Nitric oxide in brain: diffusion, targets and concentration dynamics in hippocampal subregions

Influence of formaldehyde exposure on the molecules of the NO/cGMP-cAMP signaling pathway in different brain regions of Balb/c mice

This toxicology study was conducted to assess the impact of formaldehyde, a common air pollutant found in Chinese gymnasiums, on the brain function of athletes. In this research, a total of 24 Balb/c male mice of SPF-grade were divided into four groups, each consisting of six mice. The mice were exposed to formaldehyde at different concentrations, including 0 mg/m3, 0.5 mg/m3, 3.0 mg/m3, and 3.0 mg/m3 in combination with an injection of L-NMMA (NG-monomethyl-L-arginine), which is a nitric oxide synthase antagonist. Following a one-week test period (8 h per day, over 7 days), measurements of biomarkers related to the nitric oxide (NO)/cGMP-cAMP signaling pathway were carried out on the experimental animals post-treatment. The study found that: (1) Exposure to formaldehyde can lead to brain cell apoptosis and neurotoxicity; (2) Additionally, formaldehyde exposure was found to alter the biomarkers of the NO/cGMP-cAMP signaling pathway, with some changes being statistically significant (p < 0.05 or p < 0.01); (3) The use of L-NMMA, an antagonist of the NO/cGMP-cAMP signaling pathway, was found to prevent these biomarker changes and had a protective effect on brain cells. The study suggests that the negative impact of formaldehyde on the brain function of mice is linked to the regulation of the NO/cGMP-cAMP signaling pathway.

The contribution of an imbalanced redox signalling to neurological and neurodegenerative conditions

Nitric oxide and other redox active molecules such as oxygen free radicals provide essential signalling in diverse neuronal functions, but their excess production and insufficient scavenging induces cytotoxic redox stress which is associated with numerous neurodegenerative and neurological conditions. A further component of redox signalling is mediated by a homeostatic regulation of divalent metal ions, the imbalance of which contributes to neuronal dysfunction. Additional antioxidant molecules such as glutathione and enzymes such as super oxide dismutase are involved in maintaining a physiological redox status within neurons. When cellular processes are perturbed and generation of free radicals overwhelms the antioxidants capacity of the neurons, a resulting redox damage leads to neuronal dysfunction and cell death. Cellular sources for production of redox-active molecules may include NADPH oxidases, mitochondria, cytochrome P450 and nitric oxide (NO)-generating enzymes, such as endothelial, neuronal and inducible NO synthases. Several neurodegenerative and developmental neurological conditions are associated with an imbalanced redox state as a result of neuroinflammatory processes leading to nitrosative and oxidative stress. Ongoing research aims at understanding the causes and consequences of such imbalanced redox homeostasis and its role in neuronal dysfunction.

Medical Gas Therapy for Tissue, Organ, and CNS Protection: A Systematic Review of Effects, Mechanisms, and Challenges

Gaseous molecules have been increasingly explored for therapeutic development. Here, following an analytical background introduction, a systematic review of medical gas research is presented, focusing on tissue protections, mechanisms, data tangibility, and translational challenges. The pharmacological efficacies of carbon monoxide (CO) and xenon (Xe) are further examined with emphasis on intracellular messengers associated with cytoprotection and functional improvement for the CNS, heart, retina, liver, kidneys, lungs, etc. Overall, the outcome supports the hypothesis that readily deliverable "biological gas" (CO, H₂ , H₂ S, NO, O₂ , O₃ , and N₂ O) or "noble gas" (He, Ar, and Xe) treatment may preserve cells against common pathologies by regulating oxidative, inflammatory, apoptotic, survival, and/or repair processes. Specifically, CO, in safe dosages, elicits neurorestoration via igniting sGC/cGMP/MAPK signaling and crosstalk between HO-CO, HIF-1α/VEGF, and NOS pathways. Xe rescues neurons through NMDA antagonism and PI3K/Akt/HIF-1α/ERK activation. Primary findings also reveal that the need to utilize cutting-edge molecular and genetic tactics to validate mechanistic targets and optimize outcome consistency remains urgent; the number of neurotherapeutic investigations is limited, without published results from large in vivo models. Lastly, the broad-spectrum, concurrent multimodal homeostatic actions of medical gases may represent a novel pharmaceutical approach to treating critical organ failure and neurotrauma.

Bee Venom Activates the Nrf2/HO-1 and TrkB/CREB/BDNF Pathways in Neuronal Cell Responses against Oxidative Stress Induced by Aβ1-42

Honeybee venom has recently been considered an anti-neurodegenerative agent, primarily due to its anti-inflammatory effects. The natural accumulation of amyloid-beta (Aβ) in the brain is reported to be the natural cause of aging neural ability downfall, and oxidative stress is the main route by which Aβ ignites its neural toxicity. Anti-neural oxidative stress is considered an effective approach for neurodegenerative therapy. To date, it is unclear how bee venom ameliorates neuronal cells in oxidative stress induced by Aβ. Here, we evaluated the neuroprotective effect of bee venom on Aβ-induced neural oxidative stress in both HT22 cells and an animal model. Our results indicate that bee venom protected HT22 cells against apoptosis induced by Aβ_1–42. This protective effect was explained by the increased nuclear translocation of nuclear factor erythroid 2-like 2 (Nrf2), consequently upregulating the production of heme oxygenase-1 (HO-1), a critical cellular instinct antioxidant enzyme that neutralizes excessive oxidative stress. Furthermore, bee venom treatment activated the tropomyosin-related kinase receptor B (TrkB)/cAMP response element-binding (CREB)/brain-derived neurotrophic factor (BDNF), which is closely related to the promotion of cellular antioxidant defense and neuronal functions. A mouse model with cognitive deficits induced by Aβ_1–42 intracerebroventricular (ICV) injections was also used. Bee venom enhanced animal cognitive ability and enhanced neural cell genesis in the hippocampal dentate gyrus region in a dose-dependent manner. Further analysis of animal brain tissue and serum confirmed that bee venom reduced oxidative stress, cholinergic system activity, and intercellular neurotrophic factor regulation, which were all adversely affected by Aβ_1–42. Our study demonstrates that bee venom exerts antioxidant and neuroprotective actions against neural oxidative stress caused by Aβ_1–42, thereby promoting its use as a therapeutic agent for neurodegenerative disorders.

