Effects of nitric oxide synthase gene knockout on neurotransmitter release in vivo

nNOS in Erbb4-positive neurons regulates GABAergic transmission in mouse hippocampus

Neuronal nitric oxide synthase (nNOS, gene name Nos1) orchestrates the synthesis of nitric oxide (NO) within neurons, pivotal for diverse neural processes encompassing synaptic transmission, plasticity, neuronal excitability, learning, memory, and neurogenesis. Despite its significance, the precise regulation of nNOS activity across distinct neuronal types remains incompletely understood. Erb-b2 receptor tyrosine kinase 4 (ErbB4), selectively expressed in GABAergic interneurons and activated by its ligand neuregulin 1 (NRG1), modulates GABA release in the brain. Our investigation reveals the presence of nNOS in a subset of GABAergic interneurons expressing ErbB4. Notably, NRG1 activates nNOS via ErbB4 and its downstream phosphatidylinositol 3-kinase (PI3K), critical for NRG1-induced GABA release. Genetic removal of nNos from Erbb4-positive neurons impairs GABAergic transmission, partially rescued by the NO donor sodium nitroprusside (SNP). Intriguingly, the genetic deletion of nNos from Erbb4-positive neurons induces schizophrenia-relevant behavioral deficits, including hyperactivity, impaired sensorimotor gating, and deficient working memory and social interaction. These deficits are ameliorated by the atypical antipsychotic clozapine. This study underscores the role and regulation of nNOS within a specific subset of GABAergic interneurons, offering insights into the pathophysiological mechanisms of schizophrenia, given the association of Nrg1, Erbb4, Pi3k, and Nos1 genes with this mental disorder.

Anticonvulsant effect of pterostilbene and its influence on the anxiety- and depression-like behavior in the pentetrazol-kindled mice: behavioral, biochemical, and molecular studies

RATIONALE

Pterostilbene is the 3,5-dimethoxy derivative of resveratrol with numerous beneficial effects including neuroprotective properties. Experimental studies revealed its anticonvulsant action in the acute seizure tests.

OBJECTIVES

The purpose of the present study was to evaluate the effect of pterostilbene in the pentetrazol (PTZ)-induced kindling model of epilepsy in mice as well as to assess some possible mechanisms of its anticonvulsant action in this model.

METHODS

Mice were repeatedly treated with pterostilbene (50-200 mg/kg) and its effect on the development of seizure activity in the PTZ kindling was estimated. Influence of pterostilbene on the locomotor activity and anxiety- and depression-like behavior in the PTZ-kindled mice was also assessed. To understand the possible mechanisms of anticonvulsant activity of pterostilbene, γ-aminobutyric acid (GABA) and glutamate concentrations in the prefrontal cortex and hippocampus of the PTZ-kindled mice were measured using LC-MS/MS method. Moreover, mRNA expression of BDNF, TNF-α, IL-1β, IL-6, GABRA1A, and GRIN2B was determined by RT-qPCR technique.

RESULTS

We found that pterostilbene at a dose of 200 mg/kg considerably reduced seizure activity but did not influence the locomotor activity and depression- and anxiety-like behavior in the PTZ-kindled mice. In the prefrontal cortex and hippocampus, pterostilbene reversed the kindling-induced decrease of GABA concentration. Neither in the prefrontal cortex nor hippocampus pterostilbene affected mRNA expression of IL-1β, IL-6, GABRA1A, and GRIN2B augmented by PTZ kindling. Pterostilbene at a dose of 100 mg/kg significantly decreased BDNF and TNF-α mRNA expression in the hippocampus of the PTZ-kindled mice.

CONCLUSIONS

Although further studies are necessary to understand the mechanism of anticonvulsant properties of pterostilbene, our findings suggest that it might be considered a candidate for a new antiseizure drug.

Spatial and temporal patterns of nitric oxide diffusion and degradation drive emergent cerebrovascular dynamics

Nitric oxide (NO) is a gaseous signaling molecule that plays an important role in neurovascular coupling. NO produced by neurons diffuses into the smooth muscle surrounding cerebral arterioles, driving vasodilation. However, the rate of NO degradation in hemoglobin is orders of magnitude higher than in brain tissue, though how this might impact NO signaling dynamics is not completely understood. We used simulations to investigate how the spatial and temporal patterns of NO generation and degradation impacted dilation of a penetrating arteriole in cortex. We found that the spatial location of NO production and the size of the vessel both played an important role in determining its responsiveness to NO. The much higher rate of NO degradation and scavenging of NO in the blood relative to the tissue drove emergent vascular dynamics. Large vasodilation events could be followed by post-stimulus constrictions driven by the increased degradation of NO by the blood, and vasomotion-like 0.1-0.3 Hz oscillations could also be generated. We found that these dynamics could be enhanced by elevation of free hemoglobin in the plasma, which occurs in diseases such as malaria and sickle cell anemia, or following blood transfusions. Finally, we show that changes in blood flow during hypoxia or hyperoxia could be explained by altered NO degradation in the parenchyma. Our simulations suggest that many common vascular dynamics may be emergent phenomena generated by NO degradation by the blood or parenchyma.

Genomic signatures of domestication in Old World camels

Domestication begins with the selection of animals showing less fear of humans. In most domesticates, selection signals for tameness have been superimposed by intensive breeding for economical or other desirable traits. Old World camels, conversely, have maintained high genetic variation and lack secondary bottlenecks associated with breed development. By re-sequencing multiple genomes from dromedaries, Bactrian camels, and their endangered wild relatives, here we show that positive selection for candidate genes underlying traits collectively referred to as 'domestication syndrome' is consistent with neural crest deficiencies and altered thyroid hormone-based signaling. Comparing our results with other domestic species, we postulate that the core set of domestication genes is considerably smaller than the pan-domestication set - and overlapping genes are likely a result of chance and redundancy. These results, along with the extensive genomic resources provided, are an important contribution to understanding the evolutionary history of camels and the genomic features of their domestication.

Retinal exposure to high glucose condition modifies the GABAergic system: Regulation by nitric oxide

Diabetic retinopathy is a severe retinal complication that diabetic patients are susceptible to present. Although this disease is currently characterized as a microvascular disease, there is growing evidence that neural changes occur and maybe precede vascular impairments. Using chicken retina, an avascular tissue with no direct contact with blood vessels and neural retina, this study aimed to evaluate the influence of acute exposure to high glucose concentration in the retinal GABAergic system, and the role of nitric oxide (NO) in this modulation. Therefore, in ex vivo experiments, retinas were incubated in control (10 mM glucose) or high glucose condition (35 mM) for 30 min. By using DAF-FM to evaluate NO production, it was possible to show that high glucose (HG) significantly increased NO levels in the outer nuclear layer, inner nuclear layer (outer and inner portion), and inner plexiform layer. It was also observed that HG increased GABA immunoreactivity (IR) in amacrine and horizontal cells. HG did not change glutamic acid decarboxylase-IR, whereas it decreased GABA Transporter (GAT) 1-IR and increased GAT-3-IR. The co-treatment with 7-NI, an inhibitor of neuronal nitric oxide synthase (nNOS), blocked all changes stimulated by HG exposure. The concomitant exposure with SNAP-5114, a GAT-2/3 inhibitor, blocked the increase in GABA-IR caused by HG incubation. Therefore, our data suggest that hyperglycemia induces GABA accumulation in the cytosol by modulating GABA transporters. This response is dependent on NO production and signaling.

Umbilical Cord Blood NOS1 as a Potential Biomarker of Neonatal Encephalopathy

BACKGROUND

There are no definitive markers to aid in diagnosis of neonatal encephalopathy (NE). The purpose of our study was (1) to identify and evaluate the utility of neuronal nitric oxide synthase (NOS1) in umbilical cord blood as a NE biomarker and (2) to identify the source of NOS1 in umbilical cord blood.

METHODS

This was a nested case-control study of neonates >35 weeks of gestation. ELISA for NOS1 in umbilical cord blood was performed. Sources of NOS1 in umbilical cord were investigated by immunohistochemistry, western blot, ELISA, and quantitative PCR. Furthermore, umbilical cords of full-term neonates were subjected to 1% hypoxia ex vivo.

