Validation of a suite of ERP and QEEG biomarkers in a pre-competitive, industry-led study in subjects with schizophrenia and healthy volunteers

OBJECTIVE

Complexity and lack of standardization have mostly limited the use of event-related potentials (ERPs) and quantitative EEG (QEEG) biomarkers in drug development to small early phase trials. We present results from a clinical study on healthy volunteers (HV) and patients with schizophrenia (SZ) that assessed test-retest, group differences, variance, and correlation with functional assessments for ERP and QEEG measures collected at clinical and commercial trial sites with standardized instrumentation and methods, and analyzed through an automated data analysis pipeline.

METHODS

81 HV and 80 SZ were tested at one of four study sites. Subjects were administered two ERP/EEG testing sessions on separate visits. Sessions included a mismatch negativity paradigm, a 40 Hz auditory steady-state response paradigm, an eyes-closed resting state EEG, and an active auditory oddball paradigm. SZ subjects were also tested on the Brief Assessment of Cognition (BAC), Positive and Negative Syndrome Scale (PANSS), and Virtual Reality Functional Capacity Assessment Tool (VRFCAT).

RESULTS

Standardized ERP/EEG instrumentation and methods ensured few test failures. The automated data analysis pipeline allowed for near real-time analysis with no human intervention. Test-retest reliability was fair-to-excellent for most of the outcome measures. SZ subjects showed significant deficits in ERP and QEEG measures consistent with published academic literature. A subset of ERP and QEEG measures correlated with functional assessments administered to the SZ subjects.

CONCLUSIONS

With standardized instrumentation and methods, complex ERP/EEG testing sessions can be reliably performed at clinical and commercial trial sites to produce high-quality data in near real-time.

Effects of the sigma-1 receptor agonist blarcamesine in a murine model of fragile X syndrome: neurobehavioral phenotypes and receptor occupancy

Fragile X syndrome (FXS), a disorder of synaptic development and function, is the most prevalent genetic form of intellectual disability and autism spectrum disorder. FXS mouse models display clinically-relevant phenotypes, such as increased anxiety and hyperactivity. Despite their availability, so far advances in drug development have not yielded new treatments. Therefore, testing novel drugs that can ameliorate FXS' cognitive and behavioral impairments is imperative. ANAVEX2-73 (blarcamesine) is a sigma-1 receptor (S1R) agonist with a strong safety record and preliminary efficacy evidence in patients with Alzheimer's disease and Rett syndrome, other synaptic neurodegenerative and neurodevelopmental disorders. S1R's role in calcium homeostasis and mitochondrial function, cellular functions related to synaptic function, makes blarcamesine a potential drug candidate for FXS. Administration of blarcamesine in 2-month-old FXS and wild type mice for 2 weeks led to normalization in two key neurobehavioral phenotypes: open field test (hyperactivity) and contextual fear conditioning (associative learning). Furthermore, there was improvement in marble-burying (anxiety, perseverative behavior). It also restored levels of BDNF, a converging point of many synaptic regulators, in the hippocampus. Positron emission tomography (PET) and ex vivo autoradiographic studies, using the highly selective S1R PET ligand [18F]FTC-146, demonstrated the drug's dose-dependent receptor occupancy. Subsequent analyses also showed a wide but variable brain regional distribution of S1Rs, which was preserved in FXS mice. Altogether, these neurobehavioral, biochemical, and imaging data demonstrates doses that yield measurable receptor occupancy are effective for improving the synaptic and behavioral phenotype in FXS mice. The present findings support the viability of S1R as a therapeutic target in FXS, and the clinical potential of blarcamesine in FXS and other neurodevelopmental disorders.

