The effects of memantine on prepulse inhibition

Integrative Pharmacology in the Treatment of Substance Use Disorders

The detrimental physical, mental, and socioeconomic effects of substance use disorders (SUDs) have been apparent to the medical community for decades. However, it has become increasingly urgent in recent years to develop novel pharmacotherapies to treat SUDs. Currently, practitioners typically rely on monotherapy. Monotherapy has been shown to be superior to no treatment at all for most substance classes. However, many randomized controlled trials (RCTs) have revealed that monotherapy leads to poorer outcomes when compared with combination treatment in all specialties of medicine. The results of RCTs suggest that monotherapy frequently fails since multiple dysregulated pathways, enzymes, neurotransmitters, and receptors are involved in the pathophysiology of SUDs. As such, research is urgently needed to determine how various neurobiological mechanisms can be targeted by novel combination treatments to create increasingly specific yet exceedingly comprehensive approaches to SUD treatment. This article aims to review the neurobiology that integrates many pathophysiologic mechanisms and discuss integrative pharmacology developments that may ultimately improve clinical outcomes for patients with SUDs. Many neurobiological mechanisms are known to be involved in SUDs including dopaminergic, nicotinic, N-methyl-D-aspartate (NMDA), and kynurenic acid (KYNA) mechanisms. Emerging evidence indicates that KYNA, a tryptophan metabolite, modulates all these major pathophysiologic mechanisms. Therefore, achieving KYNA homeostasis by harmonizing integrative pathophysiology and pharmacology could prove to be a better therapeutic approach for SUDs. We propose KYNA-NMDA-α7nAChRcentric pathophysiology, the "conductor of the orchestra," as a novel approach to treat many SUDs concurrently. KYNA-NMDA-α7nAChR pathophysiology may be the "command center" of neuropsychiatry. To date, extant RCTs have shown equivocal findings across comparison conditions, possibly because investigators targeted single pathophysiologic mechanisms, hit wrong targets in underlying pathophysiologic mechanisms, and tested inadequate monotherapy treatment. We provide examples of potential combination treatments that simultaneously target multiple pathophysiologic mechanisms in addition to KYNA. Kynurenine pathway metabolism demonstrates the greatest potential as a target for neuropsychiatric diseases. The investigational medications with the most evidence include memantine, galantamine, and N-acetylcysteine. Future RCTs are warranted with novel combination treatments for SUDs. Multicenter RCTs with integrative pharmacology offer a promising, potentially fruitful avenue to develop novel therapeutics for the treatment of SUDs.

Prepulse inhibition deficit as a transdiagnostic process in neuropsychiatric disorders: a systematic review

BACKGROUND

Psychopathological research is moving from a specific approach towards transdiagnosis through the analysis of processes that appear transversally to multiple pathologies. A phenomenon disrupted in several disorders is prepulse inhibition (PPI) of the startle response, in which startle to an intense sensory stimulus, or pulse, is reduced if a weak stimulus, or prepulse, is previously presented.

OBJECTIVE AND METHODS

The present systematic review analyzed the role of PPI deficit as a possible transdiagnostic process for four main groups of neuropsychiatric disorders: (1) trauma-, stress-, and anxiety-related disorders (2) mood-related disorders, (3) neurocognitive disorders, and (4) other disorders such as obsessive-compulsive, tic-related, and substance use disorders. We used Web of Science, PubMed and PsycInfo databases to search for experimental case-control articles that were analyzed both qualitatively and based on their potential risk of bias. A total of 64 studies were included in this systematic review. Protocol was submitted prospectively to PROSPERO 04/30/2022 (CRD42022322031).

RESULTS AND CONCLUSION

The results showed a general PPI deficit in the diagnostic groups mentioned, with associated deficits in the dopaminergic neurotransmission system, several areas implied such as the medial prefrontal cortex or the amygdala, and related variables such as cognitive deficits and anxiety symptoms. It can be concluded that the PPI deficit appears across most of the neuropsychiatric disorders examined, and it could be considered as a relevant measure in translational research for the early detection of such disorders.

Preventive and Therapeutic Autoantibodies Protect against Neuronal Excitotoxicity

High titers of anti-NMDAR1 IgG autoantibodies were found in the brains of patients with anti-NMDAR1 encephalitis that exhibits psychosis, impaired memory, and many other psychiatric symptoms in addition to neurological symptoms. Low titers of blood circulating anti-NMDAR1 IgG autoantibodies are sufficient to robustly impair spatial working memory in mice with intact blood-brain barriers (BBB). On the other hand, anti-NMDAR1 autoantibodies were reported to protect against neuronal excitotoxicity caused by excessive glutamate in neurological diseases. Activation of extrasynaptic NMDARs is responsible for neuronal excitotoxicity, whereas activation of synaptic NMDARs within the synaptic cleft is pro-survival and essential for NMDAR-mediated neurotransmission. Unlike small IgG, IgM antibodies are large and pentameric (diameter of ~30 nm). It is plausible that IgM anti-NMDAR1 autoantibodies may be restricted to bind extrasynaptic NMDARs and thereby specifically inhibit neuronal excitotoxicity, but physically too large to enter the synaptic cleft (width: 20-30 nm) to suppress synaptic NMDAR-mediated neurotransmission in modulation of cognitive function and neuronal pro-survival signaling. Hence, blood circulating anti-NMDAR1 IgM autoantibodies are both neuroprotective and pro-cognitive, whereas blood circulating anti-NMDAR1 IgG and IgA autoantibodies are detrimental to cognitive function. Investigation of anti-NMDAR1 IgM autoantibodies may open up a new avenue for the development of long-lasting preventive and therapeutic IgM anti-NMDAR1 autoantibodies that protect from neuronal excitotoxicity in many neurological diseases and psychiatric disorders.

Preliminary Evidence that Memantine Enhances Prepulse Effects on Startle Magnitude and Latency in Patients with Alzheimer's Disease

BACKGROUND

The uncompetitive NMDA antagonist, memantine (MEM), enhances prepulse inhibition of startle (PPI) across species. MEM is used to treat Alzheimer's disease (AD); conceivably, its acute impact on PPI might be used to predict a patient's sensitivity to MEM's therapeutic effects.

OBJECTIVE

To begin to test this possibility, we studied MEM effects on PPI and related measures in AD patients.

METHODS

18 carefully screened individuals with AD (mean age = 72.8 y; M:F=9 : 9) completed double-blind order-balanced testing with MEM (placebo versus 20 mg), assessing acoustic startle magnitude, habituation, PPI, and latency.

RESULTS

Fifteen out of 18 participants exhibited reliable startle responses. MEM did not significantly impact startle magnitude or habituation. Compared to placebo responses, PPI was significantly increased after MEM (p < 0.04; d = 0.40); this comparison reached a large effect size for the 60 ms interval (d = 0.62), where maximal MEM effects on PPI were previously detected. Prepulses reduced peak startle latency ("latency facilitation") and this effect was amplified after MEM (p = 0.03; d = 0.41; for 60 ms intervals, d = 0.69). No effects of MEM were detected on cognition, nor were MEM effects on startle associated with cognitive or clinical measures.

CONCLUSION

MEM enhances prepulse effects on startle magnitude and latency in AD; these changes in PPI and latency facilitation with MEM suggest that these measures can be used to detect an AD patient's neural sensitivity to acute MEM challenge. Studies in progress will determine whether such a "biomarker" measured at the outset on treatment can predict sensitivity to MEM's therapeutic effects.