RESULTS

NOS1 was present in umbilical cord blood and increased in NE cases compared with controls. NOS1 was expressed in endothelial cells of the umbilical cord vein, but not in artery or blood cells. In ex vivo experiments, hypoxia was associated with increased levels of NOS1 in venous endothelial cells of the umbilical cord as well as in ex vivo culture medium.

CONCLUSION

This is the first study to investigate an early marker of NE. NOS1 is elevated with hypoxia, and further studies are needed to investigate it as a valuable tool for early diagnosis of neonatal brain injury.

A multilevel prediction of physiological response to challenge: Interactions among child maltreatment, neighborhood crime, endothelial nitric oxide synthase gene (eNOS), and GABA(A) receptor subunit alpha-6 gene (GABRA6)

Physiological response to stress has been linked to a variety of healthy and pathological conditions. The current study conducted a multilevel examination of interactions among environmental toxins (i.e., neighborhood crime and child maltreatment) and specific genetic polymorphisms of the endothelial nitric oxide synthase gene (eNOS) and GABA(A) receptor subunit alpha-6 gene (GABRA6). One hundred eighty-six children were recruited at age 4. The presence or absence of child maltreatment as well as the amount of crime that occurred in their neighborhood during the previous year were determined at that time. At age 9, the children were brought to the lab, where their physiological response to a cognitive challenge (i.e., change in the amplitude of the respiratory sinus arrhythmia) was assessed and DNA samples were collected for subsequent genotyping. The results confirmed that complex Gene × Gene, Environment × Environment, and Gene × Environment interactions were associated with different patterns of respiratory sinus arrhythmia reactivity. The implications for future research and evidence-based intervention are discussed.

Regulation of brain glutamate metabolism by nitric oxide and S-nitrosylation

Nitric oxide (NO) is a signaling intermediate during glutamatergic neurotransmission in the central nervous system (CNS). NO signaling is in part accomplished through cysteine S-nitrosylation, a posttranslational modification by which NO regulates protein function and signaling. In our investigation of the protein targets and functional impact of S-nitrosylation in the CNS under physiological conditions, we identified 269 S-nitrosocysteine residues in 136 proteins in the wild-type mouse brain. The number of sites was significantly reduced in the brains of mice lacking endothelial nitric oxide synthase (eNOS(-/-)) or neuronal nitric oxide synthase (nNOS(-/-)). In particular, nNOS(-/-) animals showed decreased S-nitrosylation of proteins that participate in the glutamate/glutamine cycle, a metabolic process by which synaptic glutamate is recycled or oxidized to provide energy. (15)N-glutamine-based metabolomic profiling and enzymatic activity assays indicated that brain extracts from nNOS(-/-) mice converted less glutamate to glutamine and oxidized more glutamate than those from mice of the other genotypes. GLT1 [also known as EAAT2 (excitatory amino acid transporter 2)], a glutamate transporter in astrocytes, was S-nitrosylated at Cys(373) and Cys(561) in wild-type and eNOS(-/-) mice, but not in nNOS(-/-) mice. A form of rat GLT1 that could not be S-nitrosylated at the equivalent sites had increased glutamate uptake compared to wild-type GLT1 in cells exposed to an S-nitrosylating agent. Thus, NO modulates glutamatergic neurotransmission through the selective, nNOS-dependent S-nitrosylation of proteins that govern glutamate transport and metabolism.

Nitric oxide in the nervous system: biochemical, developmental, and neurobiological aspects

Nitric oxide (NO) is a very reactive molecule, and its short half-life would make it virtually invisible until its discovery. NO activates soluble guanylyl cyclase (sGC), increasing 3',5'-cyclic guanosine monophosphate levels to activate PKGs. Although NO triggers several phosphorylation cascades due to its ability to react with Fe II in heme-containing proteins such as sGC, it also promotes a selective posttranslational modification in cysteine residues by S-nitrosylation, impacting on protein function, stability, and allocation. In the central nervous system (CNS), NO synthesis usually requires a functional coupling of nitric oxide synthase I (NOS I) and proteins such as NMDA receptors or carboxyl-terminal PDZ ligand of NOS (CAPON), which is critical for specificity and triggering of selected pathways. NO also modulates CREB (cAMP-responsive element-binding protein), ERK, AKT, and Src, with important implications for nerve cell survival and differentiation. Differences in the regulation of neuronal death or survival by NO may be explained by several mechanisms involving localization of NOS isoforms, amount of NO being produced or protein sets being modulated. A number of studies show that NO regulates neurotransmitter release and different aspects of synaptic dynamics, such as differentiation of synaptic specializations, microtubule dynamics, architecture of synaptic protein organization, and modulation of synaptic efficacy. NO has also been associated with synaptogenesis or synapse elimination, and it is required for long-term synaptic modifications taking place in axons or dendrites. In spite of tremendous advances in the knowledge of NO biological effects, a full description of its role in the CNS is far from being completely elucidated.

Brain kinin B₁ receptor contributes to the onset of stereotypic nocifensive behavior in rat

While brain kinin B(1) receptor (B(1)R) is virtually absent in control rats, it contributes to hypertension via a midbrain dopaminergic (DA) mechanism in spontaneously hypertensive rat (SHR) and Angiotensin II (Ang II)-induced hypertension. This study aims at determining whether B(1)R can also affect stereotypic nocifensive behavior through DA and/or other neuromediators in the same models. The selective B(1)R agonist Sar[D-Phe(8)][des-Arg(9)]BK was injected i.c.v. (1 μg/site) to freely behaving SHR (16 weeks), Ang II-hypertensive rats (200 ng/kg/min × 2 weeks, s.c.) and control Wistar-Kyoto rats (WKY). Behavioral activity to the agonist was measured before and after treatment with receptor antagonists (10 μg/site i.c.v. or otherwise stated) for B(1) (SSR240612), tachykinin NK(1) (RP67580), glutamate NMDA (DL-AP5), DA D(1) (SCH23390, 0.2mg/kg s.c.) and D(2) (Raclopride, 0.16 mg/kg s.c.). Other studies included inhibitors (10 μg/site) of NOS (l-NNA) and iNOS (1400W). The possible desensitisation of B(1)R upon repeated intracerebral stimulation was also excluded. B(1)R expression was measured by qRT-PCR in selected areas and by immunohistochemistry in the ventral tegmental area. Results showed that the B(1)R agonist had no effect in WKY, yet it induced nocifensive behavioral manifestations in both models of hypertension (face washing, sniffing, head scratching, rearing, teeth chattering, grooming, digging, licking, wet-dog shakes). These responses were prevented by all antagonists and inhibitors tested, but 1400 W had a less inhibitory effect on most behaviors. Compared with WKY, B(1)R mRNA levels were markedly enhanced in hypothalamus, ventral tegmental area and nucleus accumbens of SHR and Ang II-treated rats. B(1)R was detected on DA neuron of the ventral tegmental area in SHR. Data suggest that kinin B(1)R is upregulated in midbrain DA system in hypertensive rats and its i.c.v. activation induced stereotypic nocifensive behavior that is mediated by several mediators, notably substance P, glutamate, DA and NO.

Long-term daily access to alcohol alters dopamine-related synthesis and signaling proteins in the rat striatum

Chronic alcohol exposure can adversely affect neuronal morphology, synaptic architecture and associated neuroplasticity. However, the effects of moderate levels of long-term alcohol intake on the brain are a matter of debate. The current study used 2-DE (two-dimensional gel electrophoresis) proteomics to examine proteomic changes in the striatum of male Wistar rats after 8 months of continuous access to a standard off-the-shelf beer in their home cages. Alcohol intake under group-housed conditions during this time was around 3-4 g/kg/day, a level below that known to induce physical dependence in rats. After 8 months of access rats were euthanased and 2-DE proteomic analysis of the striatum was conducted. A total of 28 striatal proteins were significantly altered in the beer drinking rats relative to controls. Strikingly, many of these were dopamine (DA)-related proteins, including tyrosine hydroxylase (an enzyme of DA biosynthesis), pyridoxal phosphate phosphatase (a co-enzyme in DA biosynthesis), DA and cAMP regulating phosphoprotein (a regulator of DA receptors and transporters), protein phosphatase 1 (a signaling protein) and nitric oxide synthase (which modulates DA uptake). Selected protein expression changes were verified using Western blotting. We conclude that long-term moderate alcohol consumption is associated with substantial alterations in the rat striatal proteome, particularly with regard to dopaminergic signaling pathways. This provides potentially important evidence of major neuroadaptations in dopamine systems with daily alcohol consumption at relatively modest levels.

