptide AT 2 R agonist Compound 21 (C21) to induce natriuresis. Sprague-Dawley rats (12 weeks old; male N=22; female N=18) were studied in the presence and absence of concurrent 24-h AT 1 R blockade with candesartan (CAND;0.01 mg/kg/min). Rats were anesthetized with Inactin 100 mg/kg i.p., uninephrectomized and instrumented for delivery of 3 cumulative 30-min i.v. infusions of C21 (100, 200, and 300 ng/kg/min) following a 30-min control infusion of vehicle. Mean arterial pressure (MAP) was measured for all periods and urine Na + excretion rate (U Na V) was calculated for the control and final C21 collection periods. To determine whether the systemically induced natriuresis is mediated by renal AT 2 Rs, PD-123319 (PD), a specific AT 2 R antagonist, was infused directly into the renal cortical interstitium(20 μg/kg/min and 10 μg/kg/min for females and males, respectively) during the i.v. C21 infusions. In female rats, C21 increased U Na V from 1.5 ± 0.20 to 7.48 ± 0.95 μmol/min (P<0.0001). This response was abrogated by concurrent intrarenal PD infusion [control 0.74 ± 0.19 vs. C21 2.02 ± 0.50 μmol/min (P<0.001from C21 alone). Systemic CAND administration augmented the natriuretic response to C21 [control 1.29 ± 0.25 vs. C21 10.68 ± 0.70 μmol/min (P<0.05 from C21 alone)]. In male rats, C21 increased U Na V from 0.46 ±0.08 to 6.21 ± 1.33 μmol/min (P<0.01). This response was blocked by concurrent intrarenal PD infusion [control 0.39 ± 0.11 vs. C21 1.69 ± 0.53 μmol/min (P<0.05 from C21 alone). Systemic CAND did not significantly alter the natriuretic response to C21 alone [control 0.49 ± 0.15 vs. C21 7.67 ± 0.72 μmol/min (P = NS from C21 alone). In female rats, CAND augmented the natriuretic response to C21 over that of male rats (P<0.01). Systemic arterial pressures were decreased by CAND in both male and female rats but were unchanged by C21 alone or together with intrarenal PD. C21 induces natriuresis via renal AT 2 R activation in both male and female rats. These data suggest the potential for AT 2 R agonist therapy in hypertension.

MK801 controls form-deprivation myopia by nitric oxide-cyclic GMP signaling pathway in guinea pig

To investigate the mechanism of myopia following intravitreous injection of MK801 (dizocipine maleate) intravitreous injected. Three-week-old guinea pigs were divided into six groups: group A (control), group B (3 weeks form-deprivation in right eye), group C ( 3 weeks form-deprivation in right eye + saline), group D (3 weeks form-deprivation in right eye + MK801 1ng), group E (3 weeks form-deprivation in right eye + MK801 10 ng), group F (3 weeks form-deprivation in right eye + MK801 100 ng). The refraction and axial length of the eyes were measured. ncNOS was measured by hybridization in situ, and cyclic GMP (cGMP) concentrations by radioimmunochemistry. The correlation between MK801 concentration and diopter degree, axial length of the eyes, and levels of ncNOS or cyclic GMP were analyzed with linear correlation in the groups C-F. Diopter degree was decreased, axial eye length was shorted and levels of ncNOS and c-GMP were decreased in groups C, D, E and F dependent on the concentration of MK801. The diopter degree had positive correlation with MK801 concentration (r=0.702, P<0.05), while the axial eye length and the levels of ncNOS and cGMP were negatively correlated (r=-0.736, -0.637, -0.725, P<0.05) MK801 injected into the vitreous humor can restrain myopia by down-regulated the expression of the nitric oxide-cyclic GMP signaling pathway. The effect is concentration dependent.

