Methylene blue adjuvant therapy of schizophrenia

Upregulation of hemeoxygenase enzymes HO-1 and HO-2 following ischemia-reperfusion injury in connection with experimental cardiac arrest and cardiopulmonary resuscitation: Neuroprotective effects of methylene blue

Oxidative stress plays an important role in neuronal injuries after cardiac arrest. Increased production of carbon monoxide (CO) by the enzyme hemeoxygenase (HO) in the brain is induced by the oxidative stress. HO is present in the CNS in two isoforms, namely the inducible HO-1 and the constitutive HO-2. Elevated levels of serum HO-1 occurs in cardiac arrest patients and upregulation of HO-1 in cardiac arrest is seen in the neurons. However, the role of HO-2 in cardiac arrest is not well known. In this review involvement of HO-1 and HO-2 enzymes in the porcine brain following cardiac arrest and resuscitation is discussed based on our own observations. In addition, neuroprotective role of methylene blue- an antioxidant dye on alterations in HO under in cardiac arrest is also presented. The biochemical findings of HO-1 and HO-2 enzymes using ELISA were further confirmed by immunocytochemical approach to localize selective regional alterations in cardiac arrest. Our observations are the first to show that cardiac arrest followed by successful cardiopulmonary resuscitation results in significant alteration in cerebral concentrations of HO-1 and HO-2 levels indicating a prominent role of CO in brain pathology and methylene blue during CPR followed by induced hypothermia leading to superior neuroprotection after return of spontaneous circulation (ROSC), not reported earlier.

Methylene Blue in the Treatment of Neuropsychiatric Disorders

Methylene blue is a long-established drug with complex pharmacology and multiple clinical indications. Its diverse mechanisms of action are most likely responsible for the large variety of its clinical effects. Of interest to psychiatrists, methylene blue has antidepressant, anxiolytic, and neuroprotective properties documented by both animal and human studies. Its stabilizing effect on mitochondrial function and dose-dependent effect on the generation of reactive oxygen species are of significant heuristic value. For these reasons, methylene blue holds promise as a proof-of-concept treatment of organic/neurodegenerative disorders and as a neuroprotective agent in general. In psychiatry, methylene blue has been used for over a century. It was tried successfully in the treatment of psychotic and mood disorders and as a memory enhancer in fear-extinction training. Particularly promising results have been obtained in both short- and long-term treatment of bipolar disorder. In these studies, methylene blue produced an antidepressant and anxiolytic effect without risk of a switch into mania. Long-term use of methylene blue in bipolar disorder led to a better stabilization and a reduction in residual symptoms of the illness. It is usually well tolerated, but caution is needed in the light of its inhibitory effect on monoamine oxidase A.

Methylene Blue Analogues with Marginal Monoamine Oxidase Inhibition Retain Antidepressant-like Activity

Methylene blue (MB) possesses diverse medical applications. Among these, MB presents with antidepressant-like effects in animals and has shown promise in clinical trials for the treatment of mood disorders. As an antidepressant, MB may act via various mechanisms which include modulation of the nitric oxide cyclic guanosine monophosphate (NO-cGMP) cascade, enhancement of mitochondrial respiration and antioxidant effects. MB is also, however, a high potency inhibitor of monoamine oxidase (MAO) A, which most likely contributes to its antidepressant effect, but also to its adverse effects profile (e.g., serotonin toxicity). The latter has raised the question whether it is possible to design out the MAO inhibition properties of MB yet retaining its clinically useful attributes. This study explores this idea further by characterizing five newly synthesized low MAO-A active MB analogues and examining their antidepressant-like properties in the acute forced swim test (FST) in rats, with comparison to imipramine and MB. The results show that all five analogues exhibit antidepressant-like properties in the FST without confounding effects on locomotor activity. The magnitude of these effects is comparable to those of imipramine and MB. Moreover, these newly synthesized MB analogues are markedly less potent MAO-A inhibitors (IC₅₀ = 0.518-4.73 μM) than MB (IC₅₀ = 0.07 μM). We postulate that such lower potency MAO-A inhibitors may present with a reduced risk of adverse effects associated with MAO-A inhibition. While low level MAO-A inhibition still may produce an antidepressant effect, we posit that other MB-related mechanisms may underlie their antidepressant effects, thereby representing a novel group of antidepressant compounds.

Methylene Blue: The Long and Winding Road From Stain to Brain: Part 2

Methylene blue was the first synthetic drug ever used in medicine, having been used to treat clinical pain syndromes, malaria, and psychotic disorders more than one century ago. Methylene blue is a cationic thiazine dye with redox-cycling properties and a selective affinity for the nervous system. This drug also inhibits the activity of monoamine oxidase, nitric oxide synthase, and guanylyl cyclase, as well as tau protein aggregation; increases the release of neurotransmitters, such as serotonin and norepinephrine; reduces amyloid-beta levels; and increases cholinergic transmission. The action of methylene blue on multiple cellular and molecular targets justifies its investigation in various neuropsychiatric disorders. Investigations of methylene blue were instrumental in the serendipitous development of phenothiazine antipsychotic drugs. Although chlorpromazine is heralded as the first antipsychotic drug used in psychiatry, methylene blue is a phenothiazine drug that had been used to treat psychotic patients half a century earlier. It has also been studied in bipolar disorder and deserves further investigation for the treatment of unipolar and bipolar disorders. More recently, methylene blue has been the subject of preclinical and clinical investigations for cognitive dysfunction, dementia, and other neurodegenerative disorders. [Journal of Psychosocial Nursing and Mental Health Services, 54(10), 21-26.].

