Auditory P50 in schizophrenics on clozapine: improved gating parallels clinical improvement and changes in plasma 3-methoxy-4-hydroxyphenylglycol

Novel N100 area reliably captures aberrant sensory processing and is associated with neurocognition in early psychosis

BACKGROUND

Despite findings from translational and genetic studies in the event-related potential (ERP) literature, the validity and reliability of P50 suppression as a schizophrenia spectrum endophenotype has been questioned. Here, we aimed to examine sensory registration and gating measures derived from P50 and N100 amplitude, as well as N100 area-a novel approach proposed herein-in early psychosis versus health.

METHODS

Individuals at clinical high risk for psychosis (CHR; n = 77), first-episode psychosis (FE; n = 52), and healthy controls (HC; n = 65) were assessed in a paired-click auditory ERP paradigm. Eight CHR converted to psychosis (CHRC) and 39 did not (CHR-NC) by 24 months, while 30 CHR were lost to follow-. Group differences, test-retest reliability, and associations with neurocognitive function were assessed in nine ERP measures.

RESULTS

Significant differences were observed in N100 S1 amplitude, S1 area, and area difference between HC and FE, as well as in N100 S1 area between HC and CHR, among the total population. Furthermore, significant differences were found in N100 S1 area between HC and CHR-NC (Cliff's delta, Δ = 0.32), as well as in N100 area difference between HC and CHR-C (Δ = 0.55). Both N100 S1 area and area difference demonstrated moderate to acceptable reliability (intraclass correlation coefficients: 0.61-0.78). Processing speed negatively correlated with both N100 S1 area and area difference, while executive function negatively correlated with N100 S1 area alone in CHR and FE.

CONCLUSION

Among the ERP measures studied, N100 area measures may serve as a reliable biomarker of aberrant sensory processing and neurocognition in early psychosis.

Neurophysiology in psychosis: The quest for disease biomarkers

Psychotic disorders affect 3% of the population at some stage in life, are a leading cause of disability, and impose a great economic burden on society. Major breakthroughs in the genetics of psychosis have not yet been matched by an understanding of its neurobiology. Biomarkers of perception and cognition obtained through non-invasive neurophysiological tools, especially EEG, offer a unique opportunity to gain mechanistic insights. Techniques for measuring neurophysiological markers are inexpensive and ubiquitous, thus having the potential as an accessible tool for patient stratification towards early treatments leading to better outcomes. In this paper, we review the literature on neurophysiological markers for psychosis and their relevant disease mechanisms, mainly covering event-related potentials including P50/N100 sensory gating, mismatch negativity, and the N100 and P300 waveforms. While several neurophysiological deficits are well established in patients with psychosis, more research is needed to study neurophysiological markers in their unaffected relatives and individuals at clinical high risk. We need to harness EEG to investigate markers of disease risk as key steps to elucidate the aetiology of psychosis and facilitate earlier detection and treatment.

Lamotrigine and retigabine increase motor threshold in transcranial magnetic stimulation at the dose required to produce an antiepileptic effect against maximal electroshock-induced seizure in rats

Transcranial magnetic stimulation (TMS) is a neurophysiological technique that enables noninvasive evaluation of neuronal excitability in the brain. In the past, a large number of antiepileptic drugs were shown to increase the motor threshold (MT) in clinical TMS studies, suggesting the inhibition of excessive neuronal excitability. To facilitate drug development, the confirmation of similar changes in neurophysiological biomarkers in both preclinical and clinical studies is crucial; however, until now, there have been no data showing the drug efficacies on neuronal excitabilities as measured using TMS in rodents. In this study, we found that the antiepileptic drugs, lamotrigine (10 mg/kg) and retigabine (5 mg/kg), significantly increased the MT in rats using TMS, which is similar to clinical study findings. In addition, we demonstrated that these drugs could inhibit maximal electroshock (MES)-induced seizures in rats when given at the same dose required to be effective in the TMS experiment. These findings suggest that the effects of antiepileptic drugs in our rat TMS system have a similar sensitivity to that of the antiepileptic effects in rats with MES-induced seizures. The measurement of MT in a TMS study may be a noninvasive translational approach for predicting antiepileptic efficacy in drug development.

Meta-analysis of auditory P50 sensory gating in schizophrenia and bipolar disorder

The ability of the brain to reduce the amount of trivial or redundant sensory inputs is called gating function. Dysfunction of sensory gating may lead to cognitive fragmentation and poor real-world functioning. The auditory dual-click paradigm is a pertinent neurophysiological measure of sensory gating function. This meta-analysis aimed to examine the subcomponents of abnormal P50 waveforms in bipolar disorder and schizophrenia to assess P50 sensory gating deficits and examine effects of diagnoses, illness states (first-episode psychosis vs. schizophrenia, remission vs. episodes in bipolar disorder), and treatment status (medication-free vs. medicated). Literature search of PubMed between Jan 1st 1980 and March 31st 2019 identified 2091 records for schizophrenia, 362 for bipolar disorder. 115 studies in schizophrenia (4932 patients), 16 in bipolar disorder (975 patients) and 10 in first-degree relatives (848 subjects) met the inclusion criteria. P50 sensory gating ratio (S2/S1) and S1-S2 difference were significantly altered in schizophrenia, bipolar disorder and their first-degree relatives. First-episode psychosis did not differ from schizophrenia, however episodes altered P50 sensory gating in bipolar disorder. Medications improve P50 sensory gating alterations in schizophrenia significantly and at trend level in bipolar disorder. Future studies should examine longitudinal course of P50 sensory gating in schizophrenia and bipolar disorder.

Abnormal beta and gamma frequency neural oscillations mediate auditory sensory gating deficit in schizophrenia

BACKGROUND

Sensory gating is a process in which the brain's response to irrelevant and repetitive stimuli is inhibited. The sensory gating deficit in schizophrenia (SZ) is typically measured by the ratio or difference score of the P50 event-related potential (ERP) amplitudes in response to a paired click paradigm. While the P50 gating effect has usually been measured in relation to the peak amplitude of the S1 and S2 P50 ERPs, there is increasing evidence that inhibitory processes may be reflected by evoked or induced oscillatory activity during the inter-click interval in the beta (20-30 Hz) and gamma (30-50 Hz) frequency bands. We therefore examined the relationship between frequency specific activity in the inter-click interval with gating effects in the time and frequency domains.

METHOD

Paired-auditory stimuli were presented to 131 participants with schizophrenia and 196 healthy controls (HC). P50 ERP amplitudes to S1 and S2as well as averaged- and single-trial beta (20-30 Hz) and gamma (30-50 Hz) frequency power during the inter-click interval were measured from the CZ electrode site.

RESULTS

In the time domain, P50 gating deficits were apparent in both ratio and difference scores. This effect was mainly due to smaller S1 amplitudes in the patient group. SZ patients exhibited less evoked beta and gamma power, particularly at the 0-100 ms time point, in response to S1. Early (0-100 ms) evoked beta and gamma responses were critical in determining the S1 amplitude and extent of P50 gating across the delay interval for both HC and SZ.

CONCLUSION

Our findings support a disruption in initial sensory registration in those with SZ, and do not support an active mechanism throughout the delay interval. The degree of response to S1 and early beta and gamma frequency oscillations in the delay interval provides information about the mechanisms supporting auditory sensory gating, and may provide a framework for studying the mechanisms that support sensory inhibition.