Neuroprotective Activity of Melittin-The Main Component of Bee Venom-Against Oxidative Stress Induced by Aβ25-35 in In Vitro and In Vivo Models

Melittin, a 26-amino acid peptide, is the main component of the venom of four honeybee species and exhibits neuroprotective actions. However, it is unclear how melittin ameliorates neuronal cells in oxidative stress and how it affects memory impairment in an in vivo model. We evaluated the neuroprotective effect of melittin on Aβ_25–35-induced neuro-oxidative stress in both in vitro HT22 cells and in vivo animal model. Melittin effectively protected against HT22 cell viability and significantly deregulated the Aβ_25–35-induced overproduction of intracellular reactive oxygen species. Western blot analysis showed that melittin suppressed cell apoptosis and regulated Bax/Bcl-2 ratio, as well as the expression of proapoptotic related factors: Apoptosis-inducing factor (AIF), Calpain, Cytochrome c (CytoC), Cleaved caspase-3 (Cleacas3). Additionally, melittin enhanced the antioxidant defense pathway by regulating the nuclear translocation of nuclear factor erythroid 2-like 2 (Nrf2) thus upregulated the production of the heme oxygenase-1 (HO-1), a major cellular antioxidant enzyme combating neuronal oxidative stress. Furthermore, melittin treatment activated the Tropomyosin-related kinase receptor B (TrkB)/cAMP Response Element-Binding (CREB)/Brain-derived neurotrophic factor (BDNF), contributing to neuronal neurogenesis, and regulating the normal function of synapses in the brain. In our in vivo experiment, melittin was shown to enhance the depleted learning and memory ability, a novel finding. A mouse model with cognitive deficits induced by Aβ_25–35 intracerebroventricular injection was used. Melittin had dose-dependently enhanced neural-disrupted animal behavior and enhanced neurogenesis in the dentate gyrus hippocampal region. Further analysis of mouse brain tissue and serum confirmed that melittin enhanced oxidant–antioxidant balance, cholinergic system activity, and intercellular neurotrophic factors regulation, which were all negatively altered by Aβ_25–35. Our study shows that melittin exerts antioxidant and neuroprotective actions against neural oxidative stress. Melittin can be a potential therapeutic agent for neurodegenerative disorders.

Duration of Social Isolation Affects Production of Nitric Oxide in the Rat Brain

Social isolation deprives rodents of social interactions that are critical for normal development of brain and behavior. Several studies have indicated that postweaning isolation rearing may affect nitric oxide (NO) production. The aim of this study was to compare selected behavioral and biochemical changes related to NO production in the brain of rats reared in social isolation for different duration. At the age of 21 days, male Sprague Dawley rats were randomly assigned into four groups reared in isolation or socially for 10 or 29 weeks. At the end of the rearing, open-field and prepulse inhibition (PPI) tests were carried out. Furthermore, in several brain areas we assessed NO synthase (NOS) activity, protein expression of nNOS and iNOS isoforms and the concentration of conjugated dienes (CD), a marker of oxidative damage and lipid peroxidation. Social isolation for 10 weeks resulted in a significant decrease in PPI, which was accompanied by a decrease in NOS activity in the cerebral cortex and the cerebellum, an increase in iNOS in the hippocampus and an increase in CD concentration in cortex homogenate. On the other hand, a 29 week isolation had an opposite effect on NOS activity, which increased in the cerebral cortex and the cerebellum in animals reared in social isolation, accompanied by a decrease in CD concentration. The decrease in NOS activity after 10 weeks of isolation might have been caused by chronic stress induced by social isolation, which has been documented in previous studies. The increased oxidative state might result in the depleted NO bioavailability, as NO reacts with superoxide radical creating peroxynitrite. After 29 weeks of isolation, this loss of NO might be compensated by the subsequent increase in NOS activity.

Antidepressant-like effect of ethanol in mice forced swimming test is mediated via inhibition of NMDA/nitric oxide/cGMP signaling pathway

There is evidence for a dramatic relationship between depression and alcohol consumption. Depressed patients may abuse ethanol because this agent reduces the symptoms of depression. In the current study, we aimed to investigate the NMDA/nitric oxide/cGMP pathway in the antidepressant-like effect of ethanol in an animal model of behavioral despair. Animals were subjected to locomotor activity in an open-field test separately, followed by a forced swimming test. During the forced swimming test (FST), ethanol (2 and 2.5 g/kg) significantly decreased the immobility time without altering the locomotor activity of animals. The antidepressant-like effect of ethanol (2.5 g/kg) was reversed by co-administration of N-methyl-D-aspartate (NMDA, 75 mg/kg), L-arginine (750 mg/kg), or sildenafil (5 mg/kg). In contrast, co-administration of MK-801 (0.05 mg/kg), ketamine (1 mg/kg), and ifenprodil (0.5 mg/kg) as antagonists of NMDAR, and NG-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg), 7-nitroindazole (7-NI, 30 mg/kg), and methylene blue (10 mg/kg) as inhibitors of nitric oxide synthase (NOS), or 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ) (20 mg/kg), a nitric oxide/cyclic-guanosine monophosphate (NO-cGMP) inhibitor, with a subeffective dose of ethanol (1.5 g/kg), significantly decreased the immobility time in the FST. Furthermore, injection of ethanol 2.5 g/kg alone or 1.5 g/kg with a 7-NI subeffective dose, significantly decreased the nitrite levels in the hippocampus and prefrontal cortex. Hence, it is concluded that blockade of NMDA receptors and the nitric oxide/cyclic-guanosine monophosphate (NO-cGMP) pathway might be involved in the antidepressant-like effect of ethanol in mice.

Modulation of AMPA Receptors by Nitric Oxide in Nerve Cells

Nitric oxide (NO) is a gaseous molecule with a large number of functions in living tissue. In the brain, NO participates in numerous intracellular mechanisms, including synaptic plasticity and cell homeostasis. NO elicits synaptic changes both through various multi-chain cascades and through direct nitrosylation of targeted proteins. Along with the N-methyl-d-aspartate (NMDA) glutamate receptors, one of the key components in synaptic functioning are α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors—the main target for long-term modifications of synaptic effectivity. AMPA receptors have been shown to participate in most of the functions important for neuronal activity, including memory formation. Interactions of NO and AMPA receptors were observed in important phenomena, such as glutamatergic excitotoxicity in retinal cells, synaptic plasticity, and neuropathologies. This review focuses on existing findings that concern pathways by which NO interacts with AMPA receptors, influences properties of different subunits of AMPA receptors, and regulates the receptors’ surface expression.