Central auditory processing deficits in schizophrenia: Effects of auditory-based cognitive training

BACKGROUND

Sensory processing abnormalities are common in schizophrenia (SZ) and impact everyday functions, such as speech perception in noisy environments. Auditory-based targeted cognitive training (TCT) is a "bottom up" cognitive remediation intervention designed to enhance the speed and accuracy of low-level auditory information processing. However, the effects of TCT on behavioral measures of central auditory processing (CAP) and the role of CAP function on verbal learning outcomes in SZ are unknown.

METHODS

SZ (n = 42) and healthy subjects (CTL; n = 18) underwent comprehensive clinical, neurocognitive, and auditory assessments, including tests of hearing sensitivity and speech recognition (Words-in-Noise (WIN), Quick Speech-in-Noise (SIN)). SZ patients were randomized to receive either treatment-as-usual (TAU); or 30-h of TCT + TAU using a stratified, parallel design. SZ patients repeated assessments ~10-12 weeks later.

RESULTS

Patients exhibited deficits in both WIN (p < 0.05, d = 0.50) and SIN (p < 0.01, d = 0.63). A treatment × time interaction on WIN (p < 0.05, d = 0.74), but not SIN discriminability, was seen in the TCT group relative to TAU. Specific enhancements in the 4-dB over background range drove gains in WIN performance. Moreover, SZ patients with greater CAP deficits experienced robust gains in verbal learning after 30-h of TCT relative to SZ patients without CAP impairment (p < 0.01, d = 1.28).

CONCLUSION

Findings demonstrate that intensive auditory training enhances the fidelity of auditory processing and perception, such that specific CAP deficits were 'normalized' and were predictive of gains in verbal learning after TCT. It is conceivable that patients with deficiencies in CAP measures may benefit most from TCT and other interventions targeting auditory dysfunction in SZ.

Oxytocin attenuates schizophrenia-like reduced sensorimotor gating in outbred and inbred rats in line with strain differences in CD38 gene expression

Prepulse inhibition (PPI) of the startle response is a measure of sensorimotor gating that is impaired in many clinical conditions, including schizophrenia. The inbred Roman high-avoidance (RHA) rats, compared to their low-avoidance (RLA) counterparts, show distinct schizophrenia-like phenotypes, such as spontaneous deficits in PPI accompanied by decreased medial prefrontal cortex (mPFC) activity and volume. Schizophrenia-like deficits are usually attenuated by antipsychotic drugs, but these drugs often produce severe side effects. In order to reduce these side effects, the neuropeptide oxytocin has been proposed as an alternative natural antipsychotic for schizophrenia. Here, we examined the effects of peripheral oxytocin administration (saline, 0.04, and 0.2 mg/kg) on PPI in the RHA vs. RLA rats, as well as in the outbred heterogeneous stock (HS) rats. Our results showed that oxytocin increased PPI in the HS rats and attenuated PPI deficits in the RHA rats, but it did not significantly affect PPI in the RLAs. To explore whether these divergent effects were associated with differences in oxytocinergic mechanisms, we analyzed gene expression of the oxytocin receptor (OXTR) and the regulator of oxytocin release (CD38) in the mPFC of the Roman rats. Consistent with the differential oxytocin effects on PPI (RHA > RLA), constitutive CD38 expression was reduced in the RHA rats compared to the RLAs, while oxytocin administration increased OXTR expression in both strains. Overall, the present work reveals that oxytocin administration shows antipsychotic-like effects on PPI in outbred and inbred rats, and it suggests that these effects may be related to basal differences in oxytocin-mediated mechanisms in the mPFC.

Fluoroethylnormemantine, A Novel Derivative of Memantine, Facilitates Extinction Learning Without Sensorimotor Deficits

BACKGROUND

Memantine, a noncompetitive N-methyl-D-aspartate receptor antagonist, has been approved for use in Alzheimer's disease, but an increasing number of studies have investigated its utility for neuropsychiatric disorders. Here, we characterized a novel compound, fluoroethylnormemtantine (FENM), which was derived from memantine with an extra Fluor in an optimized position for in vivo biomarker labeling. We sought to determine if FENM produced similar behavioral effects as memantine and/or if FENM has beneficial effects against fear, avoidance, and behavioral despair.

METHODS

We administered saline, FENM, or memantine prior to a number of behavioral assays, including paired-pulse inhibition, open field, light dark test, forced swim test, and cued fear conditioning in male Wistar rats.

RESULTS

Unlike memantine, FENM did not produce nonspecific side effects and did not alter sensorimotor gating or locomotion. FENM decreased immobility in the forced swim test. Moreover, FENM robustly facilitated fear extinction learning when administered prior to either cued fear conditioning training or tone reexposure.

CONCLUSIONS

These results suggest that FENM is a promising, novel compound that robustly reduces fear behavior and may be useful for further preclinical testing.

Association of the kynurenine pathway metabolites with clinical, cognitive features and IL-1β levels in patients with schizophrenia spectrum disorder and their siblings

OBJECTIVE

There is evidence suggesting that tryptophan (TRP)-kynurenine (KYN) pathway dysregulation is involved in the pathophysiology of schizophrenia and is regulated by inflammatory cytokines. The study investigate for the first time whether this dysregulation occurs in advanced stages of the disease as a byproduct or emerges as one of the early and inherited manifestations of schizophrenia.

METHOD

Sera of 148 patients with schizophrenia spectrum disorders (SCZ), 139 unaffected siblings (SIB) and 210 controls were investigated. Serum interleukin (IL)-1β levels were measured by ELISA, and TRP, KYN and kynurenic acid (KYNA) levels were measured by a high-performance liquid chromatography system. Also, we collected clinical data by applying Comprehensive Assessment of Symptoms and History in SCZ, and SIS-R in SIB and control groups.

RESULTS

Compared to controls, SCZ and SIB groups had lower TRP and higher KYNA levels. TRP levels showed significant differences only between SCZ and controls (p < 0.01). KYNA levels of both SCZ (p ≤ 0.001) and SIB (p < 0.05) were higher than controls. No statistical significance was found for KYN levels across groups. SCZ and SIB groups had higher serum IL-1β levels than controls (p ≤ 0.001).

CONCLUSIONS

Patients with SCZ and their siblings exhibited similar clinical features and TRP metabolite levels suggesting that TRP-KYN dysregulation may be an inherited component of the disease putatively conferring increased risk to schizophrenia. Elevation of IL-1β is one of the factors promoting overconsumption of the TRP-KYN pathway leading to increased production of neuroregulatory KYNA and presumably to neurodegeneration.

Using Biomarkers to Predict Memantine Effects in Alzheimer's Disease: A Proposal and Proof-Of-Concept Demonstration

Memantine's benefits in Alzheimer's disease (AD) are modest and heterogeneous. We tested the feasibility of using sensitivity to acute memantine challenge to predict an individual's clinical response. Eight participants completed a double-blind challenge study of memantine (placebo versus 20 mg) effects on autonomic, subjective, cognitive, and neurophysiological measures, followed by a 24-week unblinded active-dose therapeutic trial (10 mg bid). Study participation was well tolerated. Subgroups based on memantine sensitivity on specific laboratory measures differed in their clinical response to memantine, some by large effect sizes. It appears feasible to use biomarkers to predict clinical sensitivity to memantine.