Sensory processing deficiencies in patients with borderline personality disorder who experience auditory verbal hallucinations

Auditory verbal hallucinations (AVH) are common in patients with borderline personality disorder (BPD). We examined two candidate mechanisms of AVH in patients with BPD, suggested to underlie sensory processing systems that contribute to psychotic symptoms in patients with schizophrenia; sensory gating (P50 ratio and P50 difference) and change detection (mismatch negativity; MMN). Via electroencephalographic recordings P50 amplitude, P50 ratio, P50 difference and MMN amplitude were compared between 23 borderline patients with and 25 without AVH, and 26 healthy controls. Borderline patients with AVH had a significantly lower P50 difference compared with healthy controls, whereas no difference was found between borderline patients without AVH and healthy controls. The groups did not differ on MMN amplitude. The impaired sensory gating in patients with borderline personality disorder who experience AVH implies that P50 sensory gating deficiencies may underlie psychotic vulnerability in this specific patient group. Patients with borderline personality disorder with or without AVH did not have problems with auditory change detection. This may explain why they are spared from the poor outcome associated with negative symptoms and symptoms of disorganization in patients with chronic schizophrenia.

Dysregulation of auditory neuroplasticity in schizophrenia

Schizophrenia is a complex brain syndrome characterized by an array of positive symptoms (delusions, hallucinations, disorganized speech), negative symptoms (alogia, apathy, avolition) and cognitive impairments (memory, executive functions). Although investigations of the cognitive deficits in schizophrenia have primarily concentrated on disturbances affecting higher-order cognitive processes, there is an increasing realization that schizophrenia also affects early sensory processing, which might, in fact, play a significant role in the development of higher-order cognitive impairments. Recent evidence suggests that many of these early sensory processing impairments possibly arise from a dysregulation of plasticity regulators in schizophrenia, resulting in either reduced plasticity or excessive unregulated plasticity. The purpose of the present manuscript is to provide a concise overview of how the dysregulation of cortical plasticity mechanisms contributes to schizophrenia symptoms with an emphasis on auditory dysplasticity and to discuss its relevance for treatment outcomes. The idea that plasticity mechanisms are not constrained only within sensitive periods suggests that many functional properties of sensory neurons can be altered throughout the lifetime.

Clinical and Cognitive Significance of Auditory Sensory Processing Deficits in Schizophrenia

OBJECTIVE

Although patients with schizophrenia exhibit impaired suppression of the P50 event-related brain potential in response to the second of two identical auditory stimuli during a paired-stimulus paradigm, uncertainty remains over whether this deficit in inhibitory gating of auditory sensory processes has relevance for patients' clinical symptoms or cognitive performance. The authors examined associations between P50 suppression deficits and several core features of schizophrenia to address this gap.

METHOD

P50 was recorded from 52 patients with schizophrenia and 41 healthy comparison subjects during a standard auditory paired-stimulus task. Clinical symptoms were assessed with the Scale for the Assessment of Positive Symptoms and the Scale for the Assessment of Negative Symptoms. The MATRICS Consensus Cognitive Battery was utilized to measure cognitive performance in a subsample of 39 patients. Correlation and regression analyses were conducted to examine P50 suppression in relation to clinical symptom and cognitive performance measures.

RESULTS

Schizophrenia patients demonstrated a deficit in P50 suppression when compared with healthy subjects, replicating prior research. Within the patient sample, impaired P50 suppression covaried reliably with greater difficulties in attention, poorer working memory, and reduced processing speed.

CONCLUSIONS

Impaired suppression of auditory stimuli was associated with core pathological features of schizophrenia, increasing confidence that P50 inhibitory processing can inform the development of interventions that target cognitive impairments in this chronic and debilitating mental illness.

The therapeutic potential of α7 nicotinic acetylcholine receptor (α7 nAChR) agonists for the treatment of the cognitive deficits associated with schizophrenia

Homomeric α7 nicotinic acetylcholine receptors (α7 nAChRs) have implications in the regulation of cognitive processes such as memory and attention, and have shown promise as a therapeutic target for the treatment of the cognitive deficits associated with schizophrenia. Multiple α7 nAChR agonists have entered human trials; however, unfavorable side effects and pharmacokinetic issues have hindered the development of a clinical α7 nAChR agonist. Currently, EVP-6124 is in phase III clinical trials, and several other α7 nAChR agonists (GTS-21 and AQW051) are in earlier stages of development. This review will summarize the recent advances and failures of α7 nAChR agonists in clinical trials for the treatment of the aforementioned pathology.

Translational utility of rodent hippocampal auditory gating in schizophrenia research: a review and evaluation

Impaired gating of the auditory evoked P50 potential is one of the most pharmacologically well-characterized features of schizophrenia. This deficit is most commonly modeled in rodents by implanted electrode recordings from the hippocampus of the rodent analog of the P50, the P20-N40. The validity and effectiveness of this tool, however, has not been systematically reviewed. Here, we summarize findings from studies that have examined the effects of pharmacologic modulation on gating of the rodent hippocampal P20-N40 and the human P50. We show that drug effects on the P20-N40 are highly predictive of human effects across similar dose ranges. Furthermore, mental status (for example, anesthetized vs alert) does not appear to diminish the predictive capacity of these recordings. We then discuss hypothesized neuropharmacologic mechanisms that may underlie gating effects for each drug studied. Overall, this review supports continued use of hippocampal P20-N40 gating as a translational tool for schizophrenia research.

Effects of clozapine on perceptual abnormalities and sensory gating: a preliminary cross-sectional study in schizophrenia

The aim of the present study was to investigate the effect of second-generation antipsychotics (clozapine or another second-generation antipsychotic) on perceptual abnormalities related to sensory gating deficit. Although clozapine is known to improve sensory gating assessed neurophysiologically, we hypothesized that patients with schizophrenia treated with clozapine would report less perceptual abnormalities related to sensory gating deficit than patients treated with other second-generation antipsychotics do. Forty patients with a diagnosis of schizophrenia were investigated (10 patients treated with clozapine and 30 patients treated with another second-generation antipsychotic drug). Perceptual abnormalities were assessed with the Sensory Gating Inventory. Sensory gating was assessed through electroencephalogram with the auditory event-related potential method by measuring P50 amplitude changes in a dual click conditioning-testing procedure. Patients treated with clozapine present normal sensory gating and report less perceptual abnormalities related to sensory gating than patients treated with other second-generation antipsychotics do. Although the cross-sectional design of this study is limited because causal inferences cannot be clearly concluded, the present study suggests clinical and neurophysiological advantages of clozapine compared with other second-generation antipsychotics and provides a basis for future investigations on the effect of this treatment on perceptual abnormalities related to sensory gating deficit in patients with schizophrenia.

Maximizing the effect of an α7 nicotinic receptor PAM in a mouse model of schizophrenia-like sensory inhibition deficits

Positive allosteric modulators (PAMs) for the α7 nicotinic receptor hold promise for the treatment of sensory inhibition deficits observed in schizophrenia patients. Studies of these compounds in the DBA/2 mouse, which models the schizophrenia-related deficit in sensory inhibition, have shown PAMs to be effective in improving the deficit. However, the first published clinical trial of a PAM for both sensory inhibition deficits and related cognitive difficulties failed, casting a shadow on this therapeutic approach. The present study used both DBA/2 mice, and C3H Chrna7 heterozygote mice to assess the ability of the α7 PAM, PNU-120596, to improve sensory inhibition. Both of these strains of mice have reduced hippocampal α7 nicotinic receptor numbers and deficient sensory inhibition similar to schizophrenia patients. Low doses of PNU-120596 (1 or 3.33mg/kg) were effective in the DBA/2 mouse but not the C3H Chrna7 heterozygote mouse. Moderate doses of the selective α7 nicotinic receptor agonist, choline chloride (10 or 33mg/kg), were also ineffective in improving sensory inhibition in the C3H Chrna7 heterozygote mouse. However, combining the lowest doses of both PNU-120596 and choline chloride in this mouse model did improve sensory inhibition. We propose here that the difference in efficacy of PNU-120596 between the 2 mouse strains is driven by differences in hippocampal α7 nicotinic receptor numbers, such that C3H Chrna7 heterozygote mice require additional direct stimulation of the α7 receptors. These data may have implications for further clinical testing of putative α7 nicotinic receptor PAMs.