ANAVEX®2-73 (blarcamesine), a Sigma-1 receptor agonist, ameliorates neurologic impairments in a mouse model of Rett syndrome

Rett syndrome (RTT) is a severe neurodevelopmental disorder that is associated in most cases with mutations in the transcriptional regulator MECP2. At present, there are no effective treatments for the disorder. Despite recent advances in RTT genetics and neurobiology, most drug development programs have focused on compounds targeting the IGF-1 pathway and no pivotal trial has been completed as yet. Thus, testing novel drugs that can ameliorate RTT's clinical manifestations is a high priority. ANAVEX2-73 (blarcamesine) is a Sigma-1 receptor agonist and muscarinic receptor modulator with a strong safety record and preliminary evidence of efficacy in patients with Alzheimer's disease. Its role in calcium homeostasis and mitochondrial function, cellular functions that underlie pathological processes and compensatory mechanisms in RTT, makes blarcamesine an intriguing drug candidate for this disorder. Mice deficient in MeCP2 have a range of physiological and neurological abnormalities that mimic the human syndrome. We tested blarcamesine in female heterozygous mice carrying one null allele of Mecp2 (HET) using a two-tier approach, with age-appropriate tests. Administration of the drug to younger and older adult mice resulted in improvement in multiple motor, sensory, and autonomic phenotypes of relevance to RTT. The latter included motor coordination and balance, acoustic and visual responses, hindlimb clasping, and apnea in expiration. In line with previous animal and human studies, blarcamesine also showed a good safety profile in this mouse model of RTT. Clinical studies in RTT with blarcamesine are ongoing.

Pridopidine: Overview of Pharmacology and Rationale for its Use in Huntington's Disease

Despite advances in understanding the pathophysiology of Huntington’s disease (HD), there are currently no effective pharmacological agents available to treat core symptoms or to stop or prevent the progression of this hereditary neurodegenerative disorder. Pridopidine, a novel small molecule compound, has demonstrated potential for both symptomatic treatment and disease modifying effects in HD. While pridopidine failed to achieve its primary efficacy outcomes (Modified motor score) in two trials (MermaiHD and HART) there were consistent effects on secondary outcomes (TMS). In the most recent study (PrideHD) pridiopidine did not differ from placebo on TMS, possibly due to a large enduring placebo effect.

This review describes the process, based on in vivo systems response profiling, by which pridopidine was discovered and discusses its pharmacological profile, aiming to provide a model for the system-level effects, and a rationale for the use of pridopidine in patients affected by HD. Considering the effects on brain neurochemistry, gene expression and behaviour in vivo, pridopidine displays a unique effect profile. A hallmark feature in the behavioural pharmacology of pridopidine is its state-dependent inhibition or activation of dopamine-dependent psychomotor functions. Such effects are paralleled by strengthening of synaptic connectivity in cortico-striatal pathways suggesting pridopidine has potential to modify phenotypic expression as well as progression of HD. The preclinical pharmacological profile is discussed with respect to the clinical results for pridopidine, and proposals are made for further investigation, including preclinical and clinical studies addressing disease progression and effects at different stages of HD.

Co-administration of the Dopaminergic Stabilizer Pridopidine and Tetrabenazine in Rats

BACKGROUND

The efficacy of the dopaminergic stabilizer, pridopidine, in reducing the voluntary and involuntary motor symptoms of Huntington's disease (HD) is under clinical evaluation. Tetrabenazine is currently the only approved treatment for chorea, an involuntary motor symptom of HD; both compounds influence monoaminergic neurotransmission.

OBJECTIVE

To investigate pharmacological interactions between pridopidine and tetrabenazine.

METHODS

Drug-interaction experiments, supplemented by dose-response data, examined the effects of these compounds on locomotor activity, on striatal levels of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC), and on levels of activity-regulated cytoskeleton-associated (Arc) gene expression in the striatum and frontal cortex of male Sprague-Dawley rats. Haloperidol, a classical dopamine D2 receptor antagonist, was also tested for comparison.

RESULTS

Monitoring for 1 hour after co-administration of tetrabenazine 0.64 mg/kg and pridopidine 32 mg/kg revealed a reduction in locomotor activity, measured as distance travelled, in the tetrabenazine treated group, down to 61% vs. vehicle controls (p < 0.001). This was significantly alleviated by pridopidine (distance travelled reached 137% vs. tetrabenazine controls, p < 0.01). In contrast, co-administration of haloperidol 0.12 mg/kg and tetrabenazine produced increased inhibition of locomotor activity over the same period (p < 0.01, 41% vs. tetrabenazine). Co-administration of pridopidine, 10.5 mg/kg or 32 mg/kg, with tetrabenazine counteracted significantly (p < 0.05) and dose-dependently the decrease in frontal cortex Arc levels induced by tetrabenazine 0.64 mg/kg (Arc mRNA reached 193% vs. tetrabenazine mean at 32 mg/kg); this counteraction was not seen with haloperidol. Tetrabenazine retained its characteristic neurochemical effects of increased striatal DOPAC and reduced striatal dopamine when co-administered with pridopidine.