Memantine effects on auditory discrimination and training in schizophrenia patients

The uncompetitive low-affinity NMDA receptor antagonist, memantine, acutely increases electrophysiological measures of auditory information processing in both healthy subjects (HS) and patients with schizophrenia. Memantine effects on functional measures of auditory discrimination performance and learning are not known; conceivably, beneficial effects on these measures might suggest a role for memantine in augmenting the cognitive and functional impact of auditory targeted cognitive training (TCT). Here, carefully characterized HS (n = 20) and schizophrenia patients (n = 22) were tested in measures of auditory discrimination performance (words-in-noise (WIN), quick speech-in-noise (QuickSIN), gaps-in-noise) and auditory frequency modulation learning (a component of TCT) on 2 days about a week apart, after ingesting either placebo or 20 mg memantine po, in a double-blind, within-subject cross-over random order design. Memantine modestly enhanced functional measures of auditory discrimination in both schizophrenia patients (WIN) and HS (WIN and QuickSIN), as well as auditory frequency modulation learning in schizophrenia patients. These findings converge with a growing literature showing that memantine can enhance a range of metrics of auditory function. These properties could contribute to the apparent benefits of memantine as an adjunctive treatment in schizophrenia, and suggest that memantine might augment learning and potentially clinical gains from auditory-based TCT.

The Cross-Talk Between the Dopaminergic and the Immune System Involved in Schizophrenia

Dopamine is one of the neurotransmitters whose transmission is altered in a number of neural pathways in the brain of schizophrenic patients. Current evidence indicates that these alterations involve hyperactive dopaminergic transmission in mesolimbic areas, striatum, and hippocampus, whereas hypoactive dopaminergic transmission has been reported in the prefrontal cortex of schizophrenic patients. Consequently, schizophrenia is associated with several cognitive and behavioral alterations. Of note, the immune system has been found to collaborate with the central nervous system in a number of cognitive and behavioral functions, which are dysregulated in schizophrenia. Moreover, emerging evidence has associated schizophrenia and inflammation. Importantly, different lines of evidence have shown dopamine as a major regulator of inflammation. In this regard, dopamine might exert strong regulation in the activity, migration, differentiation, and proliferation of immune cells that have been shown to contribute to cognitive functions, including T-cells, microglial cells, and peripheral monocytes. Thereby, alterations in dopamine levels associated to schizophrenia might affect inflammatory response of immune cells and consequently some behavioral functions, including reference memory, learning, social behavior, and stress resilience. Altogether these findings support the involvement of an active cross-talk between the dopaminergic and immune systems in the physiopathology of schizophrenia. In this review we summarize, integrate, and discuss the current evidence indicating the involvement of an altered dopaminergic regulation of immunity in schizophrenia.

Room to move: Plasticity in early auditory information processing and auditory learning in schizophrenia revealed by acute pharmacological challenge

Many patients with chronic psychotic disorders including schizophrenia (SZ) maintain meaningful levels of plasticity (i.e., capacity for change) within neurocognition-relevant brain mechanisms, as evidenced by gains in neurocognition and function after interventions such as targeted cognitive training. However, like many clinical features of these disorders, therapeutic responses in SZ are heterogeneous, and prospectively identifying treatment-sensitive individuals and individualized treatment modalities remains an unmet challenge. We propose that available plasticity in neurocognition-relevant brain mechanisms in individual SZ patients can be detected by gains in laboratory measures of early auditory information processing (EAIP) and auditory learning after a single challenge-dose of a pharmacologic agent; here, we present supportive data for this strategy with the non-competitive NMDA antagonist, memantine, and the psychostimulant, amphetamine. We describe a novel therapeutic model where this "challenge dose" strategy is used to prospectively identify a sensitive cohort of patients, and in these patients, a therapeutic response is elicited by pairing drug-enhanced EAIP and auditory learning with auditory-based targeted cognitive training.

Sensorimotor gating characteristics of violent men with comorbid psychosis and dissocial personality disorder: Relationship with antisocial traits and psychosocial deprivation

Evidence suggests violence amongst those with psychosis is not aetiologically homogeneous, and that a large proportion of those who engage in violent behaviour have a comorbid antisocial personality disorder. Initial investigations indicate that this subgroup has distinct historical and neuropsychological characteristics, which may indicate diverse treatment needs. This study investigated sensorimotor gating characteristics of violent men with diagnoses of both psychosis and dissocial personality disorder (DPD) (n=21) relative to violent men with psychosis alone (n=12), DPD alone (n=14) and healthy, non-violent male controls (n=27), using the prepulse inhibition (PPI) paradigm. The results indicated that, relative to the psychosis alone and healthy control groups, the comorbid group had lower PPI, especially at 60-ms prepulse-to-pulse interval. The DPD group took an intermediary position and did not differ from any group. Antisocial personality traits (factor two scores of the Psychopathy Checklist - Revised), and greater severity of childhood psychosocial deprivation (including physical and sexual abuse), were significantly correlated with poor PPI across the clinical sample. The findings suggest diverse sensorimotor gating profiles amongst subgroups of violent offenders, with comorbid psychosis and DPD showing most impairment. This is consistent with a 'double dose' of deficit explanation amongst those with both diagnoses, explained at least in part by presence of antisocial personality traits and childhood psychosocial deprivation.

Auditory System Target Engagement During Plasticity-Based Interventions in Schizophrenia: A Focus on Modulation of N-Methyl-D-Aspartate-Type Glutamate Receptor Function

Cognitive deficits are predictive of long-term social and occupational functional deficits in schizophrenia but are currently without gold-standard treatments. In particular, augmentation of auditory cortical neuroplasticity may represent a rate-limiting first step before addressing higher-order cognitive deficits. We review the rationale for N-methyl-d-aspartate-type glutamate receptor (NMDAR) modulators as treatments for auditory plasticity deficits in schizophrenia, along with potential serum and electroencephalographic target engagement biomarkers for NMDAR function. Several recently published NMDAR-modulating treatment studies are covered, involving D-serine, memantine, and transcranial direct current stimulation. While all three interventions appear to modulate auditory plasticity, direct agonists (D-serine) appear to have the largest and most consistent effects on plasticity, at least acutely. We hypothesize that there may be synergistic effects of combining procognitive NMDAR-modulating approaches with auditory cortical neuroplasticity cognitive training interventions. Future studies should assess biomarkers for target engagement and patient stratification, along with head-to-head studies comparing putative interventions and potential long-term versus acute effects.

Using EEG-Guided Basket and Umbrella Trials in Psychiatry: A Precision Medicine Approach for Cognitive Impairment in Schizophrenia

Due to advances over the last several decades, many fields of medicine are moving toward a precision medicine approach where treatments are tailored to nuanced patient factors. While in some disciplines these innovations are commonplace leading to unique biomarker-guided experimental medicine trials, there are no such analogs in psychiatry. In this brief review, we will overview two unique biomarker-guided trial designs for future use in psychiatry: basket and umbrella trials. We will illustrate how such trials could be useful in psychiatry using schizophrenia as a candidate illness, the EEG measure mismatch negativity as the candidate biomarker, and cognitive impairment as the target disease dimension.

Single-Dose Memantine Improves Cortical Oscillatory Response Dynamics in Patients with Schizophrenia

Aberrant gamma-band (30-80 Hz) oscillations may underlie cognitive deficits in schizophrenia (SZ). Gamma oscillations and their regulation by NMDA receptors can be studied via their evoked power (γEP) and phase locking (γPL) in response to auditory steady-state stimulation; these auditory steady-state responses (ASSRs) may be biomarkers for target engagement and early therapeutic effects. We previously reported that memantine, an NMDA receptor antagonist, enhanced two biomarkers of early auditory information processing: prepulse inhibition and mismatch negativity (MMN) in SZ patients and healthy subjects (HS). Here, we describe memantine effects on γEP and γPL in those subjects. SZ patients (n=18) and HS (n=14) received memantine 20 mg (p.o.) and placebo over 2 test days in a double-blind, randomized, counterbalanced, cross-over design. The ASSR paradigm (1 ms, 85 dB clicks in 250-0.5 s trains at a frequency of 40 Hz; 0.5 s inter-train interval) was used to assess γEP and γPL. SZ patients had reduced γEP and γPL; memantine enhanced γEP and γPL (p<0.025 and 0.002, respectively) in both SZ and HS. In patients, significant correlations between age and memantine effects were detected for γEP and γPL: greater memantine sensitivity on γEP and γPL were present in younger SZ patients, similar to our reported findings with MMN. Memantine acutely normalized cortical oscillatory dynamics associated with NMDA receptor dysfunction in SZ patients. Ongoing studies will clarify whether these acute changes predict beneficial clinical, neurocognitive and functional outcomes. These data support the use of gamma-band ASSR as a translational end point in pro-cognitive drug discovery and early-phase clinical trials.