NMDA receptors and L-arginine/nitric oxide/cyclic guanosine monophosphate pathway contribute to the antidepressant-like effect of Yueju pill in mice

The present study aims to evaluate the involvement of N-methyl-d-aspartate receptor and nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) system in antidepressant-like effects of Yueju pill (YJ), a Chinese herbal medicine. The immobility time in tail suspension test (TST) and forced swim test (FST) was used to assess the antidepressant effects. Prior administration of L-arginine (750 mg/kg, intraperitoneal [i.p.]), a NO synthase substrate that enhances NO signaling or sildenafil (5 mg/kg, i.p.), a phosphodiesterase 5 inhibitor that enhances cGMP, blunted the antidepressant-like activity of YJ (2.7 g/kg, i.g.). Co-treatment of ineffective dose of YJ (1.35 g/kg, i.g.) with one of the reagents that suppress the NO/cGMP signaling, including methylene blue (10 mg/kg, i.p.), an inhibitor of NO synthase; 7-NI (7-nitroinidazole, 30 mg/kg, i.p.), an nNOS specific inhibitor; L-NAME (10 mg/kg, i.p.), a non-specific inhibitor of NO synthase; and MK-801 (0.05 mg/kg, i.p.), an NMDA receptor antagonist, reduced the immobility time in TST and FST, compared with those in vehicle or single drug treatment groups. Neither above drugs alone or co-administrated with YJ affected locomotor activity or anxiety behavior in open field test. Thus, our results suggest that the antidepressant-like action of YJ may depend on the inhibition of NMDA/NO/cGMP pathway.

Clathrin and GRK2/3 inhibitors block δ-opioid receptor internalization in myenteric neurons and inhibit neuromuscular transmission in the mouse colon

Endocytosis is a major mechanism through which cellular signaling by G protein-coupled receptors (GPCRs) is terminated. However, recent studies demonstrate that GPCRs are internalized in an active state and continue to signal from within endosomes, resulting in effects on cellular function that are distinct to those arising at the cell surface. Endocytosis inhibitors are commonly used to define the importance of GPCR internalization for physiological and pathophysiological processes. Here, we provide the first detailed examination of the effects of these inhibitors on neurogenic contractions of gastrointestinal smooth muscle, a key preliminary step to evaluate the importance of GPCR endocytosis for gut function. Inhibitors of clathrin-mediated endocytosis (Pitstop2, PS2) or G protein-coupled receptor kinase-2/3-dependent phosphorylation (Takeda compound 101, Cmpd101), significantly reduced GPCR internalization. However, they also attenuated cholinergic contractions through different mechanisms. PS2 abolished contractile responses by colonic muscle to SNC80 and morphine, which strongly and weakly internalize δ-opioid and μ-opioid receptors, respectively. PS2 did not affect the increased myogenic contractile activity following removal of an inhibitory neural influence (tetrodotoxin) but suppressed electrically evoked neurogenic contractions. Ca²⁺ signaling by myenteric neurons in response to exogenous ATP was unaffected by PS2, suggesting inhibitory actions on neurotransmitter release rather than neurotransmission. In contrast, Cmpd101 attenuated contractions to the cholinergic agonist carbachol, indicating direct effects on smooth muscle. We conclude that, although PS2 and Cmpd101 are effective blockers of GPCR endocytosis in enteric neurons, these inhibitors are unsuitable for the study of neurally mediated gut function due to their inhibitory effects on neuromuscular transmission and smooth muscle contractility.NEW & NOTEWORTHY Internalization of activated G protein-coupled receptors is a major determinant of the type and duration of subsequent downstream signaling events. Inhibitors of endocytosis effectively block opioid receptor internalization in enteric neurons. The clathrin-dependent endocytosis inhibitor Pitstop2 blocks effects of opioids on neurogenic contractions of the colon in an internalization-independent manner. These inhibitors also significantly impact cholinergic neuromuscular transmission. We conclude that these tools are unsuitable for examination of the contribution of neuronal G protein-coupled receptor endocytosis to gastrointestinal motility.

Palm Fruit Bioactives modulate human astrocyte activity in vitro altering the cytokine secretome reducing levels of TNFα, RANTES and IP-10

Neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease, are becoming more prevalent and an increasing burden on society. Neurodegenerative diseases often arise in the milieu of neuro-inflammation of the brain. Reactive astrocytes are key regulators in the development of neuro-inflammation. This study describes the effects of Palm Fruit Bioactives (PFB) on the behavior of human astrocytes which have been activated by IL-1β. When activated, the astrocytes proliferate, release numerous cytokines/chemokines including TNFα, RANTES (CCL5), IP-10 (CXCL10), generate reactive oxygen species (ROS), and express specific cell surface biomarkers such as the Intercellular Adhesion Molecule (ICAM), Vascular Cellular Adhesion Molecule (VCAM) and the Neuronal Cellular Adhesion Molecule (NCAM). Interleukin 1-beta (IL-1β) causes activation of human astrocytes with marked upregulation of pro-inflammatory genes. We show significant inhibition of these pro-inflammatory processes when IL-1β-activated astrocytes are exposed to PFB. PFB causes a dose-dependent and time-dependent reduction in specific cytokines: TNFα, RANTES, and IP-10. We also show that PFB significantly reduces ROS production by IL-1β-activated astrocytes. Furthermore, PFB also reduces the expression of ICAM and VCAM, both in activated and naïve human astrocytes in vitro. Since reactive astrocytes play an essential role in the neuroinflammatory state preceding neurodegenerative diseases, this study suggests that PFB may have a potential role in their prevention and/or treatment.

Molecular profiling of reticular gigantocellularis neurons indicates that eNOS modulates environmentally dependent levels of arousal

Neurons of the medullary reticular nucleus gigantocellularis (NGC) and their targets have recently been a focus of research on mechanisms supporting generalized CNS arousal (GA) required for proper cognitive functions. Using the retro-TRAP method, we characterized transcripts enriched in NGC neurons which have projections to the thalamus. The unique expression and activation of the endothelial nitric oxide (eNOS) signaling pathway in these cells and their intimate connections with blood vessels indicate that these neurons exert direct neurovascular coupling. Production of nitric oxide (NO) within eNOS-positive NGC neurons increases after environmental perturbations, indicating a role for eNOS/NO in modulating environmentally appropriate levels of GA. Inhibition of NO production causes dysregulated behavioral arousal after exposure to environmental perturbation. Further, our findings suggest interpretations for associations between psychiatric disorders and mutations in the eNOS locus.

Cross state-dependency of learning between tramadol and MK-801 in the mouse dorsal hippocampus: involvement of nitric oxide (NO) signaling pathway

RATIONALE

Tramadol, an atypical μ-opioid receptor agonist, as a psychoactive drug, is frequently abused by human beings. Understanding the neurobiological mechanisms of drug-associated learning and memory formation may help prevent drug addiction and relapse. Previous study revealed that dorsal hippocampus (CA1) plays a crucial role in the retrieval of tramadol-associated memory and that its role depends on the expression of CA1 N-methyl-D-aspartate (NMDA) receptors (Jafari-Sabet et al. Can J Physiol Pharmacol 96:45-50, 2018).

