Nitric oxide: a radical neurotransmitter in the central nervous system

Study of disorders in regulatory spatiotemporal neurodynamics of calcium and nitric oxide

Experimental studies have reported the dependence of nitric oxide (NO) on the regulation of neuronal calcium ([Ca2+]) dynamics in neurons. But, there is no model available to estimate the disorders caused by various parameters in their regulatory dynamics leading to various neuronal disorders. A mathematical model to analyze the impacts due to alterations in various parameters like buffer, ryanodine receptor, serca pump, source influx, etc. leading to regulation and dysregulation of the spatiotemporal calcium and NO dynamics in neuron cells is constructed using a system of reaction-diffusion equations. The numerical simulation is performed with the finite element approach. The disturbances in the different constitutive processes of [Ca2+] and nitric oxide including source influx, buffer mechanism, ryanodine receptor, serca pump, IP3 receptor, etc. can be responsible for the dysregulation in the [Ca2+] and NO dynamics in neurons. Also, the results reveal novel information about the magnitude and intensity of disorders in response to a range of alterations in various parameters of this neuronal dynamics, which can cause dysregulation leading to neuronal diseases like Parkinson's, cerebral ischemia, trauma, etc.

Potent, Selective, and Membrane Permeable 2-Amino-4-Substituted Pyridine-Based Neuronal Nitric Oxide Synthase Inhibitors

A series of potent, selective, and highly permeable human neuronal nitric oxide synthase inhibitors (hnNOS), based on a difluorobenzene ring linked to a 2-aminopyridine scaffold with different functionalities at the 4-position, is reported. In our efforts to develop novel nNOS inhibitors for the treatment of neurodegenerative diseases, we discovered 17, which showed excellent potency toward both rat (Ki 15 nM) and human nNOS (Ki 19 nM), with 1075-fold selectivity over human eNOS and 115-fold selectivity over human iNOS. 17 also showed excellent permeability (Pe = 13.7 × 10-6 cm s-1), a low efflux ratio (ER 0.48), along with good metabolic stability in mouse and human liver microsomes, with half-lives of 29 and >60 min, respectively. X-ray cocrystal structures of inhibitors bound with three NOS enzymes, namely, rat nNOS, human nNOS, and human eNOS, revealed detailed structure-activity relationships for the observed potency, selectivity, and permeability properties of the inhibitors.

Oxidative Stress: A Suitable Therapeutic Target for Optic Nerve Diseases?

Optic nerve disorders encompass a wide spectrum of conditions characterized by the loss of retinal ganglion cells (RGCs) and subsequent degeneration of the optic nerve. The etiology of these disorders can vary significantly, but emerging research highlights the crucial role of oxidative stress, an imbalance in the redox status characterized by an excess of reactive oxygen species (ROS), in driving cell death through apoptosis, autophagy, and inflammation. This review provides an overview of ROS-related processes underlying four extensively studied optic nerve diseases: glaucoma, Leber's hereditary optic neuropathy (LHON), anterior ischemic optic neuropathy (AION), and optic neuritis (ON). Furthermore, we present preclinical findings on antioxidants, with the objective of evaluating the potential therapeutic benefits of targeting oxidative stress in the treatment of optic neuropathies.

2-Aminopyridines with a shortened amino sidechain as potent, selective, and highly permeable human neuronal nitric oxide synthase inhibitors

A series of potent, selective, and highly permeable human neuronal nitric oxide synthase inhibitors (hnNOS) based on the 2-aminopyridine scaffold with a shortened amino sidechain is reported. A rapid and simple protocol was developed to access these inhibitors in excellent yields. Neuronal nitric oxide synthase (nNOS) is a novel therapeutic target for the treatment of various neurological disorders. The major challenges in designing nNOS inhibitors in humans focus on potency, selectivity over other isoforms of nitric oxide synthases (NOSs), and blood-brain barrier permeability. In this context, we discovered a promising inhibitor, 6-(3-(4,4-difluoropiperidin-1-yl)propyl)-4-methylpyridin-2-amine dihydrochloride, that exhibits excellent potency for rat (Ki = 46 nM) and human nNOS (Ki = 48 nM), respectively, with 388-fold human eNOS and 135-fold human iNOS selectivity. It also displayed excellent permeability (Pe = 17.3 × 10-6 cm s-1) through a parallel artificial membrane permeability assay, a model for blood-brain permeability. We found that increasing lipophilicity by incorporation of fluorine atoms on the backbone of the inhibitors significantly increased potential blood-brain barrier permeability. In addition to measuring potency, isoform selectivity, and permeability of NOS inhibitors, we also explored structure-activity relationships via structures of key inhibitors complexed to various isoforms of nitric oxide synthases.

Involvement of nitric oxide in the neurobiology of fear-like behavior

Fear is an emotional reaction that arises in dangerous situations, inducing the adaptation to an existing condition. This behavior was conserved in all vertebrates throughout evolution and is observed in mammals, birds, fish, amphibians, and reptiles. The neurocircuitry of fear involves areas of the limbic system, cortical regions, midbrain, and brainstem. These areas communicate with each other so that there is an expression of fear and memory formation to deal with the same situation at another time. The effect of nitric oxide (NO) on fear modulation has been explored. NO is a gaseous compound that easily diffuses through the cell membrane and is produced through the oxidation reaction of l-Arginine to l-citrulline catalyzed by nitric oxide synthase (NOS). Activating the intracellular NO receptor (soluble guanylyl cyclase enzyme - sGC) triggers an enzymatic cascade that can culminate in plastic events in the neuron. NOS inhibitors induce anxiolytic-like responses in fear modulation, whereas NO donors promote fear- and anxiety-like behaviors. This review describes the neurobiology of fear in mammals and non-mammals, how NO is produced in the central nervous system, and how NO acts in fear-like behavior.

Nitric Oxide Synthase Type 1 Methylation Is Associated With White Matter Microstructure in the Corpus Callosum and Greater Panic Disorder Severity Among Panic Disorder Patients

Objectives: Methylation of the neuronal nitric oxide synthase (NOS1/nNOS) gene has recently been identified as a promising biomarker of psychiatric disorders. NOS1 plays an essential role in neurite outgrowth and may thus affect the microstructure development of white matter (WM) in the corpus callosum (CC), which is known to be altered in panic disorder (PD). We examined the relationship between NOS1 methylation, WM tracts in the CC, and symptoms based on this finding.