Sensory gating disturbances in the spectrum: similarities and differences in schizotypal personality disorder and schizophrenia

BACKGROUND

DSM-5 places schizophrenia on a continuum from severe, chronic schizophrenia to the attenuated schizophrenia-like traits of schizotypal personality disorder (SPD), the prototypic schizophrenia-related personality disorder. SPD shares common genetic and neurobiological substrates with schizophrenia, including information processing abnormalities, although they are less marked. This is the first study to directly compare the P50 evoked electroencephalographic response-a measure of sensory gating and a neurophysiological endophenotype-between schizophrenia-spectrum groups. Two hypotheses were tested: (1) Compared with healthy controls (HCs), schizophrenia patients show reduced P50 suppression and SPD patients resemble schizophrenia but exhibit less marked deficits; and (2) Deficient P50 suppression in SPD is associated with greater clinical symptom severity.

METHODS

P50 was assessed in 32 schizophrenia-spectrum disorder patients (12 SPD, 20 schizophrenia patients) and 25 demographically-matched HCs. The standard conditioning (C)-testing (T) paradigm was used and P50 suppression was quantified using the T-C difference and the T/C ratio.

RESULTS

All P50 measures showed a linear, stepwise pattern with the SPD group intermediate between the HC and schizophrenia groups. Compared with HCs, both patient groups had lower conditioning and T-C difference values. Among the SPD group, greater clinical symptom severity was associated with greater conditioning-response amplitude deficits.

CONCLUSION

These findings: (1) are novel in showing that P50 deficits in SPD resemble those observed in schizophrenia, albeit less marked; (2) support the concept that the phenomenological link between SPD and schizophrenia lies in shared neurocognitive/neurophysiological pathologies; and (3) provide evidence that P50 is a neurophysiological endophenotype for schizophrenia-spectrum disorders.

Sensory processing dysfunction in the personal experience and neuronal machinery of schizophrenia

Sensory processing deficits, first investigated by Kraepelin and Bleuler as possible pathophysiological mechanisms in schizophrenia, are now being recharacterized in the context of our current understanding of the molecular and neurobiological brain mechanisms involved. The National Institute of Mental Health Research Domain Criteria position these deficits as intermediaries between molecular and cellular mechanisms and clinical symptoms of schizophrenia, such as hallucinations. The prepulse inhibition of startle responses by a weaker preceding tone, the inhibitory gating of response to paired sensory stimuli characterized using the auditory P50 evoked response, and the detection of slight deviations in patterns of sensory stimulation eliciting the cortical mismatch negativity potential demonstrate deficits in early sensory processing mechanisms, whose molecular and neurobiological bases are increasingly well understood. Deficits in sensory processing underlie more complex cognitive dysfunction and are in turn affected by higher-level cognitive difficulties. These deficits are now being used to identify genes involved in familial transmission of schizophrenia and to monitor potentially therapeutic drug effects for both treatment and prevention. This research also provides a clinical reminder that patients' sensory perception of the surrounding world, even during treatment sessions, may differ considerably from others' perceptions. A person's ability to understand and interact effectively with the surrounding world ultimately depends on an underlying sensory experience of it.

Targeting of α7 Nicotinic Acetylcholine Receptors in the Treatment of Schizophrenia and the Use of Auditory Sensory Gating as a Translational Biomarker

Accumulating evidence suggests that the α7 subtype of nicotinic acetylcholine receptors (nAChRs) plays a key role in inflammatory processes, thought to be involved in the pathophysiology of neuropsychiatric diseases, such as schizophrenia and Alzheimer's disease. Preclinical and clinical studies showed that the diminished suppression of P50 auditory evoked potentials in patients with schizophrenia may be associated with a decreased density of α7 nAChRs in the brain. This points to a role for auditory sensory gating (P50) as a translational biomarker. A number of agonists and positive allosteric modulators (PAMs) for α7 nAChR promoted beneficial effects in animal models with sensory gating and cognitive deficits. Additionally, several clinical studies showed that α7 nAChR agonists could improve suppression in auditory P50 evoked potentials, as well as cognitive deficits, and negative symptoms in patients with schizophrenia. Taken together, α7 nAChR presents as an extremely attractive therapeutic target for schizophrenia. In this article, the author discusses recent findings on α7 nAChR agonists such as DMXB-A, RG3487, TC-5619, tropisetron, EVP-6124 (encenicline), ABT-126, AQW051 and α7 nAChR PAMs such as JNJ-39393406, PNU- 120596 and AVL-3288 (also known as UCI-4083), and their potential as therapeutic drugs for neuropsychiatric diseases, such as schizophrenia.

How do high- and low-frequency repetitive transcranial magnetic stimulations modulate the temporal cortex

Few studies have examined the impact of repetitive transcranial magnetic stimulation (rTMS) on the cortical excitability of nonmotor cortices; current treatments often target the temporal or prefrontal cortex. We used auditory evoked potentials recorded in 24 healthy subjects to evaluate the neuromodulatory effects of low- and high-frequency rTMS in the temporal lobe. Both auditory evoked potential P50 amplitude, a marker of cortical excitability, and P50 ratio, a marker of sensory gating known to be impaired in patients with auditory verbal hallucinations, were compared before and after rTMS. We observed a similar effect after both stimulation frequencies, with a decrease in P50 amplitude and no significant effect on P50 ratio. Low- and high-frequency rTMS applied to the temporal lobe seemed to exert the same cortical neuromodulation effect, while auditory sensory gating may not be modulated by temporal rTMS.

Influence of aripiprazole, risperidone, and amisulpride on sensory and sensorimotor gating in healthy 'low and high gating' humans and relation to psychometry

Despite advances in the treatment of schizophrenia spectrum disorders with atypical antipsychotics (AAPs), there is still need for compounds with improved efficacy/side-effect ratios. Evidence from challenge studies suggests that the assessment of gating functions in humans and rodents with naturally low-gating levels might be a useful model to screen for novel compounds with antipsychotic properties. To further evaluate and extend this translational approach, three AAPs were examined. Compounds without antipsychotic properties served as negative control treatments. In a placebo-controlled, within-subject design, healthy males received either single doses of aripiprazole and risperidone (n=28), amisulpride and lorazepam (n=30), or modafinil and valproate (n=30), and placebo. Prepulse inhibiton (PPI) and P50 suppression were assessed. Clinically associated symptoms were evaluated using the SCL-90-R. Aripiprazole, risperidone, and amisulpride increased P50 suppression in low P50 gaters. Lorazepam, modafinil, and valproate did not influence P50 suppression in low gaters. Furthermore, low P50 gaters scored significantly higher on the SCL-90-R than high P50 gaters. Aripiprazole increased PPI in low PPI gaters, whereas modafinil and lorazepam attenuated PPI in both groups. Risperidone, amisulpride, and valproate did not influence PPI. P50 suppression in low gaters appears to be an antipsychotic-sensitive neurophysiologic marker. This conclusion is supported by the association of low P50 suppression and higher clinically associated scores. Furthermore, PPI might be sensitive for atypical mechanisms of antipsychotic medication. The translational model investigating differential effects of AAPs on gating in healthy subjects with naturally low gating can be beneficial for phase II/III development plans by providing additional information for critical decision making.

Do schizophrenia patients with low P50-suppression report more perceptual anomalies with the sensory gating inventory?

BACKGROUND

P50 amplitude changes in dual click conditioning-testing procedure might be a neurophysiological marker of deficient sensory gating in schizophrenia. However, the relationship between abnormalities in the neurophysiological and phenomenological dimensions of sensory gating in schizophrenia remains unclear. The aim of the present study was to determine if patients with low P50-suppression (below 50%) report more perceptual anomalies.

METHODS

Three groups were compared: twenty-nine schizophrenia patients with high P50-suppression (above 50% amplitude suppression), twenty-three schizophrenia patients with low P50-suppression (below 50%) and twenty-six healthy subjects. The Sensory Gating Inventory (SGI), a four-factor self-report questionnaire, was used to measure perceptual anomalies related to sensory gating. A comparison of demographic and clinical data was also carried out.