OBJECTIVE

To clarify the exact mechanisms involved, the activation of CA1 nitric oxide (NO) signaling pathway by L-arginine (a nitric oxide precursor) on the interaction between tramadol and MK-801 in memory retrieval was examined. The dorsal hippocampal CA1 regions of adult male NMRI mice were bilaterally cannulated and a single-trial step-down inhibitory avoidance apparatus was used for the assessment of memory retrieval.

RESULTS

Post-training and/or pre-test microinjection of tramadol (0.5 and 1 μg/mouse) and/or a non-competitive NMDA receptor antagonist, MK-801 (0.25 and 0.5 μg/mouse), induced amnesia which were reversed when the same doses of the drugs were administered 24 h later in a pre-test session, suggesting tramadol state-dependent learning (SDL) and MK-801 SDL. The amnesia induced by post-training microinjection of tramadol (1 μg/mouse) was reversed by pre-test microinjection of MK-801 (0.25 and 0.5 μg/mouse). Pre-test microinjection of MK-801 (0.125 and 0.25 μg/mouse) with an ineffective dose of tramadol (0.25 μg/mouse) potentiated tramadol SDL. The amnesia induced by post-training microinjection of MK-801 (0.5 μg/mouse) was reversed by pre-test microinjection of tramadol (0.5 and 1 μg/mouse). Pre-test microinjection of tramadol (0.25 and 0.5 μg/mouse) with an ineffective dose of MK-801 (0.125 μg/mouse) potentiated MK-801 SDL. Pre-test microinjection of ineffective doses of L-arginine (0.125, 025, and 0.5 μg/mouse) improved amnesia induced by the co-administration of tramadol and MK-801. Pre-test microinjection of L-arginine (0.125, 025, and 0.5 μg/mouse) could not reverse amnesia induced by post-training microinjection of tramadol while same doses of L-arginine improved MK-801 response on tramadol SDL.

CONCLUSION

The results strongly propose that activation of CA1 NO signaling pathway has a pivotal role in cross SDL among tramadol and MK-801.

Antidepressant effect of pramipexole in mice forced swimming test: A cross talk between dopamine receptor and NMDA/nitric oxide/cGMP pathway

Pramipexole is a dopamine D2 receptor agonist indicated for treating Parkinson disorder. This study was aimed to investigate the effect of pramipexole in forced swimming test (FST) in mice and the possible involvement of activation of D2 receptors and inhibition of N-methyl-d-aspartate (NMDA) receptors and nitric oxide-cyclic guanosine monophosphate (NO-cGMP) on this effect. Intraperitoneal administration of pramipexole (1-3mg/kg) reduced the immobility time in the FST similar to fluoxetine (20mg/kg, i.p.). This effect of pramipexole (1mg/kg, i.p.) was ceased when mice were pretreated with haloperidol (0.15mg/kg, i.p,) and sulpiride (5mg/kg, i.p) as D2 receptor antagonists, NMDA (75mg/kg,i.p.), l-arginine (750mg/kg, i.p., a substrate for nitric oxide synthase) or sildenafil (5mg/kg, i.p., a phosphodiesterase 5 inhibitor). The administration of MK-801 (0.05mg/kg, i.p., a NMDA receptor antagonist) l-NG-Nitro arginine methyl ester (l-NAME, 10mg/kg, i.p., a non-specific nitric oxide synthase (NOS) inhibitor), 7-nitroindazole (30mg/kg, i.p., a neuronal NOS inhibitor) and methylene blue (10mg/kg, i.p.), an inhibitor of both NOS and soluble guanylyl cyclase (sGC) in combination with the sub-effective dose of pramipexole (0.3mg/kg, i.p.) reduced the immobility. Altogether, our data suggest that the antidepressant-like effect of pramipexole is dependent on the activation of D2 receptor and inhibition of either NMDA receptors and/or NO-cGMP synthesis. These results contribute to the understanding of the mechanisms underlying the antidepressant-like effect of pramipexole and reinforce the role of D2 receptors, NMDA receptors and l-arginine-NO-GMP pathway in the antidepressant mechanism of this agent.

Involvement of NMDA receptors and L-arginine/nitric oxide/cyclic guanosine monophosphate pathway in the antidepressant-like effects of topiramate in mice forced swimming test

Topiramate (TPM) is an agent primarily used in the treatment of epilepsy. Using mice model of forced swimming test (FST) the current study was basically aimed to investigate the influence of TPM on depression by inhibiting NMDA receptor and nitric oxide-cGMP production. When TPM was administered in a dose of 20 and 30 mg/kg by i.p. route it reduced the immobility time during FST. However this effect of TPM (30 mg/kg, i.p.) in the FST was abolished when the mice were pretreated either with NMDA (75 mg/kg, i.p.), or l-arginine (750 mg/kg, i.p. NO precursor), or sildenafil (5mg/kg, i.p. Phosphodiesterase 5 inhibitor). The immobility time in the FST was reduced after administration of L-NAME (10mg/kg, i.p, a non-specific NOS inhibitor), 7-nitoinidazol (30 mg/kg, i.p. a nNOS inhibitor) or MK-801 (0.05 mg/kg, i.p, a NMDA receptor antagonist) in combination with a subeffective dose of TPM (10mg/kg, i.p.) as compared with single use of either drug. Co-administrated of lower doses of MK-801 (0.01 mg/kg) or L-NAME (1mg/kg) failed to effect immobility time. However, simultaneous administration of these two agents in the same doses with subeffective dose of TPM (10mg/kg, i.p.), reduced the immobility time during FST. None of these drugs were found to have a profound effect on the locomotor activity per se during the open field test. Taken together, our data demonstrates that TPM exhibit antidepressant-like effect which is accomplished either due to inhibition of NMDA receptors or NO-cGMP production.

Heart Alterations after Domoic Acid Administration in Rats

Domoic acid (DA) is one of the best known marine toxins, causative of important neurotoxic alterations. DA effects are documented both in wildlife and experimental assays, showing that this toxin causes severe injuries principally in the hippocampal area. In the present study we have addressed the long-term toxicological effects (30 days) of DA intraperitoneal administration in rats. Different histological techniques were employed in order to study DA toxicity in heart, an organ which has not been thoroughly studied after DA intoxication to date. The presence of DA was detected by immunohistochemical assays, and cellular alterations were observed both by optical and transmission electron microscopy. Although histological staining methods did not provide any observable tissue damage, transmission electron microscopy showed several injuries: a moderate lysis of myofibrils and loss of mitochondrial conformation. This is the first time the association between heart damage and the presence of the toxin has been observed.