Enhancing Effects of NMDA-Receptor Blockade on Extinction Learning and Related Brain Activation Are Modulated by BMI

A distributed network including prefrontal and hippocampal regions is involved in context-related extinction learning as well as in renewal. Renewal describes the recovery of an extinguished response if the context of extinction differs from the context of recall. Animal studies have demonstrated that prefrontal, but not hippocampal N-methyl-D-aspartate receptor (NMDAR) antagonism disrupted extinction learning and processing of task context. However, human studies of NMDAR in extinction learning are lacking, while NMDAR antagonism yielded contradictory results in other learning tasks. This fMRI study investigated the role of NMDAR for human behavioral and brain activation correlates of extinction and renewal. Healthy volunteers received a single dose of the NMDAR antagonist memantine prior to extinction of previously acquired stimulus-outcome associations presented in either identical or novel contexts. We observed better, and partly faster, extinction learning in participants receiving the NMDAR antagonist compared to placebo. However, memantine did not affect renewal. In both extinction and recall, the memantine group showed a deactivation in extinction-related brain regions, particularly in the prefrontal cortex, while hippocampal activity was increased. This higher hippocampal activation was in turn associated with the participants' body mass index (BMI) and extinction errors. Our results demonstrate potentially dose-related enhancing effects of memantine and highlight involvement of hippocampal NMDAR in context-related extinction learning.

Sensorimotor gating in healthy adults tested over a 15 year period

BACKGROUND

Prepulse inhibition (PPI) of startle, an operational measure of sensorimotor gating, is used to study normal and pathological brain function. From 2001 to 2016, we screened healthy subjects (HS) to establish their suitability for tests of drug effects on PPI. Because of the size and systematic characterization of this sample across variables of relevance to PPI, we now report these screening results.

METHODS

Acoustic startle and PPI were assessed in HS to identify those eligible for studies of drug effects on PPI from 2001 to 2016, yielding 457 "eligible" subjects.

RESULTS

Data confirmed the consistency of PPI across this 15-year period, and supported the role of several variables previously reported to moderate either startle or PPI.

CONCLUSIONS

Startle and PPI are robust physiological measures that are predictably moderated by specific physiological variables in healthy adults. As such, these measures serve as robust markers of neurobiological processes in healthy and patient populations.

Clinical studies of neuroinflammatory mechanisms in schizophrenia

Schizophrenia is a pervasive neurodevelopmental disorder that appears to result from genetic and environmental factors. Although the dopamine hypothesis is the driving theory behind the majority of translation research in schizophrenia, emerging evidence suggests that aberrant immune mechanisms in the peripheral and central nervous system influence the etiology of schizophrenia and the pathophysiology of psychotic symptoms that define the illness. The initial interest in inflammatory processes comes from epidemiological data and historical observations, dating back several decades. A growing body of research on developmental exposure to infection, stress-induced inflammatory response, glial cell signaling, structural and functional brain changes and therapeutic trials demonstrates the impact that inflammation has on the onset and progression of schizophrenia. Research in animal models of psychosis has helped to advance clinical and basic science investigations of the immune mechanisms disrupted in schizophrenia. However, they are limited by the inability to recapitulate the human experience of hallucinations, delusions and thought disorder that define psychosis. To date, translational studies of inflammatory mechanisms in human subjects have not been reviewed in great detail. Here, we critically review clinical studies that focus on inflammatory mechanisms in schizophrenia. Understanding the neuroinflammatory mechanisms involved in schizophrenia may be essential in identifying potential therapeutic targets to minimize the morbidity and mortality of schizophrenia by interrupting disease development.

Effects of acute memantine administration on MATRICS Consensus Cognitive Battery performance in psychosis: Testing an experimental medicine strategy

RATIONALE

Pro-cognitive agents for chronic psychotic disorders (CPDs) might be detected via experimental medicine models, in which neural targets engaged by the drug predict sensitivity to the drug's pro-cognitive effects.

OBJECTIVE

This study aims to use an experimental medicine model to test the hypothesis that "target engagement" predicts pro-cognitive effects of the NMDA antagonist, memantine (MEM), in CPDs.

METHODS

MATRICS Consensus Cognitive Battery (MCCB) performance was assessed in CPD (n = 41) and healthy subjects (HS; n = 41) in a double-blind, randomized cross-over design of acute (single dose) MEM (placebo vs. 10 or 20 mg p.o.). Measures of prepulse inhibition (PPI) and mismatch negativity previously reported from this cohort substantiated target engagement. Biomarkers predicting MEM neurocognitive sensitivity were assessed.

RESULTS

Testing confirmed MCCB deficits associated with CPD diagnosis, age, and anticholinergic exposure. MEM (20 mg p.o.) reduced MCCB performance in HS. To control for significant test order effects, an "order-corrected MEM effect" (OCME) was calculated. In CPD subjects, greater age, positive MEM effects on PPI, and SNP rs1337697 (within the ionotropic NMDA receptor gene, GRIN3A) predicted greater positive OCME with 20 mg MEM.

CONCLUSIONS

An experimental medicine model to assess acute pro-cognitive drug effects in CPD subjects is feasible but not without challenges. A single MEM 20 mg dose had a negative impact on neurocognition among HS. In CPD patients, age, MEM effects on PPI, and rs1337697 predicted sensitivity to the neurocognitive effects of MEM. Any potential clinical utility of these predictive markers for pro-cognitive effects of MEM in subgroups of CPD patients cannot be inferred without a validating clinical trial.

Memantine Effects On Sensorimotor Gating and Mismatch Negativity in Patients with Chronic Psychosis

Patients with chronic psychotic disorders (CPD) exhibit deficient sensorimotor gating (measured by prepulse inhibition (PPI) of startle) and mismatch negativity (MMN). In healthy subjects (HS), N-methyl-D-aspartate (NMDA) antagonists like memantine and ketamine increase PPI, and under some conditions, memantine enhances MMN; these findings present a challenge to understanding the basis for deficient PPI and MMN in psychotic disorders, as reduced NMDA activity is implicated in the pathogenesis of these disorders. Here we assessed for the first time the effects of memantine on PPI and MMN in CPD subjects. Baseline PPI was measured in HS and patients with a diagnosis of schizophrenia or schizoaffective disorder, depressed type. Subjects (total n=84) were then tested twice, in a double-blind crossover design, comparing either: (1) placebo vs 10 mg of memantine or (2) placebo vs 20 mg memantine. Tests included measures of acoustic startle magnitude and habituation, PPI, MMN, autonomic indices, and subjective self-rating scales. Memantine (20 mg) significantly enhanced PPI in CPD subjects, and enhanced MMN across subject groups. These effects on PPI were age dependent and most evident in older CPD patients, whereas those on MMN were most evident in younger subjects. The lower dose (10 mg) either had no detectable effect or tended to degrade these measures. The NMDA antagonist, memantine, has dose-dependent effects on preconscious, automatic measures of sensorimotor gating and auditory sensory processing that are associated with enhanced cognition and function in CPD patients. Ongoing studies will determine whether these memantine-induced changes predict acute pro-cognitive or otherwise clinically beneficial effects in CPD patients.