Methylene blue and its analogues as antidepressant compounds

Methylene Blue (MB) is considered to have diverse medical applications and is a well-described treatment for methemoglobinemias and ifosfamide-induced encephalopathy. In recent years the focus has shifted to MB as an antimalarial agent and as a potential treatment for neurodegenerative disorders such as Alzheimer's disease. Of interest are reports that MB possesses antidepressant and anxiolytic activity in pre-clinical models and has shown promise in clinical trials for schizophrenia and bipolar disorder. MB is a noteworthy inhibitor of monoamine oxidase A (MAO-A), which is a well-established target for antidepressant action. MB is also recognized as a non-selective inhibitor of nitric oxide synthase (NOS) and guanylate cyclase. Dysfunction of the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) cascade is strongly linked to the neurobiology of mood, anxiety and psychosis, while the inhibition of NOS and/or guanylate cyclase has been associated with an antidepressant response. This action of MB may contribute significantly to its psychotropic activity. However, these disorders are also characterised by mitochondrial dysfunction and redox imbalance. By acting as an alternative electron acceptor/donor MB restores mitochondrial function, improves neuronal energy production and inhibits the formation of superoxide, effects that also may contribute to its therapeutic activity. Using MB in depression co-morbid with neurodegenerative disorders, like Alzheimer's and Parkinson's disease, also represents a particularly relevant strategy. By considering their physicochemical and pharmacokinetic properties, analogues of MB may provide therapeutic potential as novel multi-target strategies in the treatment of depression. In addition, low MAO-A active analogues may provide equal or improved response with a lower risk of adverse effects.

Pharmacological targeting of redox regulation systems as new therapeutic approach for psychiatric disorders: A literature overview

Redox dysregulation occurs following a disequilibrium between reactive oxygen species (ROS) producing and degrading systems, i.e. mitochondria, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and nitric oxide synthase (NOS) on one hand and the principal antioxidant system, the glutathione, on the other hand. Increasing recent evidence points towards a pathogenetic role of an altered redox state in the development of several mental disorders, such as anxiety, bipolar disorders, depression, psychosis, autism and post-traumaticstress disorders (PTSD). In this regard, pharmacological targeting of the redox state regulating systems in the brain has been proposed as an innovative and promising therapeutic approach for the treatment of these mental diseases. This review will summarize current knowledge obtained from both pre-clinical and clinical studies in order to descant "lights and shadows" of targeting pharmacologically both the producing and degrading reactive oxygen species (ROS) systems in psychiatric disorders.

Neuronal nitric oxide synthase (NOS1) and its adaptor, NOS1AP, as a genetic risk factors for psychiatric disorders

Nitric oxide (NO) is a gaseous transmitter produced by nitric oxide synthases (NOSs). The neuronal isoform (NOS-I, encoded by NOS1) is the main source of NO in the central nervous system (CNS). Animal studies suggest that nitrinergic dysregulation may lead to behavioral abnormalities. Unfortunately, the large number of animal studies is not adequately reflected by publications concerning humans. These include post-mortem studies, determination of biomarkers, and genetic association studies. Here, we review the evidence for the role of NO in psychiatric disorders by focusing on the human NOS1 gene as well as biomarker studies. Owing to the complex regulation of NOS1 and the varying function of NOS-I in different brain regions, no simple, unidirectional association is expected. Rather, the 'where, when and how much' of NO formation is decisive. Present data, although still preliminary and partially conflicting, suggest that genetically driven reduced NO signaling in the prefrontal cortex is associated with schizophrenia and cognition. Both NOS1 and its interaction partner NOS1AP have a role therein. Also, reduced NOS1 expression in the striatum determined by a length polymorphism in a NOS1 promoter (NOS1 ex1f-VNTR) goes along with a variety of impulsive behaviors. An association of NOS1 with mood disorders, suggested by animal models, is less clear on the genetic level; however, NO metabolites in blood may serve as biomarkers for major depression and bipolar disorder. As the nitrinergic system comprises a relevant target for pharmacological interventions, further studies are warranted not only to elucidate the pathophysiology of mental disorders, but also to evaluate NO function as a biomarker.

Neurodevelopmental Animal Models Reveal the Convergent Role of Neurotransmitter Systems, Inflammation, and Oxidative Stress as Biomarkers of Schizophrenia: Implications for Novel Drug Development

Schizophrenia is a life altering disease with a complex etiology and pathophysiology, and although antipsychotics are valuable in treating the disorder, certain symptoms and/or sufferers remain resistant to treatment. Our poor understanding of the underlying neuropathological mechanisms of schizophrenia hinders the discovery and development of improved pharmacological treatment, so that filling these gaps is of utmost importance for an improved outcome. A vast amount of clinical data has strongly implicated the role of inflammation and oxidative insults in the pathophysiology of schizophrenia. Preclinical studies using animal models are fundamental in our understanding of disease development and pathology as well as the discovery and development of novel treatment options. In particular, social isolation rearing (SIR) and pre- or postnatal inflammation (PPNI) have shown great promise in mimicking the biobehavioral manifestations of schizophrenia. Furthermore, the "dual-hit" hypothesis of schizophrenia states that a first adverse event such as genetic predisposition or a prenatal insult renders an individual susceptible to develop the disease, while a second insult (e.g., postnatal inflammation, environmental adversity, or drug abuse) may be necessary to precipitate the full-blown syndrome. Animal models that emphasize the "dual-hit" hypothesis therefore provide valuable insight into understanding disease progression. In this Review, we will discuss SIR, PPNI, as well as possible "dual-hit" animal models within the context of the redox-immune-inflammatory hypothesis of schizophrenia, correlating such changes with the recognized monoamine and behavioral alterations of schizophrenia. Finally, based on these models, we will review new therapeutic options, especially those targeting immune-inflammatory and redox pathways.

L-lysine as an adjunct to risperidone in patients with chronic schizophrenia: a double-blind, placebo-controlled, randomized trial

Increasing evidence suggest that the nitric oxide signaling system of the brain may contribute to the pathophysiology of schizophrenia, making this system a target for development of novel therapeutics. The objective of this study was to investigate the efficacy and safety of L-lysine as an adjunctive to risperidone in the treatment of patients with chronic schizophrenia during an 8-week trial. Seventy-two chronic schizophrenia inpatients with a Positive and Negative Syndrome Scale (PANSS) total score of ≥ 60 participated in a randomized, double-blind, placebo-controlled trial in the active phase of their disease and underwent 8 weeks of treatment with either L-lysine (6 g/day) or placebo as an adjunctive to risperidone. Patients were evaluated using PANSS and its subscales at baseline and weeks 2, 4, 6 and 8. The primary outcome measure was to evaluate the efficacy of L-lysine in improving schizophrenia symptoms. Repeated measures analysis demonstrated significant effect for time × treatment interaction on the PANSS total (P < 0.001), negative (P < 0.001) and general psychopathology (P < 0.001) subscale scores but not the PANSS positive subscale scores (P = 0.61). The frequency of adverse events (AEs) did not differ significantly between the two treatment groups and no serious AE was observed. The present study demonstrated that l-lysine can be a tolerable and efficacious adjunctive therapy for improving negative and general psychopathology symptoms in chronic schizophrenia. However, the safety and efficacy of higher doses of l-lysine and longer treatment periods still remain unknown.