Correlation between hippocampal levels of neural, epithelial and inducible NOS and spatial learning skills in rats

In the present study, to better understand the role of different nitric oxide synthase (NOS) isoforms in hippocampus-dependent forms of learning, we examined the expression of neural, endothelial, and inducible NOS in the hippocampus of young-adult rats classified as "poor" and "good" learners on the basis of their performance in the partially baited 12-arm radial maze. Taking into consideration strain-dependent differences in learning skills and NOS expression, experiments were performed on two different lines of laboratory rats: the inbred Wistar (W) and the outcrossed Wistar/Spraque-Dawley (W/S) line. The hippocampal levels of NOS proteins were assessed by Western Blotting. In the present study, genetically more homogenous W rats showed a slower rate of learning compared to the genetically less homogenous outcrossed W/S rats. The deficient performance in the W rat group compared to outcrossed W/S rats, and in "poor" learners of both groups compared to "good" learners was due to a higher percentage of reference memory errors. The overall NOS levels were significantly higher in W group compared to outcrossed W/S rats. In both rat lines, the rate of learning positively correlated with hippocampal levels of nNOS and negatively correlated with iNOS levels. Hippocampal eNOS levels correlated negatively with animals' performance but only in the W rats. These results suggest that all 3 NOS isoforms are implemented but play different roles in neural signaling.

Role of endothelial nitric oxide in cerebrovascular regulation

Endothelial nitric oxide (NO) plays important roles in the vascular system. Animal models that show vascular dysfunction demonstrate the protective role of endothelial NO dependent pathways. This review focuses on the role of endothelial NO in the regulation of cerebral blood flow and vascular tone. We will discuss the importance of NO in cerebrovascular function using animal models with altered endothelial NO production under normal, ischemic and reperfusion conditions, as well as in hyperoxia. Pharmacological and genetic manipulations of the endothelial NO system demonstrate the essential roles of endothelial NO synthase in maintenance of vascular tone and cerebral perfusion under normal and pathological conditions.

Long-Range GABAergic Connections Distributed throughout the Neocortex and their Possible Function

Features and functions of long-range GABAergic projection neurons in the developing cerebral cortex have been reported previously, although until now their significance in the adult cerebral cortex has remained uncertain. The septo-hippocampal circuit is one exception – in this system, long-range mature GABAergic projection neurons have been well analyzed and their contribution to the generation of theta-oscillatory behavior in the hippocampus has been documented. To have a clue to the function of the GABAergic projection neurons in the neocortex, we view how the long-range GABAergic projections are integrated in the cortico-cortical, cortico-fugal, and afferent projections in the cerebral cortex. Then, we consider the possibility that the GABAergic projection neurons are involved in the generation, modification, and/or synchronization of oscillations in mature neocortical neuron activity. When markers that identify the GABAergic projection neurons are examined in anatomical and developmental studies, it is clear that neuronal NO synthetase (nNOS)-immunoreactivity can readily identify GABAergic projection neurons. GABAergic projection neurons account for 0.5% of the neocortical GABAergic neurons. To elucidate the role of the GABAergic projection neurons in the neocortex, it will be necessary to clarify the network constructed by nNOS-positive GABAergic projection neurons and their postsynaptic targets. Thus, our long-range goals will be to label and manipulate (including deleting) the GABAergic projection neurons using genetic tools driven by a nNOS promoter. We recognize that this may be a complex endeavor, as most excitatory neurons in the murine neocortex express nNOS transiently. Nevertheless, additional studies characterizing long-range GABAergic projection neurons will have great value to the overall understanding of mature cortical function.

In vivo effects of antibodies from patients with anti-NMDA receptor encephalitis: further evidence of synaptic glutamatergic dysfunction

Background

A severe encephalitis that associates with auto-antibodies to the NR1 subunit of the NMDA receptor (NMDA-R) was recently reported. Patients' antibodies cause a decrease of the density of NMDA-R and synaptic mediated currents, but the in vivo effects on the extracellular glutamate and glutamatergic transmission are unknown.

Methods

We investigated the acute metabolic effects of patients' CSF and purified IgG injected in vivo. Injections were performed in CA1 area of Ammon's horn and in premotor cortex in rats.

Results

Patient's CSF increased the concentrations of glutamate in the extracellular space. The increase was dose-dependent and was dramatic with purified IgG. Patients' CSF impaired both the NMDA- and the AMPA-mediated synaptic regulation of glutamate, and did not affect the glial transport of glutamate. Blockade of GABA-A receptors was associated with a marked elevation of extra-cellular levels of glutamate following a pretreatment with patients' CSF.

Conclusion

These results support a direct role of NMDA-R antibodies upon altering glutamatergic transmission. Furthermore, we provide additional evidence in vivo that NMDA-R antibodies deregulate the glutamatergic pathways and that the encephalitis associated with these antibodies is an auto-immune synaptic disorder.

Intraesophageal manganese superoxide dismutase-plasmid liposomes ameliorates novel total-body and thoracic radiation sensitivity of NOS1-/- mice

The effect of deletion of the nitric oxide synthase 1 gene (NOS1(-/-)) on radiosensitivity was determined. In vitro, long-term cultures of bone marrow stromal cells derived from NOS1(-/-) were more radioresistant than cells from C57BL/6NHsd (wild-type), NOS2(-/-) or NOS3(-/-) mice. Mice from each strain received 20 Gy thoracic irradiation or 9.5 Gy total-body irradiation (TBI), and NOS1(-/-) mice were more sensitive to both. To determine the etiology of radiosensitivity, studies of histopathology, lower esophageal contractility, gastrointestinal transit, blood counts, electrolytes and inflammatory markers were performed; no significant differences between irradiated NOS1(-/-) and control mice were found. Video camera surveillance revealed the cause of death in NOS1(-/-) mice to be grand mal seizures; control mice died with fatigue and listlessness associated with low blood counts after TBI. NOS1(-/-) mice were not sensitive to brain-only irradiation. MnSOD-PL therapy delivered to the esophagus of wild-type and NOS1(-/-) mice resulted in equivalent biochemical levels in both; however, in NOS1(-/-) mice, MnSOD-PL significantly increased survival after both thoracic and total-body irradiation. The mechanism of radiosensitivity of NOS1(-/-) mice and its reversal by MnSOD-PL may be related to the developmental esophageal enteric neuronal innervation abnormalities described in these mice.

Nitric Oxide Synthase Inhibitors as Antidepressants

Affective and anxiety disorders are widely distributed disorders with severe social and economic effects. Evidence is emphatic that effective treatment helps to restore function and quality of life. Due to the action of most modern antidepressant drugs, serotonergic mechanisms have traditionally been suggested to play major roles in the pathophysiology of mood and stress-related disorders. However, a few clinical and several pre-clinical studies, strongly suggest involvement of the nitric oxide (NO) signaling pathway in these disorders. Moreover, several of the conventional neurotransmitters, including serotonin, glutamate and GABA, are intimately regulated by NO, and distinct classes of antidepressants have been found to modulate the hippocampal NO level in vivo. The NO system is therefore a potential target for antidepressant and anxiolytic drug action in acute therapy as well as in prophylaxis. This paper reviews the effect of drugs modulating NO synthesis in anxiety and depression.