Methods: Thirty-two patients with PD and 22 healthy controls (HCs) were recruited after age, gender, and the education level were matched. The cell type used was whole-blood DNA, and DNA methylation of NOS1 was measured at 20 CpG sites in the promoter region. Although 25 patients with PD were assessed with the Panic Disorder Severity Scale (PDSS), diffusion tensor imaging (DTI) scans were only collected from 16 participants with PD.

Results: We observed that the PD group showed lower methylation than did the HCs group and positive correlations between the symptom severity of PD and methylation at CpG4 and CpG9. In addition, CpG9 methylation was significantly correlated with the fractional anisotropy (FA) and mean diffusivity (MD) values of the CC and its major components (the genu and the splenium) in the PD group. Furthermore, path analyses showed that CpG9 methylation offers a mediating effect for the association between the MD values of the genu of the CC and PD symptom severity (95% CI = −1.731 to −0.034).

Conclusions: The results suggest that CpG9 methylation leads to atypical development of the genu of the CC, resulting in higher PD symptom severity, adding support for the methylation of NOS1 as a future prognostic indicator of PD.

Dual Inhibition of FAAH and MAGL Counteracts Migraine-like Pain and Behavior in an Animal Model of Migraine

The endocannabinoid system exerts an important role in pain processing and modulation. Modulation of the system with hydrolase inhibitors of anandamide (AEA) or 2-arachidonyl glycerol (2-AG) has proved effective in reducing migraine-like features in animal models of migraine. Here, we investigated the effect of dual inhibition of the AEA and 2-AG catabolic pathways in the nitroglycerin-based animal model of migraine. The dual inhibitor JZL195 was administered to rats 2 h after nitroglycerin or vehicle injection. Rats were then exposed to the open field test and the orofacial formalin test. At the end of the tests, they were sacrificed to evaluate calcitonin gene-related peptide (CGRP) serum levels and gene expression of CGRP and cytokines in the cervical spinal cord and the trigeminal ganglion. The dual inhibitor significantly reduced the nitroglycerin-induced trigeminal hyperalgesia and pain-associated behavior, possibly via cannabinoid 1 receptors-mediated action, but it did not change the hypomotility and the anxiety behaviors induced by nitroglycerin. The decreased hyperalgesia was associated with a reduction in CGRP and cytokine gene expression levels in central and peripheral structures and reduced CGRP serum levels. These data suggest an antinociceptive synergy of the endocannabinoid action in peripheral and central sites, confirming that this system participates in reduction of cephalic pain signals.

Nitric oxide and sex differences in dendritic branching and arborization

Nitric oxide (NO) is an important signaling molecule with many functions in the nervous system. Derived from the enzymatic conversion of arginine by several nitric oxide synthases (NOS), NO plays significant roles in neuronal developmental events such as the establishment of dendritic branching or arbors. A brief summary of the discovery, molecular biology, and chemistry of NO, and a description of important NO-mediated signal transduction pathways with emphasis on the role for NO in the development of dendritic branching during neurodevelopment are presented. Important sex differences in neuronal nitric oxide synthase expression during neuronal development are considered. Finally, a survey of endogenous and exogenous substances that disrupt dendritic patterning is presented with particular emphasis on how these molecules may drive NO-mediated sex differences in dendritic branching.

Nitric oxide role in anxiety-like behavior, memory and cognitive impairments in animal model of chronic migraine

The occurrence of cognitive dysfunctions and anxiety and mood disorders has been shown to be higher in migraine patients. Nitric Oxide (NO) is a significant neurotransmitter in the pathophysiology of migraine, anxiety and neurodegenerative disorders. Therefore, the present study was conducted to evaluate the role of NO system in migraine-induced memory impairment and anxiety like behaviors. Nitroglycerin (NTG) was administered to the animals as an animal model of migraine and pretreatment with L-Arginine, L-NAME and saline were implemented to evaluate the role of NO system in possible cognitive impairments in animal model of migraine. Avoidance learning and memory performance, object recognition memory, anxiety-like behavior and motor activity were assessed using a shuttle box apparatus, novel object recognition, elevated plus-maze, and open field tests respectively. The data showed that the injection of nitroglycerin disturbs learning and memory and elicit anxiety like behavior in the animals. L-NAME administration suppressed the observed effect of nitroglycerin on memory and anxiety. Overall, the results indicated that nitric oxide system is implicated in memory impairments and anxiety like behavior in an animal model of migraine.

Hydroxyl-Radical Reaction Pathways for the Fast Photochemical Oxidation of Proteins Platform As Revealed by 18O Isotopic Labeling

Fast photochemical oxidation of protein (FPOP) has become an important mass spectrometry-based protein footprinting approach. Although the hydroxyl radical (•OH) generated by photolysis of hydrogen peroxide (H2O2) is most commonly used, the pathways for its reaction with amino-acid side chains remain unclear. Here, we report a systematic study of •OH oxidative modification of 13 amino acid residues by using 18O isotopic labeling. The results differentiate three classes of residues on the basis of their oxygen uptake preference toward different oxygen sources. Histidine, arginine, tyrosine, and phenylalanine residues preferentially take oxygen from H2O2. Methionine residues competitively take oxygen from H2O2 and dissolved oxygen (O2), whereas the remaining residues take oxygen exclusively from O2. Results reported in this work deepen the understanding of •OH labeling pathway on a FPOP platform, opening new possibilities for tailoring FPOP conditions in addressing many biological questions in a profound way.

The histology, physiology, neurochemistry and circuitry of the substantia gelatinosa Rolandi (lamina II) in mammalian spinal cord

The substantia gelatinosa Rolandi (SGR) was first described about two centuries ago. In the following decades an enormous amount of information has permitted us to understand - at least in part - its role in the initial processing of pain and itch. Here, I will first provide a comprehensive picture of the histology, physiology, and neurochemistry of the normal SGR. Then, I will analytically discuss the SGR circuits that have been directly demonstrated or deductively envisaged in the course of the intensive research on this area of the spinal cord, with particular emphasis on the pathways connecting the primary afferent fibers and the intrinsic neurons. The perspective existence of neurochemically-defined sets of primary afferent neurons giving rise to these circuits will be also discussed, with the proposition that a cross-talk between different subsets of peptidergic fibers may be the structural and functional substrate of additional gating mechanisms in SGR. Finally, I highlight the role played by slow acting high molecular weight modulators in these gating mechanisms.

