Differential expression of hypoxia pathway genes in honey bee (Apis mellifera L.) caste development

Diphenism in social bees is essentially contingent on nutrient-induced cellular and systemic physiological responses resulting in divergent gene expression patterns. Analyses of juvenile hormone (JH) titers and functional genomics assays of the insulin-insulin-like signaling (IIS) pathway and its associated branch, target-of-rapamycin (TOR), revealed systemic responses underlying honey bee (Apis mellifera) caste development. Nevertheless, little attention has been paid to cellular metabolic responses. Following up earlier investigations showing major caste differences in oxidative metabolism and mitochondrial physiology, we herein identified honey bee homologs of hypoxia signaling factors, HIF alpha/Sima, HIF beta/Tango and PHD/Fatiga and we investigated their transcript levels throughout critical stages of larval development. Amsima, Amtango and Amfatiga showed correlated transcriptional activity, with two peaks of occurring in both queens and workers, the first one shortly after the last larval molt and the second during the cocoon-spinning phase. Transcript levels for the three genes were consistently higher in workers. As there is no evidence for major microenvironmental differences in oxygen levels within the brood nest area, this appears to be an inherent caste character. Quantitative PCR analyses on worker brain, ovary, and leg imaginal discs showed that these tissues differ in transcript levels. Being a highly conserved pathway and linked to IIS/TOR, the hypoxia gene expression pattern seen in honey bee larvae denotes that the hypoxia pathway has undergone a transformation, at least during larval development, from a response to environmental oxygen concentrations to an endogenous regulatory factor in the diphenic development of honey bee larvae. (C) 2010 Elsevier Ltd. All rights reserved.

Effectiveness of Oral Rinse with Chlorhexidine in Preventing Nosocomial Respiratory Tract Infections among Intensive Care Unit Patients

OBJECTIVE. To evaluate the effectiveness of the oral application of a 0.12% solution of chlorhexidine for prevention of respiratory tract infections among intensive care unit (ICU) patients. DESIGN. The study design was a double-blind, randomized, placebo-controlled trial. SETTING. The study was performed in an ICU in a tertiary care hospital at a public university. PATIENTS. Study participants comprised 194 patients admitted to the ICU with a prospective length of stay greater than 48 hours, randomized into 2 groups: those who received chlorhexidine (n = 98) and those who received a placebo (n = 96). INTERVENTION. Oral rinses with chlorhexidine or a placebo were performed 3 times a day throughout the duration of the patient`s stay in the ICU. Clinical data were collected prospectively. RESULTS. Both groups displayed similar baseline clinical features. The overall incidence of respiratory tract infections (RR, 1.0 [95% confidence interval [CI], 0.63-1.60]) and the rates of ventilator-associated pneumonia per 1,000 ventilator-days were similar in both experimental and control groups (22.6 vs 22.3; P = .95). Respiratory tract infection-free survival time (7.8 vs 6.9 days; P = .61), duration of mechanical ventilation (11.1 vs 11.0 days; P = .61), and length of stay (9.7 vs 10.4 days; P = .67) did not differ between the chlorhexidine and placebo groups. However, patients in the chlorhexidine group exhibited a larger interval between ICU admission and onset of the first respiratory tract infection (11.3 vs 7.6 days; P = .05). The chances of surviving the ICU stay were similar (RR, 1.08 [95% CI, 0.72-1.63]). CONCLUSION. Oral application of a 0.12% solution of chlorhexidine does not prevent respiratory tract infections among ICU patients, although it may retard their onset.

Coping by relatives of critical care patients

OBJECTIVE: To describe the coping strategies used by the relatives of patients hospitalized in an intensive care unit. METHODS: This is a descriptive study that uses a convenience sample and both qualitative and quantitative methods. The study was conducted at a tertiary university hospital in Brazil. Participants included 41 relatives who were selected during the first 96 hours of patient hospitalization in the intensive care unit. RESULTS: The participants reported that they more frequently used Coping Strategies Based on the Stressor, followed by Religiosity/Fantasy Thinking and Seeking for Social Support. There was a statistically significant relationship (P <.01) between the use of the strategy Seeking for Social Support and elevated Acute Physiology, Age, and Chronic Health Evaluation 11 scores. Qualitative analysis allowed a clearer understanding of the relation between the patient`s condition and changes in the coping strategies used by the patient`s relatives. CONCLUSION: This study describes the coping strategies used by patients` relatives during the early hospitalization period. This investigation allowed for a better understanding of the relatives` psychologic aspects and their relation with the patient`s clinical condition. The results shall assist the design of specific interventions directed at facilitating positive coping responses on the part of relatives. (Heart Lung (R) 200 38:217-227.)