RESULTS

Patients with low P50-suppression presented: i) significantly higher scores on the SGI (for the overall SGI score and for each of the 4 factors) and ii) significantly larger P50 amplitude at the second click, than both patients with high P50-suppression and healthy subjects. There were no group differences in the most of demographic and clinical data.

DISCUSSION

The finding offers support for conceptual models wherein abnormal neurophysiologic responses to repetitive stimuli give rise to clinically relevant perceptions of being inundated and overwhelmed by external sensory stimuli. Further studies are needed to explore the contributions of clinical symptoms, medication and neuropsychological functions to the relationship between P50-suppression and the SGI, and the role of sensory "gating in" versus "gating out".

Intermittent versus continuous central administration of clozapine in DBA/2 mice, improvement in sensory inhibition deficits

Deficient sensory inhibition, the failure to inhibit responses to repeated stimuli, is a hallmark of schizophrenia, and is thought to be related to difficulties with attention and working memory. Sensory inhibition is assessed by comparing the auditory-evoked EEG responses to 2 closely-spaced identical stimuli. Normal individuals show suppressed response to the second stimulus while schizophrenia patients have responses of similar magnitude to both stimuli. This deficit has been linked to polymorphisms in the promoter for the α7 nicotinic receptor gene, resulting in reduced numbers of receptors on hippocampal interneurons. This deficit is modeled in DBA/2 mice which also show a polymorphism in the promoter for the α7 nicotinic receptor gene and reduced numbers of hippocampal α7 receptors. Systemic administration of clozapine, the most efficacious antipsychotic medication, improves sensory inhibition deficits in both schizophrenia patients and DBA/2 mice. We have previously shown that acute intracerebroventricular (ICV) injections of clozapine induced similar improvement in sensory inhibition in DBA/2 mice. Here we demonstrate the efficacy of chronic ICV clozapine administration in improving sensory inhibition in DBA2 mice. Mice received ICV vehicle, 3, 7.5, 15 or 30 μg of clozapine, either continuously or as a once-per-day injection. Mice were recorded on the 7th day of drug delivery. Both approaches produced improved sensory inhibition, but the daily bolus injection was effective at a lower dose (3 μg/day) than the continuous delivery (15 μg/day). The bolus injections also showed significant improvement up to 36 h post injection thus suggesting that this approach may be more efficacious.

P50 suppression and its neural generators in antipsychotic-naive first-episode schizophrenia before and after 6 months of quetiapine treatment

BACKGROUND

Numerous studies have demonstrated sensory gating deficits in schizophrenia. However, only a few longitudinal studies report on the effects of antipsychotic treatment on sensory gating deficits and their results are inconsistent. In the present study, P50 suppression and its neural generators were investigated in antipsychotic-naïve first-episode patients with schizophrenia before and after 6 months of treatment with quetiapine.

METHODS

Thirty-four antipsychotic-naïve first-episode schizophrenia patients and age and gender matched healthy controls were tested in an auditory sensory gating paradigm at baseline and after 6 months. During this period, the patients were treated with quetiapine, while controls received no treatment. Sixteen patients completed the study.

RESULTS

Patients showed significant reduced P50 suppression compared with controls at baseline but not at follow-up. Furthermore, a significant positive correlation between baseline P50 suppression and dose of quetiapine at follow-up was found. P50 suppression in patients receiving above median dosages of quetiapine increased significantly from baseline to follow-up. At baseline, a frontocentral source was significantly more active in patients than in controls at the time of the testing stimulus.

CONCLUSIONS

The present findings suggest that P50 suppression deficits are already present at an early stage of schizophrenia. Furthermore, particularly those patients with more severe gating deficits appeared to need higher dosages of quetiapine, although their clinical symptoms did not seem to indicate this. Quetiapine treatment significantly improved these gating deficits. Furthermore, a frontocentral source in the brain appeared to be involved in the deficient P50 gating of the patients.

Neuropsychological correlates of P50 sensory gating in patients with schizophrenia

Impaired inhibition of P50 cerebral evoked response is one of the best validated endophenotypes in schizophrenia. There are controversial data on the relationship between P50 evoked potential deficit and measures of cognitive function in schizophrenia. A comprehensive clinical and neurocognitive assessment plus an evaluation of P50 sensory gating was performed in 160 schizophrenia patients and 64 controls. Neurocognitive scores from each cognitive domain were converted to demographically-adjusted T-scores (age, gender, and years of education) for all study participants. The relationship between P50 and neurocognitive variables was assessed via parametric and nonparametric correlations and categorical strategies: we compared neuropsychological test scores in patients and controls in the lowest P50 quartile vs. the highest. Controls had better performance than schizophrenia patients in all cognitive domains. Schizophrenia patients had significantly higher P50 ratios than controls, and no significant correlation was found between P50 gating measures and neuropsychological test scores in schizophrenia patients or healthy controls. Moreover, no differences in neurocognitive performance were found between subjects in the lowest P50 ratio quartile vs. the highest in healthy controls or patients with schizophrenia. We concluded that there is no evidence of an association between P50 ratio and cognitive measures in schizophrenia patients, and this seems to be also the case in healthy controls.

Allosteric alpha-7 nicotinic receptor modulation and P50 sensory gating in schizophrenia: a proof-of-mechanism study

In this multicenter, double-blind, placebo-controlled, randomized, four way cross-over proof-of-mechanism study, we tested the effect of the positive allosteric α7 nicotinic acetylcholine receptor (nAChR) modulator JNJ-39393406 in a key translational assay (sensory P50 gating) in 39 regularly smoking male patients with schizophrenia. All patients were clinically stable and JNJ-39393406 was administered as an adjunct treatment to antipsychotics. No indication was found that JNJ-39393406 has the potential to reverse basic deficits of information processing in schizophrenia (sensory P50 gating) or has a significant effect on other tested electrophysiological markers (MMN, P300 and quantitative resting EEG). Sensitivity analyses including severity of disease, baseline P50 gating, medication and gene variants of the CHRNA7 gene did not reveal any subgroups with consistent significant effects. It is discussed that potential positive effects in subgroups not present or not large enough in the current study or upon chronic dosing are possible, but unlikely to be developed. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Nicotinic mechanisms in the treatment of psychotic disorders: a focus on the α7 nicotinic receptor

Nicotine is heavily abused by persons with schizophrenia. Nicotine better enables people with schizophrenia to filter out extraneous auditory stimuli. Nicotine also improves prepulse inhibition when compared to placebo. Nicotine similarly increases the amplitude of patients' duration mismatch negativity. The 15q13-14 region of the genome coding for the α7 nicotinic receptor is linked to schizophrenia. Multiple single nucleotide polymorphisms have been identified in this 15q13-14 gene promoter region that are more frequently present in people with schizophrenia than in normal controls. Abnormalities in expression and regulation of central nicotinic cholinoceptors with decreased α7 binding in multiple brain regions are also present. Nicotine enhances cognition in schizophrenia. Alternative agents that activate the nicotinic receptor have been tested including 3-[2,4-dimethoxybenzylidene]anabaseine (DMXB-A). This compound improved attention, working memory, and negative symptoms in an add-on study in nonsmoking patients with schizophrenia. There are multiple other nicotinic agents, including positive allosteric modulators, in the preclinical stages of development. Finally, the effects of varenicline and clozapine and their relation to smoking cessation are discussed.