CONCLUSIONS

Pridopidine alleviates tetrabenazine-induced behavioural inhibition in rats. This effect may be associated with pridopidine-induced changes in cortical activity and may justify clinical evaluation of pridopidine/tetrabenazine combination therapy.

The dopaminergic stabilizers pridopidine and ordopidine enhance cortico-striatal Arc gene expression

The dopaminergic stabilizers pridopidine [4-(3-(methylsulfonyl)phenyl)-1-propylpiperidine] and ordopidine [1-ethyl-4-(2-fluoro-3-(methylsulfonyl)phenyl)piperidine] inhibit psychostimulant-induced hyperactivity, and stimulate behaviour in states of hypoactivity. While both compounds act as dopamine D2 receptor antagonists in vitro, albeit with low affinity, their specific state-dependent behavioural effect profile is not shared by D2 receptor antagonists in general. To further understand the neuropharmacological effects of pridopidine and ordopidine, and how they differ from other dopaminergic compounds in vivo, we assessed the expression of activity-regulated cytoskeleton-associated protein/activity-regulated gene 3.1 (Arc), an immediate early gene marker associated with synaptic activation, in the frontal cortex and striatum. Furthermore, monoamine neurochemistry and locomotor activity were assessed. The effects of pridopidine and ordopidine were compared to reference dopamine D1 and D2 receptor agonists and antagonists, as well as the partial dopamine D2 agonist aripiprazole. Pridopidine and ordopidine induced significant increases in cortical Arc expression, reaching 2.2- and 1.7-fold levels relative to control, respectively. In contrast, none of the reference dopamine D1 and D2 compounds tested increased cortical Arc expression. In the striatum, significant increases in Arc expression were seen with both pridopidine and ordopidine as well as the dopamine D2 receptor antagonists, remoxipride and haloperidol. Interestingly, striatal Arc expression correlated strongly and positively with striatal 3,4-dihydroxyphenylacetic acid, suggesting that antagonism of dopamine D2 receptors increases Arc expression in the striatum. In conclusion, the concurrent increase in cortical and striatal Arc expression induced by pridopidine and ordopidine appears unique for the dopaminergic stabilizers, as it was not shared by the reference compounds tested. The increase in cortical Arc expression is hypothesized to reflect enhanced N-methyl-D-aspartic acid receptor-mediated signalling in the frontal cortex, which could contribute to the state-dependent locomotor effects of pridopidine and ordopidine.

The genetic contribution of the NO system at the glutamatergic post-synapse to schizophrenia: further evidence and meta-analysis

NO is a pleiotropic signaling molecule and has an important role in cognition and emotion. In the brain, NO is produced by neuronal nitric oxide synthase (NOS-I, encoded by NOS1) coupled to the NMDA receptor via PDZ interactions; this protein-protein interaction is disrupted upon binding of NOS1 adapter protein (encoded by NOS1AP) to NOS-I. As both NOS1 and NOS1AP were associated with schizophrenia, we here investigated these genes in greater detail by genotyping new samples and conducting a meta-analysis of our own and published data. In doing so, we confirmed association of both genes with schizophrenia and found evidence for their interaction in increasing risk towards disease. Our strongest finding was the NOS1 promoter SNP rs41279104, yielding an odds ratio of 1.29 in the meta-analysis. As findings from heterologous cell systems have suggested that the risk allele decreases gene expression, we studied the effect of the variant on NOS1 expression in human post-mortem brain samples and found that the risk allele significantly decreases expression of NOS1 in the prefrontal cortex. Bioinformatic analyses suggest that this might be due the replacement of six transcription factor binding sites by two new binding sites as a consequence of proxy SNPs. Taken together, our data argue that genetic variance in NOS1 resulting in lower prefrontal brain expression of this gene contributes to schizophrenia liability, and that NOS1 interacts with NOS1AP in doing so. The NOS1-NOS1AP PDZ interface may thus well constitute a novel target for small molecules in at least some forms of schizophrenia.