Sildenafil inhibits duodenal contractility via activation of the NO-K+ channel pathway

Phosphodiesterase type-5 (PDE5) specifically cleaves cyclic guanosine monophosphate (cGMP), a key intracellular secondary messenger. The PDE5 inhibitor sildenafil is a well-known vasodilator that also has gastrointestinal myorelaxant properties. In the present study, we further investigated sildenafil-induced myorelaxation in rat isolated duodenum, assessing its interaction with nitric oxide (NO) synthase and K+ channel opening. The spontaneous contractions of duodenal strips were reversibly inhibited by sildenafil (0.1-300 mu M) in a concentration-dependent manner [mean (95% confidence interval); EC50 = 6.8 (2.7-17.3) mu M]. The sildenafil-induced myorelaxation was significantly decreased by the NO synthase inhibitor N-nitro-L-arginine methyl ester [increasing the EC50 value to 41.9 (26.1-67.3) mu M]. Sodium nitroprusside or forskolin pretreatments enhanced the sildenafil-induced myorelaxation. In isolated strips pretreated with BaCl2 (0.2 mM), 4-aminopyridine (4-AP, 3 mM), or glybenclamide (1 mu M), the sildenafil-induced EC50 value was significantly increased to 32.8 (19.1-56.4), 27.1 (15.2-48.3) and 20.1 (16.4-24.7) mu M, respectively. Minoxidil (50 mu M) or diazoxide (100 mu M) also significantly attenuated the sildenafil-induced potency. In conclusion, the NO synthase/cyclic nucleotide pathway activation is involved in sildenafil-induced inhibition of spontaneous duodenal contractions. Its pharmacological action seems to be influenced by K+ channel opening, especially the voltage-sensitive ones, being inhibited by 4-AP and K-ATP channels, sensitive to glybenclamide.

TAC3/TACR3 Mutations Reveal Preferential Activation of Gonadotropin-Releasing Hormone Release by Neurokinin B in Neonatal Life Followed by Reversal in Adulthood

Context: Mutations in TAC3 and TACR3 (encoding neurokinin B and its receptor) have been identified in Turkish patients with idiopathic hypogonadotropic hypogonadism (IHH), but broader populations have not yet been tested and genotype-phenotype correlations have not been established. Objective: A broad cohort of normosmic IHH probands was screened for mutations in TAC3/TACR3 to evaluate the prevalence of such mutations and define the genotype/phenotype relationships. Design and Setting: The study consisted of sequencing of TAC3/TACR3, in vitro functional assays, and neuroendocrine phenotyping conducted in tertiary care centers worldwide. Patients or Other Participants: 345 probands, 18 family members, and 292 controls were studied. Intervention: Reproductive phenotypes throughout reproductive life and before and after therapy were examined. Main Outcome Measure: Rare sequence variants in TAC3/TACR3 were detected. Results: In TACR3, 19 probands harbored 13 distinct coding sequence rare nucleotide variants [three nonsense mutations, six nonsynonymous, four synonymous (one predicted to affect splicing)]. In TAC3, one homozygous single base pair deletion was identified, resulting in complete loss of the neurokinin B decapeptide. Phenotypic information was available on 16 males and seven females with coding sequence variants in TACR3/TAC3. Of the 16 males, 15 had microphallus; none of the females had spontaneous thelarche. Seven of the 16 males and five of the seven females were assessed after discontinuation of therapy; six of the seven males and four of the five females demonstrated evidence for reversibility of their hypogonadotropism. Conclusions: Mutations in the neurokinin B pathway are relatively common as causes of hypogonadism. Although the neurokinin B pathway appears essential during early sexual development, its importance in sustaining the integrity of the hypothalamic-pituitary-gonadal axis appears attenuated over time. (J Clin Endocrinol Metab 95: 2857-2867, 2010)