Clinical management of adult sickle-cell disease

This review provides an overview of the clinical management of sickle-cell disease (SCD) with recently published findings. Unfortunately, negative observations did not confirm the hope that therapies acting on nitric oxide-cyclic GMP signaling, NSAIDs or Gardos channel inhibitor would control SCD vaso-occlusive crises. The safety of hydroxycarbamide was further supported by two observational studies covering 20 years and over 2 years in young children. Concerning the management of chronic visceral complications of SCD, the STOP II trial showed the risk of discontinuing blood exchange transfusion for children with transcranial Doppler-assessed accelerated blood-flow velocities. The French multicenter Etendard study found that only 25% of SCD patients with tricuspid regurgitation velocity (TRV) 2.5 m/s or more on echocardiograms had catheterization-confirmed pulmonary hypertension. However, elevated TRV, regardless of its cause, was associated with higher mortality. Finally, recent results identified new therapeutic strategies for the treatment and prevention of renal dysfunction, priapism and skin ulcers, but prospective studies are needed to confirm those findings. SCD treatment relies on concomitant preventive and curative measures to control its acute and chronic manifestations. Pathophysiologic advances have enabled better management, with new therapeutics highly likely in the near future.

Nitric Oxide-Cyclic GMP Signaling in Stem Cell Differentiation

Nitric Oxide-Cyclic GMP Signaling in Stem Cell Differentiation

A New Day for PAH

When the editorial board first considered an issue devoted to recent clinical trial results, clinicians had 6 FDA approved drugs to treat pulmonary arterial hypertension (PAH). We now have 7, and it seems conceivable that we might have an 8th before the end of 2009. With collaborative, international efforts, the pace of progress has quickened in the last 5 years, and indeed, a “New Day is Dawning” on treatment options for our patients.In this issue, Bob Schilz and I wanted to provide an authoritative update on recent clinical trials and to highlight therapies that have “graduated” from bench science to bedside investigation. An author on the pivotal epoprostenol report, David Langleben has a long perspective and remains committed to bench research on mechanisms of vascular dysfunction in PAH. His article highlights Phases I and II trial data that have been reported only in abstract form at international meetings in the last 2 years. He also invites readers to consider an important question about whether our current therapies address fundamental disease mechanisms. I think readers will especially appreciate the figure illustrating how cicletanine, riociguat, and phospho-diesterase inhibitors are related in the nitric oxide-cyclic GMP signaling pathway.Murali Chakinala's information-packed article summarizes key data from recently published or presented combination trials including PACES (adding sildenafil), TRIUMPH (adding inhaled treprostinil), and PHIRST (adding tadalafil). A useful table in the paper shows trends in the baseline characteristics of patients over the last decade, and his thoughtful analysis on endpoints highlights the limitations of our current approach in drug development and invites us to “Raise the bar” for future investigations.Finally, I reviewed the progress toward a highly effective oral prostanoid; unfortunately, I had to conclude that we as investigators have endured a large amount of backsliding down a steep learning curve. We still have a mountain to master!Scott Halpern has a research interest in the ethics of clinical research. We invited him to moderate a round table discussion with 3 leaders in clinical drug development over the last 20 years: Mike McGoon, David Badesch, and Myung Park. The questions were provocative, and I think you'll really learn from the lively dialogue among these authorities with very different perspectives.Bob Schilz and I enjoyed planning this issue, and we hope that it will serve as a valuable reference point for readers who wish to update their knowledge about the drugs (and cells!) that will heavily influence therapeutic approaches now and in the next 5 years.

Nitric oxide–cyclic GMP signaling pathway limits inflammatory degeneration of midbrain dopaminergic neurons: Cell type-specific regulation of heme oxygenase-1 expression

Excessive production of nitric oxide (NO) by microglia is at least in part responsible for the pathogenesis of various neurodegenerative disorders including Parkinson disease, but at the same time NO may also play a distinct role as a signaling molecule such as an activator of soluble guanylyl cyclase. Here we investigated potential roles of the NO-soluble guanylyl cyclase–cyclic GMP signaling pathway in the regulation of dopaminergic neurodegeneration. Activation of microglia by interferon-γ (IFN-γ) followed by lipopolysaccharide (LPS) caused dopaminergic cell death in rat midbrain slice cultures, which was dependent on NO production. 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a soluble guanylyl cyclase inhibitor, as well as KT5823, an inhibitor of cyclic GMP-dependent protein kinase, exacerbated dopaminergic cell death induced by IFN-γ/LPS. Conversely, 8-bromo-cyclic GMP attenuated IFN-γ/LPS cytotoxicity on dopaminergic neurons. Notably, although heme oxygenase-1 (HO-1) was expressed prominently in cells other than dopaminergic neurons in control cultures, robust expression of HO-1 was induced in surviving dopaminergic neurons challenged with IFN-γ/LPS. ODQ and KT5823 decreased, whereas 8-bromo-cyclic GMP increased, the number of dopaminergic neurons expressing HO-1 after IFN-γ/LPS challenge, without parallel changes in HO-1 expression in other cell populations. An NO donor 3-(4-morpholinyl)sydnonimine hydrochloride also induced HO-1 expression in dopaminergic neurons, which was abolished by ODQ and augmented by 8-bromo-cyclic GMP. Moreover, IFN-γ/LPS-induced dopaminergic cell death was augmented by zinc protoporphyrin IX, an HO-1 inhibitor. The NO donor cytotoxicity on dopaminergic neurons was also augmented by ODQ and zinc protoporphyrin IX. These results indicate that the NO-cyclic GMP signaling pathway promotes the induction of HO-1 specifically in dopaminergic neurons, which acts as an endogenous protective system to limit inflammatory degeneration of this cell population.