Excessive nNOS/NO/AMPK signaling activation mediated by the blockage of the CBS/H2S system contributes to oxygen‑glucose deprivation‑induced endoplasmic reticulum stress in PC12 cells

Hypoxic‑ischemia stress causes severe brain injury, leading to death and disability worldwide. Although it has been reported that endoplasmic reticulum (ER) stress is an essential step in the progression of hypoxia or ischemia‑induced brain injury, the underlying molecular mechanisms are and have not yet been fully elucidated. Accumulating evidence has indicated that both nitric oxide (NO) and hydrogen sulfide (H2S) play an important role in the development of cerebral ischemic injury. In the present study, we aimed to investigate the effect of the association between NO signaling and the cystathionine β‑synthase (CBS)/H2S system on ER stress in a cell model of cerebral hypoxia‑ischemia injury. We found that oxygen‑glucose deprivation (OGD) markedly increased the NO level and neuronal NO synthase (nNOS) activity. 3‑Bromo‑7‑nitroindazole (3‑Br‑7‑NI), a relatively selective nNOS inhibitor, abolished the OGD‑induced inhibition of cell viability and the increased expression of ER stress‑related proteins, including glucose‑regulated protein 78 (GRP78), C/EBP homologous protein (CHOP) and cleaved caspase‑12 in PC12 cells, indicating the contribution of excessive nNOS/NO signaling to OGD‑induced ER stress. Furthermore, we found that OGD increased the phosphorylated AMP‑activated protein kinase (p‑AMPK)/AMPK ratio, and the AMPK activator, 5‑aminoimidazole‑4‑carboxamide‑1‑β‑D‑ribofuranoside (AICAR), attenuated the effects on OGD‑induced ER stress, suggesting that OGD‑induced NO overproduction results in AMPK activation in PC12 cells. We also found that OGD induced the downregulation of the CBS/H2S system, as indicated by the decreased H2S level in the culture supernatant and CBS activity in PC12 cells. In addition, we found that treatment with NaHS (a H2S donor) or S‑adenosyl‑L‑methionine (SAM, a CBS agonist) mitigated OGD‑induced ER stress, as well as the NO level, nNOS activity and AMPK phosphorylation in PC12 cells. On the whole, these results suggest that the inhibition of the CBS/H2S system, which facilitated excessive nNOS/NO/AMPK activation, contributes to OGD‑induced ER stress.

Substance P NK1 receptor in the rat corpus callosum during postnatal development

INTRODUCTION

The expression of substance P (SP) receptor (neurokinin 1, NK1) was studied in the rat corpus callosum (cc) from postnatal day 0 (the first 24 hr from birth, P0) to P30.

METHODS

We used immunocytochemistry to study the presence of intracallosal NK1-immunopositive neurons (NK1_IP-n) during cc development.

RESULTS

NK1_IP-n first appeared on P5. Their number increased significantly between P5 and P10, it remained almost constant between P10 and P15, then declined slightly until P30. The size of intracallosal NK1_IP-n increased constantly from P5 (102.3 μm²) to P30 (262.07 μm²). From P5 onward, their distribution pattern was adult-like, that is, they were more numerous in the lateral and intermediate parts of the cc, and declined to few or none approaching the midline. At P5, intracallosal NK1_IP-n had a predominantly round cell bodies with primary dendrites of different thickness from which originated thinner secondary branches. Between P10 and P15, dendrites were longer and more thickly branched, and displayed several varicosities as well as short, thin appendages. Between P20 and P30, NK1_IP-n were qualitatively indistinguishable from those of adult animals and could be classified as bipolar (fusiform and rectangular), round-polygonal, and pyramidal (triangular-pyriform).

CONCLUSIONS

Number of NK1_IP-n increase between P5 and P10, then declines, but unlike other intracallosal neurons, NK1_IP-n make up a significant population in the adult cc. These findings suggest that NK1_IP-n may be involved in the myelination of callosal axons, could play an important role in their pathfinding. Since they are also found in adult rat cc, it is likely that their role changes during lifetime.

Chronic Nonmodulated Microwave Radiations in Mice Produce Anxiety-like and Depression-like Behaviours and Calcium- and NO-related Biochemical Changes in the Brain

The present study was aimed to investigate behavioural and biochemical effects of chronic exposure of amplitude modulated and non-modulated microwave radiation on laboratory mice. Chronic microwave exposures were executed with 2.45 GHz of either modulated (power density, 0.029 mW/cm²; specific absorption rate, 0.019 W/Kg with sinusoidal modulation of 400 Hz) or nonmodulated continuous sinusoidal wave (power density, 0.033 mW/cm²; specific absorption rate, 0.023 W/Kg) for 2 hrs daily for 1 month. Mice subjected to non-modulated microwave exposure had significantly increased acetylcholinesterase activity and increased intracellular calcium and nitric oxide levels in the cerebral cortex and hippocampus, and also had increased glucose and corticosterone levels in blood compared to control mice. These non-modulated microwave-exposed mice exhibited anxiety-like and depression-like behaviours. In contrast, mice exposed to modulated microwave for the same period did not show such changes in concomitant biochemical and behavioural analyses. These results suggest that chronic non-modulated microwave, but not modulated microwave, radiation may cause anxiety-like and depression-like behaviours and calcium- and NO-related biochemical changes in the brain.

Nitric oxide synthase and structure-based inhibitor design

Once it was discovered that the enzyme nitric oxide synthase (NOS) is responsible for the biosynthesis of NO, NOS became a drug target. Particularly important is the over production of NO by neuronal NOS (nNOS) in various neurodegenerative disorders. After the various NOS isoforms were identified, inhibitor development proceeded rapidly. It soon became evident, however, that isoform selectivity presents a major challenge. All 3 human NOS isoforms, nNOS, eNOS (endothelial NOS), and iNOS (inducible NOS) have nearly identical active site structures thus making selective inhibitor design especially difficult. Of particular importance is the avoidance of inhibiting eNOS owing to its vital role in the cardiovascular system. This review summarizes some of the history of NOS inhibitor development and more recent advances in developing isoform selective inhibitors using primarily structure-based approaches.