Brain Pathology in Adult Rats Treated With Domoic Acid

Domoic acid (DA) is a neurotoxin reported to produce damage to the hippocampus, which plays an important role in memory. The authors inoculated rats intraperitoneally with an effective toxic dose of DA to study the distribution of the toxin in major internal organs by using immunohistochemistry, as well as to evaluate the induced pathology by means of histopathologic and immunohistochemical methods at different time points after toxin administration (6, 10, and 24 hours; 5 and 54 days). DA was detected by immunohistochemistry exclusively in pyramidal neurons of the hippocampus at 6 and 10 hours after dosing. Lesions induced by DA were prominent at 5 days following treatment in selected regions of the brain: hippocampus, amygdala, piriform and perirhinal cortices, olfactory tubercle, septal nuclei, and thalamus. The authors found 2 types of lesions: delayed death of selective neurons and large areas of necrosis, both accompanied by astrocytosis and microgliosis. At 54 days after DA exposure, the pathology was characterized by still-distinguishable dying neurons, calcified lesions in the thalamus, persistent astrocytosis, and pronounced microgliosis. The expression of nitric oxide synthases suggests a role for nitric oxide in the pathogenesis of neuronal degeneration and chronic inflammation induced by DA in the brain.

Age-associated changes of nitric oxide concentration dynamics in the central nervous system of Fisher 344 rats

The increase in life expectancy is accompanied by an increased risk of developing neurodegenerative disorders and age is the most relevant risk factor for the appearance of cognitive decline. While decreased neuronal count has been proposed to be a major contributing factor to the appearance of age-associated cognitive decline, it appears to be insufficient to fully account for the decay in mental function in aged individuals. Nitric oxide ((•)NO) is a ubiquitous signaling molecule in the mammalian central nervous system. Closely linked to the activation of glutamatergic transmission in several structures of the brain, neuron-derived (•)NO can act as a neuromodulator in synaptic plasticity but has also been linked to neuronal toxicity and degenerative processes. Many studies have proposed that changes in the glutamate-(•)NO signaling pathway may be implicated in age-dependent cognitive decline and that the exact effect of such changes may be region specific. Due to its peculiar physical-chemical properties, namely hydrophobicity, small size, and rapid diffusion properties, the rate and pattern of (•)NO concentration changes are critical determinants for the understanding of its bioactivity in the brain. Here we show a detailed study of how (•)NO concentration dynamics change in the different regions of the brain of Fisher 344 rats (F344) during aging. Using microelectrodes inserted into the living brain of anesthetized F344 rats, we show here that glutamate-induced (•)NO concentration dynamics decrease in the hippocampus, striatum, and cerebral cortex as animals age. performance in behavior testing of short-term and spatial memory, suggesting that the impairment in the glutamate:nNOS pathway represents a functional critical event in cognitive decline during aging.

Effects of chronic nicotine administration on body weight, food intake and nitric oxide concentration in female and male rats

Nicotine is readily consumed through cigarettes; however it is also easily consumed through the various forms of non-prescription nicotine replacement therapy. It has been shown to possess potential therapeutic value for the management of neurologic and neurodegenerative diseases in the last decade. Hence, this study examined the effects of chronic subcutaneous nicotine administration on food intake and body weight as well as on nitric oxide concentrations and total antioxidant capacity in female and male rats. Nicotine was administered to rats via subcutaneous injections at doses of 0.25, 2 and 4mg/kg body weight for 28 days. Control groups received normal saline; the vehicle for nicotine. Food intake by each group was monitored daily and body weight of the animals was measured twice weekly. At the end of drug administration, blood was obtained from each animal via cardiac puncture for biochemical determination of serum total antioxidant capacity (TAC) and nitric (NO) concentrations using standard assay kits. Results show significant loss (p<0.05) of body weight in all nicotine treated female rats. In contrast, male rats showed weight gain, though this was significantly lower (p<0.001) in nicotine treated groups compared to control. Nicotine significantly reduced (p<0.001) food consumed in both female and male rats; however dose related changes were observed in only male rats. No significant difference was observed in TAC following nicotine treatments for both female and male rats. Furthermore, only males exhibited changes in NO concentrations following nicotine treatment, as it significantly increased (p<0.01) NO concentrations in all male treated groups. In conclusion, this study has shown that modulation of body weight, food consumption and nitric oxide formation by nicotine is sexually dimorphic. Also, the study suggests that nicotine modulation of food intake and body weight and its modulation of NO may be independent of each other.

Biomimetic sensor based on hemin/carbon nanotubes/chitosan modified microelectrode for nitric oxide measurement in the brain

A novel biomimetic microsensor for measuring nitric oxide (NO) in the brain in vivo was developed. The sensor consists of hemin and functionalized multi-wall carbon nanotubes covalently attached to chitosan via the carbodiimide crosslinker EDC followed by chitosan electrodeposition on the surface of carbon fiber microelectrodes. Cyclic voltammetry supported direct electron transfer from the Fe(III)/Fe(II) couple of hemin to the carbon surface at -0.370 V and -0.305 V vs. Ag/AgCl for cathodic and anodic peaks, respectively. Square wave voltammetry revealed a NO reduction peak at -0.762 V vs. Ag/AgCl that increased linearly with NO concentration between 0.25 and 1 μM. The average sensitivity of the microsensors was 1.72 nA/μM and the limit of detection was 25 nM. Oxygen and hydrogen peroxide reduction peaks were observed at -0.269 V and -0.332 V vs. Ag/AgCl, respectively and no response was observed for other relevant interferents, namely ascorbate, nitrite and dopamine. The microsensor was successfully applied to the measurement of exogenously applied NO in the rat brain in vivo.

Hemoglobin: a nitric-oxide dioxygenase

Members of the hemoglobin superfamily efficiently catalyze nitric-oxide dioxygenation, and when paired with native electron donors, function as NO dioxygenases (NODs). Indeed, the NOD function has emerged as a more common and ancient function than the well-known role in O2 transport-storage. Novel hemoglobins possessing a NOD function continue to be discovered in diverse life forms. Unique hemoglobin structures evolved, in part, for catalysis with different electron donors. The mechanism of NOD catalysis by representative single domain hemoglobins and multidomain flavohemoglobin occurs through a multistep mechanism involving O2 migration to the heme pocket, O2 binding-reduction, NO migration, radical-radical coupling, O-atom rearrangement, nitrate release, and heme iron re-reduction. Unraveling the physiological functions of multiple NODs with varying expression in organisms and the complexity of NO as both a poison and signaling molecule remain grand challenges for the NO field. NOD knockout organisms and cells expressing recombinant NODs are helping to advance our understanding of NO actions in microbial infection, plant senescence, cancer, mitochondrial function, iron metabolism, and tissue O2 homeostasis. NOD inhibitors are being pursued for therapeutic applications as antibiotics and antitumor agents. Transgenic NOD-expressing plants, fish, algae, and microbes are being developed for agriculture, aquaculture, and industry.