Chronic nitric oxide synthase blockade desensitizes the heart to the negative metabolic effects of nitric oxide

The consequences of chronic nitric oxide synthase (NOS) blockade on the myocardial metabolic and guanylyl cyclase stimulatory effects of exogenous nitric oxide (NO) were determined. Thirty-three anesthetized open-chest rabbits were randomized into four groups: control, NO donor S-nitroso- N-acetyl-penicillamine (SNAP, 10 − 4 M), NOS blocking agent N G-nitro- l-arginine methyl ester ( l-NAME, 20 mg/kg/day) for 10 days followed by a 24 hour washout and l-NAME for 10 days followed by a 24 hour washout plus SNAP. Myocardial O 2 consumption was determined from coronary flow (microspheres) and O 2 extraction (microspectrophotometry). Cyclic GMP and guanylyl cyclase activity were determined by radioimmunoassay. There were no baseline metabolic, functional or hemodynamic differences between control and l-NAME treated rabbits. SNAP in controls caused a reduction in O 2 consumption (SNAP 5.9 ± 0.6 vs. control 8.4 ± 0.8 ml O 2/min/100 g) and a rise in cyclic GMP (SNAP 18.3 ± 3.8 vs. control 10.4 ± 0.9 pmol/g). After chronic l-NAME treatment, SNAP caused no significant changes in O 2 consumption (SNAP 7.1 ± 0.8 vs. control 6.4 ± 0.7) or cyclic GMP (SNAP 14.2 ± 1.8 vs. control 12.1 ± 1.3). In controls, guanylyl cyclase activity was significantly stimulated by SNAP (216.7 ± 20.0 SNAP vs. 34.4 ± 2.5 pmol/mg/min base), while this increase was blunted after l-NAME (115.9 ± 24.5 SNAP vs. 24.9 ± 4.7 base). These results demonstrated that chronic NOS blockade followed by washout blunts the response to exogenous NO, with little effect on cyclic GMP or myocardial O 2 consumption. This was related to reduced guanylyl cyclase activity after chronic l-NAME. These results suggest that, unlike many receptor systems, the NO–cyclic GMP signal transduction system becomes downregulated upon chronic inhibition.

Negative Inotropic Effect of Low-Dose Ethanol in Mouse Ventricular Myocytes is Mediated by Activation of Endothelial Nitric Oxide Synthase

Low doses of ethanol can produce negative functional effects in ventricular myocytes. This may be related to the nitric oxide-cyclic GMP signal transduction system. We tested the hypothesis that ethanol stimulated endothelial nitric oxide synthase and this caused the negative functional effects in cardiac myocytes. This hypothesis was tested in ventricular myocytes isolated from endothelial nitric oxide synthase-knockout (eNOS-/-) and wild-type (WT) control mice. Cell function was determined with a video edge detector at 37 degrees C. Myocytes were administered 5 or 10 mM ethanol alone or after 10(-6) M L-nitro-arginine-methyl ester (L-NAME, nitric oxide synthase inhibitor) or 10(-6) M 1H[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ, soluble guanylyl cyclase inhibitor). There were no differences in basal perecentage shortening (2.6+/-0.2% WT versus 2.4+/-0.2% eNOS) or maximal rate of shortening (44+/-6 WT versus 47+/-6 microms eNOS) between groups. In the WT mice, 10 mM ethanol significantly decreased percentage shortening (1.8+/-0.1) and maximal rate of shortening (35+/-4). These effects were blocked by L-NAME and ODQ. In the eNOS-/- mice, these values were not affected by ethanol. Similar data were seen for both maximal rate of shortening and relaxation. These data provide both pharmacological and direct genetic proof that these low doses of ethanol act as a stimulator of endothelial nitric oxide synthase, and this leads to the negative functional effects in ventricular myocytes.