TRIAL REGISTRATION

Iranian registry of clinical trials (www.irct.ir): IRCT201202201556N33.

Critical role of nitric oxide in the modulation of prepulse inhibition in Swiss mice

RATIONALE

Nitric oxide (NO) modulates the dopamine uptake and release processes and appears to be implicated in dopamine-related pathologies, such as schizophrenia. However, it is unclear whether there is excess or deficient NO synthesis in schizophrenia pathophysiology. Analyses of the intracellular pathways downstream of NO system activation have identified the cyclic nucleotide cyclic guanosine monophosphate (cGMP) as a possible target for drug development. Defects in the sensorimotor gating of the neural mechanism underlying the integration and processing of sensory information have been detected across species through prepulse inhibition (PPI).

OBJECTIVES

The aim of this study was to investigate the effects of NO/cGMP increase on sensorimotor gating modulation during dopamine hyperfunction.

METHODS

Mice were treated with NO donors and subjected to the PPI test. Treatment with the NO donor sodium nitroprusside was preceded by pretreatment with a soluble guanylate cyclase (sGC) inhibitor. Additionally, the mice were treated with NO donors and phosphodiesterases inhibitors prior to amphetamine treatment.

RESULTS

Pretreatment with the NO donors enhanced the PPI response and attenuated the amphetamine-disruptive effects on the PPI. The sGC inhibitor did not modify the sodium nitroprusside effects. Additionally, the cGMP increase induced by a specific phosphodiesterase inhibitor did not modify the amphetamine-disruptive effect.

CONCLUSIONS

This study provides the first demonstration that an increase in NO can improve the PPI response and block the amphetamine-disruptive effects on the PPI response. Our data are consistent with recent clinical results. However, these effects do not appear to be related to an increase in cGMP levels, and further investigation is thus required.

Therapeutic and preventive effects of methylene blue on Alzheimer's disease pathology in a transgenic mouse model

Methylene blue (MB) belongs to the phenothiazinium family. It has been used to treat a variety of human conditions and has beneficial effects on the central nervous system in rodents with and without brain alteration. The present study was designed to test whether chronic MB treatment taken after (therapeutic effect) or before (preventive effect) the onset of beta-amyloid pathology influences cognition in a transgenic mouse model (APP/PS1). In addition, the present study aims at revealing whether these behavioral effects might be related to brain alteration in beta-amyloid deposition. To this end, we conducted an in vivo study and compared two routes of drug administration, drinking water versus intraperitoneal injection. Results showed that transgenic mice treated with MB orally or following intraperitoneal injection were protected from cognitive impairments in a variety of social, learning, and exploratory tasks. Immunoreactive beta-amyloid deposition was significantly reduced in the hippocampus and adjacent cortex in MB-treated transgenic mice. Interestingly, these beneficial effects were observed independently of beta-amyloid load at the time of MB treatment. This suggests that MB treatment is beneficial at both therapeutic and preventive levels. Using solid-state High Resolution Magic Angle Spinning Nuclear Magnetic Resonance (HRMAS-NMR), we showed that MB administration after the onset of amyloid pathology significantly restored the concentration of two metabolites related to mitochondrial metabolism, namely alanine and lactate. We conclude that MB might be useful for the therapy and prevention of Alzheimer's disease. This article is part of the Special Issue entitled 'The Synaptic Basis of Neurodegenerative Disorders'.

Glutamate neurocircuitry: theoretical underpinnings in schizophrenia

The Dopamine Hypothesis of Schizophrenia is actively being challenged by the NMDA Receptor Hypofunctioning Hypothesis of Schizophrenia. The latter hypothesis may actually be the starting point in neuronal pathways that ultimately modifies dopamine pathways involved in generating both positive and negative symptoms of schizophrenia postulated by the former hypothesis. The authors suggest that even this latter, NMDA receptor-based, hypothesis is likely too narrow and offer a review of typical glutamate and dopamine-based neurocircuitry, propose genetic vulnerabilities impacting glutamate neurocircuitry, and provide a broad interpretation of a possible etiology of schizophrenia. In conclusion, there is a brief review of potential schizophrenia treatments that rely on the etiologic theory provided in the body of the paper.

Azure B, a metabolite of methylene blue, is a high-potency, reversible inhibitor of monoamine oxidase

Methylene blue (MB) has been shown to act at multiple cellular and molecular targets and as a result possesses diverse medical applications. Among these is a high potency reversible inhibition of monoamine oxidase A (MAO-A) that may, at least in part, underlie its adverse effects but also its psycho- and neuromodulatory actions. MB is metabolized to yield N-demethylated products of which azure B, the monodemethyl species, is the major metabolite. Similar to MB, azure B also displays a variety of biological activities and may therefore contribute to the pharmacological profile of MB. Based on these observations, the present study examines the interactions of azure B with recombinant human MAO-A and -B. The results show that azure B is a potent MAO-A inhibitor (IC₅₀=11 nM), approximately 6-fold more potent than is MB (IC₅₀=70 nM) under identical conditions. Measurements of the time-dependency of inhibition suggest that the interaction of azure B with MAO-A is reversible. Azure B also reversibly inhibits the MAO-B isozyme with an IC₅₀ value of 968 nM. These results suggest that azure B may be a hitherto under recognized contributor to the pharmacology and toxicology of MB by blocking central and peripheral MAO-A activity and as such needs to be considered during its use in humans and animals.

