Effects of nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester on phencyclidine-induced effects in rats

Inducible Nitric Oxide Inhibitors Block NMDA Antagonist-Stimulated Motoric Behaviors and Medial Prefrontal Cortical Glutamate Efflux

Nitric oxide (NO) plays a critical role in the motoric and glutamate releasing action of N-methyl-D-aspartate (NMDA)-antagonist stimulants. Earlier studies utilized neuronal nitric oxide synthase inhibitors (nNOS) for studying the neurobehavioral effects of non-competitive NMDA-antagonist stimulants such as dizocilpine (MK-801) and phencyclidine (PCP). This study explores the role of the inducible nitric oxide synthase inhibitors (iNOS) aminoguanidine (AG) and (-)-epigallocatechin-3-gallate (EGCG) in NMDA-antagonist induced motoric behavior and prefrontal cortical glutamate efflux. Adult male rats were administered a dose range of AG, EGCG, or vehicle prior to receiving NMDA antagonists MK-801, PCP, or a conventional psychostimulant (cocaine) and tested for motoric behavior in an open arena. Glutamate in the medial prefrontal cortex (mPFC) was measured using in vivo microdialysis after a combination of AG or EGCG prior to MK-801. Acute administration of AG or EGCG dose-dependently attenuated the locomotor and ataxic properties of MK-801 and PCP. Both AG and EGCG were unable to block the motoric effects of cocaine, indicating the acute pharmacologic action of AG and EGCG is specific to NMDA antagonism and not generalizable to all stimulant class drugs. AG and EGCG normalized MK-801-stimulated mPFC glutamate efflux. These data demonstrate that AG and EGCG attenuates NMDA antagonist-stimulated motoric behavior and cortical glutamate efflux. Our results suggest that EGCG-like polyphenol nutraceuticals (contained in “green tea” and chocolate) may be clinically useful in protecting against the adverse behavioral dissociative and cortical glutamate stimulating effects of NMDA antagonists. Medications that interfere with NMDA antagonists such as MK-801 and PCP have been proposed as treatments for schizophrenia.

Role of nitric oxide in the regulation of motor function. An overview of behavioral, biochemical and histological studies in animal models

A compelling body of evidence suggests that nitric oxide (NO), a unique gaseous neurotransmitter and neuromodulator plays a key role in the regulation of motor function. Recently, the interest of researchers concentrates on the NO - soluble guanylyl cyclase (sGC) - cyclic GMP (cGMP) signaling pathway in the striatum as a new target for the treatment of Parkinson's disease (PD). The aim of the study is to review the available literature referring to the role of NO in the integration of basal ganglia functions. First, attention has been focused on behavioral effects of NO donors and neuronal nitric oxide synthase (nNOS) inhibitors in the modulation of motor behavior. Then, disturbances in the nitrergic neurotransmission in PD and its 6-OHDA animal model have been presented. Moreover, the most current data demonstrating the contribution of both dopamine and glutamate to the regulation of NO biosynthesis in the striatum have been analyzed. Finally, the role of NO in the tonic and phasic dopamine release as well as in the regulation of striatal output pathways also has been discussed.

Effects of acute and chronic administration of MK-801 on c-Fos protein expression in mice brain regions implicated in schizophrenia with or without clozapine

This study investigated the effects of acute and chronic administration of the non-competitive NMDA receptor antagonists MK-801 on c-Fos protein expression in different brain regions of mice with or without clozapine. MK-801 (0.6 mg/kg) acute administration produced a significant increase in the expression of c-Fos protein in the layers III-IV of posterior cingulate and retrosplenial (PC/RS) cortex, which was consistent with the previous reports. Moreover, we presented a new finding that MK-801 (0.6 mg/kg) chronic administration for 8 days produced a significant increase of c-Fos protein expression in the PC/RS cortex, prefrontal cortex (PFC) and hypothalamus of mice. Among that, c-Fos protein expression in the PC/RS cortex of mice was most significant. Compared to acute administration, we found that MK-801 chronic administration significantly increased the expression of c-Fos protein in the PC/RS cortex, PFC and hypothalamus. Furthermore, pretreatment of mice with clozapine significantly decreased the expression of c-Fos protein induced by MK-801 acute and chronic administration. These results suggest that c-Fos protein, the marker of neuronal activation, might play an important role in the chronic pathophysiological process of schizophrenic model induced by NMDA receptor antagonist.