Modulation of dural nociceptor mechanosensitivity by the nitric oxide-cyclic GMP signaling cascade.

The role of the nitric oxide (NO)-cGMP signaling cascade in modulation of peripheral nociception is controversial. Although behavioral studies have suggested both pro- and anti-nociceptive effects, little is known about the direct action of this signaling cascade on primary afferent nociceptive neurons that mediate these behaviors. Here, using single-unit recordings, we examined the direct effect of NO-cGMP signaling on spontaneous activity and mechanical responses of nociceptive afferents that innervate the dura mater. We found that the NO donor sodium nitroprusside (SNP), when applied topically to the neuronal receptive field, induced both sensitization and inhibition of the mechanical responses, albeit in different populations of neurons, which could be distinguished based on their baseline mechanical thresholds. SNP, however, did not change the level of spontaneous activity. Administration of the cGMP analogue 8-pCPT-cGMP mimicked only the inhibitory effect. When SNP was co-applied with either an inhibitor of guanylyl cyclase or a cGMP blocker, sensitization never occurred, and the inhibitory effect of SNP could also be blocked. Our findings suggest that NO can either increase or decrease the mechanical responsiveness of nociceptors and that its action might depend, in part, on the baseline level of neuronal excitability. Our results also implicate cGMP in mediating the inhibitory effect of NO.

NMDA receptor-mediated extracellular adenosine accumulation in rat forebrain neurons in culture is associated with inhibition of adenosine kinase.

The effect of N-methyl-d-aspartate (NMDA) on regulation of extracellular adenosine was investigated in rat forebrain neurons in culture. NMDA evoked accumulation of extracellular adenosine with an EC50 value of 4.8 +/- 1.2 microM. The effect of NMDA was blocked by (+)-5-methyl-10,11-dihydro-5H-dibenzo [a, d] cyclohepten-5,10-imine hydrogen maleate indicating that NMDA receptor activation was involved. The NMDA effect was also blocked by chelation of extracellular Ca2+ indicating that influx of calcium was required. The nitric oxide-cyclic GMP signalling pathway was not involved, as nitric oxide synthase inhibitors were unable to block, and cGMP analogs were unable to mimic, the effect of NMDA. The source for extracellular adenosine was likely to be intracellular adenosine as the ecto-5'-nucleotidase inhibitor alpha beta-methylene-ADP was unable to block the effect of NMDA. One possible cause of intracellular adenosine accumulation might be NMDA receptor-mediated inhibition of mitochondrial function and ATP hydrolysis. We found that NMDA caused a concentration dependent depletion of intracellular ATP with an EC50 value of 21 +/- 8 microM. NMDA also caused a significant decrease in adenosine kinase activity, assayed by two different methods. Consistent with the hypothesis that inhibition of adenosine kinase is sufficient to cause an increase in extracellular adenosine, inhibition of adenosine kinase by 5'-iodotubercidin resulted in elevation of extracellular adenosine. However, in the presence of a concentration of 5'-iodotubercidin that inhibited over 90% of adenosine kinase activity, exposure to NMDA still caused adenosine accumulation. These studies suggest that several possible mechanisms are likely to be involved in NMDA-evoked extracellular adenosine accumulation.

Nitric oxide-cyclic GMP signaling pathway in the regulation of rabbit clitoral cavernosum tone.

We investigated the role of nitric oxide (NO)-guanosine 3',5'-cyclic monophosphate (cGMP) signaling in the regulation of rabbit clitoral cavernosum (CC) tone. Tension measurements, reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and NADPH-diaphorase staining were performed in CC. In the precontracted CC strips with phenylephrine (10(-5) M), acetylcholine (ACh) relaxed, dependent on dosage. Pretreatment with atropine, N(omega) nitro-L-arginine-methyl ester (NAME) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), guanylate cyclase inhibitor abolished the ACh-induced relaxations, but tetrodotoxin (TTX) did not. Sodium nitroprusside relaxed the strips in the presence of atropine and NAME, but not in the presence of ODQ. Electrical field stimulation (EFS) relaxed the strips dependent on stimulus strength. Pretreatment with TTX, NAME, or ODQ abolished the EFS-induced relaxation, but atropine did not. L-Arginine partially restored the inhibited response to ACh and EFS. The inducible NO synthase (iNOS) and neuronal NOS (nNOS) mRNAs and iNOS and endothelial NOS (eNOS) proteins were identified in the CC. NADPH-diaphorase staining revealed the positivity on the nerve trunks and fine nerve fibers in the CC. Finally, results demonstrate that the nNOS, ENOS, and the NO-cGMP signaling pathway are involved in the regulation of clitoral tumescence.