Physiology and Pathophysiology of Nitric Oxide in the Retina

The role of nitric oxide (NO) signaling in the retina can be simply termed as "extensive." The picture remains incomplete, but it is now known that NO has many sites of production and action in the retina, both physiological and pathophysiological in nature. Perspectives from retinal neurophysiology and clinical pathology have merged in a number of studies examining NO action, but renewed emphasis is needed to discover the links between the roles of NO in the neurons, glia, and vasculature of the retina. NEUROSCIENTIST 3:357-360, 1997

■ REVIEW : Glial NO: Normal and Pathological Roles

All nervous system cell types can be induced with cytokines or bacterial products to make nitric oxide, at least in culture. The signaling pathways invoked by inducers that result in transcriptional activation of the nitric oxide synthase gene are becoming clear, and modulators of this induction have been discovered. Much suggestive and, recently, more definitive evidence has accumulated for induction of nitric oxide synthase in glial cells in vivo associated with viral infection, as well as in animal models of trauma, ischemia, and autoimmunity. Whether nitric oxide from this source contributes to or limits the attendant conditions is not yet clear. The Neuroscientist 2:90-99, 1996

Propitious Therapeutic Modulators to Prevent Blood-Spinal Cord Barrier Disruption in Spinal Cord Injury

The blood-spinal cord barrier (BSCB) is a specialized protective barrier that regulates the movement of molecules between blood vessels and the spinal cord parenchyma. Analogous to the blood-brain barrier (BBB), the BSCB plays a crucial role in maintaining the homeostasis and internal environmental stability of the central nervous system (CNS). After spinal cord injury (SCI), BSCB disruption leads to inflammatory cell invasion such as neutrophils and macrophages, contributing to permanent neurological disability. In this review, we focus on the major proteins mediating the BSCB disruption or BSCB repair after SCI. This review is composed of three parts. Section 1. SCI and the BSCB of the review describes critical events involved in the pathophysiology of SCI and their correlation with BSCB integrity/disruption. Section 2. Major proteins involved in BSCB disruption in SCI focuses on the actions of matrix metalloproteinases (MMPs), tumor necrosis factor alpha (TNF-α), heme oxygenase-1 (HO-1), angiopoietins (Angs), bradykinin, nitric oxide (NO), and endothelins (ETs) in BSCB disruption and repair. Section 3. Therapeutic approaches discusses the major therapeutic compounds utilized to date for the prevention of BSCB disruption in animal model of SCI through modulation of several proteins.

Potent and Selective Human Neuronal Nitric Oxide Synthase Inhibition by Optimization of the 2-Aminopyridine-Based Scaffold with a Pyridine Linker

Neuronal nitric oxide synthase (nNOS) is an important therapeutic target for the treatment of various neurodegenerative disorders. A major challenge in the design of nNOS inhibitors focuses on potency in humans and selectivity over other NOS isoforms. Here we report potent and selective human nNOS inhibitors based on the 2-aminopyridine scaffold with a central pyridine linker. Compound 14j, the most promising inhibitor in this study, exhibits excellent potency for rat nNOS (Ki = 16 nM) with 828-fold n/e and 118-fold n/i selectivity with a Ki value of 13 nM against human nNOS with 1761-fold human n/e selectivity. Compound 14j also displayed good metabolic stability in human liver microsomes, low plasma protein binding, and minimal binding to cytochromes P450 (CYPs), although it had little to no Caco-2 permeability.

Acute restraint stress induces specific changes in nitric oxide production and inflammatory markers in the rat hippocampus and striatum

Chronic mild stress has been shown to cause hippocampal neuronal nitric oxide synthase (NOS) overexpression and the resultant nitric oxide (NO) production has been implicated in the etiology of depression. However, the extent of nitrosative changes including NOS enzymatic activity and the overall output of NO production in regions of the brain like the hippocampus and striatum following acute stress has not been characterized. In this study, outbred male Wistar rats aged 6-7 weeks were randomly allocated into 0 (control), 60, 120, or 240 min stress groups and neural regions were cryodissected for measurement of constitutive and inducible NOS enzymatic activity, nitrosative status, and relative gene expression of neuronal and inducible NOS. Hippocampal constitutive NOS activity increased initially but was superseded by the inducible isoform as stress duration was prolonged. Interestingly, hippocampal neuronal NOS and interleukin-1β mRNA expression was downregulated, while the inducible NOS isoform was upregulated in conjunction with other inflammatory markers. This pro-inflammatory phenotype within the hippocampus was further confirmed with an increase in the glucocorticoid-antagonizing macrophage migration inhibitory factor, Mif, and the glial surveillance marker, Ciita. This indicates that despite high levels of glucocorticoids, acute stress sensitizes a neuroinflammatory response within the hippocampus involving both pro-inflammatory cytokines and inducible NOS while concurrently modulating the immunophenotype of glia. Furthermore, there was a delayed increase in striatal inducible NOS expression while no change was found in other pro-inflammatory mediators. This suggests that short term stress induces a generalized increase in inducible NOS signaling that coincides with regionally specific increased markers of adaptive immunity and inflammation within the brain.

Interneuronal Nitric Oxide Signaling Mediates Post-synaptic Long-Term Depression of Striatal Glutamatergic Synapses

Experience-driven plasticity of glutamatergic synapses on striatal spiny projection neurons (SPNs) is thought to be essential to goal-directed behavior and habit formation. One major form of striatal plasticity, long-term depression (LTD), has long appeared to be expressed only pre-synaptically. Contrary to this view, nitric oxide (NO) generated by striatal interneurons was found to induce a post-synaptically expressed form of LTD at SPN glutamatergic synapses. This form of LTD was dependent on signaling through guanylyl cyclase and protein kinase G, both of which are abundantly expressed by SPNs. NO-LTD was unaffected by local synaptic activity or antagonism of endocannabinoid (eCb) and dopamine receptors, all of which modulate canonical, pre-synaptic LTD. Moreover, NO signaling disrupted induction of this canonical LTD by inhibiting dendritic Ca(2+) channels regulating eCb synthesis. These results establish an interneuron-dependent, heterosynaptic form of post-synaptic LTD that could act to promote stability of the striatal network during learning.