Evidence for association between the 5' flank of the NOS1 gene and schizophrenia in the Chinese population

Nitric oxide (NO) plays an important role in the dopaminergic and serotonergic system as the second messenger of the NMDA receptor and has possible roles in neurotransmission, neurosecretion, synaptic plasticity, and tissue injury in many neurological disorders, including schizophrenia. There is also genetic evidence to support the human NOS1 (neuronal nitric oxide synthase 1) gene as a promising candidate gene associated with schizophrenia. In this paper we conducted a case-control association study involving 1705 Chinese subjects and 12 genetic markers [11 single nucleotide polymorphisms (SNPs) and 1 microsatellite] mainly in the 5' flank region of the gene by direct sequencing and capillary electrophoresis. We identified SNP rs3782206 and several haplotypes derived from it as being significantly associated with schizophrenia and, specifically, in a paranoid subgroup. Our results strongly support a previous hypothesis that NOS1 contributes to the genetic risk of schizophrenia and suggest that further research on more NOS1 variants and its regular elements are warranted.

Reduced plasma nitric oxide metabolites before and after antipsychotic treatment in patients with schizophrenia compared to controls

BACKGROUND

Nitric oxide (NO) is believed to have a role in the pathophysiology of schizophrenia. We examined plasma levels of NO metabolites in patients with schizophrenia and normal controls. We also determined the impact of 6-week risperidone treatment on circulating NO metabolites in patients with schizophrenia.

METHOD

Plasma NO metabolite (NO(x)) levels were measured in 55 schizophrenia patients before and after 6-week treatment with risperidone and in 55 normal controls. Severity of schizophrenia and response to treatment were assessed with the positive and negative syndrome scale (PANSS) for schizophrenia. NO(x) levels were estimated by the Griess method.

RESULTS

Pre-treatment plasma NO(x) levels in schizophrenia patients (8.97+/-6.74 micromol/L) were lower than those of normal controls (14.51+/-6.30 micromol/L) (p<0.01). Schizophrenia patients had lower post-treatment NO(x) levels (10.99+/-8.31 micromol/L) than those of normal controls (p<0.01). There was marginal significant change between plasma NO(x) levels before and after 6-week treatment (p=0.056). Moreover, in 37 treatment responders (> or = 30% improvement in PANSS score), post-treatment plasma NO(x) significantly increased in comparison to pre-treatment NO(x) (p=0.028).

CONCLUSIONS

Plasma levels of NO(x) in patients with schizophrenia were significantly lower than normal controls both before and after the treatment. Our findings suggest that the improvement of psychiatric symptoms can lead to partially normalize a deficiency of NO after treatment in schizophrenia patients. Our findings support the hypothesis that the NO system is dampened in schizophrenia.

Minocycline, a second-generation tetracycline, as a neuroprotective agent in an animal model of schizophrenia

Minocycline is a second-generation tetracycline with a distinct neuroprotective profile. The current study assessed the effects of minocycline in an animal model of schizophrenia, the non-competitive NMDA antagonist (dizocilpine maleate; MK801). The effects of minocycline were compared to those of haloperidol, a dopamine antagonist used for the treatment of schizophrenia. The study protocol involved daily intraperitoneal injections of minocycline (35 mg/kg) for three consecutive days. On the fourth day, the rats were injected with MK801 and assessed for visual-spatial memory (Morris water maze) and sensorimotor gating (acoustic startle response, ASR, and the prepulse inhibition of the ASR). The findings indicate that MK801 caused cognitive visuo-spatial memory deficits and changes in sensorimotor gating, similar to those evident in schizophrenia. Minocycline reversed these cognitive effects of MK801 and this effect was similar to that of haloperidol. The results of this study suggest that minocycline may have protective properties against the cognitive effects of the MK801 animal model of schizophrenia. The discussion addresses potential mechanisms underlying the effects of minocycline and possible directions for future research.

Imbalanced free radicals and antioxidant defense systems in schizophrenia: a comparative study

OBJECTIVE

To examine changes of blood oxidative-antiovidative level in schizophrenic patients and its relationship with clinical symptoms.

METHODS

Forty-six Chinese patients met DSM-IV (Diagnostic and Statistical Manual of Mental Disorders-IV) criteria for schizophrenia and fifty age- and sex-matched healthy controls were enrolled in the present study. Baseline psychiatric symptom severity was assessed with brief psychiatric rating scale, positive and negative syndrome scale on the blood draw day. Fresh blood samples were collected to measure levels of nitric oxide and lipid peroxide in plasma as well as activities of superoxide dismutase, catalase and glutathione peroxidase in red blood cells by spectrophotometric assays simultaneously.