Neurometabolic mechanisms for memory enhancement and neuroprotection of methylene blue

This paper provides the first review of the memory-enhancing and neuroprotective metabolic mechanisms of action of methylene blue in vivo. These mechanisms have important implications as a new neurobiological approach to improve normal memory and to treat memory impairment and neurodegeneration associated with mitochondrial dysfunction. Methylene blue's action is unique because its neurobiological effects are not determined by regular drug-receptor interactions or drug-response paradigms. Methylene blue shows a hormetic dose-response, with opposite effects at low and high doses. At low doses, methylene blue is an electron cycler in the mitochondrial electron transport chain, with unparalleled antioxidant and cell respiration-enhancing properties that affect the function of the nervous system in a versatile manner. A major role of the respiratory enzyme cytochrome oxidase on the memory-enhancing effects of methylene blue is supported by available data. The memory-enhancing effects have been associated with improvement of memory consolidation in a network-specific and use-dependent fashion. In addition, low doses of methylene blue have also been used for neuroprotection against mitochondrial dysfunction in humans and experimental models of disease. The unique auto-oxidizing property of methylene blue and its pleiotropic effects on a number of tissue oxidases explain its potent neuroprotective effects at low doses. The evidence reviewed supports a mechanistic role of low-dose methylene blue as a promising and safe intervention for improving memory and for the treatment of acute and chronic conditions characterized by increased oxidative stress, neurodegeneration and memory impairment.

Myricitrin, a nitric oxide and protein kinase C inhibitor, exerts antipsychotic-like effects in animal models

Myricitrin is a nitric oxide (NO) and protein kinase C (PKC) inhibitor that has central nervous system activity, including anxiolytic-like action. Nitric oxide inhibitors blocked the behavioral effects of apomorphine, suggesting an antipsychotic-like effect. Furthermore, PKC inhibition reduced psychotic symptoms in acute mania patients and blocked amphetamine-induced hyperlocomotion, suggesting a potential antipsychotic-like effect. The present study evaluated the effects of myricitrin in animal models that assess antipsychotic-like effects (apomorphine-induced stereotypy and climbing and the paw test) and extrapyramidal side effects (catalepsy test and paw test). Olanzapine was used as a positive control. 7-Nitroindazole (7-NI), a NOS inhibitor, and l-arginine, a NO precursor, were used to evaluate nitrergic modulation, and tamoxifen was used to test the effect of PKC inhibition. In mice, myricitrin dose-dependently and olanzapine blocked the stereotypy and climbing induced by apomorphine at doses that did not induce catalepsy. 7-Nitroindazole also blocked apomorphine-induced stereotypy and climbing, which were reversed by l-arginine pretreatment. l-arginine only attenuated the effects of myricitrin on apomorphine's effects. Tamoxifen also blocked apomorphine-induced stereotypy and climbing. In the paw test in rats, myricitrin and olanzapine increased hindlimb retraction time at doses that did not affect forelimb reaction time, whereas haloperidol affected both parameters at the same dose. Myricitrin did not induce catalepsy in the bar test. Tamoxifen did not affect hindlimb retraction time or forelimb retraction time, whereas 7-NI significantly increased hindlimb reaction time. Thus, myricitrin exhibited an antipsychotic-like profile at doses that did not induce catalepsy, and this effect may be related to nitrergic action.

L-lysine as adjunctive treatment in patients with schizophrenia: a single-blinded, randomized, cross-over pilot study

BACKGROUND

Accumulating evidence suggests that the brain's nitric oxide (NO) signalling system may be involved in the pathophysiology of schizophrenia and could thus constitute a novel treatment target. The study was designed to investigate the benefit of L-lysine, an amino acid that interferes with NO production, as an add-on treatment for schizophrenia.

METHODS

L-lysine, 6 g/day, was administered to 10 patients with schizophrenia as an adjunctive to their conventional antipsychotic medication. The study was designed as a single-blinded, cross-over study where patients were randomly assigned to initial treatment with either L-lysine or placebo and screened at baseline, after four weeks when treatment was crossed over, and after eight weeks.

RESULTS

L-lysine treatment caused a significant increase in blood concentration of L-lysine and was well tolerated. A significant decrease in positive symptom severity, measured by the Positive And Negative Syndrome Scale (PANSS), was detected. A certain decrease in score was also observed during placebo treatment and the effects on PANSS could not unequivocally be assigned to the L-lysine treatment. Furthermore, performance on the Wisconsin Card Sorting Test was significantly improved compared to baseline, an effect probably biased by training. Subjective reports from three of the patients indicated decreased symptom severity and enhanced cognitive functioning.

CONCLUSIONS

Four-week L-lysine treatment of 6 g/day caused a significant increase in blood concentration of L-lysine that was well tolerated. Patients showed a significant decrease in positive symptoms as assessed by PANSS in addition to self-reported symptom improvement by three patients. The NO-signalling pathway is an interesting, potentially new treatment target for schizophrenia; however, the effects of L-lysine need further evaluation to decide the amino acid's potentially beneficial effects on symptom severity in schizophrenia.

Cellular and molecular actions of Methylene Blue in the nervous system

Methylene Blue (MB), following its introduction to biology in the 19th century by Ehrlich, has found uses in various areas of medicine and biology. At present, MB is the first line of treatment in methemoglobinemias, is used frequently in the treatment of ifosfamide-induced encephalopathy, and is routinely employed as a diagnostic tool in surgical procedures. Furthermore, recent studies suggest that MB has beneficial effects in Alzheimer's disease and memory improvement. Although the modulation of the cGMP pathway is considered the most significant effect of MB, mediating its pharmacological actions, recent studies indicate that it has multiple cellular and molecular targets. In the majority of cases, biological effects and clinical applications of MB are dictated by its unique physicochemical properties including its planar structure, redox chemistry, ionic charges, and light spectrum characteristics. In this review article, these physicochemical features and the actions of MB on multiple cellular and molecular targets are discussed with regard to their relevance to the nervous system.

Information processing deficits and nitric oxide signalling in the phencyclidine model of schizophrenia

RATIONALE

Schizophrenia-like cognitive deficits induced by phencyclidine (PCP), a drug commonly used to model schizophrenia in experimental animals, are attenuated by nitric oxide (NO) synthase inhibitors. Furthermore, PCP increases NO levels and sGC/cGMP signalling in the prefrontal cortex in rodents. Hence, a cortical NO/sGC/cGMP signalling pathway may constitute a target for novel pharmacological therapies in schizophrenia.