Kinetics of nitric oxide-cyclic GMP signalling in CNS cells and its possible regulation by cyclic GMP.

Physiologically, nitric oxide (NO) signal transduction occurs through soluble guanylyl cyclase (sGC), which catalyses cyclic GMP (cGMP) formation. Knowledge of the kinetics of NO-evoked cGMP signals is therefore critical for understanding how NO signals are decoded. Studies on cerebellar astrocytes showed that sGC undergoes a desensitizing profile of activity, which, in league with phosphodiesterases (PDEs), was hypothesized to diversify cGMP responses in different cells. The hypothesis was tested by examining the kinetics of cGMP in rat striatal cells, in which cGMP accumulated in neurones in response to NO. Based on the effects of selective PDE inhibitors, cGMP hydrolysis following exposure to NO was attributed to a cGMP-stimulated PDE (PDE 2). Analysis of NO-induced cGMP accumulation in the presence of a PDE inhibitor indicated that sGC underwent marked desensitization. However, the desensitization kinetics determined under these conditions described poorly the cGMP profile observed in the absence of the PDE inhibitor. An explanation shown plausible theoretically was that cGMP determines the level of sGC desensitization. In support, tests in cerebellar astrocytes indicated an inverse relationship between cGMP level and recovery of sGC from its desensitized state. We suggest that the degree of sGC desensitization is related to the cGMP concentration and that this effect is not mediated by (de)phosphorylation.

The Neuroanatomy of Nitric Oxide–Cyclic GMP Signaling in the Locust: Functional Implications for Sensory Systems1

Abstract Recent studies have investigated the source and target neurons for the diffusible neuronal messenger molecule nitric oxide (NO) in the nervous system of the locust. Here we compare the neuroarchitecture of NO signaling between different sensory systems. The available neuroanatomical data implicate NO in sensory processing for modalities as diverse as mechanoreception, vision, olfaction, gustation and hearing. All respective first-order sensory neuropils are innervated by NOS-containing interneurons. The corresponding sensory receptor neurons lack NOS but seem to express soluble guanylyl cyclase (sGC), the main receptor molecule for NO in the nervous system. The axonal projections of sensory neurons must therefore be considered the primary target of NO in these sensory neuropils. An exception is the antennal olfactory system where sGC is apparently expressed in interneurons, in partial colocalization with NOS. We discuss these anatomical findings in relation to the spatiotemporal characteristics o...

The Neuroanatomy of Nitric Oxide–Cyclic GMP Signaling in the Locust: Functional Implications for Sensory Systems

Recent studies have investigated the source and target neurons for the diffusible neuronal messenger molecule nitric oxide (NO) in the nervous system of the locust. Here we compare the neuroarchitecture of NO signaling between different sensory systems. The available neuroanatomical data implicate NO in sensory processing for modalities as diverse as mechanoreception, vision, olfaction, gustation and hearing. All respective first-order sensory neuropils are innervated by NOS-containing interneurons. The corresponding sensory receptor neurons lack NOS but seem to express soluble guanylyl cyclase (sGC), the main receptor molecule for NO in the nervous system. The axonal projections of sensory neurons must therefore be considered the primary target of NO in these sensory neuropils. An exception is the antennal olfactory system where sGC is apparently expressed in interneurons, in partial colocalization with NOS. We discuss these anatomical findings in relation to the spatiotemporal characteristics of NO signaling. Many sensory neuropils are organized into maps that reflect neuronal response properties (i.e., tuning or receptive fields). A local release of NO within such maps will therefore most strongly affect neurons with similar coding properties. If sensory receptor activity triggers NO synthesis locally in the map, this mechanism could link groups of similarly tuned receptors dynamically according to stimulus intensity. Furthermore, we explore the functional implications of differences between sensory systems in the anatomy of NOS-expressing interneurons, using the compound eye and the thoracic tactile system as examples.