RESULTS

Comparison of the biochemical parameters indicated that the level of nitric oxide and lipid peroxide increased in patient group, which represented a positive correlation with positive scale scores; while the activities of three critical enzymes decreased and showed a negative linear correlation.

CONCLUSION

This study showed that there are dysregulation of free radical metabolism and poor activities of the antioxidant defense systems in schizophrenic patients. Excess free radicals formation may play a critical role in the etiology of schizophrenia. Using antioxidants might be an effective therapeutic approach to partially alleviate or prevent the symptoms of schizophrenia.

A neuronal nitric oxide synthase (NOS-I) haplotype associated with schizophrenia modifies prefrontal cortex function

Nitric oxide (NO) is a gaseous neurotransmitter thought to play important roles in several behavioral domains. On a neurobiological level, NO acts as the second messenger of the N-methyl-D-aspartate receptor and interacts with both the dopaminergic as well as the serotonergic system. Thus, NO is a promising candidate molecule in the pathogenesis of endogenous psychoses and a potential target in their treatment. Furthermore, the chromosomal locus of the gene for the NO-producing enzyme NOS-I, 12q24.2, represents a major linkage hot spot for schizophrenic and bipolar disorder. To investigate whether the gene encoding NOS-I (NOS1) conveys to the genetic risk for those diseases, five NOS1 polymorphisms as well as a NOS1 mini-haplotype, consisting of two functional polymorphisms located in the transcriptional control region of NOS1, were examined in 195 chronic schizophrenic, 72 bipolar-I patients and 286 controls. Single-marker association analysis showed that the exon 1c promoter polymorphism was linked to schizophrenia (SCZ), whereas synonymous coding region polymorphisms were not associated with disease. Long promoter alleles of the repeat polymorphism were associated with less severe psychopathology. Analysis of the mini-haplotype also revealed a significant association with SCZ. Mutational screening did not detect novel exonic polymorphisms in patients, suggesting that regulatory rather than coding variants convey the genetic risk on psychosis. Finally, promoter polymorphisms impacted on prefrontal functioning as assessed by neuropsychological testing and electrophysiological parameters elicited by a Go-Nogo paradigm in 48 patients (continuous performance test). Collectively these findings suggest that regulatory polymorphisms of NOS1 contribute to the genetic risk for SCZ, and modulate prefrontal brain functioning.

Nitric oxide donor molsidomine attenuates psychotomimetic effects of the NMDA receptor antagonist MK-801

There is experimental evidence indicating that the non-competitive NMDA receptor antagonist MK-801 impairs cognition and produces a series of schizophrenia-like symptoms in rodents (hypermotility, stereotypies, and ataxia). The present study was designed to investigate the efficacy of the nitric oxide (NO) donor molsidomine in counteracting these MK-801-induced behavioral effects in the rat. In a first study, post-training administration of molsidomine (at 4 but not 2 mg/kg) successfully antagonized MK-801-induced performance deficits in a recognition memory test. In a subsequent study, molsidomine (2 and 4 mg/kg) was shown to be unable to reverse MK-801-induced hypermotility but attenuated stereotypies (continuous movement whole cage, body sway, and head weaving) produced by MK-801. Moreover, at 4 mg/kg this NO donor counteracted MK-801-induced ataxia. Our findings indicate that molsidomine attenuates behavioral effects related to the hypofunction of the NMDA receptor suggesting that NO might be involved in the psychotomimetic effects of non-competitive NMDA receptor antagonists.

The many faces of nitric oxide in schizophrenia. A review

Intense research has been conducted in an effort to identify specific biological markers of schizophrenia. The gas nitric oxide (NO) is one of the most important signaling molecules involved in a plethora of cellular events that take place in the cardiovascular, immune and nervous systems of animals. This survey aims to demonstrate that NO and its metabolites play important roles in schizophrenia and have a significant influence on our understanding of the development, progression and treatment of the disease. Special emphasis is given to the impact of NO metabolism on processes known to be disturbed in schizophrenia (i.e., cell migration, formation of synapses, NMDA receptor mediated neurotransmission, membrane pathology and cognitive abilities). However, when comparing data on the NO metabolism in the brain tissue and body fluids of schizophrenics with those obtained from patients with other neurological and psychiatric diseases, it becomes clear that alterations of NO metabolism are not unique to, or indicative of, schizophrenia. Thus, NO and its metabolites are not suitable diagnostic tools to distinguish schizophrenia from psychically healthy control cases or from other brain disorders.