[Association of Schizophrenia and its Clinical Implications with the NOS1AP Gene in the Colombian Population]

INTRODUCTION

The nitric oxide synthase 1 adaptor protein (NOS1AP) gene is possibly implicated in schizophrenia etiopathogenesis.

OBJECTIVE

To determine the association of NOS1AP gene variants with schizophrenia and the relationship of variants with the clinical dimensions of the disorder in the Colombian population.

METHODOLOGY

It is a case-control study with 255 subjects per group. Markers within the NOS1AP gene were typified as well as other informative material of genetic origin so as to adjust by population stratification. A factorial analysis of the main components for each item in the Scales for Evaluating Negative Symptoms (SENS) together with the Scales for Evaluating Positive Symptoms (SEPS) to determine clinical dimensions.

RESULTS

Association between the C/C genotype of the rs945713 marker with schizophrenia (OR = 1.79, 95% CI: 1.13 - 2.84) was found. The C/C genotype of the rs945713 was related to higher scores in the "affective flattening and alogia" dimension; and the A/A genotype of the rs4657181 marker was associated to lower scores in the same dimension.

CONCLUSIONS

Significant associations of markers inside the NOS1AP gene with schizophrenia and the "affective flattening and alogia" clinical dimension were found. These results are consistent with previous studies and support the possibility that NOS1AP influences schizophrenia susceptibility. Furthermore, NOS1AP might be a modifier of schizophrenia clinical characteristics.

NMDA receptors in hippocampal GABAergic synapses and their role in nitric oxide signaling

GABAergic inhibition plays a central role in the control of pyramidal cell ensemble activities; thus, any signaling mechanism that regulates inhibition is able to fine-tune network patterns. Here, we provide evidence that the retrograde nitric oxide (NO)-cGMP cascade triggered by NMDA receptor (NMDAR) activation plays a role in the control of hippocampal GABAergic transmission in mice. GABAergic synapses express neuronal nitric oxide synthase (nNOS) postsynaptically and NO receptors (NO-sensitive guanylyl cyclase) in the presynaptic terminals. We hypothesized that--similar to glutamatergic synapses--the Ca(2+) transients required to activate nNOS were provided by NMDA receptor activation. Indeed, administration of 5 μm NMDA induced a robust nNOS-dependent cGMP production in GABAergic terminals, selectively in the CA1 and CA3c areas. Furthermore, using preembedding, postembedding, and SDS-digested freeze-fracture replica immunogold labeling, we provided quantitative immunocytochemical evidence that NMDAR subunits GluN1, GluN2A, and GluN2B were present in most somatic GABAergic synapses postsynaptically. These data indicate that NMDARs can modulate hippocampal GABAergic inhibition via NO-cGMP signaling in an activity-dependent manner and that this effect is subregion specific in the mouse hippocampus.

Brain nitric oxide inactivation is governed by the vasculature

The mechanisms underlying nitric oxide ((•)NO) synthesis and inactivation in the brain are essential determinants of (•)NO neuroactivity. Although (•)NO production is well characterized, the pathways of inactivation in vivo remain largely unknown. Here, we characterize the kinetics and the major mechanism of (•)NO inactivation in the rat brain cortex and hippocampus in vivo by measuring locally applied (•)NO with carbon-fiber microelectrodes (CFMs) and ceramic-based microelectrode arrays (MEAs). An apparent first-order clearance was observed in both brain regions, with decay rate constants (k) of (•)NO signals of 0.67 to 0.84 per second, significantly higher than the k obtained in agarose gel (0.099 per second), used as a (•)NO diffusion-control medium. (•)NO half-life in vivo, estimated by mathematical modeling, was 0.42 to 0.75 s. Experiments using MEAs support that the (•)NO diffusion radius is heterogeneous and related to local metabolic activity and vascular density. After global ischemia, k decreased to control values of diffusion in gel, but during anoxia, k decreased only 21%. Additionally, k in brain slices was threefold to fivefold lower than that in vivo, and hemorrhagic shock induced a 53% decrease in k. Overall, the results support that (•)NO scavenging by circulating erythrocytes constitutes the major (•)NO-inactivation pathway in the brain.

Involvement of NMDA receptors and L-arginine-nitric oxide-cyclic guanosine monophosphate pathway in the antidepressant-like effects of escitalopram in the forced swimming test

Escitalopram is a serotonin reuptake inhibitor used in the treatment of depression and anxiety disorders. This study investigated the effect of escitalopram in forced swimming test (FST) and in the tail suspension test (TST) in mice, and tested the hypothesis that the inhibition of NMDA receptors and NO-cGMP synthesis is implicated in its mechanism of action in the FST. Escitalopram administered by i.p. route reduced the immobility time both in the FST (0.3-10 mg/kg) and in the TST (0.1-10 mg/kg). Administration of escitalopram by p.o route (0.3-10 mg/kg) also reduced the immobility time in the FST. The antidepressant-like effect of escitalopram (3mg/kg, p.o.) in the FST was prevented by the pretreatment of mice with NMDA (0.1 pmol/site, i.c.v.), l-arginine (750 mg/kg, i.p., a substrate for nitric oxide synthase) or sildenafil (5mg/kg, i.p., a phosphodiesterase 5 inhibitor). The administration of 7-nitroindazole (50 mg/kg, i.p., a neuronal nitric oxide synthase inhibitor), methylene blue (20 mg/kg, i.p., an inhibitor of both nitric oxide synthase and soluble guanylate cyclase) or ODQ (30 pmol/site i.c.v., a soluble guanylate cyclase inhibitor) in combination with a subeffective dose of escitalopram (0.1 mg/kg, p.o.) reduced the immobility time in the FST as compared with either drug alone. None of the drugs produced significant effects on the locomotor activity in the open-field test. Altogether, our data suggest that the antidepressant-like effect of escitalopram is dependent on inhibition of either NMDA receptors or NO-cGMP synthesis. The results contribute to the understanding of the mechanisms underlying the antidepressant-like effect of escitalopram and reinforce the role of NMDA receptors and l-arginine-NO-GMP pathway in the mechanism of action of antidepressant agents.