Nitric oxide regulates antagonistically phagocytic and neurite outgrowth inhibiting capacities of microglia

Traumatic injury or the pathogenesis of some neurological disorders is accompanied by inflammatory cellular mechanisms, mainly resulting from the activation of central nervous system (CNS) resident microglia. Under inflammatory conditions, microglia up-regulate the inducible isoform of NOS (iNOS), leading to the production of high concentrations of the radical molecule nitric oxide (NO). At the onset of inflammation, high levels of microglial-derived NO may serve as a cellular defense mechanism helping to clear the damaged tissue and combat infection of the CNS by invading pathogens. However, the excessive overproduction of NO by activated microglia has been suggested to govern the inflammation-mediated neuronal loss causing eventually complete neurodegeneration. Here, we investigated how NO influences phagocytosis of neuronal debris by BV-2 microglia, and how neurite outgrowth of human NT2 model neurons is affected by microglial-derived NO. The presence of NO greatly increased microglial phagocytic capacity in a model of acute inflammation comprising lipopolysaccharide (LPS)-activated microglia and apoptotic neurons. Chemical manipulations suggested that NO up-regulates phagocytosis independently of the sGC/cGMP pathway. Using a transwell system, we showed that reactive microglia inhibit neurite outgrowth of human neurons via the generation of large amounts of NO over effective distances in the millimeter range. Application of a NOS blocker prevented the LPS-induced NO production, totally reversed the inhibitory effect of microglia on neurite outgrowth, but reduced the engulfment of neuronal debris. Our results indicate that a rather simple notion of treating excessive inflammation in the CNS by NO synthesis blocking agents has to consider functionally antagonistic microglial cell responses during pharmaceutic therapy.

Highly sensitive amperometric Pt-Nafion gas phase nitric oxide sensor: Performance and application in characterizing nitric oxide-releasing biomaterials

A highly sensitive amperometric gas-phase nitric oxide (NO) sensor based on a Pt working electrode chemically deposited on a Nafion film is described. The Pt electrode is chemically deposited on a Nafion 117 membrane by impregnating the film with Pt(NH3)4(2+) ions, which are then exposed to NaBH4 to precipitate conductive Pt metal. The sensor was characterized with a mass-flow controlled 1 ppm NO standard gas and has an electrochemical surface area of 34 ± 9 cm(2), low limits of detection (4.3 ± 1.1 ppb) and a fast response time (<5s) toward changes in gas phase NO levels. Good correlation was found for measurements with the new amperometric Pt-Nafion sensor vs. chemiluminescence results for detecting the rates of NO release from Carbosil2080A polymer films doped with S-nitroso-N-acetylpenicillamine (R = 0.999, m = 0.999, n = 6) and for electrochemical reduction of nitrite to NO (R = 0.999, m = 0.938, n = 3) mediated by a copper(II)-tri(2-pyridylmethyl)amine complex.

Baclofen or nNOS inhibitor affect molecular and behavioral alterations evoked by traumatic spinal cord injury in rat spinal cord

BACKGROUND CONTEXT

The loss of descending control after spinal cord injury (SCI) and incessant stimulation of Ia monosynaptic pathway, carrying proprioceptive impulses from the muscles and tendons into the spinal cord, evoke exaggerated α-motoneuron activity leading to increased reflex response. Previous results from our laboratory have shown that Ia monosynaptic pathway is nitrergic.

PURPOSE

The aim of this study was to find out whether nitric oxide produced by neuronal nitric oxide synthase (nNOS) plays a role in setting the excitability of α-motoneurons after thoracic spinal cord transection.

STUDY DESIGN

We tested the hypothesis that the inhibition of nNOS in α-motoneurons after SCI could have a neuroprotective effect on reflex response.

METHODS

Rats underwent spinal cord transection at Th10 level followed by 7, 10, and 14 days of survival. The animals were treated with Baclofen (a gamma aminobutyric acid B receptor agonist, 3 μg/two times per day/intrathecally) applied for 3 days from the seventh day after transection; N-nitro-l-arginine (NNLA) (nNOS blocator) applied for the first 3 days after injury (20 mg/kg per day, intramuscularly); NNLA and Baclofen; or NNLA (60 mg/kg/day, single dose) applied on the 10th day after transection. We detected the changes in the level of nNOS protein, nNOS messenger RNA, and nNOS immunoreactivity. To investigate the reflex response to heat-induced stimulus, tail-flick test was monitored in treated animals up to 16 days after SCI.

RESULTS

Our data indicate that Baclofen therapy is more effective than the combined treatment with NNLA and Baclofen therapy. The single dose of NNLA (60 mg/kg) applied on the 10th day after SCI or Baclofen therapy reduced nNOS expression in α-motoneurons and suppressed symptoms of increased reflex activity.

CONCLUSIONS

The results clearly show that increased nNOS expression in α-motoneurons after SCI may be pharmacologically modifiable with Baclofen or bolus dose of nNOS blocker.

Protective effects of Echium amoenum Fisch. and C.A. Mey. against cerebral ischemia in the rats

Background:

This study was designed to evaluate the protective effect of Echium amoenum total anthocyanin extract (ETAE) on partial/transient cerebral ischemia in the rats.

Materials and Methods:

Rats received ETAE (50, 100 and 200 mg/kg, i.p.) 30 min before the induction of cerebral ischemia. Cerebral ischemia was induced by bilateral common carotid arteries occlusion (BCCAO) for 30 min, followed by 72 h reperfusion. The neurological deficit, brain performance, and sensory motor function were assessed 48 h and 72 h after surgery. After sacrification, the brains were evaluated for myeloperoxidase (MPO) activity and histopathological changes.

Results:

Our results showed that motor function significantly decreased in ischemia/reperfusion (I/R) group as compared to the sham group. Histopathological analysis exhibited the shrinkage and atrophy of the neurons in I/R group. ETAE at the dose of 200 mg/kg improved spontaneous activity and memory induced by cerebral ischemia compared to the control group and also decreased brain MPO activity following cerebral ischemia. However, it could not affect the ability to climbing, body proprioception, vibrissae touch and brain water content. In addition, pretreatment with ETAE at higher doses significantly reduced ischemia-induced neuronal loss of the brain.

Conclusion:

The anthocyanin rich fraction from E. amoenum was found to have protective effects against some brain damages postischemic reperfusion. However, further researches are required for investigating the exact mechanisms of the effect of this plant in the prevention of cerebral ischemia in human.

Intracallosal neuronal nitric oxide synthase neurons colocalize with neurokinin 1 substance P receptor in the rat

The corpus callosum (cc) contains nitric oxide (NO)-producing neurons. Because NO is a potent vasodilator, these neurons could translate neuronal signals into vascular responses that can be detected by functional brain imaging. Substance P (SP), one of the most widely expressed peptides in the CNS, also produces vasomotor responses by inducing calcium release from intracellular stores through its preferred neurokinin 1 (NK1) receptor, thus inducing NO production via activation of neuronal NO synthase (nNOS). Single- and double-labeling experiments were performed to establish whether NK1-immunopositive neurons (NK1IP -n) are found in the rat cc and the extent of NK1 colocalization with nNOS. NK1IP -n were seen to constitute a large neuronal population in the cc and had a distribution similar to that of nNOSIP neurons (nNOSIP -n). NK1IP -n were numerous in the lateral cc and gradually decreased in the more medial portions, where they were few or absent. Intracallosal NK1IP -n and their dendritic trees were intensely labeled, allowing classification into four morphological types: bipolar, round, polygonal, and pyramidal. Confocal microscopic examination demonstrated that nearly all NK1IP -n contained nNOS (96.43%) and that 84.59% of nNOSIP -n co-expressed NK1. These data suggest that the majority of intracallosal neurons can release NO as a result of the action of SP. A small proportion of nNOSIP -n does not contain NK1 and is not activated by SP; these neurons may release NO via alternative mechanisms. The possible mechanisms by which intracallosal neurons release NO are also reviewed.