Abnormal plasma monoamine metabolism in schizophrenia and its correlation with clinical responses to risperidone treatment

Abnormalities in plasma monoamine metabolism reflect partly the illness of schizophrenia and sometimes the symptoms. Such studies have been repeatedly reported but have rarely taken both metabolites and parent amines or inter-amine activity ratios into account. In this study, the monoamines, their metabolites, turnovers and between-metabolite ratios in plasma were measured longitudinally in 32 schizophrenic patients treated with risperidone for 6 weeks, to examine possible biochemical alterations in schizophrenia, and to examine the association between treatment responses and psychopathology assessed according to the Positive and Negative Syndrome Scale (PANSS). The results showed lower level of plasma 3,4-dihydroxyphenylacetic acid (DOPAC) in relapsed versus first-episode schizophrenic patients, higher norepinephrine (NE) turnover rate (TR) in undifferentiated in comparison to paranoid schizophrenic patients and relatively higher metabolic activity of dopamine (DA) to serotonin (5-HT) in first-episode versus relapsed schizophrenic patients. Risperidone treatment induced a decrement of plasma DA levels and increments of plasma DOPAC and DA TR in the total group of schizophrenic patients. The turnover rate of 5-HT was was reduced in undifferentiated and relapsed subgroups of schizophrenic patients. The linkages between 5-HT TR, DA/NE relative activity and clinical symptomatology were also identified. These findings are consistent with an involvement of these systems in the pathogenesis of schizophrenia as well as in the responses to treatment, and the usefulness of certain biochemical indices as markers for subgrouping.

Evidence of abnormalities in mid-latency auditory evoked responses (MLAER) in cognitive subtypes of patients with schizophrenia

Abnormalities in measures of mid-latency auditory evoked responses (MLAER) have frequently been reported in schizophrenia, while few studies have examined whether these measures could distinguish cognitive subtypes of schizophrenia. The aim of this study was to investigate whether patterns of performance on MLAER measures could differentiate a cognitive subtype of patients characterized by pervasive cognitive deficits (CD) from patients with only mild cognitive deficits (CS) and controls. An auditory paired-click conditioning test was administered to 55 schizophrenia patients (26 CD, 29 CS) and 49 healthy controls. Amplitudes, latencies and sensory gating indices of the P50, N100, and P200 MLAER were analysed. The results showed that CD patients exhibited smaller S1 amplitudes of N100 and P200 than controls, while CS patients were comparable to controls. Binary logistic regression identified the P200 S1 amplitude as a significant predictor of patients' membership in the CD subtype. However, none of the other MLAER measures could differentiate the two subtypes of schizophrenia. These findings suggest that the abnormal pathophysiologic mechanisms underlying the electrophysiological brain responses to auditory stimulation are associated with the pervasive cognitive deficits, which characterize the CD subtype of schizophrenia. This finding might provide additional electrophysiological endophenotypes for future genetic research of schizophrenia.

Involvement of the cholinergic system in conditioning and perceptual memory

The cholinergic systems play a pivotal role in learning and memory, and have been the centre of attention when it comes to diseases containing cognitive deficits. It is therefore not surprising, that the cholinergic transmitter system has experienced detailed examination of its role in numerous behavioural situations not least with the perspective that cognition may be rescued with appropriate cholinergic 'boosters'. Here we reviewed the literature on (i) cholinergic lesions, (ii) pharmacological intervention of muscarinic or nicotinic system, or (iii) genetic deletion of selective receptor subtypes with respect to sensory discrimination and conditioning procedures. We consider visual, auditory, olfactory and somatosensory processing first before discussing more complex tasks such as startle responses, latent inhibition, negative patterning, eye blink and fear conditioning, and passive avoidance paradigms. An overarching reoccurring theme is that lesions of the cholinergic projection neurones of the basal forebrain impact negatively on acquisition learning in these paradigms and blockade of muscarinic (and to a lesser extent nicotinic) receptors in the target structures produce similar behavioural deficits. While these pertain mainly to impairments in acquisition learning, some rare cases extend to memory consolidation. Such single case observations warranted replication and more in-depth studies. Intriguingly, receptor blockade or receptor gene knockout repeatedly produced contradictory results (for example in fear conditioning) and combined studies, in which genetically altered mice are pharmacological manipulated, are so far missing. However, they are desperately needed to clarify underlying reasons for these contradictions. Consistently, stimulation of either muscarinic (mainly M(1)) or nicotinic (predominantly α7) receptors was beneficial for learning and memory formation across all paradigms supporting the notion that research into the development and mechanisms of novel and better cholinomimetics may prove useful in the treatment of neurodegenerative or psychiatric disorders with cognitive endophenotypes.

The moderating role of the dopamine transporter 1 gene on P50 sensory gating and its modulation by nicotine

Although schizophrenia has been considered primarily a disease of dopaminergic neurotransmission, the role of dopamine in auditory sensory gating deficits in this disorder and their amelioration by smoking/nicotine is unclear. Hypothesizing that individual differences in striatal dopamine levels may moderate auditory gating and its modulation by nicotine, this preliminary study used the mid-latency (P50) auditory event-related potential (ERP) to examine the single dose (6 mg) effects of nicotine (vs. placebo) gum on sensory gating in 24 healthy nonsmokers varying in the genetic expression of the dopamine transporter (DAT). Consistent with an inverted-U relationship between dopamine level and the drug effects, individuals carrying the 9R (lower gene expression) allele, which is related to greater striatal dopamine levels, tended to evidence increased baseline gating compared to 10R (higher gene expression) allele carriers and showed a reduction in gating with acute nicotine. The present results may help to understand the link between excessive smoking and sensory gating deficits in schizophrenia and to explain the potential functional implications of genetic disposition on nicotinic treatment in schizophrenia.

Continuous administration of a selective alpha7 nicotinic partial agonist, DMXBA, improves sensory inhibition without causing tachyphylaxis or receptor upregulation in DBA/2 mice

Stimulation of nicotinic receptors, specifically the alpha7 subtype, improves sensory inhibition and cognitive function in receptor deficient humans and rodents. However, stimulation with a full agonist, such as nicotine, produces rapid tachyphylaxis of the P20N40-measured sensory inhibition process. 3-(2,4-dimethoxybenzylidine) anabaseine (DMXBA, also GTS-21) selectively activates the alpha7 nicotinic receptor, and in acute administration studies, has been shown to improve deficient sensory inhibition in both humans and rodents with repeated dosing. Unlike nicotine, this partial agonist acted without inducing tachyphylaxis. Here, we assessed the ability of DMXBA to improve sensory inhibition in DBA/2 mice after 7 days of continuous administration via a subcutaneously implanted osmotic minipump. When assessed on day 8, mice receiving saline showed the characteristic deficient sensory inhibition seen with untreated DBA/2 mice. The 25- and 50-mg/ml infusion concentrations of DMXBA, but not the 100-mg/ml, produced significantly improved sensory inhibition in the mice, exclusively through a decrease in test amplitude. No concentration significantly upregulated hippocampal alpha7 receptor levels. DMXBA levels in the brain were higher than plasma at 2 of the 3 concentrations infused. These data suggest that continuous exposure to DMXBA does not significantly affect the underlying responsiveness of the sensory inhibition pathway to this partial agonist, nor cause receptor upregulation, at these relatively low brain concentrations. The ability of DMXBA to maintain its effectiveness during constant administration conditions may be due to an ability to activate alpha7 receptors at low concentrations, and consequently low fractional occupancy of the five possible binding sites on this homomeric receptor.

Sensory gating and sensorimotor gating in medication-free obsessive-compulsive disorder patients

Obsessive-compulsive disorder (OCD) is associated with deficits in inhibition mechanisms. This is reflected in reports showing impaired sensorimotor and sensory gating in OCD patients, as measured with prepulse inhibition (PPI) of the startle reflex and P50 suppression paradigms. However, most of the patients in these studies used medication and the results were not controlled for menstrual cycle phase in women. In this study PPI and P50 suppression were tested in 25 medication-free OCD patients and 25 healthy controls, using auditory stimuli and controlling for menstrual cycle effects. Subgroups were established, based on clinical variables (e.g. 'washers' and 'checkers'). No impairments in PPI or P50 suppression were found in the OCD group when compared with healthy controls. However, a subgroup of OCD patients ('checkers', n=12) showed increased P50 suppression. It was concluded that sensorimotor and sensory gating is not impaired in drug-free OCD patients, taking into account the menstrual cycle effects in women. These results do not support hypotheses linking deficits in these inhibition paradigms and the pathogenesis of OCD. The finding of an increased P50 suppression in the subgroup of 'checkers' deserves further investigation and underlines the value of studying subgroups of OCD.