Concepts of neural nitric oxide-mediated transmission

As a chemical transmitter in the mammalian central nervous system, nitric oxide (NO) is still thought a bit of an oddity, yet this role extends back to the beginnings of the evolution of the nervous system, predating many of the more familiar neurotransmitters. During the 20 years since it became known, evidence has accumulated for NO subserving an increasing number of functions in the mammalian central nervous system, as anticipated from the wide distribution of its synthetic and signal transduction machinery within it. This review attempts to probe beneath those functions and consider the cellular and molecular mechanisms through which NO evokes short- and long-term modifications in neural performance. With any transmitter, understanding its receptors is vital for decoding the language of communication. The receptor proteins specialised to detect NO are coupled to cGMP formation and provide an astonishing degree of amplification of even brief, low amplitude NO signals. Emphasis is given to the diverse ways in which NO receptor activation initiates changes in neuronal excitability and synaptic strength by acting at pre- and/or postsynaptic locations. Signalling to non-neuronal cells and an unexpected line of communication between endothelial cells and brain cells are also covered. Viewed from a mechanistic perspective, NO conforms to many of the rules governing more conventional neurotransmission, particularly of the metabotropic type, but stands out as being more economical and versatile, attributes that presumably account for its spectacular evolutionary success.

Nitric oxide signaling in the medial prefrontal cortex is involved in the biochemical and behavioral effects of phencyclidine

The prefrontal cortex (PFC) is believed to play an important role in the cognitive impairments observed in schizophrenia and has also been shown to be involved in the modulation of prepulse inhibition (PPI), a measure of preattentive information processing that is impaired in schizophrenic individuals. Phencyclidine (PCP), a noncompetitive inhibitor of the NMDA receptor, exerts psychotomimetic effects in humans, disrupts PPI, and causes hypofrontality in rodents and monkeys. We have previously demonstrated that interfering with the production of nitric oxide (NO) can prevent a wide range of PCP-induced behavioral deficits, including PPI disruption. In the present study, the role of NO signaling for the behavioral and biochemical effects of PCP was further investigated. Dialysate from the medial PFC of mice receiving systemic treatment with PCP and/or the NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME, 40 mg/kg), was analyzed for cGMP content. Furthermore, a specific inhibitor of NO-sensitive soluble guanylyl cyclase (sGC), 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ, 0.01-1 mM), was administered into the medial PFC of mice in combination with systemic injections of PCP, followed by PPI and locomotor activity testing. PCP (5 mg/kg) caused an increase in prefrontal cGMP that could be attenuated by pretreatment with the NO synthase inhibitor, L-NAME. Moreover, bilateral microinjection of the sGC inhibitor, ODQ, into the medial PFC of mice attenuated the disruption of PPI, but not the hyperlocomotion, caused by PCP. The present study shows that NO/sGC/cGMP signaling pathway in the medial PFC is involved in specific behavioral effects of PCP that may have relevance for the disabling cognitive dysfunction found in patients with schizophrenia.

NO/cGMP-dependent modulation of synaptic transmission

Nitric oxide (NO) is a multifunctional messenger in the CNS that can signal both in antero- and retrograde directions across synapses. Many effects of NO are mediated through its canonical receptor, the soluble guanylyl cyclase, and the second messenger cyclic guanosine-3',5'-monophosphate (cGMP). An increase of cGMP can also arise independently of NO via activation of membrane-bound particulate guanylyl cyclases by natriuretic peptides. The classical targets of cGMP are cGMP-dependent protein kinases (cGKs), cyclic nucleotide hydrolysing phosphodiesterases, and cyclic nucleotide-gated (CNG) cation channels. The NO/cGMP/cGK signalling cascade has been linked to the modulation of transmitter release and synaptic plasticity by numerous pharmacological and genetic studies. This review focuses on the role of NO as a retrograde messenger in long-term potentiation of transmitter release in the hippocampus. Presynaptic mechanisms of NO/cGMP/cGK signalling will be discussed with recently identified potential downstream components such as CaMKII, the vasodilator-stimulated phosphoprotein, and regulators of G protein signalling. NO has further been suggested to increase transmitter release through presynaptic clustering of a-synuclein. Alternative modes of NO/cGMP signalling resulting in inhibition of transmitter release and long-term depression of synaptic activity will also be addressed, as well as anterograde NO signalling in the cerebellum. Finally, emerging evidence for cGMP signalling through CNG channels and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels will be discussed.

Long-range GABAergic projection neurons in the cat neocortex

Neocortical gamma-aminobutyric acid (GABA)ergic neurons have been previously described as largely involved in local intracortical circuitry. However, our recent findings in the murine model described select neocortical GABAergic neurons that project to both neighboring and more distant neocortical regions. Here, we investigated whether such GABAergic projection neurons are also found in the cat neocortex. Wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) was injected into the visual, auditory, or somatosensory cortex, in order to label efferent cortical neurons retrogradely and to label axons and terminals orthogradely. Staining for nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d), an enzyme involved in nitric oxide synthesis, was employed, and co-localization with WGA-HRP was determined by means of both polarizing and brightfield microscopy. We concluded that neurons double-labeled with WGA-HRP and NADPH-d in a distant region from the WGA-HRP-injection site are GABAergic neurons with long-range projection axons. All double-labeled neurons were found in cortical layers VIa and VIb and in the white matter. Neurons with intense NADPH-d reactivity (type I) were determined to be neuronal nitric oxide synthase (nNOS) positive in all cases. However, weakly NADPH-d-reactive neurons (type II) lacked nNOS immunoreactivity. Moreover, nNOS often co-localized with GABA, neuropeptide-Y, and somatostatin in the cat neocortex. In summary, the GABAergic neurons described here projected in a manner similar to that previously described for neocortical principal neurons, although some unique GABAergic long-range projections were also demonstrated.

Tonic and phasic nitric oxide signals in hippocampal long-term potentiation

Nitric oxide (NO) participates in long-term potentiation (LTP) and other forms of synaptic plasticity in many different brain areas but where it comes from and how it acts remain controversial. Using rat and mouse hippocampal slices, we tested the hypothesis that tonic and phasic NO signals are needed and that they derive from different NO synthase isoforms. NMDA increased NO production in a manner that was potently inhibited by three different neuronal NO synthase (nNOS) inhibitors. Tonic NO could be monitored after sensitizing guanylyl cyclase-coupled NO receptors, allowing the very low ambient NO concentrations to be detected by cGMP measurement. The levels were unaffected by inhibition of NMDA receptors, nNOS, or the inducible NO synthase (iNOS). iNOS was also undetectable in protein or activity assays. Tonic NO was susceptible to agents inhibiting endothelial NO synthase (eNOS) and was missing in eNOS knock-out mice. The eNOS knock-outs exhibited a deficiency in LTP resembling that seen in wild-types treated with a NO synthase inhibitor. LTP in the knock-outs could be fully restored by supplying a low level of NO exogenously. Inhibition of nNOS also caused a major loss of LTP, particularly of late-LTP. Again, exogenous NO could compensate, but higher concentrations were needed compared with those restoring LTP in the eNOS knock-outs. It is concluded that tonic and phasic NO signals are both required for hippocampal LTP and the two are generated, respectively, by eNOS and nNOS, the former in blood vessels and the latter in neurons.

mRNA and protein expression and activities of nitric oxide synthases in the lumbar spinal cord of neonatal rats after sciatic nerve transection and melatonin administration

Sciatic axotomy in 2-day-old rats (P2) causes lumbar motoneuron loss, which could be associated with nitric oxide (NO) production. NO may be produced by three isoforms of synthase (NOS): neuronal (nNOS), endothelial (eNOS) and inducible (iNOS). We investigated NOS expression and NO synthesis in the lumbar enlargement of rats after sciatic nerve transection at P2 and treatment with the antioxidant melatonin (sc; 1 mg/kg). At time points ranging from P2 to P7, expression of each isoform was assessed by RT-PCR and immunohistochemistry; catalytic rates of calcium-dependent (nNOS, eNOS) and independent (iNOS) NOS were measured by the conversion of [3H]L-arginine to [3H]L-citrulline. All NOS isoforms were expressed and active in unlesioned animals. nNOS and iNOS were detected in some small cells in the parenchyma. Only endothelial cells were positive for eNOS. No NOS isoform was detected in motoneurons. Axotomy did not change these immunohistochemical findings, nNOS and iNOS mRNA expression and calcium-independent activity at all survival times. However, sciatic nerve transection reduced eNOS mRNA levels at P7 and increased calcium-dependent activity at 1 and 6 h. Melatonin did not alter NOS expression. Despite having no action on NOS activity in unlesioned controls the neurohormone enhanced calcium-dependent activity at 1 and 72 h and reduced calcium-independent catalysis at 72 h in lesioned rats. These results suggest that NOS isoforms are constitutive in the neonatal lumbar enlargement and are not overexpressed after sciatic axotomy. Changes in NO synthesis induced by axotomy and melatonin administration in the current model are discussed considering some beneficial and deleterious effects that NO may have.