OBJECTIVES

The objective of this study was to further investigate the role of NO signalling for a PCP-induced deficit in pre-attentive information processing.

MATERIALS AND METHODS

Male Sprague-Dawley rats were surgically implanted with NO-selective amperometric microsensors aimed at the prefrontal cortex, ventral hippocampus or nucleus accumbens, and NO levels and prepulse inhibition (PPI) were simultaneously assessed.

RESULTS

PCP treatment increased NO levels in the prefrontal cortex and ventral hippocampus, but not in the nucleus accumbens. The increase in NO levels was not temporally correlated to the deficit in PPI induced by PCP. Furthermore, pretreatment with the neuronal NO synthase inhibitor N-propyl-L-arginine dose-dependently attenuated both the increase in prefrontal cortex NO levels and the deficit in PPI.

CONCLUSIONS

These findings support a demonstrated role of NO in the behavioural and neurochemical effects of PCP. Furthermore, this effect is brain region-specific and mainly involves the neuronal isoform of NOS. However, a temporal correlation between a PCP-induced disruption of PPI and an increase in prefrontal cortex NO levels was not demonstrated, suggesting that the interaction between PCP and the NO system is more complex than previously thought.

Neurosyphilis, malaria, and the discovery of antipsychotic agents

Four of the most disabling human diseases are syphilis, malaria, schizophrenia, and manic-depressive illness. The history of the development of treatments for these seemingly unrelated disorders intersects at several points. Treatment of tertiary cerebral syphilis (general paresis) by inducing fever with malaria led to a Nobel Prize. Although attempts to synthesize quinine, a plant product effective against malaria, failed, these efforts encouraged industrial organic chemists to synthesize many useful substances, including dyes, antibiotics, and antihistamines. The aniline-derived dye methylene blue was a member of a new class of polycyclic chemicals, the phenothiazines. Efforts to modify phenothiazines to find an antimalarial agent also failed but led to novel antiemetic-sedative antihistamines, including promethazine, promazine, and eventually chlorpromazine--the first effective treatment for schizophrenia and mania. Chlorpromazine has antipsychotic and antimanic properties, and it revolutionized the therapeutics of psychotic illnesses.

A placebo-controlled study of sildenafil effects on cognition in schizophrenia

BACKGROUND

Phosphodiesterase 5 (PDE5) inhibitors increase cyclic guanosine monophosphate (cGMP) concentrations in the intracellular pathway activated by N-methyl-D-aspartic acid receptors which is believed to mediate long-term potentiation and memory consolidation. The PDE5 inhibitor sildenafil has been shown to enhance memory in animal models. In addition, neuronal nitric oxide synthase, another component of the NMDA/nitric oxide/cGMP intracellular pathway, has been reported to be dysregulated in schizophrenia patients.

MATERIALS AND METHODS

Seventeen adult schizophrenia outpatients treated with a stable dose of antipsychotic received a single oral dose of placebo, sildenafil 50 mg, and sildenafil 100 mg in random order with a 48-h interval between administrations. Psychiatric symptom ratings and a cognitive battery were performed at baseline and 1 hour following each administration of the study drug. In addition, memory consolidation was examined by testing recall 48 h later, prior to the next administration of the study drug.

RESULTS

Fifteen subjects completed all three treatment conditions. One subject developed irritability and required hospitalization 2 days after receiving sildenafil 100 mg. Neither dose of sildenafil significantly affected cognitive performance or symptom ratings compared to the placebo.

CONCLUSION

Despite evidence for cognitive-enhancing effects of sildenafil in animal models, the strategy for treating putative NMDA receptor-mediated memory deficits in schizophrenia with sildenafil 50 and 100 mg was not successful. It is possible that the doses used in this study were not optimal or that repeated dosing may be necessary to achieve therapeutic effects. Agents under development that inhibit other subtypes of PDE remain promising for schizophrenia and dementia.

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.

Nitric oxide synthase inhibition attenuates phencyclidine-induced disruption of cognitive flexibility

Schizophrenia encompasses, amongst other symptoms, a heavy load of cognitive dysfunctionality. Using the psychotomimetic agent, phencyclidine (PCP), we have previously found that PCP-induced disruptions of cognitive function in translational rodent models of schizophrenia are dependent on nitric oxide (NO) production. In the present study, male Sprague-Dawley rats were subjected to a Morris water maze task designed to assess cognitive flexibility (i.e. the ability to cope with an increasingly demanding cognitive task) by means of a "constant reversal learning paradigm". Experiments were conducted to evaluate the effects of the NO synthase inhibitor, L-NAME (10 mg/kg), on PCP-induced (2 mg/kg) impairments. Control animals significantly improved their learning over the first 3 consecutive days, whereas PCP-treated animals failed to show any significant learning. Pretreatment with L-NAME normalized the PCP-induced disruption of learning to control levels. These findings suggest that PCP-induced disruptions of cognitive flexibility (i.e. ability to modify behaviour according to an increasingly demanding cognitive task) are dependent upon NO production. These observations, together with accumulated clinical findings, suggest that the NO system is a potential treatment target for cognitive dysfunctions in schizophrenia.

The effects of methylene blue on renal scarring due to pyelonephritis in rats

The aim of this study was to evaluate the efficiency of methylene blue (MB) in preventing renal scar formation after the induction of pyelonephritis (PNP) in a rat model with delayed antimicrobial therapy. An inoculum of the K-12 strain of Escherichia coli was injected into both kidneys. Control groups received isotonic saline instead of bacterial solution. Four equal groups were then formed: the PNP group was untreated and the PNP ciprofloxacin (CIP) treated group was treated only with CIP intraperitoneally (i.p.) starting on the third day following bacterial inoculation. In the PNP (MB)-treated group, MB was given i.p., and in the PNP MB + CIP-treated group, MB + CIP were administered i.p.. In the sixth week following bacterial inoculation, all rats were sacrificed, and both kidneys of the rats in all groups were examined biochemically and histopathologically for renal scarring. Renal scar was significant in the groups treated with MB alone or MB + CIP combination compared with untreated or antibiotic only groups. Delayed treatment with antibiotics had no effect on scarring. These results suggest that the addition of MB to the delayed antibiotic therapy might be beneficial in preventing PNP-induced oxidative renal tissue damage.