Animal Models of Deficient Sensorimotor Gating in Schizophrenia: Are They Still Relevant?

Animal models of impaired sensorimotor gating, as assessed by prepulse inhibition (PPI) of startle, have demonstrated clear validity at face, predictive, and construct levels for schizophrenia therapeutics, neurophysiological endophenotypes, and potential causative insults for this group of disorders. However, with the growing recognition of the heterogeneity of the schizophrenias, and the less sanguine view of the clinical value of antipsychotic (AP) medications, our field must look beyond "validity," to assess the actual utility of these models. At a substantial cost in terms of research support and intellectual capital, what has come from these models, that we can say has actually helped schizophrenia patients? Such introspection is timely, as we are reassessing not only our view of the genetic and pathophysiological diversity of these disorders, but also the predominant strategies for SZ therapeutics; indeed, our field is gaining awareness that we must move away from a "find what's broke and fix it" approach, toward identifying spared neural and cognitive function in SZ patients, and matching these residual neural assets with learning-based therapies. Perhaps, construct-valid models that identify evidence of "spared function" in neural substrates might reveal opportunities for future therapeutics and allow us to study these substrates at a mechanistic level to maximize opportunities for neuroplasticity. Such an effort will require a retooling of our models, and more importantly, a re-evaluation of their utility. For animal models to remain relevant in the search for schizophrenia therapeutics, they will need to focus less on what is valid and focus more on what is useful.

Blockade of growth hormone secretagogue receptor 1A signaling by JMV 2959 attenuates the NMDAR antagonist, phencyclidine-induced impairments in prepulse inhibition

RATIONALE

Schizophrenic-spectrum patients commonly display deficits in preattentive information processing as evidenced, for example, by disrupted prepulse inhibition (PPI), a measure of sensorimotor gating. Similar disruptions in PPI can be induced in rodents and primates by the psychotomimetic drug phencyclidine (PCP), a noncompetitive inhibitor of the NMDA receptor. Mounting evidence suggests that the hunger hormone ghrelin and its constitutively active receptor influences neuronal circuits involved in the regulation of mood and cognition.

OBJECTIVES

In the present series of experiments, we investigated the effects of ghrelin and the growth hormone secretagogue receptor (GHS-R1A) neutral antagonist, JMV 2959, on acoustic startle responses (ASR), PPI, and PCP-induced alterations in PPI.

RESULTS

Intraperitoneal (i.p.) administration of ghrelin (0.033, 0.1, and 0.33 mg/kg) did not alter the ASR or PPI in rats. Conversely, i.p. injection of JMV 2959 (1, 3, and 6 mg/kg), dose dependently decreased the ASR and increased PPI. Pretreatment with JMV 2959 at a dose with no effect on ASR or PPI per se, completely blocked PCP-induced (2 mg/kg) deficits in PPI while pretreatment with the highest dose of ghrelin did not potentiate or alter PPI responses of a sub-threshold dose of PCP (0.75 mg/kg).

CONCLUSION

These findings indicate that the GHS-R1A is involved in specific behavioral effects of PCP and may have relevance for patients with schizophrenia.

Varenicline disrupts prepulse inhibition only in high-inhibitory rats

Varenicline, a widely used smoking cessation drug, has partial agonistic activity at α4β2 nicotinic receptors, and full agonistic activity at α7 nicotinic receptors. Thus it may interact with cognitive processes and may alleviate some of the cognitive disturbances observed in psychotic illnesses such as schizophrenia. We aimed to test the effects of varenicline on sensorimotor gating functioning, which is crucial for normal cognitive processes, especially for the integration of sensory and cognitive information processing and the execution of appropriate motor responses. Prepulse inhibition (PPI) of the acoustic startle reflex was used to test the sensorimotor gating functioning. First, the effects of varenicline and nicotine on rats having high or low baseline PPI levels were evaluated; then, varenicline was applied prior to apomorphine (0.5 mg/kg), and MK-801 (0.15 mg/kg), which are used as comparative models of PPI disruption. Varenicline (0.5-3 mg/kg) did not change PPI when given alone in naïve animals. When rats were selected according to their baseline PPI values, varenicline (1 mg/kg) significantly decreased PPI in high-inhibitory (HI) but not in low-inhibitory (LI) rats. Nicotine (1 mg/kg; tartrate salt) produced a similar activity in LI and HI groups. In combination experiments, varenicline did not reverse either apomorphine or the MK-801-induced disruption of PPI. These results demonstrate that the effects of both varenicline and nicotine on sensorimotor gating are influenced by the baseline PPI levels. Moreover, varenicline has no effect on apomorphine or the MK-801-induced disruption of PPI.

Effect of L-theanine on sensorimotor gating in healthy human subjects

AIM

l-Theanine (N-ethyl-l-glutamine) is an amino acid uniquely found in green tea. Growing evidence has suggested the possible effects of l-theanine on cognition. Previously, we found that l-theanine attenuates MK-801-induced deficit in prepulse inhibition (PPI) in mice. In this study, we examined the effect of l-theanine in increasing the PPI in healthy humans.

METHODS

The subjects were 14 healthy adults who underwent PPI testing as a measure of sensorimotor gating 90 min after an oral intake of l-theanine (0, 200, 400, or 600 mg). PPI tests were done by examiners who were blind to the dose.

RESULTS

The administration of 200 mg of l-theanine and that of 400 mg, but not 600 mg, significantly increased the % PPI compared to the baseline (0 mg). There was no significant relation between the dose of l-theanine and the startle magnitude or the habituation of startle response. The plasma concentrations of l-theanine correlated with the dose of l-theanine.

CONCLUSION

The observed effect with 200-400 mg of l-theanine on PPI suggested that l-theanine at a particular dose range increases sensorimotor gating in humans.

Amphetamine effects on MATRICS Consensus Cognitive Battery performance in healthy adults

BACKGROUND

Cognitive deficits contribute strongly to functional disability in schizophrenia. The cost of identifying and testing candidate procognitive agents is substantial. Conceivably, candidate drugs might be first identified by positive effects on cognitive domains in sensitive subgroups of healthy subjects. Here, we examined whether the MATRICS Consensus Cognitive Battery (MCCB) detected procognitive drug effects in subgroups of healthy individuals.

METHODS

The effects of 20 mg amphetamine (AMPH) on MCCB performance were tested in a double-blind, placebo-controlled crossover study of 60 healthy adults. AMPH effects were compared in subgroups of subjects characterized by low vs. high placebo MCCB scores, and by extreme values on personality subscales associated with schizophrenia-relevant biomarkers.

RESULTS

AMPH produced autonomic and subjective effects, but did not significantly change MCCB composite scores or individual domain scores across the inclusive sample of 60 subjects. AMPH-induced MCCB changes were significantly (inversely) related to placebo MCCB performance: among individuals with lower placebo scores, AMPH enhanced performance; while among individuals with higher placebo scores, it impaired performance. A potential impact of regression to the mean was assessed and could not be ruled out. Both placebo MCCB performance and AMPH effects on MCCB scores were significantly related to personality domains associated with schizophrenia-linked genetic- and/or neurophysiological substrates.

CONCLUSIONS

Among healthy adults, AMPH effects on MCCB performance were detected only among specific subgroups, and in specific cognitive domains. Strategies that utilize drug-induced changes in MCCB performance in healthy subjects to screen for candidate procognitive drugs should consider the use of "enriched" subgroups with specific neurocognitive or personality characteristics.