P50 gating in deficit and nondeficit schizophrenia

Dysfunctional auditory sensory processing has generally been found in schizophrenia and it has been suggested that these deficits might be related to clinical and psychosocial variables. The present study included P50 recordings using a simple-paired click auditory evoked potential paradigm in sixty patients with deficit schizophrenia (DS), sixty patients with nondeficit schizophrenia (NDS), and sixty comparison subjects. The Schedule for the Deficit Syndrome was used to categorize patients as DS or NDS. The two patient groups did not differ in clinical variables, except for higher negative dimension and lower community outcome scores in DS than in NDS patients. There were no differences in P50 ratios between deficit and nondeficit subgroups; compared with normal subjects both groups of schizophrenia patients showed impaired P50 ratios (p<0.0001). This ratio appears to be independent of positive and negative symptoms. However, impairment in P50 gating correlated with poorer community outcome. The data document the existence of early auditory sensory processing abnormalities in DS and NDS, and might suggest that common neuronal network abnormalities underlie both forms of schizophrenia. Deficient P50 gating may be associated with impaired functional outcome in schizophrenia.

Antipsychotic effects on auditory sensory gating in schizophrenia patients

P50 sensory gating deficit has repeatedly been demonstrated in schizophrenia. Studies have produced inconsistent findings with respect to normalization of P50 gating in patients with schizophrenia receiving treatment with different antipsychotics. The current study was designed to determine whether there is a difference in P50 gating in schizophrenia patients treated with first-generation antipsychotics (FGAs) and second-generation antipsychotics (SGAs), including clozapine. P50 evoked potential recordings were obtained from 160 patients with schizophrenia and 77 healthy comparison subjects. Forty-three patients were being treated with clozapine, sixty-eight were taking SGAs (33 risperidone, 21 olanzapine, 11 aripiprazole, and 3 combinations of SGAs) and 49 were being treated with FGAs. Schizophrenia patients exhibited significantly higher P50 ratios than healthy subjects. When patients treated with different antipsychotics were compared, there were no differences in any of the neurophysiological findings. Second-generation antipsychotics were not related to more normal sensory gating in this population of patients with chronic schizophrenia.

Recent advances in treating cognitive impairment in schizophrenia

INTRODUCTION

Schizophrenia is often associated with chronic disability and poor outcome. In addition to positive symptoms, such as hallucinations and delusions, and negative symptoms including poverty of speech and blunted affect, schizophrenia is also associated with deficits in cognitive function. It has been increasingly recognized that the severity of cognitive impairment is a major determinant of outcome. Therefore, interventions to improve cognitive function also have the capacity to improve quality of life and social and occupational outcomes. Whilst some of the antipsychotic drugs have shown some selective benefits, there is some controversy about the extent of these benefits.

OBJECTIVES

This article provides an overview of research into drugs that might enhance cognition in schizophrenia.

CONCLUSION

Drugs such as modafanil and galantamine are being evaluated, and a number of new drugs are currently in development. Standardized cognitive assessment measures are being developed so studies can be compared more easily. This field is advancing rapidly, but as yet, no widely applicable, evidence-based treatments are available to the clinician.

P50 gating at acute and post-acute phases of first-episode schizophrenia

Deficit in P50 sensory gating has repeatedly been shown in schizophrenia. In order to determine the contribution of trait and/or state features to P50 gating deficit in schizophrenia we evaluated the P50 gating in patients with first-episode schizophrenia (FES) at acute and post-acute phases. Subject groups comprised 16 patients with FES and 24 healthy controls. Patients were tested at the acute phase of the illness and retested at the post-acute phase when their positive symptoms improved. During the testing at the acute phase five patients were neuroleptic-naive and the others were taking atypical antipsychotics which were started recently in order to control the acute excitation. Patients were receiving risperidone, olanzapine or quetiapine treatment at the post-acute phase. P50 gating was impaired in patients at the acute phase compared to controls. However, at the post-acute phase P50 gating was increased compared to the acute phase, reaching to the gating values of controls. P50 gating improvement might be emerged from atypical antipsychotic medication, although this can only be definitively determined by randomized studies including different antipsychotics.

Olanzapine improves deficient sensory inhibition in DBA/2 mice

Most schizophrenia patients do not inhibit their P50 auditory evoked potential to the second of duplicate auditory stimuli, reflecting a failure to inhibit responses to irrelevant sensory input. Typical antipsychotic drugs do not improve this deficit while some atypical antipsychotics do. A previous study using an animal model, deficient P20-N40 (which corresponds to the human P50) inhibitory processing in DBA/2 mice found that sensory inhibition was improved by clozapine, the prototypical atypical antipsychotic, but not by haloperidol, a typical antipsychotic. The improvement after clozapine was mediated by alpha7 nicotinic receptors. The present study addresses whether another atypical antipsychotic, olanzapine, will also improve sensory inhibition deficits in the mouse model. In vivo electrophysiological recordings of the P20-N40 auditory evoked potential in anesthetized DBA/2 mice, which spontaneously exhibit a schizophrenia-like inhibitory processing deficit, were obtained after olanzapine alone (0.01, 0.033, 0.1, 0.33 mg/kg, IP) and the efficacious dose of olanzapine (0.033 mg/kg, IP) in combination with either the alpha7 nicotinic receptor antagonist alpha-bungarotoxin or the alpha4beta2 nicotinic receptor antagonist di-hydro-beta-erythroidine. All doses of olanzapine produced improved P20-N40 inhibitory processing in DBA/2 mice. The normalization observed after the 0.033 mg/kg dose of olanzapine was due to a selective decrease in response to the second auditory stimulus indicating an increase in inhibitory processing. This improvement was blocked by pre-administration of alpha-bungarotoxin but not di-hydro-beta-erythroidine. Like clozapine, olanzapine acts via alpha7 nicotinic receptors to elicit improved inhibitory processing of auditory stimuli.

Differential effects of acute serotonin and dopamine depletion on prepulse inhibition and p50 suppression measures of sensorimotor and sensory gating in humans

Schizophrenia is associated with impairments of sensorimotor and sensory gating as measured by prepulse inhibition (PPI) of the acoustic startle response and P50 suppression of the auditory event-related potential respectively. While serotonin and dopamine play an important role in the pathophysiology and treatment of schizophrenia, their role in modulating PPI and P50 suppression in humans is yet to be fully clarified. To further explore the role of serotonin and dopamine in PPI and P50 suppression, we examined the effects of acute tryptophan depletion (to decrease serotonin) and acute tyrosine/phenylalanine depletion (to decrease dopamine) on PPI and P50 suppression in healthy human participants. In addition, we also examined for the first time, the effects of simultaneous serotonin and dopamine depletion (ie combined monoamine depletion) on PPI and P50 suppression. The study was a double-blind, placebo-controlled cross-over design in which 16 healthy male participants completed the PPI and P50 paradigms under four acute treatment conditions: (a) balanced/placebo control, (b) acute tryptophan depletion, (c) acute tyrosine/phenylalanine depletion, and (d) acute tyrosine/phenylalanine/tryptophan depletion (combined monoamine depletion). Selective depletion of dopamine had no significant effect on either PPI or P50 suppression, whereas selective serotonin depletion significantly disrupted PPI, but not P50 suppression. Finally, the simultaneous depletion of both serotonin and dopamine resulted in significant reduction of both PPI and P50 suppression. We suggest these results can be explained by theories relating to optimal levels of monoaminergic neurotransmission and synergistic interactions between serotonergic and dopaminergic systems for normal 'gating' function. These findings suggest that a dysfunction in both serotonin and dopamine neurotransmission may, in part, be responsible for the gating deficits observed in schizophrenia, and their normalization following administration of atypical antipsychotic drugs.