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.

Noise benefit in prepulse inhibition of the acoustic startle reflex

RATIONALE

Under some conditions, external sensory noise enhances cognitive functions, a phenomenon possibly involving stochastic resonance and/or enhanced central dopamine transmission. Prepulse inhibition (PPI) of the startle reflex is a robust measure of sensorimotor gating and can be modulated by activity in the cortex and basal ganglia, including the central dopamine pathways.

OBJECTIVES

Previous empirical studies suggest a differential effect of acoustic noise in normal children and children with attention-deficit hyperactivity disorder (ADHD). This study investigated the effect of acoustic noise on PPI and if dopamine transmission interacts with acoustic noise effects in a rat ADHD model.

METHODS

The effect of background acoustic noise on acoustic startle response and PPI were measured with a constant prepulse to background noise ratio of 9 dB(A). Spontaneously hypertensive (SH) rats were used as the ADHD model and compared with Wistar and Sprague-Dawley rats. Microdialysis, methylphenidate treatment and 6-OHDA lesions were used to investigate interaction with dopamine transmission.

RESULTS

Background noise facilitated PPI differently in SH rats and controls. The prefrontal cortex in SH rats had low basal dopamine concentrations, a high DOPAC/dopamine ratio and blunted dopamine release during PPI testing. Methylphenidate had small, but strain-specific, effects on startle and PPI. Bilateral 6-hydroxydopamine lesions did not alter startle or PPI.

CONCLUSIONS

Prefrontal dopamine transmission is altered in SH rats during the sensorimotor gating task of PPI of the acoustic startle, indicating increased dopamine reuptake in this ADHD rat model. We propose that noise benefit could be explored as a non-pharmacological alternative for treating neuropsychiatric disorders.

Prefrontal NMDA receptor antagonism reduces impairments in pre-attentive information processing

A well established theory proposes that glutamate signalling via the NMDA receptor is compromised in patients with schizophrenia. Deficits related to NMDA receptor signalling can be observed in several brain regions including the prefrontal cortex (PFC), an area extensively linked to the cognitive dysfunction in this disease and notably affected by NMDA receptor antagonists such as phencyclidine (PCP). In addition, a number of studies suggest that normalizing of PFC function could constitute a treatment rationale for schizophrenia. To further study the role of PFC function we investigated the effect of local PFC NMDA receptor blockade on impaired prepulse inhibition (PPI) induced by systemic administration of PCP. Mice received prefrontal injections of PCP (0.01, 0.1 or 1mM) before PCP treatment (5mg/kg) and were thereafter tested for PPI. PCP induced deficits in PPI were ameliorated by prefrontal PCP (0.1mM) treatment whereas PPI was not affected by prefrontal cortex PCP administration per se at any of the doses tested. Taken together, inhibition of NMDA receptors in the PFC does not seem to be enough to impair PPI per se but NMDA receptor mediated signalling in the PFC may be a key factor for the PPI-disruptive effects of global NMDA receptor inhibition. This indicates that targeting PFC NMDA receptor signalling may have potential as a treatment target for schizophrenia although further studies are needed to understand pharmacology and pathophysiological role of PFC NMDA receptors.

Contributions of dopamine D1, D2, and D3 receptor subtypes to the disruptive effects of cocaine on prepulse inhibition in mice