Activation of a nitric-oxide-sensitive cAMP pathway with phencyclidine: elevated hippocampal cAMP levels are temporally associated with deficits in prepulse inhibition

RATIONALE

Schizophrenic patients show deficits in pre-attentive information processing as evidenced, for example, by disrupted prepulse inhibition, a measure of sensorimotor gating. A similar disruption can be observed in animals treated with the psychotomimetic agent, phencyclidine (PCP). However, the mechanism by which PCP alters brain function has not been fully elucidated. Recent studies have demonstrated that certain behavioural and neurochemical effects of PCP in rats and mice are blocked by nitric oxide (NO) synthase inhibition, suggesting an important role for NO in the effects of PCP.

OBJECTIVE

The aim of the present study was to investigate the effects of PCP on cAMP production in the ventral hippocampus and the role of NO in these effects using in vivo microdialysis in rats. Furthermore, the effects of PCP on acoustic startle reactivity and prepulse inhibition of acoustic startle were compared with changes in cAMP levels in the ventral hippocampus.

RESULTS

Significant increases in cAMP levels were observed in the ventral hippocampus following both local infusion (10(-4) mol/l and 10(-3) mol/l) and systemic administration (2 mg/kg) of PCP. The PCP-induced changes in prepulse inhibition and startle reactivity were associated in magnitude and duration with the increase in cAMP levels in the hippocampus. Furthermore, systemic administration of the NO synthase inhibitor, L: -NAME (10 mg/kg), blocked both the changes in cAMP levels and the behavioural responses induced by PCP.

CONCLUSIONS

These findings indicate that the effects of PCP on prepulse inhibition and startle reactivity are associated with an increase in cAMP levels in the ventral hippocampus, and that this change in cAMP response may be linked to the production of NO.

Selective interaction of nitric oxide synthase inhibition with phencyclidine: behavioural and NMDA receptor binding studies in the rat

The psychotomimetic drugs, phencyclidine (PCP) and MK-801, are non-competitive antagonists of the N-methyl-d-aspartate (NMDA) receptor and used as pharmacological tools to mimic a possible NMDA receptor hypofunction in schizophrenia. These drugs were tested in two behavioural paradigms in the present study: prepulse inhibition (PPI) of acoustic startle and locomotor activity (LMA) in an open field. Recent studies show that several behavioural and biochemical effects of PCP are blocked by nitric oxide synthase (NOS) inhibition. Hence, it is likely that some effects of PCP are mediated via an increase in NO production, an assumption not in accordance with the NMDA receptor antagonistic effect of PCP. Experiments were conducted in rats to further elucidate the involvement of NO-dependent mechanisms in the effects of PCP and MK-801, and how these effects may involve the NMDA receptor. The NOS inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME) (10 mg/kg) normalised the disruptive effect of PCP (2 mg/kg) on PPI and the stimulatory effect of PCP (4 mg/kg) on LMA. In contrast to these observations, the deficit in PPI induced by MK-801 (0.1 mg/kg) was not affected by L-NAME (10, 20 or 40 mg/kg). MK-801 (0.15 mg/kg)-induced hyperlocomotion was not affected by L-NAME (10 mg/kg), but attenuated by L-NAME (40 mg/kg). Furthermore, receptor binding studies aimed at investigating the influence of L-NAME on the binding of PCP to the MK-801-sensitive NMDA receptor binding site failed to show such an influence. These results suggest that the NO-sensitive effects of PCP are not sufficiently explained by its antagonistic effect at the NMDA receptor channel complex.

Involvement of NO/cGMP pathway in toluene-induced locomotor hyperactivity in female rats

RATIONALE

Nitric oxide (NO) is implicated in the acute locomotor activating effects of some addictive drugs such as amphetamine, caffeine, and PCP, but has not been investigated in the case of toluene.

OBJECTIVES

This study determined the contribution of the NO-cyclic GMP (cGMP) pathway to locomotor stimulant effects of toluene.