Crucial Role of TNF Receptors 1 and 2 in the Control of Polymicrobial Sepsis

Sepsis is still a major cause of mortality in the intensive critical care unit and results from an overwhelming immune response to the infection. TNF signaling pathway plays a central role in the activation of innate immunity in response to pathogens. Using a model of polymicrobial sepsis by i.p. injection of cecal microflora, we demonstrate a critical role of TNFR1 and R2 activation in the deregulated immune responses and death associated with sepsis. A large and persistent production of TNF was found in wild-type (B6) mice. TNFR1/R2-deficient mice, compared with B6 mice, survive lethal polymicrobial infection with enhanced neutrophil recruitment and bacterial clearance in the peritoneal cavity. Absence of TNFR signaling leads to a decreased local and systemic inflammatory response with diminished organ injury. Furthermore, using TNFR1/R2-deficient mice, TNF was found to be responsible for a decrease in CXCR2 expression, explaining reduced neutrophil extravasation and migration to the infectious site, and in neutrophil apoptosis. In line with the clinical experience, administration of Enbrel, a TNF-neutralizing protein, induced however only a partial protection in B6 mice, with no improvement of clinical settings, suggesting that future TNF immunomodulatory strategies should target TNFR1 and R2. In conclusion, the present data suggest that the endogenous TNFR1/R2 signaling pathway in polymicrobial sepsis reduces neutrophil recruitment contributing to mortality and as opposed to pan-TNF blockade is an important therapeutic target for the treatment of polymicrobial sepsis. The Journal of Immunology, 2009, 182: 7855-7864.

The diagonal band of Broca is involved in the pressor pathway activated by noradrenaline microinjected into the periaqueductal gray area of rats

Aims: The dorsal periaqueductal gray area (dPAG) is involved in cardiovascular modulation. Previously, we reported that noradrenaline (NA) microinjection into the dPAG caused a pressor response that was mediated by vasopressin release into the circulation. However, the neuronal pathway that mediates this response is as yet unknown. There is evidence that chemical stimulation of the diagonal band of Broca (dbB) also causes a pressor response mediated by systemic vasopressin release. In the present study, we evaluated the participation of the dbB in the pressor response caused by NA microinjection into the dPAG as well as the existence of neural connections between these areas. Main methods: With the above goal, we verified the effect of the pharmacological ablation of the dbB on the cardiovascular response to NA microinjection into the dPAG of unanesthetized rats. In addition, we microinjected the neuronal tracer biotinylated-dextran-amine (BDA) into the dPAG and looked for efferent projections from the dPAG to the dbB. Key findings: The pharmacologically reversible ablation of the dbB with local microinjection of CoCl(2) significantly reduced the pressor response caused by NA microinjection (15 nmol/50 nL) into the dPAG. In addition, BDA microinjection into the dPAG labeled axons in the dbB, pointing to the existence of direct connections between these areas. Significance: The present results indicate that synapses within the dbB are involved in the pressor pathway activated by NA microinjection into the VAG and direct neural projection from the dPAG to the dbB may constitute the neuroanatomic substrate for this pressor pathway. (C) 2009 Elsevier Inc. All rights reserved.

Activation of the ET-1/ETA Pathway Contributes to Erectile Dysfunction Associated with Mineralocorticoid Hypertension

The cavernosal tissue is highly responsive to endothelin-1 (ET-1), and penile smooth muscle cells not only respond to but also synthesize ET-1. Considering that ET-1 is directly involved in end-organ damage in salt-sensitive forms of hypertension, we hypothesized that activation of the ET-1/ET(A) receptor pathway contributes to erectile dysfunction (ED) associated with mineralocorticoid hypertension. Wistar rats were uninephrectomized and submitted to deoxycorticosterone acetate (DOCA)-salt treatment for 5 weeks. Control (Uni [uninephrectomized control]) animals were uninephrectomized and given tap water. Uni and DOCA-salt rats were simultaneously treated with vehicle or atrasentan (ET(A) receptor antagonist, 5 mg/Kg/day). Cavernosal reactivity to ET-1, phenylephrine (PE), ET(B) receptor agonist (IRL-1620) and electric field stimulation (EFS) were evaluated in vitro. Expression of ROCK alpha, ROCK beta, myosin phosphatase target subunit 1 (MYPT-1), and extracellular signal-regulated kinase 1/2 (ERK 1/2) were evaluated by western blot analysis. ET-1 and ET(A) receptor mRNA expression was evaluated by real-time reverse-transcriptase polymerase chain reaction. Voltage-dependent increase in intracavernosal pressure/mean arterial pressure (ICP/MAP) was used to evaluate erectile function in vivo. ET(A) receptor blockade prevents DOCA-salt-associated ED. Cavernosal strips from DOCA-salt rats displayed augmented preproET-1 expression, increased contractile responses to ET-1 and decreased relaxation to IRL-1620. Contractile responses induced by EFS and PE were enhanced in cavernosal tissues from DOCA-salt hypertensive rats. These functional changes were associated with increased activation of the RhoA/Rho-kinase and ERK 1/2 pathways. Treatment of rats with atrasentan completely prevented changes in cavernosal reactivity in DOCA-salt rats and restored the decreased ICP/MAP, completely preventing ED in DOCA-salt rats. Activation of the ET-1/ET(A) pathway contributes to mineralocorticoid hypertension-associated ED. ET(A) receptor blockade may represent an alternative therapeutic approach for ED associated with salt-sensitive hypertension and in pathological conditions where increased levels of ET-1 are present. Carneiro FS, Nunes KP, Giachini FRC, Lima VV, Carneiro ZN, Nogueira EF, Leite R, Ergul A, Rainey WE, Webb RC, and Tostes RC. Activation of the ET-1/ETA pathway contributes to erectile dysfunction associated with mineralocorticoid hypertension. J Sex Med **;**:**-**.