N-methyl-aspartate receptor and neuronal nitric oxide synthase activation mediate bilirubin-induced neurotoxicity

Hyperbilirubinemia may lead to neurotoxicity and neuronal death. Although the mechanisms of nerve cell damage by unconjugated bilirubin (UCB) appear to involve a disruption of the redox status and excitotoxicity, the contribution of nitric oxide (NO·) and of N-methyl-D-aspartate (NMDA) glutamate receptors is unclear. We investigated the role of NO· and NMDA glutamate receptors in the pathways of nerve cell demise by UCB. Neurons were incubated with 100 micromol/L UCB, in the presence of 100 micromol/L human serum albumin for 4 h at 37ºC, alone or in combination with N-ω-nitro-L-arginine methyl ester (L-NAME) (an inhibitor of neuronal nitric oxide synthase [nNOS]), hemoglobin (an NO· scavenger) or (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) (an NMDA-receptor antagonist). Exposure to UCB led to increased expression of nNOS and production of both NO· and cyclic guanosine 3',5'-monophosphate (cGMP), along with protein oxidation and depletion of glutathione. These events concurred for cell dysfunction and death and were counteracted by L-NAME. Moreover, the UCB-induced loss of neuronal viability was abolished by hemoglobin, whereas the activation of nNOS and production of both NO· and cGMP were counteracted by MK-801, resulting in significant protection from cell dysfunction and death. These results reinforce the involvement of oxidative stress by showing that nerve cell damage by UCB is mediated by NO· and therefore is counteracted by NO· inhibitors or scavengers. Our findings strongly suggest that the activation of nNOS and neurotoxicity occur through the engagement of NMDA receptors. These data reveal a role for overstimulation of glutamate receptors in mediating oxidative damage by UCB.

Nitric oxide- and cGMP-active compounds affect the discharge of substantia nigra pars reticulata neurons: in vivo evidences in the rat

The nitric oxide (NO)-active drugs influence on the bioelectric activity of neurons of the pars reticulata of the substantia nigra was studied in urethane-anesthetized rats. A first group of animals was treated with 7-nitro-indazole (7-NI), a preferential inhibitor of neuronal NO synthase. In a second group of rats, electrophysiological recordings were coupled with microiontophoretic administration of Nomega-nitro-L-arginine methyl ester (L-NAME, a NO synthase inhibitor), 3-morpholino-sydnonimin-hydrocloride (SIN-1, a NO donor) and 8-Br-cGMP (a cell-permeable analogue of cGMP, the main second-messenger of NO neurotransmission). 7-NI and L-NAME caused a statistically significant decrease in the firing rate of most of the responsive cells, while application of SIN-1 and 8-Br-CGMP induced statistically significant excitatory effects. The results suggest a NO mediated excitatory modulation of the SNr neurons activity with a possible involvement of the cGMP pathway.

NO dioxygenase activity in hemoglobins is ubiquitous in vitro, but limited by reduction in vivo

Genomics has produced hundreds of new hemoglobin sequences with examples in nearly every living organism. Structural and biochemical characterizations of many recombinant proteins reveal reactions, like oxygen binding and NO dioxygenation, that appear general to the hemoglobin superfamily regardless of whether they are related to physiological function. Despite considerable attention to “hexacoordinate” hemoglobins, which are found in nearly every plant and animal, no clear physiological role(s) has been assigned to them in any species. One popular and relevant hypothesis for their function is protection against NO. Here we have tested a comprehensive representation of hexacoordinate hemoglobins from plants (rice hemoglobin), animals (neuroglobin and cytoglobin), and bacteria (Synechocystis hemoglobin) for their abilities to scavenge NO compared to myoglobin. Our experiments include in vitro comparisons of NO dioxygenation, ferric NO binding, NO-induced reduction, NO scavenging with an artificial reduction system, and the ability to substitute for a known NO scavenger (flavohemoglobin) in E. coli. We conclude that none of these tests reveal any distinguishing predisposition toward a role in NO scavenging for the hxHbs, but that any hemoglobin could likely serve this role in the presence of a mechanism for heme iron re-reduction. Hence, future research to test the role of Hbs in NO scavenging would benefit more from the identification of cognate reductases than from in vitro analysis of NO and O₂ binding.

The lack of effects of zinc and nitric oxide in initial state of pilocarpine-induced seizures

In this study we investigated whether intracerebroventricular (i.c.v.) injection of L-NAME (a nitric oxide synthase inhibitor) or CaEDTA (an extracellular zinc chelator) or the combination of the two could affect the initial phase of pilocarpine induced (2 h) seizures. Two groups of rats were used. Animals from both groups were given with i.c.v. injections of either saline (10 microl), L-NAME (150 microg/10 microl), CaEDTA (100 mM/10 microl) or L-NAME and CaEDTA. One group received pilocarpine HCl (380 mg/kg i.p.) the other served as control. Pilocarpine HCl was injected intraperitoneally 10 min later. The behavior of the animals was observed for 2h and the intensity of their seizures was scored. The rats were then sacrificed and their brains were removed and analyzed for zinc ions by using the immersion autometallography and the TSQ fluorescence staining. All the animals which received pilocarpine HCl developed seizures. Despite treatment with L-NAME and/or CaEDTA we found that the latency and the intensity of seizures were similar in both groups investigated. The distribution of stainable zinc ions and the intensity of staining in hippocampus were not affected by pilocarpine and found unchanged after L-NAME and/or CaEDTA injections in both the control animals and the pilocarpine treated animals. The data suggest that the nitric oxide system and zinc ions do not affect pilocarpine-induced seizures in their initial state.

Coincident glutamatergic and cholinergic inputs transiently depress glutamate release at rat schaffer collateral synapses

The mammalian hippocampus, together with subcortical and cortical areas, is responsible for some forms of learning and memory. Proper hippocampal function depends on the highly dynamic nature of its circuitry, including the ability of synapses to change their strength for brief to long periods of time. In this study, we focused on a transient depression of glutamatergic synaptic transmission at Schaffer collateral synapses in acute hippocampal slices. The depression of evoked excitatory postsynaptic current (EPSC) amplitudes, herein called transient depression, follows brief trains of synaptic stimulation in stratum radiatum of CA1 and lasts for 2-3 min. Depression results from a decrease in presynaptic glutamate release, as NMDA-receptor-mediated EPSCs and composite EPSCs are depressed similarly and depression is accompanied by an increase in the paired-pulse ratio. Transient depression is prevented by blockade of metabotropic glutamate and acetylcholine receptors, presumably located presynaptically. These two receptor types--acting together--cause depression. Blockade of a single receptor type necessitates significantly stronger conditioning trains for triggering depression. Addition of an acetylcholinesterase inhibitor enables depression from previously insufficient conditioning trains. Furthermore, a strong coincident, but not causal, relationship existed between presynaptic depression and postsynaptic internal Ca(2+) release, emphasizing the potential importance of functional interactions between presynaptic and postsynaptic effects of convergent cholinergic and glutamatergic inputs to CA1. These convergent afferents, one intrinsic to the hippocampus and the other likely originating in the medial septum, may regulate CA1 network activity, the induction of long-term synaptic plasticity, and ultimately hippocampal function.