The amino acid L-lysine blocks the disruptive effect of phencyclidine on prepulse inhibition in mice

RATIONALE

The cognitive and attentional deficits observed in schizophrenic patients are now considered central to the pathophysiology of the disorder. These deficits include an inability to filter sensory input as measured by, e.g., prepulse inhibition (PPI) reflex. Administration of phencyclidine (PCP), a drug that can induce a schizophrenia-like psychosis in humans, disrupts PPI in experimental animals. In rodents, this PCP-induced deficit can be blocked by pretreatment with nitric oxide (NO) synthase inhibitors. This suggests that some of the behavioral effects of PCP are mediated via NO. The substrate for in vivo NO production is L-arginine, and active transport of L-arginine via the cationic amino acid transporter may serve as a regulatory mechanism in NO production.

OBJECTIVES

The aim of the present study was to study the effects of L-arginine transport inhibition, using acute and repeated L-lysine treatment, on PCP-induced disruption of PPI in mice.

RESULTS

Subchronic, and to some extent acute, pretreatment with L-lysine blocked a PCP-induced deficit in PPI without affecting basal PPI.

CONCLUSIONS

L-lysine has been shown to block L-arginine transport in vitro, most likely via a competitive blockade and down regulation of cationic amino acid transporters. However, the importance of L-arginine transport as a regulatory mechanism in NO production in vivo is still not clear. The present results lend further support to the notion that some of the effects of PCP in the central nervous system are mediated via NO and that L-arginine transport may play a role in the regulation of NO production in the brain.

Pharmacological treatment of primary negative symptoms in schizophrenia: a systematic review

BACKGROUND

Optimal treatment of primary negative symptoms is important because their presence is associated with poor outcome.

AIMS

To systematically review all studies dealing with the efficacy of pharmacological agents on primary negative symptoms.

METHOD

A comprehensive search of the relevant literature was undertaken using electronic database, reference lists and personal contact.

RESULTS

There is a lack of standardized research designs. Amisulpride is the most extensively studied drug with respect to efficacy against primary negative symptoms. At low doses it demonstrates a consistent, modest effect compared to placebo, though not to conventional antipsychotics and has yet to be tested against other atypicals. Evidence from multiple studies that used simple statistical analyses and inclusion criteria for patients with primary negative symptoms does not support a direct effect for clozapine. Path-analysis studies support the direct effects of risperidone, olanzapine, sertindole and aripiprazole, however, different statistical analyses of the same risperidone study produced conflicting results and the direct effects of olanzapine were not confirmed in selected patients with primary negative symptoms. There are no studies supporting the use of ziprasidone or quetiapine. The effects of typical antipsychotics on primary negative symptoms are inconclusive and likely to depend on drug dosages. Selective serotonin reuptake inhibitors (SSRIs), mirtazepine and NMDA agonists show early promise but require further study. Novel agents such as selegiline, naltrexone, dehydroepiandrosterone, galantamine, Ginkgo, nitric oxide, L-deprenyl and pergolide show positive effects on general negative symptoms but remain untested against primary negative symptoms.

CONCLUSIONS

Further studies using standardized selective inclusion criteria and controlling for chronicity are needed. Research guidelines are discussed.

Effects of phencyclidine on spatial learning and memory: Nitric oxide-dependent mechanisms

Cognitive deficits of schizophrenia constitute a disabling part of the disease predicting treatment success as well as functional outcome. Phencyclidine (PCP), a non-competitive NMDA receptor antagonist was used to model schizophrenic cognitive dysfunctions of learning and memory using the Morris water maze paradigm for reference memory. In experiment 1 male Sprauge-Dawley rats were acutely administered PCP (0.5, 1.0 and 2.0 mg/kg s.c.) before the first swim session on each of the four acquisition days. Probe test for reference memory was performed 2 days after the last acquisition day; the first probe without drug treatment to assess reference memory and a second probe with prior drug treatment to control for state dependency effects of PCP. In experiment 2 the effects of pre-treatment (10 min before PCP) with the nitric oxide synthase inhibitor, L-NAME (10 mg/kg s.c.), on the PCP (2 mg/kg)-induced spatial memory deficit was evaluated in the Morris water maze paradigm for reference memory. The results showed that PCP in a dose of 2 mg/kg disrupts spatial learning as estimated by prolonged search time to find platform during acquisition as well as the reference memory test as measured by less time spent in target quadrant during probe trial. No state dependency effects of PCP were found. Pre-treatment with L-NAME completely reversed the PCP-induced disruption of acquisition learning. The reference memory disruption was, however, not completely restored as measured by probe trial.

Plasma nitrate values in patients with obsessive-compulsive disorder

Recently there has been increasing evidence that free oxygen species may play an important role in the pathophysiology of various neuropsychiatric disorders. The present study was performed to assess the changes in plasma nitric oxide (NO) levels in patients with obsessive-compulsive disorder (OCD) compared to age- and sex-matched normal controls. Twenty-three patients with OCD and 23 healthy volunteers were included in the study. NO values were determined in the plasma of normal healthy controls and the OCD patients. Plasma nitrate levels in OCD patients were significantly higher than those in controls and were significantly and positively correlated with Yale-Brown Obsession Compulsion Scale scores but not related to age or to the duration of illness. These findings indicated a possible role of increased NO may be relevant to the pathophysiology of OCD.

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.