Endothelial NO Synthase Activity in Nucleus Tractus Solitarii Contributes to Hypertension in Spontaneously Hypertensive Rats

NO is implicated as a major modulator of central nervous circuits regulating cardiovascular activity. Based on previous data, we hypothesized that overactivity of endothelial NO synthase (eNOS) within the nucleus tractus solitarii (NTS) could contribute to the hypertension in the spontaneously hypertensive rat (SHR). Using real-time PCR, we found that endogenous eNOS mRNA was greater in the NTS of mature, but not juvenile prehypertensive SHRs compared with aged-matched Wistar Kyoto (WKY) rats. To test the functional significance of this, we chronically blocked eNOS activity in the NTS in the adult SHR by in vivo adenoviral-mediated gene transfer of a dominant-negative form of eNOS; data were compared with WKY rats. This resulted in a fall in arterial pressure in the SHR but not WKY rats. In both rat strains, cardiac baroreceptor reflex gain and the high-frequency spectral component of heart rate variability increased. Thus, endogenous eNOS activity in the NTS plays a major role in determining the set point of arterial pressure in the SHR and contributes to maintaining high arterial blood pressure in this animal model of human hypertension.

Signaling from blood vessels to CNS axons through nitric oxide

Brain function is usually perceived as being performed by neurons with the support of glial cells, the network of blood vessels situated nearby serving simply to provide nutrient and to dispose of metabolic waste. Revising this view, we find from experiments on a rodent central white matter tract (the optic nerve) in vitro that microvascular endothelial cells signal persistently to axons using nitric oxide (NO) derived from the endothelial NO synthase (eNOS). The endogenous NO acts to stimulate guanylyl cyclase-coupled NO receptors in the axons, leading to a raised cGMP level which then causes membrane depolarization, apparently by directly engaging hyperpolarization-activated cyclic nucleotide-gated ion channels. The tonic depolarization and associated endogenous NO-dependent cGMP generation was absent in optic nerves from mice lacking eNOS, although such nerves responded to exogenous NO, with raised cGMP generation in the axons and associated depolarization. In addition to the tonic activity, exposure of optic nerves to bradykinin, a classical stimulator of eNOS in endothelial cells, elicited reversible NO- and cGMP-dependent depolarization through activation of bradykinin B2 receptors, to which eNOS is physically complexed. No contribution of other NO synthase isoforms to either the action of bradykinin or the continuous ambient NO level could be detected. The results suggest that microvascular endothelial cells participate in signal processing in the brain and can do so by generating both tonic and phasic NO signals.

New insights on brain stem death: From bedside to bench

As much as brain stem death is currently the clinical definition of death in many countries and is a phenomenon of paramount medical importance, there is a dearth of information on its mechanistic underpinnings. A majority of the clinical studies are concerned only with methods to determine brain stem death. Whereas a vast amount of information is available on the cellular and molecular mechanisms of cell death, rarely are these studies directed specifically towards the understanding of brain stem death. This review presents a framework for translational research on brain stem death that is based on systematically coordinated clinical and laboratory efforts that center on this phenomenon. It begins with the identification of a novel clinical marker from patients that is related specifically to brain stem death. After realizing that this "life-and-death" signal is related to the functional integrity of the brain stem, its origin is traced to the rostral ventrolateral medulla (RVLM). Subsequent laboratory studies on this neural substrate in animal models of brain stem death provide credence to the notion that both "pro-life" and "pro-death" programs are at work during the progression towards death. Those programs (mitochondrial functions, nitric oxide, peroxynitrite, superoxide anion, coenzyme Q10, heat shock proteins and ubiquitin-proteasome system) hitherto identified from the RVLM are presented, along with their cellular and molecular mechanisms. It is proposed that outcome of the interplay between the "pro-life" and "pro-death" programs (dying) in this neural substrate determines the final fate of the individual (being dead). Thus, identification of additional programs in the RVLM and delineation of their regulatory mechanisms should shed new lights on future directions for clinical management of life-and-death.

Demonstration of long-range GABAergic connections distributed throughout the mouse neocortex

Gamma-aminobutyric acid (GABA)ergic neurons in the neocortex have been mainly regarded as interneurons and thought to provide local interactions. Recently, however, glutamate decarboxylase (GAD) immunocytochemistry combined with retrograde labeling experiments revealed the existence of GABAergic projection neurons in the neocortex. We further studied the network of GABAergic projection neurons in the neocortex by using GAD67-green fluorescent protein (GFP) knock-in mice for retrograde labeling and a novel neocortical GABAergic neuron labeling method for axon tracing. Many GFP-positive neurons were retrogradely labeled after Fast Blue injection into the primary somatosensory, motor and visual cortices. These neurons were labeled not only around the injection site, but also at a long distance from the injection site. Of the retrogradely labeled GABAergic neurons remote from the injection sites, the vast majority (91%) exhibited somatostatin immunoreactivity, and were preferentially distributed in layer II, layer VI and in the white matter. In addition, most of GABAergic projection neurons were positive for neuropeptide Y (82%) and neuronal nitric oxide synthase (71%). We confirmed the long-range projections by tracing GFP-labeled GABAergic neurons with axon branches traveled rostro-caudally and medio-laterally. Axon branches could be traced up to 2 mm. Some (n = 2 of 4) were shown to cross the areal boundaries. The GABAergic projection neurons preferentially received neocortical inputs. From these results, we conclude that GABAergic projection neurons are distributed throughout the neocortex and are part of a corticocortical network.

The spinal nitric oxide involved in the inhibitory effect of midazolam on morphine-induced analgesia tolerance

Previous studies had shown that pretreatment with midazolam inhibited morphine-induced tolerance and dependence. The present study was to investigate the role of spinal nitric oxide (NO) in the inhibitory effect of midazolam on the development of morphine-induced analgesia tolerance. Subcutaneous injection of 100 mg/kg morphine to mice caused an acute morphine-induced analgesia tolerance model. To develop chronic morphine tolerance in mice, morphine was injected for three consecutive days (10, 20, 50 mg/kg sc on Day 1, 2, 3, respectively). In order to develop chronic tolerance model in rats, 10 mg/kg of morphine was given twice daily at 12 h intervals for 10 days. Midazolam was intraperitoneally injected 30 min prior to administration of morphine. Tail-flick test, hot-plate and formalin test were conducted to assess the nociceptive response. Immunocytochemistry, histochemistry and western blot were performed to determine the effect of midazolam on formalin-induced expression of Fos protein, nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) and nitric oxide synthase (NOS) in chronic morphine-tolerant rats, respectively. The results showed that pretreatment with midazolam significantly inhibited the development of acute and chronic morphine tolerance in mice, which could be partially reversed by intrathecal injection of NO precursor L-arginine (L-Arg). In chronic morphine-tolerant rats, pretreatment with midazolam significantly decreased the formalin-induced expression of Fos and Fos/NADPH-d double-labeled neurons in the contralateral spinal cord and NADPH-d positive neurons in the bilateral spinal cord. Both inducible NOS (iNOS) and neuronal NOS (nNOS) protein levels in the spinal cord were significantly increased after injection of formalin, which could be inhibited by pretreatment with midazolam. The above results suggested that the decrease of the activity and expression of NOS contributed to the inhibitory effect of midazolam on the development of morphine tolerance.