The expression of contextual fear conditioning involves activation of an NMDA receptor-nitric oxide pathway in the medial prefrontal cortex

The ventral portion of medial prefrontal cortex (vMPFC) is involved in contextual fear-conditioning expression in rats. In the present study, we investigated the role of local N-methyl-D-aspartic acid (NMDA) glutamate receptors and nitric oxide (NO) in vMPFC on the behavioral (freezing) and cardiovascular (increase of arterial pressure and heart rate) responses of rats exposed to a context fear conditioning. The results showed that both freezing and cardiovascular responses to contextual fear conditioning were reduced by bilateral administration of NMDA receptor antagonist LY235959 (4 nmol/200 nL) into the vMPFC before reexposition to conditioned chamber. Bilateral inhibition of neuronal NO synthase (nNOS) by local vMPFC administration of the N omega-propyl-L-arginine (N-propyl, 0.04 nmol/200 nL) or the NO scavenger carboxy-PTI0 (1 nmol/200 A) caused similar results, inhibiting the fear responses. We also investigated the effects of inhibiting glutamate- and NO-mediated neurotransmission in the vMPFC at the time of aversive context exposure on reexposure to the same context. It was observed that the 1st exposure results in a significant attenuation of the fear responses on reexposure in vehicle-treated animals, which was not modified by the drugs. The present results suggest that a vMPFC NMDA-NO pathway may play an important role on expression of contextual fear conditioning.

Phlebotomine salivas inhibit immune inflammation-induced neutrophil migration via an autocrine DC-derived PGE(2)/IL-10 sequential pathway

In the present study, we investigated whether saliva from Phlebotomus papatasi and Phlebotomus duboscqi inhibited antigen-induced neutrophil migration and the mechanisms involved in these effects. The pretreatment of immunized mice with salivary gland extracts (SGE) of both phlebotomines inhibited OVA challenge-induced neutrophil migration and release of the neutrophil chemotactic mediators, MIP-1 alpha, TNF-alpha, and leukotriene B-4 (LTB4). Furthermore, SGE treatment enhanced the production of anti-inflammatory mediators, IL-10 and PGE(2). SGE treatments failed to inhibit neutrophil migration and MIP-1 alpha and LTB4 production in IL-10(-/-) mice, also failing in mice treated with nonselective (indomethacin) or selective (rofecoxibe) cyclooxygenase (COX) inhibitors. COX inhibition resulted in diminished SGE-induced IL-10 production, and PGE(2) release triggered by SGE remained increased in IL-10(-/-) mice, suggesting that prostanoids are acting through an IL-10-dependent mechanism. SGE treatments in vivo reduced the OVA-induced lymphoproliferation of spleen-derived cells. Further, the in vitro incubation of bone marrow-derived dendritic cells (DC) with SGE inhibited the proliferation of CD4(+) T cells from OVA-immunized mice, which was reversed by indomethacin and anti-IL-10 antibody treatments. Supporting these results, SGE induced the production of PGE(2) and IL-10 by DC, which were blocked by COX inhibition. These effects were associated with the reduction of DC-membrane expression of MHC-II and CD86 by SGE treatment. Altogether, the results showed that Phlebotomine saliva inhibits immune inflammation-induced neutrophil migration by an autocrine DC sequential production of PGE(2)/IL-10, suggesting that the saliva constituents might be promising therapeutic molecules to target immune inflammatory diseases.