Nitric oxide regulation of mitochondrial oxygen consumption I: cellular physiology

Mitochondrial biochemistry is complex, expanding from oxygen consumption, oxidative phosphorylation, lipid catabolism, heme biosynthesis, to apoptosis, calcium homeostasis, and production of reactive oxygen species, including nitric oxide (NO). The latter molecule is produced by a mitochondrial NO synthase (mtNOS). The rates of consumption and production determine the steady-state concentration of NO at subcellular levels, leading to regulation of mitochondrial events. Temporospatial processes tightly regulate production of NO in mitochondria to maximize target effects and minimize deleterious reactions. Temporal regulatory mechanisms of mtNOS include activation by calcium signaling and transcriptional/translational regulations. Calcium-activated mtNOS inhibits mitochondrial respiration, resulting in a decrease of the oxygen consumption. This negative regulation antagonizes the effects of calcium on calcium-dependent dehydrogenases in the citric acid cycle, preventing the formation of anoxic foci. Temporal regulation of NO production by intracellular calcium signaling is a complex process, considering the heterogeneous intracellular calcium response and distribution. NO production in mitochondria is spatially regulated by mechanisms that determine subcellular localization of mtNOS, likely acylation and protein-protein interactions, in addition to transcriptional regulation as neuronal NOS. Because NO rapidly decays in mitochondria, subcellular localization of mtNOS is crucial for NO to function as a signal molecule. These temporospatial processes are biologically important to allow NO to act as an effective signal molecule to regulate mitochondrial events such as oxygen consumption and reactive oxygen species production.

Nitric oxide inhibition of respiration involves both competitive (heme) and noncompetitive (copper) binding to cytochrome c oxidase

NO reversibly inhibits mitochondrial respiration via binding to cytochrome c oxidase (CCO). This inhibition has been proposed to be a physiological control mechanism and/or to contribute to pathophysiology. Oxygen reacts with CCO at a heme iron:copper binuclear center (a(3)/Cu(B)). Reports have variously suggested that during inhibition NO can interact with the binuclear center containing zero (fully oxidized), one (singly reduced), and two (fully reduced) additional electrons. It has also been suggested that two NO molecules can interact with the enzyme simultaneously. We used steady-state and kinetic modeling techniques to reevaluate NO inhibition of CCO. At high flux and low oxygen tensions NO interacts predominantly with the fully reduced (ferrous/cuprous) center in competition with oxygen. However, as the oxygen tension is raised (or the consumption rate is decreased) the reaction with the oxidized enzyme becomes increasingly important. There is no requirement for NO to bind to the singly reduced binuclear center. NO interacts with either ferrous heme iron or oxidized copper, but not both simultaneously. The affinity (K(D)) of NO for the oxygen-binding ferrous heme site is 0.2 nM. The noncompetitive interaction with oxidized copper results in oxidation of NO to nitrite and behaves kinetically as if it had an apparent affinity of 28 nM; at low levels of NO, significant binding to copper can occur without appreciable enzyme inhibition. The combination of competitive (heme) and noncompetitive (copper) modes of binding enables NO to interact with mitochondria across the full in vivo dynamic range of oxygen tension and consumption rates.

PROLACTIN SECRETION IN HYPOTHYROID ENDOTOXEMIC RATS: INVOLVEMENT OF L-ARGININE AND NITRIC OXIDE SYNTHASE

The identification of nitric oxide (NO) within the hypothalamus and pituitary gland has suggested its role as modulator of the activity on hypothalamic-pituitary axis. Hypothalamic NO synthase (NOS) is known to be regulated by thyroid hormones. We investigated the effects of previous injection of N-nitro-L-arginine methyl ester (L-NAME), a NOS inhibitor, and L-arginine (L-Arg), the substrate for NO synthesis, on prolactin (PRL) secretion, through the lipopolysaccharide (LPS)-induced inflammatory response in thyroidectomized (TX) rats. TX or sham-operated (N) rats were intraperitoneally (i.p.) injected with L-NAME (10 mg kg) or L-Arg (200 mg kg) or the same volume of vehicle (saline solution) 30 min before endotoxemia-induction with LPS at 250 mug (100 g body weight), i.p.. In N rats, NO increased PRL release in response to endotoxemia, whereas in hypothyroid rats, NO appeared to have the opposite effect. Our data support the hypothesis that NO exerts a modulatory influence on PRL secretion after LPS-induced inflammatory response.

Involvement of nitric oxide in sexual learning via action in the medial preoptic area: theoretical comment on Lagoda et al. (2004)

Repeated exposure to female-related stimuli causes functional alterations in the neural circuitry mediating male rat sexual behavior. In a study published in the current issue of this journal, G. M. Lagoda, J. W. Muschamp, A. Vigdorchik, and E. M. Hull (2004) provide interesting new evidence as to the mechanisms responsible for this effect, namely via activity of nitric oxide (NO) in the medial preoptic area. Given the history of NO in mediating neural plasticity in other systems, the results point to common mechanisms of plasticity between the processes underlying acquisition of sexual experience and those involved in learning and memory.

Temperature dependence of NO binding modes in human neuroglobin

Both the ferrous and ferric forms of wild-type neuroglobin are found to be hexacoordinated with axial ligation of the F8-His and E7-His. Rapidly growing Escherichia coli cell cultures with low O2 concentration generate nitric oxide (NO). Combined electron paramagnetic resonance (EPR) and optical measurements show that wild-type human recombinant neuroglobin, overexpressed in such E. coli cells, still favors the F8His-Fe2+ -E7His conformation, whereby only a small fraction of the protein binds NO. Upon mutation of the E7-His to Leu and Gln, the competition with the distal histidine disappears and the nitrosyl ferrous form is readily observed. At low temperature, the EPR spectra of the NO-ligated Ngb proteins consist of contributions from two geometrically different NO-heme conformations. In combination with EPR data of vertebrate hemoglobins and myoglobins, the temperature dependence of the EPR spectra of the NO adducts of ferrous hNgb and its E7-mutants proves a strong stabilization of one isomer by the E7-histidine in wt hNgb. It is shown that this is not related to the polarity of histidine, but to its specific binding characteristics.