P50 sensory gating ratios in schizophrenics and controls: a review and data analysis

Many studies have found that the P50 sensory gating ratio in a paired click task is smaller in normal control subjects than in patients with schizophrenia, indicating more effective sensory gating. However, a wide range of gating ratios has been reported in the literature for both groups. The purpose of this study was to compile these findings and to compare reported P50 gating ratios in controls and patients with schizophrenia. Current data collected from individual controls in eight studies from the University of California, Irvine (UCI), Indiana University (IU), and Yale University also are reported. The IU, UCI, and Yale data showed that approximately 40% of controls had P50 ratios within 1 S.D. below the mean of means for patients with schizophrenia. The meta-analysis rejected the null hypothesis that all studies showed no effect. The meta-analysis also showed that the differences were not the same across all studies. The mean ratios in 45 of the 46 group comparisons were smaller for controls than for patients, and the observed difference in means was significant for 35 of those studies. Reported gating ratios for controls from two laboratories whose findings were reported in the literature differed from all the other control groups. Variables affecting the gating ratio included band pass filter setting, rules regarding the inclusion of P30, sex, and age. Standards of P50 collection and measurement would help determine whether the gating ratio can be sufficiently reliable to be labeled an endophenotype, and suggestions are made toward this goal.

An initial animal proof-of-concept study for central administration of clozapine to schizophrenia patients

While clozapine is the acknowledged superior pharmacotherapeutic for the treatment of schizophrenia, the side effect profile, which includes potentially fatal complications, limits its usefulness. Central administration of clozapine directly into the brain could circumvent many of the side effect issues due to the dramatic reduction in dose and the limitation of the drug primarily to the CNS. The present study demonstrates that clozapine can be formulated as a stable solution at physiological pH, which does not have in vitro neurotoxic effects at concentrations which may be effective at treating symptoms. Acute central administration improved auditory gating deficits in a mouse model of schizophrenia-like deficits. Assessment of behavioral alterations in rats receiving chronic central infusions of clozapine via osmotic minipump was performed with the open field and elevated plus mazes. Neither paradigm revealed any detrimental effects of the infusion. While these data represent only an initial investigation, they none-the-less suggest that central administration of clozapine may be a viable alternate therapeutic approach for schizophrenia patients which may be effective in symptom reduction without causing behavioral or neurotoxic effects.

The effects of increased serotonergic activity on human sensory gating and its neural generators

RATIONALE

Schizophrenia is a disabling illness with deficits in core mental functions such as sensory gating. The P50 amplitude is an (usually auditory) evoked brain potential that, in a so-called double-click paradigm, can be used to quantify sensory gating. Reports on serotonergic modulation of P50 suppression are sparse.

OBJECTIVE

The objective of this study was to study the effects of increased serotonergic activity on parameters of P50 suppression in healthy volunteers.

MATERIALS AND METHODS

In a double-blind placebo-controlled crossover design, 21 healthy male volunteers received either placebo or a dose of 10 mg of escitalopram (selective serotonin reuptake inhibitor), after which they were tested in a P50 suppression paradigm. Furthermore, an attempt was made to identify the neural generators of the P50 evoked potential.

RESULTS

Escitalopram did not affect P50 suppression but was found to increase P50 amplitude to the first (or conditioning) stimulus. Two bilateral sources located in the temporal cortex, two bilaterally located near the eyes, and one in a fronto-central location were identified, the latter correlating positively with the P50 amplitude.

CONCLUSIONS

In the current study, escitalopram did not affect P50 suppression in healthy male volunteers, which indicates that sensory gating is not affected by a nonspecific increase in serotonergic activity. Furthermore, a generator with a fronto-central location in the brain (possibly the anterior cingulate) was found to be the primary source of the P50 evoked potential.

Treating schizophrenia symptoms with an alpha7 nicotinic agonist, from mice to men

Current antipsychotic treatments fail to fully address the range of symptoms of schizophrenia, particularly with respect to social and occupational dysfunctions. Recent work has highlighted the role of nicotinie in both cognitive and attentional deficits as well as deficient processing of repetitive sensory information. The predilection for schizophrenia patients to be extremely heavy cigarette smokers may be related to their attempt to compensate for a reduction in hippocampal alpha7 nicotinic cholinergic receptors by delivering exogenous ligand to the remaining receptors. Studies in rodent models of both learning and memory deficits and deficits in sensory inhibition have confirmed a role for the alpha7 subtype of the nicotinic cholinergic receptor in these processes. Rodent studies also demonstrated the efficacy of a selective partial alpha7 nicotinic agonist, DMXBA, to improve these deficits. Subsequent human clinical trials demonstrated improved sensory inhibition in 12 schizophrenia patients and showed improvement in several subtests of the RBANS learning and memory assessment instrument. These data suggest that therapeutic agents selected for alpha7 nicotinic activity may have utility in treating certain symptoms of schizophrenia.

P50 auditory evoked potential suppression in bipolar disorder patients with psychotic features and their unaffected relatives

BACKGROUND

Diminished suppression of the P50 response, a consistent finding in schizophrenia, has also been reported in patients with psychotic bipolar disorder. It is a promising endophenotype for schizophrenia, but its relationship to genetic liability in bipolar disorder is unknown. We therefore assessed whether diminished P50 suppression is associated with familial risk for psychotic bipolar disorder.

METHODS

The P50 response was collected in a conditioning (C)--testing (T) paradigm from 42 outpatients with bipolar 1 disorder who had experienced psychotic symptoms and 44 of their unaffected first-degree relatives, all from families multiply affected with bipolar disorder or another non-organic psychotic disorder; 48 healthy control subjects were also studied. The T/C ratio was compared between the groups, with linear regression analyses and robust variance estimators for clustered data.

RESULTS

Both patients (estimated mean difference in T/C ratio to control subjects, 32, 95% confidence interval [CI] 15-48, p=.001) and unaffected relatives (20, 95% CI 7-32, p=.002) demonstrated higher T/C ratio, thus indicating diminished P50 suppression compared with control subjects.

CONCLUSIONS

To our knowledge, this is the first report of diminished P50 gating in unaffected relatives of psychotic bipolar disorder patients from multiply affected families. Our results suggest that impaired P50 gating is a putative endophenotype for psychotic bipolar disorder and thus might reflect the impact of susceptibility genes across psychosis.

The neurobiological characteristics of rapid eye movement (REM) sleep are candidate endophenotypes of depression, schizophrenia, mental retardation and dementia

Animal models are a promising method to approach the basic mechanisms of the neurobiological disturbances encountered in mental disorders. Depression is characterized by a decrease of REM sleep latency and an increase of rapid eye movement density. In schizophrenia, electrophysiological, tomographic, pharmacological and neurochemical activities are all encountered during REM sleep. Mental retardation and dementia are characterized by rather specific REM sleep disturbances. Identification of the genetic support for these abnormalities (endophenotypes) encountered during REM sleep could help to develop specific treatments.

Schizophrenia and the alpha7 nicotinic acetylcholine receptor

In addition to the devastating symptoms of psychosis, many people with schizophrenia also suffer from cognitive impairment. These cognitive symptoms lead to marked dysfunction and can impact employability, treatment adherence, and social skills. Deficits in P50 auditory gating are associated with attentional impairment and may contribute to cognitive symptoms and perceptual disturbances. This nicotinic cholinergic-mediated inhibitory process represents a potential new target for therapeutic intervention in schizophrenia. This chapter will review evidence implicating the nicotinic cholinergic, and specifically, the alpha7 nicotinic receptor system in the pathology of schizophrenia. Impaired auditory sensory gating has been linked to the alpha7 nicotinic receptor gene on the chromosome 15q14 locus. A majority of persons with schizophrenia are heavy smokers. Although nicotine can acutely reverse diminished auditory sensory gating in people with schizophrenia, this effect is lost on a chronic basis due to receptor desensitization. The alpha7 nicotinic agonist 3-(2,4 dimethoxy)benzylidene-anabaseine (DMXBA) can also enhance auditory sensory gating in animal models. DMXBA is well tolerated in humans and a new study in persons with schizophrenia has found that DMXBA enhances both P50 auditory gating and cognition. alpha7 Nicotinic acetylcholine receptor agonists appear to be viable candidates for the treatment of cognitive disturbances in schizophrenia.