Peroxisome proliferator-activated receptor-gamma ligand, 15-deoxy-Delta A(12,14)-prostaglandin J(2), reduces neutrophil migration via a nitric oxide pathway

Ligands for peroxisome proliferator-activated receptor gamma (PPAR-gamma), such as 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) have been implicated as a new class of anti-inflammatory compounds with possible clinical applications. Based on this concept, this investigation was designed to determine the effect of 15d-PGJ(2)-mediated activation of PPAR-gamma ligand on neutrophil migration after an inflammatory stimulus and clarify the underlying molecular mechanisms using a mouse model of peritonitis. Our results demonstrated that 15d-PGJ(2) administration decreases leukocyte rolling and adhesion to the inflammated mesenteric tissues by a mechanism dependent on NO. Specifically, pharmacological inhibitors of NO synthase remarkably abrogated the 15d-PGJ(2)-mediated suppression of neutrophil migration to the inflammatory site. Moreover, inducible NOS(-/-) mice were not susceptible to 15d-PGJ(2)-mediated suppression of neutrophil migration to the inflammatory sites when compared with their wild type. In addition, 15d-PGJ(2)-mediated suppression of neutrophil migration appeared to be independent of the production of cytokines and chemokines, since their production were not significantly affected in the carrageenan-injected peritoneal cavities. Finally, up-regulation of carrageenan-triggered ICAM-I expression in the mesenteric microcirculation vessels was abrogated by pretreatment of wild-type mice with 15d-PGJ(2), whereas 15d-PGJ(2) inhibited F-actin rearrangement process in neutrophils. Taken together these findings demonstrated that 15d-PGJ(2) suppresses inflammation-initiated neutrophil migration in a mechanism dependent on NO production in mesenteric tissues.

Essential Role of CCR2 in Neutrophil Tissue Infiltration and Multiple Organ Dysfunction in Sepsis

Rationale Sepsis is defined as a systemic inflammatory response to infection, which in its severe form is associated with multiple organ dysfunction syndrome (MODS). The precise mechanisms by Which MODS develops remain unclear. Neutrophils have a pivotal role in the defense against infections; however, overwhelming activation of neutrophils is known to elicit tissue damage. Objectives: We investigated the role of the chemokine receptor CCR2 in driving neutrophil infiltration and eliciting tissue damage in remote organs during sepsis. Methods: Sepsis was induced in wild-type mice treated with CCR2 antagonist (RS504393) or CCR2(-/-) mice by cecal ligation and puncture (CLP) model. Neutrophil infiltration into the organs was measured by myeloperoxidase activity and fluorescence-activated cell sorter. CCR2 expression and chemotaxis were determined in neutrophils stimulated with Toll-like receptor agonists or isolated from septic mice and patients. Measurements and Main Results: CCR2 expression and responsiveness to its ligands was induced in circulating neutrophils during CLP-induced sepsis by a mechanism dependent on Toll-like receptor/nuclear factor-kappa B pathway. Genetic or pharmacologic inhibition of CCR2 protected mice from CLP-induced mortality. This protection was associated with lower infiltration of neutrophils into the lungs, heart, and kidneys and reduced serum biochemical indicators of organ injury and dysfunction. Importantly, neutrophils from septic patients express high levels of CCR2, and the severity of patient illness correlated positively with increasing neutrophil chemotaxis to CCR2 ligands. Conclusions: Collectively, these data identify CCR2 as a key receptor that drives the inappropriate infiltration of neutrophils into remote organs during sepsis. Therefore, CCR2 blockade is a novel potential therapeutic target for treatment of sepsis-induced MODS.

Gastroprotective effect of heme-oxygenase 1/biliverdin/CO pathway in ethanol-induced gastric damage in mice