Anti-inflammatory treatment in schizophrenia

Antipsychotics, which act predominantly as dopamine D2 receptor antagonists, have several shortcomings. The exact pathophysiological mechanism leading to dopaminergic dysfunction in schizophrenia is still unclear, but inflammation has been postulated to be a key player in the pathophysiology of the disorder. A dysfunction in activation of the type 1 immune response seems to be associated with an imbalance in tryptophan/kynurenine metabolism; the degrading enzymes involved in this metabolism are regulated by cytokines. Kynurenic acid (KYNA), an N-methyl-d-aspartate antagonist, was found to be increased in critical regions of the central nervous system (CNS) in schizophrenia, resulting in reduced glutamatergic neurotransmission. The differential activation of microglial cells and astrocytes as functional carriers of the immune system in the CNS may also contribute to this imbalance. The immunological effects of many existing antipsychotics, however, rebalance in part the immune imbalance and overproduction of KYNA. The immunological imbalance results in an inflammatory state combined with increased prostaglandin E(2) production and increased cyclo-oxygenase-2 (COX-2) expression. Growing evidence from clinical studies with COX-2 inhibitors points to favorable effects of anti-inflammatory therapy in schizophrenia, in particular in an early stage of the disorder. Further options for immunomodulating therapies in schizophrenia will be discussed.

Update: studies of prepulse inhibition of startle, with particular relevance to the pathophysiology or treatment of Tourette Syndrome

Prepulse inhibition of the startle reflex (PPI) is an operational measure of sensorimotor gating, in which the motor response to an abrupt, intense stimulus is inhibited by a weak lead stimulus. PPI is reduced in several brain disorders, including Tourette Syndrome (TS); it is regulated by forebrain circuitry, including portions of the basal ganglia implicated in the pathophysiology of TS, and is also heritable and under strong genetic control. PPI has been the focus of numerous translational models, because it is expressed by most mammalian species, with remarkable conservation of response characteristics and underlying neural circuitry between rodents and primates. Several of these models have recently explored causative factors in TS - from genes to specific basal ganglia perturbations - as well as potential TS therapeutics, including novel pharmacological and neurosurgical interventions. With the focus on Comprehensive Behavioral Interventions for Tics (CBIT) in the evolving treatment model for TS, future studies might apply PPI as a predictive measure for CBIT response, or for identifying medications that might augment CBIT efficacy. In the end, a measure based on a simple pontine-based reflex will have limitations in its ability to explicate any complex behavioral phenotype.

The role of memantine in the treatment of psychiatric disorders other than the dementias: a review of current preclinical and clinical evidence

Memantine, a non-competitive NMDA receptor antagonist approved for Alzheimer's disease with a good safety profile, is increasingly being studied in a variety of non-dementia psychiatric disorders. We aimed to critically review relevant literature on the use of the drug in such disorders. We performed a PubMed search of the effects of memantine in animal models of psychiatric disorders and its effects in human studies of specific psychiatric disorders. The bulk of the data relates to the effects of memantine in major depressive disorder and schizophrenia, although more recent studies have provided data on the use of the drug in bipolar disorder as an add-on. Despite interesting preclinical data, results in major depression are not encouraging. Animal studies investigating the possible usefulness of memantine in schizophrenia are controversial; however, interesting findings were obtained in open studies of schizophrenia, but negative placebo-controlled, double-blind studies cast doubt on their validity. The effects of memantine in anxiety disorders have been poorly investigated, but data indicate that the use of the drug in obsessive-compulsive disorder and post-traumatic stress disorder holds promise, while findings relating to generalized anxiety disorder are rather disappointing. Results in eating disorders, catatonia, impulse control disorders (pathological gambling), substance and alcohol abuse/dependence, and attention-deficit hyperactivity disorder are inconclusive. In most psychiatric non-Alzheimer's disease conditions, the clinical data fail to support the usefulness of memantine as monotherapy or add-on treatment However, recent preclinical and clinical findings suggest that add-on memantine may show antimanic and mood-stabilizing effects in treatment-resistant bipolar disorder.

Characterization of neurophysiologic and neurocognitive biomarkers for use in genomic and clinical outcome studies of schizophrenia

Background

Endophenotypes are quantitative, laboratory-based measures representing intermediate links in the pathways between genetic variation and the clinical expression of a disorder. Ideal endophenotypes exhibit deficits in patients, are stable over time and across shifts in psychopathology, and are suitable for repeat testing. Unfortunately, many leading candidate endophenotypes in schizophrenia have not been fully characterized simultaneously in large cohorts of patients and controls across these properties. The objectives of this study were to characterize the extent to which widely-used neurophysiological and neurocognitive endophenotypes are: 1) associated with schizophrenia, 2) stable over time, independent of state-related changes, and 3) free of potential practice/maturation or differential attrition effects in schizophrenia patients (SZ) and nonpsychiatric comparison subjects (NCS). Stability of clinical and functional measures was also assessed.

Methods

Participants (SZ n = 341; NCS n = 205) completed a battery of neurophysiological (MMN, P3a, P50 and N100 indices, PPI, startle habituation, antisaccade), neurocognitive (WRAT-3 Reading, LNS-forward, LNS-reorder, WCST-64, CVLT-II). In addition, patients were rated on clinical symptom severity as well as functional capacity and status measures (GAF, UPSA, SOF). 223 subjects (SZ n = 163; NCS n = 58) returned for retesting after 1 year.

Results

Most neurophysiological and neurocognitive measures exhibited medium-to-large deficits in schizophrenia, moderate-to-substantial stability across the retest interval, and were independent of fluctuations in clinical status. Clinical symptoms and functional measures also exhibited substantial stability. A Longitudinal Endophenotype Ranking System (LERS) was created to rank neurophysiological and neurocognitive biomarkers according to their effect sizes across endophenotype criteria.

Conclusions

The majority of neurophysiological and neurocognitive measures exhibited deficits in patients, stability over a 1-year interval and did not demonstrate practice or time effects supporting their use as endophenotypes in neural substrate and genomic studies. These measures hold promise for informing the “gene-to-phene gap” in schizophrenia research.

Prepulse inhibition in patients with fragile X-associated tremor ataxia syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late onset neurodegenerative disorder that affects carriers of the fragile X premutation, typically after age 50. Common symptoms include intention tremor, ataxia, neuropathy, autonomic dysfunction, cognitive decline, and dementia. The objectives of this study were to determine if patients with FXTAS have altered prepulse inhibition (PPI; a measure of sensorimotor gating), and to study possible correlations between PPI, molecular status, and cognitive performance. A passive acoustic PPI paradigm was applied in 163 subjects; 121 carriers of the fragile X premutation, and 42 healthy controls. There were significant differences in PPI between premutation carriers with FXTAS and controls at PPI 60 ms, and at 120 ms. This effect was more prominent in the male FXTAS patients. There was a tendency to an impaired PPI in female premutation carriers at the 120 ms condition. There was a significant correlation between the PPI deficit and a higher CGG repeat number. The results show an impairment in sensorimotor gating processes in male carriers of the fragile X premutation, which is more prominent in patients with FXTAS.