Distribution of nitric oxide-producing cells along spinal cord in urodeles

Nitric oxide is a unique neurotransmitter, which participates in many physiological and pathological processes in the organism. There are little data about the neuronal nitric oxide synthase immunoreactivity in the spinal cord of amphibians. In this respect, the present study aims to investigate the distribution of nitric oxide producing cells in the spinal cord of urodele and to find out the possibility of a functional locomotory role to this neurotransmitter. The results of the present study demonstrate a specific pattern of NADPH-d labeling in the selected amphibian model throughout the spinal cord length as NADPH-d-producing cells and fibers were present in almost all segments of the spinal cord of the salamander investigated. However, their number, cytological characteristics and labeling intensity varied significantly. It was noticed that the NO-producing cells (NO-PC) were accumulated in the ventral side of certain segments in the spinal cord corresponding to the brachial and sacral plexuses. In addition, the number of NO-PC was found to be increased also at the beginning of the tail and this could be due to the fact that salamanders are tetrapods having bimodal locomotion, namely swimming and walking.

Characterization of NO-producing neurons in the rat corpus callosum

INTRODUCTION

The aim of this study was to determine the presence and distribution of nitric oxide (NO)-producing neurons in the rat corpus callosum (cc).

MATERIAL AND METHODS

To investigate this aspect of cc organization we used nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and neuronal NO synthase (nNOS) immunocytochemistry.

RESULTS

Intense NADPH-d-positive (NADPH-d+) neurons were found along the rostrocaudal extension of the cc (sagittal sections). They were more numerous in the lateral cc and gradually decreased in the more medial regions, where they were very few or absent. The Golgi-like appearance of NADPH-d+ intracallosal neurons allowed dividing them into five morphological types: (1) bipolar; (2) fusiform; (3) round; (4) polygonal; and (5) pyramidal. The number of NADPH-d+ neurons (both hemispheres) was counted in two brains using 50-μm thick sections. In the first brain, counts involved 145 sections and neurons were 2959; in the second, 2227 neurons were counted in 130 sections. The distribution and morphology of nNOS-immunopositive (nNOSIP) neurons was identical to that of NADPH-d+neurons. Some of these neurons were observed in the cc ependymal region, where they might be in contact with cerebrospinal fluid (CSF), monitoring its composition, pH, and osmolality changes, or playing a role in regulating the synthesis and release of several peptides. The somatic, dendritic, and axonal processes of many NADPH-d+/nNOSIP neurons were closely associated with intracallosal blood vessels.

CONCLUSIONS

Such close relationship raises the possibility that these neurons are a major source of NO during neural activity. As NO is a potent vasodilator, these findings strongly suggest that NO-positive neurons transduce neuronal signals into vascular responses in selected cc regions, thus giving rise to hemodynamic changes detectable by neuroimaging.

Nitric oxide/cyclic GMP signaling regulates motility of a microglial cell line and primary microglia in vitro

Microglia are the resident immune cells of the brain, which become rapidly activated and migrate to the site of insult in brain infection and disease. Activated microglia generate large amounts of the highly reactive messenger molecule nitric oxide (NO). NO is able to raise cyclic GMP levels via binding to soluble guanylyl cyclase. We investigated potential mechanistic links between inflammation, NO signaling, and microglial migration. To monitor cell migration, we used a scratch wound assay and compared results obtained in the BV-2 microglial line to primary microglia. Incubation with lipopolysaccharide (LPS) as stimulator of acute inflammatory processes enhanced migration of both microglial cell types. LPS activated NO production in BV-2 cells and application of an NO donor increased BV-2 cell migration while an NO scavenger reduced motility. Pharmacological inhibition of soluble guanylyl cyclase and the resulting decrease in motility can be rescued by a membrane permeant analog of cGMP. Despite differences in the threshold towards stimulation with the chemical agents, both BV-2 cells and primary microglia react in a similar way. The important role of NO/cGMP as positive regulator of microglial migration, the downstream targets of the signaling cascade, and resulting cytoskeletal changes can be conveniently investigated in a microglial cell line.

Role of hypothalamic corticotropin-releasing factor in mediating alcohol-induced activation of the rat hypothalamic-pituitary-adrenal axis

Alcohol stimulates the hypothalamic-pituitary-adrenal (HPA) axis through brain-based mechanisms in which endogenous corticotropin-releasing factor (CRF) plays a major role. This review first discusses the evidence for this role, as well as the possible importance of intermediates such as vasopressin, nitric oxide and catecholamines. We then illustrate the long-term influence exerted by alcohol on the HPA axis, such as the ability of a first exposure to this drug during adolescence, to permanently blunt neuroendocrine responses to subsequent exposure of the drug. In view of the role played by CRF in addiction, it is likely that a better understanding of the mechanisms through which this drug stimulates the HPA axis may lead to the development of new therapies used in the treatment of alcohol abuse, including clinically relevant CRF antagonists.