Our objective was to evaluate the role of heme-oxygenase 1 (HO-1)/biliverdin/CO pathway in gastric defense against ethanol-induced gastric damage in mice. Mice were pre-treated with saline, hemin (HO-1 inducer), biliverdin (HO-1 product), dimanganese decacarbonyl (DMDC, CO donor) or zinc protoporphyrin IX (ZnPP IX, HO-1 antagonist). Another group received soluble guanylate cyclase (sGC) inhibitor (ODQ) 30 min before hemin, biliverdin or DMDC. After 30 min, gastric damage was induced by ethanol. After one hour, rats were sacrificed. Gastric lesions were measured using a computer planimetry program, and gastric corpus pieces were assayed for malonylaldehyde (MDA), glutathione (GSH) or bilirubin. HO-1 expression was determined after saline or ethanol administration by polymerase chain reaction (PCR) or immunohistochemistry. Ethanol (25% or 50%) induced gastric damage, increased MDA levels and reduced GSH in the gastric tissue. Ethanol 50% increased HO-1 mRNA transcripts, HO-1 immunoreactivity, and bilirubin concentration in gastric mucosa. Pre-treatment with hemin reduced gastric damage and MDA formation and increased GSH concentration in the gastric mucosa. ZnPP IX amplified the ethanol-induced gastric lesion, increased MDA formation and decreased GSH concentration in gastric mucosa. Biliverdin and DMDC reduced gastric damage and MDA formation and increased GSH concentration in the gastric tissue. ODQ completely abolished the DMDC protective gastric effect However, effects of hemin or biliverdin did not change with ODQ treatment. Our results suggest that HO-1/biliverdin/CO pathway plays a protective role against ethanol-induced gastric damage through mechanisms that can be dependent (CO) or independent (biliverdin) of sGC activation. (C) 2010 Elsevier B.V. All rights reserved.

Hydrogen Sulfide Improves Neutrophil Migration and Survival in Sepsis via K(ATP)(+) Channel Activation

Rationale Recovering the neutrophil migration to the infectious focus improves survival in severe sepsis. Recently, we demonstrated that the cystathionine gamma-lyase (CSE)/hydrogen sulfide (H(2)S) pathway increased neutrophil recruitment to inflammatory focus during sterile inflammation. Objectives: To evaluate if H(2)S administration increases neutrophil migration to infectious focus and survival of mice. Methods. Sepsis was induced by cecal ligation and puncture (CLP) Measurements and Main Results. The pretreatments of mice with H2S donors (NaHS or Lawesson`s reagent) improved leukocyte rolling/adhesion in the mesenteric microcirculation as well as neutrophil migration. Consequently, bacteremia levels were reduced, hypotension and lung lesions were prevented, and the survival rate increased from approximately 13% to approximately 80% Even when treatment was delayed (6 h after CLP), a highly significant reduction in mortality compared with untreated mice was observed Moreover, H(2)S pretreatment prevented the down-regulation of CXCR2 and L-selectin and the up-regulation of CD11b and G protein-coupled receptor kinase 2 in neutrophils during sepsis. H(2)S also prevented the reduction of intercellular adhesion molecule-1 expression in the endothelium of the mesenteric microcirculation in severe sepsis Confirming the critical role of H(2)S on sepsis outcome, pretreatment with dl-propargylglycine (a CSE inhibitor) inhibited neutrophil migration to the infectious focus, enhanced lung lesions, and induced high mortality in mice subjected to nonsevere sepsis (from 0 to similar to 80%). The beneficial effects of H(2)S were blocked by glibenclamide (a ATP-dependent K(+) channel blocker). Conclusions: These results showed that H(2)S restores neutrophil migration to the infectious focus and improves survival outcome in severe sepsis by an ATP-dependent K(+) channel-dependent mechanism.

Role of the spinal cord NO/cGMP pathway in the control of arterial pressure and heart rate

The modulatory effect of nitric oxide/cyclic guanosine monophosphate (NO/cGMP) pathway on sympathetic preganglionic neurons still deserves further investigation. The present study was designed to examine the role of the spinal cord NO/cGMP pathway in controlling mean arterial pressure and heart rate. We observed that intrathecal administration of the NO synthase inhibitor N omega-Nitro-L-arginine methyl ester hydrochloride (L-NAME) causes an increase in mean arterial pressure but does not affect heart rate. Intrathecal administration of the soluble guanylyl cyclase inhibitor 1H-[1,2,4] Oxadiazolo[4,3-a] quinoxalin-1-one (ODQ) does not change mean arterial pressure and heart rate. The precursor for NO synthesis, L-arginine, reduces both mean arterial pressure and heart rate while administration of ODQ before L-arginine impaired decreases in mean arterial pressure and heart rate. Administration of the N-methyl-D-aspartate (NMDA) receptor antagonist DL-2-amino-5-phosphonopentanoic acid (AP5) after L-NAME does not affect increases in mean arterial pressure promoted by NO synthase inhibition. Although the hypotensive and bradycardic responses induced by intrathecal administration of L-arginine depend on cGMP, our results indicate that NO acts to tonically inhibit SPNs, independent of either cGMP or NMDA receptors.