Deficits in prepulse inhibition (PPI) of startle, an operational measure of sensorimotor gating, are characteristics of schizophrenia and related neuropsychiatric disorders. Previous studies in mice demonstrate a contribution of dopamine (DA) D(1)-family receptors in modulating PPI and DA D(2) receptors (D2R) in mediating the PPI-disruptive effects of amphetamine. To examine further the contributions of DA receptor subtypes in PPI, we used a combined pharmacological and genetic approach. In congenic C57BL/6 J wild-type mice, we tested whether the D1R antagonist SCH23390 or the D2/3R antagonist raclopride would attenuate the effects of the indirect DA agonist cocaine (40 mg/kg). Both the D1R and D2/3R antagonists attenuated the cocaine-induced PPI deficit. We also tested the effect of cocaine on PPI in wild-type and DA D1R, D2R, or D3R knockout mice. The cocaine-induced PPI deficit was influenced differently by the three DA receptor subtypes, being absent in D1R knockout mice, partially attenuated in D2R knockout mice, and exaggerated in D3R knockout mice. Thus, the D1R is necessary for the PPI-disruptive effects of cocaine, while the D2R partially contributes to these effects. Conversely, the D3R appears to inhibit the PPI-disruptive effects of cocaine. Uncovering neural mechanisms involved in PPI will further our understanding of substrates of sensorimotor gating and could lead to better therapeutics to treat complex cognitive disorders such as schizophrenia.

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.

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.

The atypical antipsychotic, aripiprazole, blocks phencyclidine-induced disruption of prepulse inhibition in mice

RATIONALE

The psychotomimetic drug, phencyclidine, induces schizophrenia-like behavioural changes in both humans and animals. Phencyclidine-induced disruption of sensory motor gating mechanisms, as assessed by prepulse inhibition of the acoustic startle, is widely used in research animals as a screening model for antipsychotic properties in general and may predict effects on negative and cognitive deficits in particular. Dopamine (DA) stabilizers comprise a new generation of antipsychotics characterized by a partial DA receptor agonist or antagonist action and have been suggested to have a more favourable clinical profile.

OBJECTIVE

The aim of the present study was to investigate the ability of first, second and third generation antipsychotics to interfere with the disruptive effect of phencyclidine on prepulse inhibition in mice.

RESULTS

Aripiprazole blocked the phencyclidine-induced disruption of prepulse inhibition. The atypical antipsychotic clozapine was less effective, whereas olanzapine, and the typical antipsychotic haloperidol, failed to alter the effects of phencyclidine on prepulse inhibition.

CONCLUSIONS

The somewhat superior efficacy of clozapine compared to haloperidol may be explained by its lower affinity and faster dissociation rate for DA D2 receptors possibly combined with an interaction with other receptor systems. Aripiprazole was found to be more effective than clozapine or olanzapine, which may be explained by a partial agonist activity of aripiprazole at DA D2 receptors. In conclusion, the present findings suggest that partial DA agonism leading to DA stabilizing properties may have favourable effects on sensorimotor gating and thus tentatively on cognitive dysfunctions in schizophrenia.

Phencyclidine affects memory in a nitric oxide-dependent manner: Working and reference memory

Phencyclidine (PCP), a non-competitive NMDA receptor antagonist, was used to model schizophrenia-like cognitive dysfunctions of learning and memory in rats using the Morris water maze model for spatial memory. A protocol introduced by Baldi and co-workers was used to distinguish working memory from reference memory. Male Sprague-Dawley rats were administered PCP (2.0 mg/kg) before the first swimming trial on each of five spatial memory acquisition days, either alone or after pre-treatment with the nitric oxide synthase inhibitor, L-NAME (10 mg/kg). Probe tests for memory were conducted before and after each acquisition session. The results showed that PCP disrupted the acquisition of both working and reference memory. Pre-treatment with L-NAME reversed both these effects of PCP. L-NAME treatment by itself did not significantly alter either acquisition or retention of spatial memory.

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.

Effects of phencyclidine on acoustic startle and prepulse inhibition in neuronal nitric oxide synthase deficient mice

Prepulse inhibition of acoustic startle is a behavioural response, which is used to estimate sensorimotor gating deficits in schizophrenia. Recent studies show that several behavioural effects of the psychotomimetic drug, phencyclidine (PCP), in rodents are blocked by nitric oxide synthase (NOS) inhibitors suggesting that NO plays an important role in the pharmacological effects of PCP. The present study was conducted to examine the effects of PCP on prepulse inhibition in neuronal NOS (nNOS) deficient mice. PCP treatment caused a significant and dose-related increase in prepulse inhibition in nNOS-/- mice whereas prepulse inhibition was not significantly affected in +/+ and +/- mice. Basal prepulse inhibition level did not differ significantly between the groups. Furthermore, PCP caused a dose-related decrease in startle response reactivity in +/+ mice but did not significantly affect this measure in +/- and -/- mice. Basal startle response level did not differ between +/+ and +/- but was significantly lower in -/- mice. It is concluded that nNOS plays a role in the NO-sensitive effects of PCP.