Differential distribution of parvalbumin- and calbindin-D28K-immunoreactive neurons in the rat periaqueductal gray matter and their colocalization with enzymes producing nitric oxide

The distribution, colocalization with enzymes producing nitric oxide (NO), and the synaptic organization of neurons containing two calcium-binding proteins (CaBPs) - parvalbumin (Parv) and calbindin-D28K (Calb) - were investigated in the rat periaqueductal gray matter (PAG). Parv-immunopositive (ParvIP) neurons were detected in the mesencephalic nucleus and rarely in the PAG. CalbIP neurons were found both in the dorsolateral (PAG-dl) and ventrolateral PAG (PAG-vl); their size ranged from 112.96 μm(2) (PAG-dl) to 125.13 μm(2) (PAG-vl). Ultrastructurally Parv and Calb immunoreactivity was mostly found in dendritic profiles. Axon terminals containing each of the two CaBPs formed symmetric synapses. Moreover both Parv and Calb were used to label a subpopulation of NO-producing neurons. Colocalization was investigated using two protocols: (i) a combination of Calb and Parv immunocytochemistry (Icc) with nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry (Hi) and (ii) neuronal NO synthase-Icc (nNOS) (immunofluorescence). Both techniques demonstrated a complete lack of colocalization of Parv and NADPH-d/nNOS in PAG neurons. Double-labeled (DL) neurons (Calb-NADPH-d; Calb-nNOS) were detected in PAG-dl. NADPH-d-Hi/Calb-Icc indicated that 41-47% of NADPH-d-positive neurons contained Calb, whereas 17-23% of CalbIP cells contained NADPH-d. Two-color immunofluorescence revealed that 53-66% of nNOSIP cells colocalized with Calb and 24-34% of CalbIP neurons contained nNOS. DL neuron size was 104.44 μm(2); neurons labeled only with NADPH-d or Calb measured 89.793 μm(2) and 113.48 μm(2), respectively. Together with previous findings (Barbaresi et al. [2012]) these data suggest that: Therefore the important aspect of the PAG intrinsic organization emerging from this and previous double-labeling studies is the chemical diversity of NO-synthesizing neurons, which is likely related to the different functions in which these neurons are involved.

PKC-Dependent Signaling Pathways within PAG and Thalamus Contribute to the Nitric Oxide-Induced Nociceptive Behavior

Nitric oxide (NO) is an important molecule involved in nociceptive processing in the central nervous system. The release of NO within the spinal cord has long been implicated in the mechanisms underlying exaggerated pain sensitivity, and administration of NO donors can induce hyperalgesia. To elucidate the supraspinal mechanism responsible for NO-induced nociceptive hypersensitivity, we investigated the modulation of protein kinase C (PKC) and downstream effectors following treatment with the NO donors nitroglycerin and sodium nitroprusside. Both compounds induced a prolonged cold allodynia and heat hyperalgesia, increased levels of c-Fos and IL-1β, and activated NF-κB within periaqueductal grey matter and thalamus. Simultaneously, an increased expression and phosphorylation of PKC γ and ε were detected. To clarify the cellular mechanism involved in the NO-induced hypernociception, we examined the expression of transcription factors that act as PKC downstream effectors. A dramatic hyperphosphorylation of CREB and STAT1 was observed. The i.c.v. administration of the PKC blocker calphostin C prevented the NO-induced hypernociception, the hyperphosphorylation of CREB and STAT1, and partially reduced NF-κB activation. Conversely, the increase of IL-1β was unmodified by calphostin C. These results suggest the relevance of cerebral PKC-mediated CREB and STAT1 activation in the NO donor-induced nociceptive behavior.

Astrogliosis and HSP 70 activation in neonate rats' brain exposed to sodium metavanadate through lactation

The effect of sodium metavanadate (NaVO3) exposure on lipid oxidative damage in the CNS of suckling rats was studied. Using histological markers of cellular injury, we also studied the morphological alterations of neurons and astroglial cells in different regions of neonate rats CNS after NaVO3 exposure. Dams of treated litters were intraperitoneally injected with 3mgNaVO3/kgbody weight/day during 12days starting on post-natal day (PND) 10. On the 21st PND, four pups of each litter were sacrificed by decapitation and six brain areas were removed for lipid peroxidation assay by the thiobarbituric acid (TBA) reaction, the other four were transcardially perfused-fixed and their brains were removed and cut with a cryostat. Brain sections were processed for: NADPHd histochemistry and anti-HSP70, anti-GFAP and anti-S100 immunohistochemistry. The relative optical density of the NADPHd stained layers and of S100 (+) astrocytes and the GFAP (+) astrocyte surface area in Cer and Hc were measured. Although MDA levels, S100 immunostaining and NADPHd activity didn't show differences between experimental and control groups, both astrogliosis and HSP70 activation were detected in Cer, while only the former was detected in Hc of V-exposed pups.

Purinergic stimulation of carotid body efferent glossopharyngeal neurones increases intracellular Ca2+ and nitric oxide production

The mammalian carotid body (CB) is a peripheral chemosensory organ that controls ventilation and is innervated by both afferent and efferent nerve fibres. The afferent pathway is stimulated by chemoexcitants, such as hypoxia, hypercapnia and acidosis. The efferent pathway causes inhibition of the sensory discharge via release of NO that originates mainly from neuronal nitric oxide synthase (nNOS)-positive autonomic neurones within the glossopharyngeal nerve (GPN). Recent studies in the rat indicate that these inhibitory GPN neurones and their processes express purinergic P2X receptors and can be activated by ATP, a key excitatory CB neurotransmitter. Here we tested the hypothesis that purinergic agonists stimulate a rise in [Ca(2+)]i, leading to nNOS activation and NO production in isolated GPN neurones, using the fluorescent probes fura-2 and 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM DA), respectively. ATP caused a dose-dependent increase in [Ca(2+)]i in GPN neurones (EC50 ≈ 1.92 μm) that was markedly inhibited by a combination of 100 μm suramin (a non-specific P2X blocker) and 100 nm Brilliant Blue G (a selective P2X7 blocker). ATP also stimulated NO production in GPN neurones, as revealed by an increase in DAF fluorescence; this NO signal was inhibited by purinergic blockers, chelators of extracellular Ca(2+), the nNOS inhibitor l-NAME and the NO scavenger carboxy-PTIO. The P2X2/3 and P2X7 agonists α,β,-methylene ATP and benzoyl ATP mimicked the effects of ATP. Taken together, these data indicate that ATP may contribute to negative feedback inhibition of CB sensory discharge via purinergic stimulation of NO production in efferent fibres.

Protein oxidation in aging and the removal of oxidized proteins

Reactive oxygen species (ROS) are generated constantly within cells at low concentrations even under physiological conditions. During aging the levels of ROS can increase due to a limited capacity of antioxidant systems and repair mechanisms. Proteins are among the main targets for oxidants due to their high rate constants for several reactions with ROS and their abundance in biological systems. Protein damage has an important influence on cellular viability since most protein damage is non-repairable, and has deleterious consequences on protein structure and function. In addition, damaged and modified proteins can form cross-links and provide a basis for many senescence-associated alterations and may contribute to a range of human pathologies. Two proteolytic systems are responsible to ensure the maintenance of cellular functions: the proteasomal (UPS) and the lysosomal system. Those degrading systems provide a last line of antioxidative protection, removing irreversible damaged proteins and recycling amino acids for the continuous protein synthesis. But during aging, both systems are affected and their proteolytic activity declines significantly. Here we highlight the recent advantages in the understanding of protein oxidation and the fate of these damaged proteins during aging. This article is part of a Special Issue entitled: Posttranslational Protein modifications in biology and Medicine.