Enhanced release of synaptic glutamate underlies the potentiation of oxygen-glucose deprivation-induced neuronal injury after induction of NOS-2

Reactive nitrogen oxide species (RNOS) may contribute to the progression/enhancement of ischemic injury by augmentation of glutamate release, reduction of glutamate uptake, or a combination of both. Consistent with this, induction of nitric oxide synthase (NOS-2) in murine neocortical cell cultures potentiated neuronal cell death caused by combined oxygen-glucose deprivation in association with a net increase in extracellular glutamate accumulation. However, uptake of glutamate via high affinity, sodium-dependent glutamate transporters was unimpaired by induction of NOS-2 under either aerobic or anaerobic conditions. Further, blocking possible routes of extra-synaptic glutamate release with NPPB [5-nitro-2-(3-phenylpropylamino)-benzoic acid], a volume-sensitive organic anion channel blocker, or TBOA (d,l-threo-beta-benzyloxyaspartate), an inhibitor of glutamate transport, exacerbated rather than ameliorated injury. Finally, treatment with riluzole or tetanus toxin attenuated the enhancement in both glutamate accumulation and oxygen-glucose deprivation-induced neuronal injury supporting the idea that increased synaptic release of glutamate underlies, at least in part, the potentiation of neuronal injury by RNOS after NOS-2 induction.

Water deprivation increases the expression of neuronal nitric oxide synthase (nNOS) but not orexin-A in the lateral hypothalamic area of the rat

The discovery that the lateral hypothalamic area (LHA) might be important in modulating drinking behavior and fluid balance has led to numerous studies aimed at identifying the key neurotransmitters/neuromodulators and pathways involved. While past studies have demonstrated the presence of neuronal nitric oxide synthase (nNOS) within the LHA, its role in the regulation of fluid homeostasis is not known. In light of this, and the mounting evidence suggesting a role for nitric oxide in osmotic regulation within the hypothalamus, this study sought to determine the effects of 24- and 72-hours of water deprivation on nNOS protein expression within the LHA of the rat with immunohistochemistry. In euhydrated control animals we observed nNOS-like immunoreactivity throughout all levels of the LHA. Following 24 hours of dehydration the number of nNOS-like immunopositive neurons was significantly increased in the rostral but not the caudal regions of LHA. Seventy-two hours of water deprivation lead to further increases in nNOS-like immunoreactivity at different levels of the LHA. Interestingly, however, we observed increased nNOS-like immunoreactivity in the caudal regions of the LHA that was not evident after 24 hours of water deprivation. Double-labeling immunofluorescence histochemistry revealed that the nNOS-like immunoreactive neurons were not colocalized with the orexin-A-containing neurons. These results suggest that an osmotic challenge leads to an upregulation of nNOS immunoreactivity within discrete areas of the LHA. This altered neurochemistry within the LHA further highlights the potential importance of nitric oxide and the LHA in central regulation of fluid homeostasis.

Phencyclidine-induced behaviour in mice prevented by methylene blue

Schizophrenia is a major public health problem that affects approximately 1% of the population worldwide. Schizophrenia-like symptoms can be induced in humans by phencyclidine (PCP), a drug with marked psychotomimetic properties. Phencyclidine disrupts prepulse inhibition of acoustic startle in rodents, a measure which has also been shown to be disrupted in schizophrenic patients. This effect is blocked by nitric oxide synthase (NOS) inhibitors, suggesting that nitric oxide plays an important role in this effect of phencyclidine. Methylene blue, a guanylate cyclase and nitric oxide syntase inhibitor, has shown therapeutic value as an adjuvant to conventional antipsychotics in the therapy of schizophrenia. The aim of the present study was to investigate if phencyclidine-(4 mg/kg)induced disruption of prepulse inhibition could be affected by methylene blue (50 or 100 mg/kg) in mice. Furthermore, the effect of methylene blue (50 mg/kg) on phencyclidine-(4 mg/kg)induced hyperlocomotion was investigated. The present study shows that phencyclidine readily disrupts prepulse inhibition in mice without affecting pulse-alone trials. It was also found that methylene blue prevents the decrease in prepulse inhibition caused by phencyclidine in a dose-related manner. Furthermore, the increase in locomotor activity caused by phencyclidine was reduced by pretreatment with methylene blue. The results from the present study further support the suggestion that the nitric oxide synthase/guanylate cyclase pathway is involved in pharmacological and behavioural effects of phencyclidine. Since phencyclidine as well exerts psychotomimetic characteristics, agents that interfere with the nitric oxide synthase/guanylate cyclase pathway may be of therapeutic value also in the treatment of schizophrenia.

Cerebrovascular inflammation after brief episodic hypoxia: modulation by neuronal and endothelial nitric oxide synthase

Obstructive sleep apnea, apnea of prematurity, and sudden infant death syndrome are associated with a high risk of morbidity and mortality secondary to the neuronal and cerebrovascular consequences of the associated intermittent hypoxia. We hypothesized that episodic hypoxia (EH) promotes inflammation in the cerebral microcirculation and that nitric oxide (NO) produced by the endothelial and neuronal isoforms of NO synthase (eNOS and nNOS, respectively) modulates this response. Anesthetized and ventilated Swiss-Webster ND4 mice, wild-type mice, and NO synthase knockout mice were subjected to a 1-h period of EH (twelve 30-s periods of hypoxia every 5 min). Four, 24, or 48 h later, mice were reanesthetized for imaging of leukocyte dynamics in the cortical venular microcirculation by epifluorescence videomicroscopy through closed cranial windows. In Swiss-Webster ND4 mice, leukocyte adherence increased 2.1-fold at 4 h, 3.4-fold at 24 h, and 1.8-fold at 48 h relative to time-matched, normoxic controls; there was no evidence of delayed hippocampal CA1 pyramidal cell death. A similar response was noted in wild-type mice. However, in eNOS knockouts, leukocyte-endothelial cell adherence was elevated to 4.4-fold over baseline 24 h after EH, and a significant fraction of these animals showed evidence of delayed CA1 cell death. Conversely, in nNOS knockouts, no increase in adherence was noted at 24 h and CA1 viability remained unaffected. We conclude that NO derived from nNOS promotes an inflammatory response in the cerebrovascular microcirculation after short-term EH and that NO produced by eNOS blunts the extent of this response and exerts neuroprotective effects.

Secretagogue-stimulated pancreatic secretion is differentially regulated by constitutive NOS isoforms in mice

Nitric oxide (NO) and NO synthase (NOS) play controversial roles in pancreatic secretion. NOS inhibition reduces CCK-stimulated in vivo pancreatic secretion, but it is unclear which NOS isoform is responsible, because NOS inhibitors lack specificity and three NOS isoforms exist: neuronal (nNOS), endothelial (eNOS), and inducible (iNOS). Mice having individual NOS gene deletions were used to clarify the NOS species and cellular interactions influencing pancreatic secretion. In vivo secretion was performed in anesthetized mice by collecting extraduodenal pancreatic duct juice and measuring protein output. Nonselective NOS blockade was induced with N(omega)-nitro-L-arginine (L-NNA; 10 mg/kg). In vivo pancreatic secretion was maximal at 160 pmol.kg(-1).h(-1) CCK octapeptide (CCK-8) and was reduced by NOS blockade (45%) and eNOS deletion (44%). Secretion was unaffected by iNOS deletion but was increased by nNOS deletion (91%). To determine whether the influence of NOS on secretion involved nonacinar events, in vitro CCK-8-stimulated secretion of amylase from isolated acini was studied and found to be unaltered by NOS blockade and eNOS deletion. Influence of NOS on in vivo secretion was further examined with carbachol. Protein secretion, which was maximal at 100 nmol.kg(-1).h(-1) carbachol, was reduced by NOS blockade and eNOS deletion but unaffected by nNOS deletion. NOS blockade by L-NNA had no effect on carbachol-stimulated amylase secretion in vitro. Thus constitutive NOS isoforms can exert opposite effects on in vivo pancreatic secretion. eNOS likely plays a dominant role, because eNOS deletion mimics NOS blockade by inhibiting CCK-8 and carbachol-stimulated secretion, whereas nNOS deletion augments CCK-8 but not carbachol-stimulated secretion.