Treatments for schizophrenia: a critical review of pharmacology and mechanisms of action of antipsychotic drugs

The treatment of schizophrenia has evolved over the past half century primarily in the context of antipsychotic drug development. Although there has been significant progress resulting in the availability and use of numerous medications, these reflect three basic classes of medications (conventional (typical), atypical and dopamine partial agonist antipsychotics) all of which, despite working by varying mechanisms of actions, act principally on dopamine systems. Many of the second-generation (atypical and dopamine partial agonist) antipsychotics are believed to offer advantages over first-generation agents in the treatment for schizophrenia. However, the pharmacological properties that confer the different therapeutic effects of the new generation of antipsychotic drugs have remained elusive, and certain side effects can still impact patient health and quality of life. Moreover, the efficacy of antipsychotic drugs is limited prompting the clinical use of adjunctive pharmacy to augment the effects of treatment. In addition, the search for novel and nondopaminergic antipsychotic drugs has not been successful to date, though numerous development strategies continue to be pursued, guided by various pathophysiologic hypotheses. This article provides a brief review and critique of the current therapeutic armamentarium for treating schizophrenia and drug development strategies and theories of mechanisms of action of antipsychotics, and focuses on novel targets for therapeutic agents for future drug development.

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.

Pathophysiological role of nitric oxide and adrenomedullin in autism

Several studies indicate that nitric oxide (NO) is involved in the aetiopathogenesis of many neuropsychiatric disorders such as schizophrenia, bipolar disorder, depression, Alzheimer's disease, Hungtington disease and stroke. Although it has not been investigated yet, several recent studies proposed that NO may have a pathophysiological role in autism. Adrenomedullin (AM), a recently discovered 52-amino acid peptide hormone, induces vasorelaxation by activating adenylate cyclase and also by stimulating NO release. AM immune reactivity is present in the brain consistent with a role as a neurotransmitter. It has been stated that NO and AM do function in the regulation of many neurodevelopmental processes. We hypothesized that NO and AM activities have been affected in autistic patients and aimed to examine these molecules. Twenty-six autistic patients and 22 healthy control subjects were included in this study. AM and total nitrite (a metabolite of NO) levels have been measured in plasma. The mean values of plasma total nitrite and AM levels in the autistic group were significantly higher than control values, respectively (p < 0.001, p = 0.028). There is no correlation between total nitrite and AM levels (r = 0.11, p = 0.31). Certainly, this subject needs much further research investigating autistic patients in earlier periods of life and with subtypes of the disorder.

The possible pathophysiological role of plasma nitric oxide and adrenomedullin in schizophrenia

Evidence is accumulating for a possible role of nitric oxide (NO) in schizophrenia. Adrenomedullin (AM) induces vasorelaxation by activating adenylate cyclase and also by stimulating the release of NO. AM immune reactivity is present in the brain consistent with a role as neurotransmitter. We aimed to examine plasma levels of nitrite (a metabolite of NO) and AM in schizophrenic patients. Eighty-two patients with schizophrenia and 21 healthy control subjects were included in this study. DSM-IV diagnosis of chronic schizophrenia was established on the basis of independent structured clinical interviews and review of records by two qualified psychiatrists which included the Brief Psychiatric Rating Scale (BPRS), The Scale for the Assessment of Negative Symptoms (SANS) and The Scale for the Assessment of Positive Symptoms (SAPS). Total nitrite and AM have been studied in plasma. The mean values of plasma nitrite and AM levels in schizophrenic group were significantly higher than control values, respectively (P=0.03, P<0.0001). AM levels of schizophrenic patients were three fold higher than controls. In correlation analyses, there were statistically significant positive correlations between AM level and SAPS-delusion subscale (r=0.27, P=0.04); SAPS-bizarre behavior subscale (r=0.28, P=0.03) and SAPS-total (r=0.36, P=0.005). There is no correlation between total nitrite and AM levels (r=0.11, P=0.31). Both NO and AM may have a pathophysiological role in schizophrenia, and clinically symptomatology and prognosis of schizophrenia. This subject needs further study including treatment response and subtypes of schizophrenia.

The indices of endogenous oxidative and antioxidative processes in plasma from schizophrenic patients. The possible role of oxidant/antioxidant imbalance

There is great evidence in recent years that oxygen free radicals play an important role in the pathophysiology of schizophrenia. The present study was performed to assess the changes in plasma nitric oxide (NO) and thiobarbituric acid-reactive substances (TBARS) levels, and superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and xanthine oxidase (XO) activities in schizophrenic patients compared to age- and sex-matched normal controls. A hundred patients with schizophrenia and 51 healthy volunteers were included in the study. XO, SOD, and GSH-Px activities as well as NO and TBARS levels were estimated by standard biochemical techniques in the plasma of normal healthy controls and schizophrenia patients. In schizophrenia, increased plasma XO activity (P < .0001) and NO levels (P < .0001), decreased SOD activity (P < .0001), and unchanged GSH-Px activity were detected compared to control group. Plasma TBARS levels were increased in schizophrenic patients (P < .01), especially in the residual subtype. TBARS levels in nonsmoker schizophrenic patients were found to be higher than nonsmoker controls. Although TBARS levels in both patients and controls were found to be higher in smokers as compared to nonsmokers, it was not statistically significant. No effects of duration of the illness, gender, and low and high dose of daily neuroleptic treatment equivalent to chlorpromazine on oxidant and antioxidant parameters were observed. Because the dose and the duration of treatment with drugs have no influence on the results, it can be interpreted that the findings are more likely to be related mainly to the underlying disease. These findings indicated a possible role of increased oxidative stress and diminished enzymatic antioxidants, both of which may be relevant to the pathophysiology of schizophrenia. On the other hand, increased NO production by nitric oxide synthetases (NOSs) suggests a possible role of NO in the pathophysiological process of schizophrenia. These findings may also suggest some clues for the new treatment strategies with antioxidants and NO synthase (NOS) inhibitors in schizophrenia.

Transplacental exposure to methylene blue initiates teratogenesis in the mouse: preliminary evidence for a mechanistic implication of cyclic GMP pathway disruption

BACKGROUND

The vital dye methylene blue (MB) has been shown to be teratogenic when injected into the amnion in the second trimester. On the other hand, the teratogenic potential of transplacental exposure to MB has not been determined.

METHODS

MB was administered subcutaneously to ICR (CD-1) mice at 0, 35, 50, 60, or 70 mg/kg on gestation day 8 (plug day = day 0). Teratological assessments were carried out at term gestation, on gestation day 18. Since MB inhibits soluble guanylate cyclase enzyme activity, zaprinast (ZPN), a selective cGMP-phosphodiesterase type V inhibitor, was administered to prevent developmental disorders initiated by MB at 50 mg/kg.