The effect of pregabalin on sensorimotor gating in 'low' gating humans and mice

Pregabalin, an anticonvulsant and anxiolytic compound that binds to α2-δ auxiliary subunit Types 1 and 2 of voltage-gated calcium channels, has been shown to reduce excitatory neurotransmission partially through modulation of glutamatergic signaling. Prepulse inhibition (PPI) of startle is an operational measure of sensorimotor gating impacted by disruption of the glutamatergic system and is reduced in schizophrenia patients. Dysregulation of the glutamatergic system has also been implicated in the pathophysiology of schizophrenia. Here we tested the hypothesis that pregabalin may ameliorate PPI in a model of deficient gating in humans and mice. In study 1, 14 healthy human subjects participated in a within subjects, cross-over study with placebo, 50 mg or 200 mg pregabalin treatment prior to undergoing a PPI task. In study 2, 24 C57BL/6 mice underwent a similar procedure with vehicle, 30 and 100 mg/kg dose treatments. In both studies, subjects were assigned to a "Low" or "High" gating group using a median split procedure based on their PPI performance during placebo/vehicle. Drug effects were then examined across these groups. In humans, pregabalin treatment significantly increased PPI performance in the "low gating" group. In mice, pregabalin treatment significantly increased PPI in the low gating group but reduced PPI in the high gating group. Across species, pregabalin treatment improves PPI in subjects with low gating. These data support further exploration of pregabalin as a potential treatment for disorders characterized by sensorimotor gating deficits and glutamatergic hypersignaling, such as schizophrenia.

Inflammation in schizophrenia

Although there is no doubt that the dopaminergic neurotransmission is strongly involved in the pathophysiology of schizophrenia, the exact mechanism leading to dopaminergic dysfunction is still unclear. A disbalance in the immune response associated with a slight inflammatory process of the central nervous system (CNS) has been postulated. Such a mechanism is the basis for the "mild encephalitis" concept. A dysfunction in the activation of the type-1 immune response seems to be associated with decreased activity of the key enzyme of the tryptophan/kynurenine metabolism, indoleamine 2,3-dioxygenase (IDO). Theoretically, a decreased activity of IDO results in the increased production of kynurenic acid, an N-methyl-D-aspartate antagonist in the CNS, and a reduced glutamatergic neurotransmission in schizophrenia. Accordingly, in animal models of schizophrenia, increased levels of kynurenic acid in critical regions of the CNS were described, although studies of peripheral blood levels of kynurenic acid in schizophrenic patients showed controversial results. The immunological effects of a lot of existing antipsychotics, however, rebalance in part the immune imbalance and the overweight of the production of kynurenic acid. The inflammatory state in schizophrenia is associated with increased prostaglandin E(2) production and increased cyclooxygenase-2 (COX-2) expression. Growing evidence from clinical studies with COX-2 inhibitors points to favorable effects of anti-inflammatory therapy in schizophrenia, in particular in an early stage of the disorder. Further options for immunomodulating therapies in schizophrenia will be discussed.

Towards medication-enhancement of cognitive interventions in schizophrenia

Current antipsychotic medications do little to improve real-life function in most schizophrenia patients. A dispassionate view of the dispersed and variable neuropathology of schizophrenia strongly suggests that it is not currently, and may never be, correctable with drugs. In contrast, several forms of cognitive therapy have been demonstrated to have modest but lasting positive effects on cognition, symptoms, and functional outcomes in schizophrenia patients. To date, attempts to improve clinical outcomes in schizophrenia by adding pro-cognitive drugs to antipsychotic regimens have had limited success, but we propose that a more promising strategy would be to pair drugs that enhance specific neurocognitive functions with cognitive therapies that challenge and reinforce those functions. By using medications that engage spared neural resources in the service of cognitive interventions, it might be possible to significantly enhance the efficacy of cognitive therapies. We review and suggest several laboratory measures that might detect potential pro-neurocognitive effects of drugs in individual patients, using a "test dose" design, aided by specific biomarkers predicting an individual's drug sensitivity. Lastly, we argue that drug classes viewed as "counter-intuitive" based on existing models for the pathophysiology of schizophrenia-including pro-catecholaminergic and NMDA-antagonistic drugs-might be important candidate "pro-cognitive therapy" drugs.

α7 nicotinic ACh receptors as a ligand-gated source of Ca(2+) ions: the search for a Ca(2+) optimum

The spatiotemporal distribution of cytosolic Ca(2+) ions is a key determinant of neuronal behavior and survival. Distinct sources of Ca(2+) ions including ligand- and voltage-gated Ca(2+) channels contribute to intracellular Ca(2+) homeostasis. Many normal physiological and therapeutic neuronal functions are Ca(2+)-dependent, however an excess of cytosolic Ca(2+) or a lack of the appropriate balance between Ca(2+) entry and clearance may destroy cellular integrity and cause cellular death. Therefore, the existence of optimal spatiotemporal patterns of cytosolic Ca(2+) elevations and thus, optimal activation of ligand- and voltage-gated Ca(2+) ion channels are postulated to benefit neuronal function and survival. Alpha7 nicotinic -acetylcholine receptors (nAChRs) are highly permeable to Ca(2+) ions and play an important role in modulation of neurotransmitter release, gene expression and neuroprotection in a variety of neuronal and non-neuronal cells. In this review, the focus is placed on α7 nAChR-mediated currents and Ca(2+) influx and how this source of Ca(2+) entry compares to NMDA receptors in supporting cytosolic Ca(2+) homeostasis, neuronal function and survival.

Are we studying and treating schizophrenia correctly?

New findings are rapidly revealing an increasingly detailed image of neural- and molecular-level dysfunction in schizophrenia, distributed throughout interconnected cortico-striato-pallido-thalamic circuitry. Some disturbances appear to reflect failures of early brain maturation, that become codified into dysfunctional circuit properties, resulting in a substantial loss of, or failure to develop, both cells and/or appropriate connectivity across widely dispersed brain regions. These circuit disturbances are variable across individuals with schizophrenia, perhaps reflecting the interaction of multiple different risk genes and epigenetic events. Given these complex and variable hard-wired circuit disturbances, it is worth considering how new and emerging findings can be integrated into actionable treatment models. This paper suggests that future efforts towards developing more effective therapeutic approaches for the schizophrenias should diverge from prevailing models in genetics and molecular neuroscience, and focus instead on a more practical three-part treatment strategy: 1) systematic rehabilitative psychotherapies designed to engage healthy neural systems to compensate for and replace dysfunctional higher circuit elements, used in concert with 2) medications that specifically target cognitive mechanisms engaged by these rehabilitative psychotherapies, and 3) antipsychotic medications that target nodal or convergent circuit points within the limbic-motor interface, to constrain the scope and severity of psychotic exacerbations and thereby facilitate engagement in cognitive rehabilitation. The use of targeted cognitive rehabilitative psychotherapy plus synergistic medication has both common sense and time-tested efficacy with numerous other neuropsychiatric disorders.

Startle reactivity and prepulse inhibition in prodromal and early psychosis: effects of age, antipsychotics, tobacco and cannabis in a vulnerable population

The use of biomarkers in the study of the prodrome and first episode of psychosis provides a means of not only identifying individuals at greatest risk for psychosis but also understanding neurodevelopmental abnormalities early in the course of illness. Prepulse inhibition (PPI), a marker that is deficient in schizophrenia and after developmental manipulations in animal models, was assessed in 75 early psychosis (EP), 89 at risk (AR) for psychosis and 85 comparison subjects (CS) at baseline and 6 months. Consistent with findings in chronic schizophrenia, PPI was stable with repeated assessment and EP subjects had reduced PPI but this was most evident in tobacco smokers. A significant positive PPI and age association in AR and EP samples, but not CS, demonstrated potential neurodevelopmental differences in early psychosis. Unexpected findings included the fact that medication naive EP subjects, as well as AR subjects who later developed psychosis, had greater PPI, introducing the possibility of early compensatory changes that diverge from findings in chronic patients. In addition, subjects with a history of cannabis use had greater startle reactivity while EP and AR subjects who used cannabis and were also taking an antipsychotic had greater PPI, again highlighting the potentially important cannabis/psychosis association.