Further evidence for enhancing effects of NO on monosynaptic and polysynaptic spinal reflexes in cats

There are a number of studies on the effects of different NO donors and inhibitors on spinal cord with quite contradictory results. The aim of this study was to investigate the effects of sodium nitroprusside (SNP), a NO donor, and N(G)-nitro-L-arginine methyl ester (L-NAME), a nonselective NOS inhibitor, on monosynaptic and polysynaptic spinal reflexes in anesthetized and spinalized cats. After a dorsal laminectomy between L5 and S1, monosynaptic and polysynaptic spinal reflexes were evoked by stimulation of gastrocnemius nerves. Following control recordings, administration of L-NAME in 100, 200, 500 microM (local) and 10, 20, 50 mg/kg (i.v.) doses decreased significantly the monosynaptic and polysynaptic reflex amplitudes in a dose-dependent manner. Administration of SNP in 100, 200, 500 microM (local) and 100, 200, 500 microg/kg (i.v.) doses enhanced significantly the both reflex amplitudes in a dose-dependent manner. In another series of experiments it has been observed that the maximal decrease in reflex amplitudes caused by 500 microM local L-NAME administration in the 15th minute was reversed by locally administered SNP (500 microM). Our results support the hypothesis stating that NO may play a role in the modulation of mono- and polysynaptic spinal reflexes and the NO appears to have an enhancing role on these responses.

Sulpiride injections into the medial septum reverse the influence of intra-medial septum injection of L-arginine on expression of place conditioning-induced by morphine in rats

Effects of intra-medial septum injections of L-arginine, a precursor of nitric oxide, N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase, and sulpiride, a selective antagonist of dopamine D2 receptor on morphine-induced conditioned place preference (CPP) in male Wistar rats were examined. Using a 3-day schedule of conditioning, morphine (0.5-7.5 mg/kg, s.c.) produced a significant place preference in a dose-dependent manner. The maximum response was observed with 5.0 mg/kg of opioid. Sulpiride (0.3, 1.0 and 3.0 microg/rat), but not L-arginine (0.3, 1.0 and 3.0 microg/rat) or L-NAME (0.3, 1.0 and 3.0 microg/rat), in combination with morphine (5.0 mg/kg), during conditioning, significantly altered morphine-induced CPP. Single doses (0.3, 1.0 and 3.0 microg/rat) of either L-arginine or L-NAME, during conditioning, did not induce CPP. Sulpiride at 0.3-3.0 microg/rat, intra-medial septum, during conditioning, produced a significant conditioned place aversion. Intra-medial septum injections of L-arginine but not L-NAME or sulpiride, 1-2 min before testing, increased the expression of morphine-induced CPP. The administration of sulpiride (0.3, 1.0 and 3.0 microg/rat), but not L-NAME (0.3, 1.0 and 3.0 microg/rat), 1-2 min before the injection of L-arginine (0.3 microg/rat) on day of test, significantly attenuated the response to L-arginine. L-Arginine (0.3-3.0 microg/rat), during conditioning, showed a statistically significant increase in locomotor activity compared with that to control group. Moreover, sulpiride decreased locomotion by itself or in combination with morphine during conditioning and on the test day of morphine CPP. It can be concluded that L-arginine, a precursor of nitric oxide, in the rat median septum may play a role in expression of morphine conditioning due to dopamine release in this area.

Effects of the nitric oxide donor, DEA/NO on cortical spreading depression

Cortical spreading depression (CSD) is a transient disruption of local ionic homeostasis that may promote migraine attacks and the progression of stroke lesions. We reported previously that the local inhibition of nitric oxide (NO) synthesis with Nomega-nitro-L-arginine methyl ester (L-NAME) delayed markedly the initiation of the recovery of ionic homeostasis from CSD. Here we describe a novel method for selective, controlled generation of exogenous NO in a functioning brain region. It is based on microdialysis perfusion of the NO donor, 2-(N,N-diethylamino)-diazenolate-2-oxide (DEA/NO). As DEA/NO does not generate NO at alkaline pH, and as the brain has a strong acid-base buffering capacity, DEA/NO was perfused in a medium adjusted at alkaline (but unbuffered) pH. Without DEA/NO, such a microdialysis perfusion medium did not alter CSD. DEA/NO (1, 10 and 100 microM) had little effect on CSD by itself, but it reversed in a concentration-dependent manner the effects of NOS inhibition by 1 mM L-NAME. These data demonstrate that increased formation of endogenous NO associated with CSD is critical for subsequent, rapid recovery of cellular ionic homeostasis. In this case, the molecular targets for NO may be located either on brain cells to suppress mechanisms directly involved in CSD genesis, or on local blood vessels to couple flow to the increased energy demand associated with CSD.

Anti-epileptic drugs as possible neuroprotectants in cerebral ischemia

Many similarities exist between cerebral ischemia and epilepsy regarding brain-damaging and auto-protective mechanisms that are activated following the injurious insult. Therefore, drugs that are effective in minimizing seizure-induced brain damage may also be useful in minimizing ischemic injury. Use of such drugs in stroke victims may have important clinical and financial advantages. Therefore, the authors conducted a Medline search of studies involving the use of anti-epileptic drugs (AEDs) as possible neuroprotectants and summarize the data. Most AEDs have been tested in animal models of focal or global ischemia and some were already tested in humans, for a possible neuroprotective effect. The existing data is rather scant and insufficient but it appears that only drugs that have multiple mechanisms of action seem to have some potential in conferring a degree of neuroprotection that could be clinically applicable to stroke patients. In conclusion, some of the newer AEDs show promise as possible neuroprotectants in the setup of acute ischemic stroke but more studies are needed before clinical trials in humans could be undertaken.

Antidepressant- and anxiolytic-like effects of selective neuronal NOS inhibitor 1-(2-trifluoromethylphenyl)-imidazole in mice

Various inhibitors of nitric oxide synthase (NOS) have been shown to possess antidepressant- and anxiolytic-like properties in animal models. The aim of this study was to compare the behavioural effects of NOS inhibitor 7-nitroindazole (7-NI) with the more selective neuronal NOS inhibitor 1-(2-trifluoromethylphenyl)imidazole (TRIM) in animal models predictive of antidepressant- and anxiolytic-like activity in order to clarify the role of distinct isoforms of NOS in the regulation of depression and anxiety. Both TRIM (50 mg/kg) and 7-NI (50 mg/kg) decreased the immobility time in the forced swimming test. The magnitude of the effect was comparable to that of the tricyclic antidepressant imipramine (15 mg/kg). The antidepressant-like effect of TRIM was counteracted by pretreatment with L-arginine (250 mg/kg). The systemic administration of TRIM (50 mg/kg), but not 7-NI (up to 50 mg/kg) increased the time spent in the light side of the apparatus in the light-dark compartment test. The anxiolytic-like effect of TRIM was antagonised by pretreatment with L-arginine. Both TRIM and 7-NI decreased the locomotion of animals in the open field and caused motor incoordination on rotarod. These motor side effects were more pronounced in the case of 7-NI and were not diminished by pretreatment with L-arginine. We conclude that neuronal NOS seems to play the key role in the antidepressant- and anxiolytic-like effects of NOS inhibitors.

Cortico-striatal synaptic plasticity in endothelial nitric oxide synthase deficient mice

Nitric oxide (NO) is a retrograde messenger involved in the processes of learning and memory. The role of the endothelial isoform of nitric oxide synthase (eNOS) in striatal synaptic plasticity was investigated in eNOS-deficient (eNOS(-/-)) and wild type (WT) mice. Tetanic stimulation of cortical afferents in WT mice evoked either long-term potentiation (LTP), or long-term depression (LTD) of cortico-striatal transmission. Both these plasticity related phenomena were NMDA-receptor-dependent; LTD was blocked by sulpiride, a dopamine D2-receptor antagonist. LTP occurrence in slices from eNOS(-/-) mice was significantly reduced when compared with WT mice. The NOS inhibitor NL-ARG reduced the occurrence of LTP and increased the occurrence of LTD in WT mice, resembling the balance of LTP/LTD in eNOS(-/-) mice. Impairment of NO-synthesis thus shifts striatal plasticity towards LTD. This indicates a possible involvement of eNOS from endothelia in neuronal modulation.