RESULTS

There was a dose-dependent increment of embryolethality. MB treatment also produced axial skeleton and neural tube defects. Coadministration of ZPN (20 mg/kg per three times) abolished completely MB-induced neural tube defects and reduced by one-half the incidence of fetuses exhibiting axial skeletal defects. ZPN did not provide protection against the embryocidal effects of MB.

CONCLUSIONS

This study showed that transplacental exposure to MB is teratogenic in the mouse. Coadministration of ZPN prevented partly MB-induced teratogenesis, which supports the hypothesis that imbalance of cGMP pathway accounts, in part, for the teratogenicity of MB.

Withdrawal-associated changes in peripheral nitrogen oxides and striatal cyclic GMP after chronic haloperidol treatment

The irreversible nature of haloperidol-induced tardive dyskinesia suggests a neurotoxic etiology, although the causes are unknown. Since nitric oxide demonstrates neurotoxic as well as neuroprotectant properties, and antipsychotics can inhibit nitric oxide (NO) synthase in vitro, this study investigates the NO-cGMP pathway as a pre-determining factor in chronic haloperidol-associated dyskinesia in rats. Sprague-Dawley rats were administered either water, oral haloperidol (0.25 mg/kg per day po), the guanylyl cyclase-nNOS inhibitor, methylene blue (MB; 5 mg/kg per day ip) or haloperidol plus MB for 3 weeks. In a second protocol, rats received water or haloperidol orally for 17 weeks, followed by 3 weeks withdrawal. Either saline (ip) or MB (ip) was administered for 3 weeks prior to haloperidol withdrawal. Vacous chewing movements (VCMs) were continuously monitored, followed by the determination of serum nitrogen oxides (NO(x)) and striatal cGMP at week 20. Chronic haloperidol engendered significant VCMs, with acute withdrawal resulting in significantly reduced plasma NO(x) and striatal cGMP. Furthermore, NO(x) and cGMP suppression was amplified by pre-withdrawal MB administration. Sub-acute haloperidol similarly induced incremental VCMs, but without effect on NO(x) or cGMP. However, haloperidol plus MB also induced significantly greater VCMs with decreased cGMP compared to haloperidol alone. Thus, NO(x)-cGMP inhibition persists pronounced after long-term haloperidol treatment and withdrawal. MB potentiation of these effects suggests that haloperidol inhibits a NO-dependent neuro-protective response to oxidative stress in the striatum that may pre-determine TD development.

The ascending reticular activating system--from aminergic neurons to nitric oxide

The cholinergic neurons of the laterodorsal and pedunculopontine tegmental neurons are thought to comprise an important portion of the ascending reticular activating system. More recent work has demonstrated that the neurons of this cell group also released a number of neruoactive peptides and can produce nitric oxide in response to increases in intracellular calcium. The release of NO from the nerve terminals of these cells within the thalamus varies with behavioural state, being much lower during slow wave sleep than during wake and paradoxical sleep states. The NO release in the thalamus appears to act via the type II cGMP-dependent protein kinase present at high levels in the thalamic neurons. Thus the NO-cGMP signal transduction system can play an important role in regulating thalamic activity across behavioural states.

Clozapine and several other antipsychotic/antidepressant drugs preferentially block the same 'core' fraction of GABA(A) receptors

Clozapine and several other antipsychotic/antidepressant drugs that fully or partially block GABA(A) receptors were tested at concentrations that reversed the inhibitory effect of 1 microM GABA on 35S-t-butylbicyclophosphorothionate ([35S]TBPS) binding to rat forebrain membranes only about 20-30%, here designated "core" fractions. Clozapine at 10 microM reverses 1 microM GABA 25+/-4.0% (n = 23) (its "core" fraction). Fourty three compounds were tested alone, and pairwise together with 10 microM Clozapine. The "core" fractions of some of the compounds yielded significant additive reversals together with 10 microM Clozapine, while others did not. A group of 14 compounds of which 7 are clinically effective antipsychotic drugs, including Chlorprothixene, Clomacran, Clopipazan, Fluotracen, Sulforidazine, Thioproperazine, and cis-Thiothixene, were statistically non-additive with 10 microM Clozapine, suggesting that all of these drugs selectively block the same core population of GABA(A) receptors as Clozapine. These non-additivities also suggest that Clozapine at 10 microM fully saturates a subset of GABA(A) receptors blocked by 1 microM GABA. Therefore, Clozapine probably blocks 2 or more types of GABA(A)receptors, but only half of the receptors that are sensitive to 1 microM GABA. A second group of 12 compounds of which 6 are clinically active antidepressant/antipsychotic drugs including Amoxapine, Clothiapine, Dibenzepine, Inkasan (Metralindole), Metiapine and Zimelidine were slightly, but significantly, additive with Clozapine suggesting that these compounds block most of Clozapine's core fraction, plus a small additional fraction. A third group consisted of ten compounds that yielded larger (R > 80) and statistically highly significant additivities with Clozapine. Complete additivity was obtained with Bathophenanthroline disulfonate, and Isocarboxazid, suggesting that they block GABA(A) receptors other than those blocked by 10 microM Clozapine. Seven "classical" GABA(A) receptor blockers, also tested at concentrations yielding 21 to 33% reversal alone, were all significantly additive with 10 microM Clozapine, but in no case was the additivity complete. The largest additivity was obtained with Pitrazepine (21%) and the smallest with Tubocurarine (9%). These results provide further support for the notion that selective blockade of the same subset of GABA(A) receptors may contribute to the clinical antipsychotic/antidepressant effects of Clozapine. The deltaB(opt) values for Clozapine are 50+/-1.7% and 26+/-2.6% (n = 3) in whole rat forebrain and cerebellum, respectively, confirming that clozapine-sensitive GABA(A) receptors are unevenly distributed in the brain. The sedative and anxiolytic properties of Clozapine and other antipsychotic drugs may be due to selective blockade of GABergic disinhibition at certain interneurons.