Antagonism of the nitric oxide synthase inhibitor, L-NAME, of the effects of phencyclidine on latent inhibition in taste aversion conditioning

Latent inhibition (LI) is a behavioural procedure used to evaluate the potential propsychotic and antipsychotic properties of psychoactive drugs. In the present study, a conditioned taste aversion (CTA) procedure was used to investigate the effects of the nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), and the psychotomimetic drugs, phencyclidine (PCP) and d-amphetamine (d-AMP) on LI. PCP (2 mg/kg) and d-AMP (0.5 mg/kg) were both found to enhance LI in this procedure. The effect of d-AMP on LI was less pronounced and this drug also caused a weak disruption of taste aversion conditioning. Pretreatment with L-NAME (10 mg/kg) blocked the LI enhancing effect of PCP on LI but not that of d-AMP. L-NAME by itself caused an attenuation of LI. L-NAME has been shown to block also other behavioural and biochemical effects of PCP in previous studies and these results and the present findings suggest that at least some of the effects PCP are dependent on NO and possibly also that some NOS inhibitors may exert antipsychotic properties.

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.

The neuronal selective nitric oxide synthase inhibitor, Nomega-propyl-L-arginine, blocks the effects of phencyclidine on prepulse inhibition and locomotor activity in mice

Phencyclidine has frequently been used to model schizophrenia in animals. In the present study, the ability of the neuronal selective nitric oxide synthase (NOS) inhibitor, Nomega-propyl-L-arginine, to block the behavioural effects of phencyclidine in mice was investigated. N(omega)-propyl-L-arginine (20 mg/kg) was found to block both phencyclidine (4 mg/kg)-induced disruption of prepulse inhibition and phencyclidine-induced stimulation of locomotor activity in the mice tested. It is concluded that the NOS-sensitive behavioural effects of phencyclidine in rodents is dependent on neuronal NOS and that NO may play a role in the psychotomimetic effects of phencyclidine.

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.

The effects of phencyclidine on latent inhibition in taste aversion conditioning: differential effects of preexposure and conditioning

Latent inhibition (LI) is a behavioural procedure in which preexposure to a stimulus not followed by reinforcement retards subsequent conditioning to this stimulus when it is paired with reinforcement. Changes in LI thus reflect greater or lesser retardation of learning which essentially implies a potentiation or an attenuation of the LI effect. LI has proved sensitive to psychotomimetic and antipsychotic treatment, which has encouraged its use to model learning and attention deficits in schizophrenia. In the present study, experiments were conducted to evaluate the effects of the psychotomimetic drug, phencyclidine (PCP, 2 mg/kg), and compare it with D-amphetamine (D-AMP, 0.33 and 1 mg/kg), on LI using a conditioned taste aversion procedure. PCP was found to potentiate LI when administered acutely prior to the conditioning trails, while no such effect was observed when administered prior to the preexposure trials. D-AMP, on the other hand, disrupted LI possibly due to a failure to induce a persistent taste aversion conditioning.

Habituation of acoustic startle is disrupted by psychotomimetic drugs: differential dependence on dopaminergic and nitric oxide modulatory mechanisms

RATIONALE

A deficit in attention and information processing has been considered a central feature in schizophrenia, which might lead to stimulus overload and cognitive fragmentation. It has been shown that patients with schizophrenia display a relative inability to gate incoming stimuli. Thus, patients repeatedly subjected to acoustic startle-eliciting stimuli habituate less to these stimuli than controls. Furthermore, schizophrenia-like symptoms can be induced by pharmacological manipulations in humans by psychotomimetic drugs, e.g. phencyclidine (PCP) and D-amphetamine (D-AMP). Recent studies show that the behavioural and biochemical effects of PCP in rodents are blocked by nitric oxide synthase (NOS) inhibitors, suggesting that NO plays an important role in at least the pharmacological effects of PCP.