Differential engagements of glutamate and GABA receptors in cardiovascular actions of endogenous nNOS or iNOS at rostral ventrolateral medulla of rats

1. We evaluated in Sprague-Dawley rats anaesthetized with propofol the engagement of soluble guanylyl cyclase (sGC)/cGMP cascade, glutamatergic and GABAergic neurotransmission in the cardiovascular actions of endogenous nitric oxide (NO) at the rostral ventrolateral medulla (RVLM). 2. Microinjection bilaterally into the RVLM of a selective iNOS inhibitor, S-methylisothiourea (SMT, 250 pmoles), or a selective nNOS inhibitor, 7-nitroindazole (7-NI, 5 pmoles), induced respectively an enhancement or a reduction in systemic arterial pressure, heart rate and power density of the vasomotor components in the spectrum of arterial blood pressure signals, our experimental index for sympathetic neurogenic vasomotor tone. 3. The cardiovascular actions of SMT or 7-NI in the RVLM were significantly antagonized by co-administration into the RVLM of the sGC inhibitor, 1H-[1,2,4]Oxadiazole[4,3-alpha]quinoxalin-1-one (ODQ, 250 or 500 pmoles). 4. The cardiovascular excitatory effects after blockade of endogenous iNOS activity were significantly attenuated when N-methyl-D-aspartate (NMDA) receptor antagonist, dizocilpine (20 or 50 pmoles), or non-NMDA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (250 or 500 pmoles), was co-microinjected bilaterally into the RVLM. 5. On the other hand, the cardiovascular depressive responses to blockade of endogenous nNOS activity were significantly antagonized on co-administration of GABA(A) receptor antagonist, bicuculline methiodine (5 or 10 pmoles), but not GABA(B) receptor antagonist, 2-hydroxy saclofen (50 or 100 pmoles). 6. We conclude that the cardiovascular actions of endogenous NO in the RVLM engage the sGC/cGMP pathway. In addition, whereas NO derived from nNOS induced sympathoexcitation via both NMDA and non-NMDA receptors in the RVLM, NO generated by iNOS elicited sympathoinhibition via GABA(A) receptors.

Ischemia-reperfusion-related repair deficit after oxidative stress: implications of faulty transcripts in neuronal sensitivity after brain injury

Diseases of the heart are the No. 1 killer in industrialized countries. Brain injury can develop as a result of cerebral ischemia-reperfusion due to stroke (brain attack) and other cardiovascular diseases. Learning about the disease is the best way to reduce disability and death. We present here whether gene repair activities are associated with neuronal death in an ischemia-reperfusion model that simulates stroke in male Long-Evans rats. This experimental stroke model is known to induce necrosis in the ischemic cortex. Cerebral ischemia causes overactivation of membrane receptors and accumulation of extracellur glutamate and intracellular calcium, which activates neuronal nitric oxide synthase, causing damage to lipids, proteins, and nucleic acids, and reduces energy sources with consequent functional deterioration, leading to cell death. Restoration processes normally repair genes with few errors. However, ischemia elevates oxidative DNA lesions despite these repair mechanisms. These episodes concurrently occur with the induction of immediate-early genes that critically activate other late genes in the signal transduction pathway. Damage, repair, and transcription of the c-FOS gene are presented here as examples, because Fos peptide, one of the components of activator protein 1, activates nerve growth factor and repair mechanisms. The results of our studies show that treatments with 7-nitroindazole, a specific inhibitor of nitric oxide synthase known to attenuate nitric oxide, oxidative DNA lesions, and necrosis, increase intact c-fos mRNA levels after stroke. This suggests that the accuracy of gene expression could be accounted for the recovery of cellular function after cerebral injury.

Chronic inhibition of endothelial nitric oxide synthase activity in nucleus tractus solitarii enhances baroreceptor reflex in conscious rats

In acute experiments, we demonstrated previously that nitric oxide (NO) donors exogenously applied to the nucleus tractus solitarii (NTS) depressed the baroreceptor cardiac reflex. In this study, we determined a role for endogenous endothelial nitric oxide synthase (eNOS) activity in the NTS for chronically regulating baroreceptor reflex function in conscious rats. A recombinant adenoviral vector directing expression of a truncated form of eNOS was microinjected bilaterally into the NTS to inhibit endogenous eNOS activity. Arterial pressure was monitored continuously using radio-telemetry in freely moving animals and spontaneous baroreceptor reflex gain (sBRG) determined by a time-series method. sBRG showed a gradual increase from day 7 to 21 after gene transfer and the value at day 21 (1.68 +/- 0.20 ms mmHg(-1), n = 6) was significantly higher than that before gene transfer (1.13 +/- 0.09 ms mmHg(-1), P < 0.001). This value was also significantly higher than that in rats in which enhanced green fluorescent protein (eGFP) was expressed in the NTS (1.04 +/- 0.21 ms mmHg(-1); n = 6, P < 0.01) and saline-treated groups (1.12 +/- 0.15 ms mmHg(-1); n = 4, P < 0.05), which did not change from control levels. In addition, heart rate decreased from 336 +/- 6 to 318 +/- 8 b.p.m. (P < 0.05) 21 days after gene transfer. This value was also significantly lower than that in control groups (eGFP: 348 +/- 9 b.p.m., n = 6, P < 0.01; saline: 347 +/- 5 b.p.m., n = 4, P < 0.05). Gene transfer did not affect arterial pressure. These findings suggest that in the conscious rat eNOS is constitutively active within the NTS and is a factor regulating baroreceptor reflex gain and heart rate.

Transcripts of damaged genes in the brain during cerebral oxidative stress

Recent studies using ischemia/reperfusion models of brain injury suggest that there is a period of time during which the formation of oxidative DNA lesions (ODLs) exceeds removal. This interval is a window of opportunity in which to study the effect of gene damage on gene expression in the brain, because the presence of excessive ODLs mimics a deficiency in gene repair, which has been shown to be associated with neurological disorders. Evidence from studies using similar models indicates that expression of faulty transcripts from ODL-infested genes and non-sense mutation in repaired genes occur before the process of cell death. Preventing the formation of ODLs and enhancing ODL repair are shown to increase the expression of intact transcripts and attenuate cell death. Understanding this mechanism could lead to the development of therapeutic techniques (physiologic, pharmacological, and/or genomic) that can enhance recovery.

Blocking NO synthesis: how, where and why?

Nitric oxide (NO) is a key physiological mediator, and the association of disordered NO generation with many pathological conditions has led to much interest in pharmacologically modulating NO levels. However, the wide range of processes in which NO has been implicated, and the fact that increases or decreases in NO levels might be therapeutically desirable depending on the condition or even at different stages of the same condition, pose considerable challenges for drug development. Here, we focus on the rationale and potential for approaches that reduce NO synthesis, which have led to the development of several compounds that will shortly be entering clinical trials.

Aged endothelial nitric oxide synthase knockout mice exhibit higher mortality concomitant with impaired open-field habituation and alterations in forebrain neurotransmitter levels

Endothelial nitric oxide synthase (eNOS) has been implicated in various brain and peripheral pathologies such as renal failure, heart failure or stroke. Consequently, the mortality rate of aged eNOS knockout mice (eNOS-/-) was higher than that of age-matched (18-22 months old) controls. Only seven of the original 14 eNOS-/- animals that participated in the study reached the age of 18 months or older, whereas no control mice died during this life span. In order to assess the behavioral and neurochemical consequences of chronic eNOS deficiency we examined whether the surviving aged eNOS-/- mice showed changes in terms of motor, emotional, exploratory and neurochemical parameters. Aged eNOS-/- mice showed reduced exploratory activity in the open-field with no habituation observable neither within sessions nor after repeated exposures. Pole test performance of eNOS-/- mice was comparable to controls. In the elevated plus-maze eNOS-/- mice did not differ from controls in terms of time spent in and entries into arms, but showed less locomotion on the open arms. The most prominent neurochemical alterations in the forebrains of aged eNOS-/- mice were: (a) increased acetylcholine levels in the neostriatum; (b) decreased noradrenaline concentrations in the ventral striatum; and (c) lower serotonin levels in the frontal cortex and ventral striatum. The present findings suggest that mice which survived chronic eNOS-deficiency into old age, show some behavioral and neurochemical phenotypes distinct from adult eNOS-/- mice.