Event-related potentials in psychiatry

Electrophysiological assessments of psychiatric disorders have produced a number of promising, highly replicable findings and thus carry the potential of becoming clinically utilizable in the diagnostic or prognostic evaluation of psychopathological conditions. The procedures involved are rather complex technically and the interpretation of the findings require a combined neurophysiological and clinical expertise. On the other hand, electrophysiological techniques are in general non-invasive and relatively inexpensive, and neurophysiology laboratories are widely available in the clinical setting. Among these techniques, event-related potentials (ERPs) are of major interest in psychiatry, particularly since these tools can indicate cortical neuronal dysfunctions, which play a major role in various neuropsychiatric disorders.

Deconstructing schizophrenia: an overview of the use of endophenotypes in order to understand a complex disorder

The genetics of schizophrenia has been approached utilizing a variety of methods. One emerging strategy is the use of endophenotypes in order to understand and identify the functional importance of genetically transmitted, brain-based deficits across schizophrenia kindreds. The endophenotype strategy is a topic of this issue of Schizophrenia Bulletin. Endophenotypes are quantitative, heritable, trait-related deficits typically assessed by laboratory-based methods rather than clinical observation. Endophenotypes are seen as closer to genetic variation than are clinical symptoms of schizophrenia, and are therefore closely linked to heritable risk factors. There has been a broad expansion of opportunities available to psychiatric neuroscientists who use the endophenotype strategy to understand the genetic basis of schizophrenia. In this context, genetic variation such as single nucleotide polymorphisms (SNPs) induces abnormalities in endophenotypic domains such as neurocognition, neurodevelopment, metabolism, and neurophysiology. This article discusses the challenges that abound in genetic research of schizophrenia, including issues in ascertainment, epistasis, ethnic diversity, and the potentially normalizing effects of second-generation antipsychotic medications on neurocognitive and neurophysiological measures. Robust strategies for meeting these challenges are discussed in this review and the subsequent articles in this issue. This article summarizes conceptual advances and progress in the measurement and use of endophenotypes in schizophrenia that form the basis of the multisite National Institute of Mental Health Consortium on the Genetics of Schizophrenia. The endophenotype strategy offers powerful and exciting opportunities to understand the genetically conferred neurobiological vulnerabilities and possible new strong inference and molecularly based treatments for schizophrenia.

Review of clinical correlates of P50 sensory gating abnormalities in patients with schizophrenia

A large percentage of patients with schizophrenia are characterized by an abnormality in P50 sensory gating. This abnormality has been shown to be genetically linked to the alpha-7 nicotinic receptor and is transiently reversed by acute nicotine administration. These observations have led to the development of pharmacological treatments designed to improve sensory gating. However, if normalization of P50 gating abnormalities is to guide drug development, then it becomes important to delineate the clinical correlates of enhanced P50 gating. We conducted a review of all available articles through March 2005 that have examined this issue. We found that, despite the prominent role that P50 abnormalities have played in our understanding of schizophrenia, there is a relative dearth of data examining P50 clinical correlates. There is evidence suggestive of an association between P50 and measures of attention, and multiple studies have failed to document a cross-sectional or longitudinal relationship between P50 and positive, negative, or other symptoms. These results suggest that considerably more work needs to be done to understand and validate the clinical significance of this impairment.

Discovery ofN-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]furo[2,3-c]pyridine-5-carboxamide, an Agonist of the α7 Nicotinic Acetylcholine Receptor, for the Potential Treatment of Cognitive Deficits in Schizophrenia: Synthesis and Structure−Activity Relationship

N-[(3R)-1-Azabicyclo[2.2.2]oct-3-yl]furo[2,3-c]pyridine-5-carboxamide (14, PHA-543,613), a novel agonist of the alpha7 neuronal nicotinic acetylcholine receptor (alpha7 nAChR), has been identified as a potential treatment of cognitive deficits in schizophrenia. Compound 14 is a potent and selective alpha7 nAChR agonist with an excellent in vitro profile. The compound is characterized by rapid brain penetration and high oral bioavailability in rat and demonstrates in vivo efficacy in auditory sensory gating and, in an in vivo model to assess cognitive performance, novel object recognition.

The use of neurophysiological endophenotypes to understand the genetic basis of schizophrenia

Specifying the complex genetic architecture of the “fuzzy” clinical phenotype of schizophrenia is an imposing problem. Utilizing metabolic, neurocognitive, and neurophysiological “intermediate” endophenotypic measures offers significant advantages from a statistical genetics stand-point. Endophenotypic measures are amenable to quantitative genetic analyses, conferring upon them a major methodological advantage compared with largely qualitative diagnoses using the Diagnostic and Statistical Manual of Mental Health, 4th Edition (DSM-IV). Endophenotypic deficits occur across the schizophrenia spectrum in schizophrenia patients, schizotypal patients, and clinically unaffected relatives of schizophrenia patients, Neurophysiological measures, such as P50 event-related suppression and the prepulse inhibition (PPI) of the startle response, are endophenotypes that can be conceptualized as being impaired because of a single genetic abnormality in the functional cascade of DNA to RNA to protein. The “endophenotype approach” is also being used to understand other medical disorders, such as colon cancer, hemochromatosis, and hypertension, where there is interplay between genetically conferred vulnerability and nongenetic stressors. The power and utility of utilizing endophenotypes to understand the genetics of schizophrenia is discussed in detail in this article.

Genetic bases for endophenotypes in psychiatric disorders

This article reviews the concept of an endophenotype, with particular reference to heritability as well as diagnostic specificity. An endophenotype need not be heritable, for example, the possible influence of in utero viral infections for schizophrenia. However, heritability is a useful characteristic for a potential endophenotype, as it can be studied in relation to a plausible candidate gene. It should be noted that the traditional methods of demonstrating heritability eg, twin studies, can be supplemented with DNA sequence studies, suggesting heritability. Endophenotypes need not be specific to a given nosological class of psychiatric disorders, as these classes do not reflect biological categories. Evidence for two useful schizophrenia endophenotypes, the P50 abnormalities and cognitive deficits, is summarized.

Tropisetron improves deficient inhibitory auditory processing in DBA/2 mice: role of alpha 7 nicotinic acetylcholine receptors

RATIONALE

Deficient inhibitory processing of the P50 auditory evoked potential is a pathophysiological feature of schizophrenia. Several lines of evidence suggest that alpha 7 nicotinic receptors play a critical role in this phenomenon. Similar to schizophrenic patients, DBA/2 mice spontaneously exhibit a deficit in inhibitory processing of the P20-N40 auditory evoked potential, which is thought to be a rodent analog of the human P50 auditory evoked potential.

OBJECTIVE

The present study was undertaken to examine whether tropisetron, a partial agonist at alpha 7 nicotinic receptors and an antagonist at 5-hydroxytryptamine-3 receptors, improves this deficit in DBA/2 mice.

RESULTS

Administration of tropisetron (1 mg/kg i.p.) significantly improved the deficient inhibitory processing of the P20-N40 auditory evoked potential in DBA/2 mice. Coadministration of methyllycaconitine (MLA; 3 mg/kg i.p.), a partially selective antagonist at alpha 7 nicotinic receptors, significantly blocked the normalizing effect of tropisetron. Furthermore, MLA alone did not alter the deficient inhibitory processing of the P20-N40 auditory evoked potential in DBA/2 mice.

CONCLUSIONS

The data suggest that tropisetron improves the deficient inhibitory processing of the P20-N40 auditory evoked potential in DBA/2 mice by effects on alpha 7 and perhaps alpha 4 beta 2 nicotinic receptors. Tropisetron may be useful for the treatment of deficient inhibitory processing in schizophrenia.