OBJECTIVES

The first aim of the present study was to investigate if PCP, MK-801 and D-AMP impair habituation of acoustic startle in mice. Secondly, we examine the effect of the NOS inhibitor, L-NAME, and the dopamine receptor antagonist, haloperidol, on drug-induced deficit in habituation.

RESULTS

PCP (4 mg/kg), MK-801 (0.4 mg/kg) and D-AMP (5.0 mg/kg), impaired habituation of the acoustic startle response in mice. This effect was reversed by the NOS inhibitor, L-NAME. The typical antipsychotic, haloperidol, reversed the effects of PCP and D-AMP, but not that of MK-801.

CONCLUSIONS

The finding that PCP, MK-801 and D-AMP impair habituation in mice is consistent with the idea that these treatments model certain filter deficits seen in schizophrenic patients. Furthermore, the present results suggest that NO is critically involved in these effects on habituation, whereas that of dopamine is less clear.

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.

Prevalence of cdtABC genes encoding cytolethal distending toxin among Haemophilus ducreyi and Actinobacillus actinomycetemcomitans strains

The aim of this study was to investigate the presence of the three cdtABC genes responsible for production of cytolethal distending toxin (CDT) in Haemophilus ducreyi and Actinobacillus actinomycetemcomitans strains. Of 100 H. ducreyi strains from the culture collection of the University of Göteborg (CCUG), 27 strains with low or intermediate cytotoxic titre (< 1 in 10(4)) and 23 of the remaining isolates with a high cytotoxic titre (> or = 1 in 10(4)) were selected. Twenty-nine strains of H. ducreyi were isolated recently from patients with chancroid and 50 A. actinomycetemcomitans strains from patients with periodontitis. The cytotoxic activity on HEp-2 cells and the presence of cdtABC genes were studied by cytotoxicity assay of bacterial sonicates and PCR with primers specific for individual cdtA, B, and C genes of H. ducreyi in bacterial DNA preparations, respectively. All strains that manifested a cytotoxic titre in sonicate > or = 1 in 100 possessed all the three cdt genes. Eighteen of the 50 strains selected from the culture collection were negative and 32 positive for cdt genes. As all strains with a high cytotoxic titre gave positive PCR results, it can be assumed that the remaining 50 strains, which have high cytotoxic titre, would have been positive as well. Thus, it can be estimated that 82% of the culture collection strains had cdtABC genes. Similarly, 24 (83%) of 29 recent H. ducreyi isolates expressed the CDT activity and displayed all cdtABC genes. Forty-three (86%) of 50 strains of the closely related A. actinomycetemcomitans, expressing a cytotoxic activity > or = 1 in 100, also possessed all three genes. Furthermore, the nucleotide sequence of the cdtABC genes was highly conserved among H. ducreyi strains from different geographic areas. These results indicate that the majority of pathogenic H. ducreyi and A. actinomycetemcomitans strains express a CDT activity encoded by all three cdtABC.

The nitric oxide synthase inhibitor, L-NAME, block phencyclidine-induced disruption of prepulse inhibition in mice

RATIONALE

Schizophrenia is a major public health problem that affects approximately 1% of the population worldwide. Schizophrenia-like syndromes can be induced in humans by phencyclidine (PCP), a drug with marked psychomimetic properties. Recent studies show that the behavioural and biochemical effects of PCP in rats are blocked by nitric oxide synthase (NOS) inhibitors, suggesting that NO plays an important role in the pharmacological effects of PCP.

OBJECTIVE

The aim of this study was to investigate if PCP-induced disruption of prepulse inhibition of acoustic startle could be blocked by the NOS inhibitor, L-NAME, in mice.

RESULTS

The present study shows that PCP readily disrupts prepulse inhibition in mice normally without affecting pulse-alone trials. Furthermore, L-NAME blocked the PCP-induced disruption of prepulse inhibition in a dose-related manner.

CONCLUSIONS

The PCP-induced disruption of prepulse inhibition and the ability of L-NAME to block this effect in both rats and mice suggest that this is a general and not a species-specific effect. The results of the present study further suggest that PCP exerts at least some of its actions in the central nervous system by a NO-dependent mechanism.