Effect of Treatment with Cyanidin-3-O-β-D-Glucoside on Rat Ischemic/Reperfusion Brain Damage

This study investigated the effect of cyanidin-3-O-β-glucoside on an experimental model of partial/transient cerebral ischemia in the rats in order to verify the effectiveness of both pre- and posttreatments. Cyanidin-3-O-β-glucoside-pretreated rats were injected with 10 mg/Kg i.p. 1 h before the induction of cerebral ischemia; in posttreated rats, the same dosage was injected during reperfusion (30 min after restoring blood flow). Cerebral ischemia was induced by bilateral clamping of common carotid arteries for 20 min. Ischemic rats were sacrificed immediately after 20 min ischemia; postischemic reperfused animals were sacrificed after 3 or 24 h of restoring blood flow. Results showed that treatment with cyanidin increased the levels of nonproteic thiol groups after 24 h of postischemic reperfusion, significantly reduced the lipid hydroperoxides, and increased the expression of heme oxygenase and γ-glutamyl cysteine synthase; a significant reduction in the expression of neuronal and inducible nitric oxide synthases and the equally significant increase in the endothelial isoform were observed. Significant modifications were also detected in enzymes involved in metabolism of endogenous inhibitors of nitric oxide. Most of the effects were observed with both pre- and posttreatments with cyanidin-3-O-β-glucoside suggesting a role of anthocyanin in both prevention and treatment of postischemic reperfusion brain damage.

Contrasting Effects of the Neuropeptides Substance P, Somatostatin, and Neuropeptide Y on the Methamphetamine-Induced Production of Striatal Nitric Oxide in Mice

Several laboratories have shown that methamphetamine (METH) neurotoxicity is associated with increases of nitric oxide (NO) production in striatal tissue and blockade of NO production protects from METH. Because substance P modulates NO production, we tested the hypothesis that intrinsic striatal neuropeptides such as somatostatin and neuropeptide Y (NPY) modulate striatal NO production in the presence of METH. To that end, METH (30 mg/kg, IP) was injected into adult male mice alone or in combination with pharmacological agonists or antagonists of the neurokinin-1 (substance P), somatostatin or NPY receptors and 3-nitrotyrosine (an indirect index of NO production) was assessed utilizing HPLC or a histological method. Pre-treatment with the systemic neurokinin-1 receptor antagonist WIN-51,708 significantly attenuated the METH-induced production of striatal 3-NT measured at two hours post-METH. Conversely, intrastriatal injection of NPY1 or 2 receptor agonists inhibited the METH-induced production of striatal 3-NT. Similarly, intrastriatal infusion of the somatostatin receptor agonist octreotide attenuated the METH-induced striatal production of 3-NT. Taken together, our results suggest the hypothesis that the neuropeptide substance P is pro-damage while the neuropeptides somatostatin and NPY are anti-damage in the presence of METH by targeting the production of NO.

Immunocytochemical localization of calretinin-containing neurons in the rat periaqueductal gray and colocalization with enzymes producing nitric oxide: a double, double-labeling study

The pattern of distribution and colocalization of the calcium-binding protein calretinin (Cal) and of enzymes producing nitric oxide (NO) was examined in the rat periaqueductal gray matter (PAG) using two different experimental approaches, by combining Cal immunocytochemistry with NADPH-diaphorase (NADPH-d) histochemistry and with NOS immunocytochemistry, respectively. Cal-immunopositive neurons were found throughout the rostrocaudal extension of both dorsolateral (PAG-dl) and ventrolateral PAG (PAG-vl). Double-labeled neurons were found only in PAG-dl. The first experimental approach indicated that 33-41% of the NADPH-d-positive (Nadph+) cells were immunoreactive for Cal, whereas NADPH-d activity appeared in 19-26% of the Cal-immunopositive (Cal(IP) ) neurons. Two-color immunofluorescence revealed that ∼39-43% of NOS-immunoreactive (NOS(IR) ) neurons were double-labeled with Cal and ∼23% of Cal(IP) neurons expressed NOS immunoreactivity. Measurement in semithin sections of the size of the three neuronal populations found in PAG-dl, showed that Cal(IP) neurons had a cross-sectional area of 94.7 μm², whereas Nadph+ neurons and double-labeled neurons were slightly smaller, having a cross-sectional area of 90.5 and 91.4 μm², respectively. On electron microscopy, Cal(IP) axon terminals formed either symmetric or asymmetric synapses; although the latter synapses were more numerous, both types contacted preferentially Cal(IP) dendrites. These experiments suggest that PAG-dl is characterized by a high degree of heterogeneity.

Thymoquinone produced antianxiety-like effects in mice through modulation of GABA and NO levels

The aim of the present study was to investigate the role of GABAergic and nitriergic modulation in the antianxiety effect of thymoquinone, a major constituent of Nigella sativa, in mice under unstressed and stressed conditions. Thymoquinone (10 and 20 mg/kg), methylene blue (1 mg/kg) and diazepam (2 mg/kg) were administered followed by behavioral testing using an elevated plus maze, the light/dark test and the social interaction test in both unstressed and stressed mice (mice subjected to 6 h immobilization). The effects of the above-mentioned drugs on plasma nitrite, a stable metabolite of nitric oxide (NO) and brain GABA content were also studied. Diazepam (2 mg/kg) produced significant anxiolytic-like effects only in unstressed mice. However, diazepam significantly increased the GABA content in both unstressed and stressed mice as compared with their respective control groups. Thymoquinone (10 and 20 mg/kg) produced significant antianxiety effects in unstressed mice without altering nitrite levels, but only the higher dose (20 mg/kg) of thymoquinone increased the GABA content in unstressed mice. In stressed mice, thymoquinone (20 mg/kg) showed anxiolytic effects, with a significant decrease in plasma nitrite and reversal of the decreased brain GABA content. Pre-treatment with methylene blue enhanced the antianxiety effect of thymoquinone in both unstressed and stressed mice. Therefore, the present study suggests an involvement of NO-cGMP and GABAergic pathways in the anxiolytic-like activity of thymoquinone.