METHODS

Locomotor activity was measured for 90 min immediately following toluene (500-1,000 mg/kg, IP) or corn oil treatments in Sprague-Dawley female rats. A NO generator, sodium nitroprusside (SNP) (3 and 6 mg/kg), a NO precursor, L-arginine ( L-Arg) (250 mg/kg), a NO synthase inhibitor, N(G)-nitro- L-arginine methyl ester (L-NAME) (5-20 mg/kg, IP), and a soluble guanylyl cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 mg/kg) were injected 5 min before toluene (750 mg/kg, IP) treatment. The combination effects of SNP with L-NAME, L-arginine with L-NAME, SNP with ODQ and L-arginine with ODQ on toluene-induced locomotor hyperactivity were also determined. RESULTS. The locomotor hyperactivity induced by toluene was significantly inhibited by SNP and L-arginine, but enhanced by L-NAME and ODQ. SNP and L-arginine completely reversed the combined effects of L-NAME and toluene to a basal level and abolished the enhancing effects of ODQ.

CONCLUSIONS

The results suggested that NO/cGMP-dependent mechanism might be involved in toluene-induced locomotor activity in rats.

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.

Expression of nNOS and soluble guanylate cyclase in schizophrenic brain

Recent evidence suggests that nitric oxide (NO) systems are affected in the pathophysiology of schizophrenia. We quantified levels of neuronal NO synthase (nNOS) and soluble guanylate cyclase (sGC) subunit mRNAs in the prefrontal cortex of post-mortem brains from individuals with schizophrenia and controls using real-time quantitative PCR, to determine whether levels of nNOS and sGC subunits are altered in 'schizophrenic' brains. Neuronal NOS expression in the prefrontal cortex was significantly higher in individuals with schizophrenia, whereas no significant changes were found in sGC subunit mRNAs in people with schizophrenia or in controls. Abnormalities of nNOS expression in the brain might contribute to the development of schizophrenia.

Neonatal nitric oxide synthase inhibition: social interaction deficits in adulthood and reversal by antipsychotic drugs

Nitric oxide synthase (NOS) is thought to migrate improperly during development in the brains of schizophrenic patients. Also it is known that nitric oxide (NO) effects synaptogenesis during development of the CNS. Previously we have shown that neonatal treatment with a NOS inhibitor effects an animal's sensitivity to amphetamine and PCP. In the present study, neonatal rats were challenged with a NOS inhibitor (L-nitroarginine, 10mg/kg, s.c.) daily on post-natal days (PD) three, four and five. L-Nitroarginine (L-NoArg) treated male rats at adulthood (PD56 and older) had a deficit in social interaction (SI) when placed in an environment with another foreign male rat and this deficit was reproducible on a weekly basis for at least five weeks. Haloperidol failed to significantly reverse this deficit before pronounced secondary effects on general behavior were seen at high doses. However, the atypical antipsychotics, clozapine and olanzapine, were able to significantly reverse this deficit at doses which did not effect baseline SI values. In a separate cohort of animals the effect of DOI was investigated, this was done to ascertain if there was a differential sensitivity of serotonergic pathways in this model. There was no difference in the behavioral score elicited from control or NoArg-treated rats. It is suggested that the SI deficits seen here may be more sensitive to atypical antipsychotics rather than haloperidol.

Minocycline blocks nitric oxide-induced neurotoxicity by inhibition p38 MAP kinase in rat cerebellar granule neurons

Minocycline, a semisynthetic second-generation tetracycline, was reported to have neuroprotective effects in models of global and focal cerebral ischemia, the R6/2 mouse model of Huntington disease, as well as glutamate-induced neurotoxicity in mixed neuronal/glial cultures. It was suggested that neuroprotective effects of minocycline resulted from inhibition of microglial/astroglial activation 'Proc. Natl. Acad. Sci. USA 95 1998 15769'. To determine whether or not minocycline is able to directly protect neurons against injury insults and to delineate its neuroprotective mechanism(s), we treated cultured rat cerebellar granule neurons (CGN) with nitric oxide (NO) in the presence or absence of minocycline. We found that minocycline protected neurons against NO-induced neuronal death in a concentration-dependent fashion. Consistent to other reports, NO was able to induce p38 MAP kinase phosphorylation at 3-6 h and such an induction could be significantly inhibited by minocycline. Furthermore, SB 203580, a p38 MAP kinase inhibitor, almost completely attenuated NO-induced neuronal death of CGN as well. These results suggest that minocycline is able to block NO-induced neurotoxicity in CGN by inhibiting NO-induced phosphorylation of p38 MAP kinase. Our finding may explain the neuroprotective mechanism of minocycline in those neurodegenerative models.