Recent advances in psychoneuroimmunology: Inflammation in psychiatric disorders

Psychiatric disorders are common and complex and their precise biological underpinnings remain elusive. Multiple epidemiological, molecular, genetic and gene expression studies suggest that immune system dysfunction may contribute to the risk for developing psychiatric disorders including schizophrenia, bipolar disorder, and major depressive disorder. However, the precise mechanisms by which inflammation-related events confer such risk are unclear. In this review, we examine the peripheral and central evidence for inflammation in psychiatric disorders and the potential molecular mechanisms implicated including inhibition of neurogenesis, apoptosis, the HPA-axis, the role of brain-derived neurotrophic factor and the interplay between the glutamatergic, dopaminergic and serotonergic neurotransmitter systems.

Immune System and Schizophrenia

Although an immune dysfunction and the involvement of infectious agents in the pathophysiology of schizophrenia are discussed since decades, the field never came into the mainstream of research. In schizophrenia a blunted type-1 immune response seems to be associated with a dysbalance in the activation of the enzyme indoleamine 2,3-dioxygenase (IDO) and in the tryptophan - kynurenine metabolism resulting in increased production of kynurenic acid in schizophrenia. This is associated with an imbalance in the glutamatergic neurotransmission, leading to an NMDA antagonism in schizophrenia. The immunological effects of antipsychotics rebalance partly the immune imbalance and the overweight of the production of the kynurenic acid. This immunological imbalance results in an inflammatory state combined with increased prostaglandin E(2) (PGE(2)) production and increased cyclo-oxygenase-2 (COX-2) expression. COX-2 inhibitors have been tested in clinical trials, pointing to favourable effects in schizophrenia.

Acetylcholinesterase inhibitors and memantine for neuroenhancement in healthy individuals: a systematic review

The term neuroenhancement refers to improvement in the cognitive, emotional and motivational functions of healthy individuals through, inter alia, the use of drugs. Of known interventions, psychopharmacology provides readily available options, such as the anti-dementia drugs, e.g. acetylcholinesterase inhibitors (donepezil, galantamine, rivastigmine) and memantine. Based on a systematic review we found that expectations about the potential of these drugs exceed their actual effects, as has been demonstrated in randomised controlled trials. Both single and repeated dose trials were included in the systematic review, however repeated dose trials have only been conducted for donepezil. In six small trials lasting 14-42 days, the following results emerged: donepezil improved the retention of training on complex aviation tasks and verbal memory for semantically processed words. In one study episodic memory was improved, whereas in others it remained unaffected by donepezil. In a sleep deprivation trial, donepezil reduced the memory and attention deficits resulting from 24h of sleep deprivation. Two studies reported even transient negative effects. Regarding the safety profile of donepezil, these studies found that it was rather well tolerated. In any case, since large longitudinal studies are not available no conclusions can be drawn. Seven small studies about the effects of a single dose of memantine, and one study with a single dose of rivastigmine have been reported. Again, these studies are not adequate to answer our research question. If, as here and elsewhere suggested, the concept of pharmaceutical neuroenhancement is not to be rejected in principle, the decision of healthy individuals to take drugs for the purpose of neuroenhancement should be based on exhaustive information. At the moment, the research that would support or oppose the use of acetylcholinesterase inhibitors and memantine for neuroenhancement by healthy individuals has not yet been performed.

Prepulse inhibition of the startle reflex: a window on the brain in schizophrenia

Prepulse inhibition (PPI) of the startle response is an important measure of information processing deficits and inhibitory failure in schizophrenia patients. PPI is especially useful because it occurs in the same lawful manner in all mammals, from humans to rodents, making it an ideal candidate for cross-species translational research. PPI deficits occur across the "schizophrenia spectrum" from schizophrenia patients to their clinically unaffected relatives. Parallel animal model and human brain imaging studies have demonstrated that PPI is modulated by cortico-striato-pallido-thalamic (and pontine) circuitry. This circuitry is also implicated in schizophrenia neuropathology and neurophysiology. The finding of PPI deficits in schizophrenia patients has been replicated by many groups, and these deficits correlate with measures of thought disorder and appear to be "normalized" by second generation antipsychotic (SGA) medications. Consistent pharmacological effects on PPI have been demonstrated; among these, dopamine agonists induce PPI deficits and (in animal models) these are reversed by first and SGA medications. PPI is also significantly heritable in humans and animals and can be used as a powerful endophenotype in studies of families of schizophrenia patients. Genomic regions, including the NRGL-ERBB4 complex with its glutamatergic influences, are strongly implicated in PPI deficits in schizophrenia. PPI continues to hold promise as an exciting translational cross-species measure that can be used to understand the pathophysiology and treatment of the schizophrenias via pharmacological, anatomic, and genetic studies.

The impact of neuroimmune dysregulation on neuroprotection and neurotoxicity in psychiatric disorders--relation to drug treatment

An inflammatory pathogenesis has been postulated for schizophrenia and major depression (MD). In schizophrenia and depression, opposing patterns oftype-1 vs type-2 immune response seem to be associated with differences in the activation of the enzyme indoleamine 2,3-dioxygenase and in the tryptophan-kynurenine metabolism, resulting in increased production of kynurenic acid in schizophrenia and decreased production of kynurenic acid in depression. These differences are associated with an imbalance in the glutamatergic neurotransmission, which may contribute to an excessive agonist action of N-methyl-D-aspartate (NMDA) in depression and of NMDA antagonism in schizophrenia. Regarding the neuroprotective function of kynurenic acid and the neurotoxic effects of quinolinic acid (QUIN), different patterns of immune activation may also lead to an imbalance between the neuroprotective and the neurotoxic effects of the tryptophanlkynurenine metabolism. The differential activation of microglia cells and astrocytes may be an additional mechanism contributing to this imbalance. The immunological imbalance results in an inflammatory state combined with increased prostaglandin E2 production and increased cyclo-oxygenase-2 (COX-2) expression. The immunological effects of many existing antipsychotics and antidepressants, however, partly correct the immune imbalance and the excess production of the neurotoxic QUIN, COX-2 inhibitors have been tested in animal models of depression and in preliminary clinical trials, pointing to favorable effects in schizophrenia and in MD.

Pramipexole effects on startle gating in rats and normal men

BACKGROUND

Dopamine D3 receptors regulate sensorimotor gating in rats, as evidenced by changes in prepulse inhibition (PPI) of startle after acute administration of D3 agonists and antagonists. In this study, we tested the effects of the D3-preferential agonist, pramipexole, on PPI in normal men and Sprague-Dawley rats.

MATERIALS AND METHODS

Acoustic startle and PPI were tested in clinically normal men, comparing the effects of placebo vs. 0.125 mg (n = 20) or placebo vs. 0.1875 mg (n = 20) pramipexole, in double blind, crossover designs. These measures were also tested in male Sprague-Dawley rats using a parallel design [vehicle vs. 0.1 mg/kg (n = 8), vehicle vs. 0.3 mg/kg (n = 8) or vehicle vs. 1.0 mg/kg pramipexole (n = 8)]. Autonomic and subjective measures of pramipexole effects and several personality instruments were also measured in humans.

RESULTS

Pramipexole increased drowsiness and significantly increased PPI at 120-ms intervals in humans; the latter effect was not moderated by baseline PPI or personality scale scores. In rats, pramipexole causes a dose-dependent reduction in long-interval (120 ms) PPI, while low doses actually increased short-interval (10-20 ms) PPI. Effects of pramipexole on PPI in rats were independent of baseline PPI and changes in startle magnitude.

CONCLUSION

The preferential D3 agonist pramipexole modifies PPI in humans and rats. Unlike indirect DA agonists and mixed D2/D3 agonists, pramipexole increases long-interval PPI in humans, in a manner that is independent of baseline PPI and personality measures. These findings are consistent with preclinical evidence for differences in the D2- and D3-mediated regulation of sensorimotor gating.