Daniel C. Javitt - US grants

The principle goal of the proposed project is to evaluate the role of N-methyl-D-aspartate (NMDA) receptors in the generation of long-latency, processing-contingent components (PCCs) of the auditory event-related potential (AEP). As opposed to obligate components which reflect the psychoacoustic properties of presented stimuli, PCCs index attentional and cognitive processing operations. NMDA receptors uniquely mediate long-duration, "conditional" depolarizations within cortex, suggesting that NMDA receptor activation may contribute selectively to PCC generation. A second goal of this project is to test the hypothesis that pharmacological antagonists of NMDA receptors can induce PCC abnormalities, including deficits in "mismatch" and "processing" negativity generation, that are analogous to those seen in patients with schizophrenia. The proposed project will utilize unanesthetized, behaving old world monkeys (M. fascicularis), as the closest feasible model for human AEP. The characteristic timing and epidural distribution of monkey potentials corresponding to the human mismatch and processing negativities will be determined using passive and active "oddball" paradigms analogous to those employed in clinical studies. The location and extent of neural generators for identified PCCs will be determined using three dimensional mapping techniques and moveable intracranial multicontact electrodes inserted through implanted epidural guide tubes. These procedures are ideal for rapidly surveying large areas. Initial studies will focus on the posterior region of the superior temporal plane, which has been proposed as a source of both the mismatch and processing negativities. Later studies will focus also on temporal and prefrontal regions which receive auditory afferents. The laminar profile of activity will be analyzed using one-dimensional current source density (CSD) techniques which provides an index of the magnitude, location and duration of intralaminar transmembrane current flow (i.e. "sources" and "sinks"). Concomitant recording of multiunit activity (MUA) will define the firing rate of neurons in the vicinity of the recording electrode and will permit the interpretation of current sources and sinks as indices of net excitatory and inhibitory synaptic processes. The possible contribution of NMDA receptor-mediated neurotransmission to PCCs will be assessed by systemic injection and intracortical microinfusion of competitive and noncompetitive NMDA receptor antagonists.Phencyclidine (PCP, "angel dust") has been shown to induce psychotic symptoms and neuropsychological deficits similar to those observed in schizophrenia at doses at which it selectively inhibits NMDA receptor-mediated neurotransmission. The proposed studies will evaluate the possibility that dysfunction of NMDA receptor-mediated neurotransmission may also contribute to the neurophysiological dysfunction associated with schizophrenia.

The goal of the proposed research remains the elucidation of neurobiological mechanisms underlying mediation of drug-abuse and psychotic states by the phencyclidine (PCP)/NMDA receptor-channel complex. During the initial project period we identified specific PCP receptors in brain membranes and provided biochemical and pharmacological evidence that these sites mediate the unique actions of PCP-related drugs. All PCP-like agents are noncompetitive antagonists of the N-methyl-D-aspartate (NMDA) type of excitatory amino acid receptor; the PCP receptor is situated within the NMDA receptor-gated ion channel. Therefore binding characteristics of ligands to the PCP receptor are sensitive to the state of the ion channel, and elucidation of mechanisms of action of PCP-related drugs requires determination of mechanisms governing regulation of NMDA receptor activation by its agonists, antagonists and modulators. During the previous project period we published evidence from PCP receptor binding studies carried out at equilibrium and by kinetic techniques which support a complex model of the interaction of PCP-related drugs with the NMDA receptor channel. We reported that PCP receptor binding characteristics cannot be explained on the basis of a single affinity component of binding in equilibrium studies or by single exponentials of association/dissociation in kinetic studies, as would be predicted by the "open-channel blocker" model of PCP action proposed by others. We were able to account for our findings on the basis of a multistate model of NMDA receptor activation in which PCP receptor ligands bind differentially to open and to closed, agonist-associated states of the NMDA channel, and to demonstrate a requirement for multiple molecules of agonist for NMDA channel activation. These techniques now provide us with an analytical tool which will serve as a methodological focus for further elucidation of mechanisms governing NMDA receptor activation and PCP effects in the proposed research. We shall determine the mechanistic basis of the actions of polyamines upon the NMDA/PCP receptor and detect whether their effects are mediated by independent mechanisms or by modulation of the effects of other regulators. The mechanistic basis of the biochemical and functional heterogeneity of NMDA/PCP receptors in cerebellum vs. forebrain will be determined. Acute PCP effects, mediated by the PCP receptor, include induction of a psychotic state in normal subjects closely resembling schizophrenia, and specific exacerbation of illness in schizophrenics. The mechanistic relationship between PCP-induced psychosis and schizophrenia will be determined by studies comparing the detailed characteristics of PCP receptor binding and mechanisms governing NMDA receptor activation in postmortem brain samples derived from schizophrenics vs. matched controls. Together, the proposed studies will significantly advance our understanding of an important mechanism underlying drug abuse and psychiatric illness.

schizophrenia; cognition; neurochemistry; evoked potentials; auditory cortex; brain electrical activity; nitric oxide; excitatory aminoacid; GABA receptor; neurotransmitters; functional magnetic resonance imaging; electrodes; implant; Macaca fascicularis;

The present proposal is a four site multi-center application designed to assess the efficacy of the glutamatergic agents, d-cycloserine and glycine, for the treatment of persistent negative symptoms and cognitive impairments in patients with schizophrenia. These manifestations of schizophrenia account for much of the long-term morbidity, impaired social and occupational functioning, and poor quality of life observed in patients with schizophrenia. Persistent negative symptoms may either by primary (deficit symptoms) or secondary. At present, conventional and novel anti-psychotics have limited efficacy for known effective treatments for these deficit symptoms. There are also no known agents with robust efficacy for cognitive impairments. The long-term objective of this application is to develop an effective treatment for persistent negative symptoms, both primary and secondary, and cognitive impairments. The long-term objective of this application is to develop an effective treatment for persistent negative symptoms, both primary and secondary, and cognitive impairments. The Specific Aims are to examine whether: 1) d-cycloserine and/or glycine is superior to placebo for the treatment of persistent primary and secondary negative symptoms; and 2) d-cycloserine and/or glycine is superior to placebo in the treatment of cognitive impairments in deficit and non-deficit patients. Secondary goals include: a) to establish a standard clinical trial methodology to assess the therapeutic efficacy of potential treatments of persistent negative symptoms and cognitive impairments; and b) to describe the relationship between cognitive impairments, as assessed by neuropsychological test performance, and negative symptoms in the clinical trial context. The study will be a 16-week double-blind, parallel groups comparison of adjunctive medication (i.e., d-cycloserine and glycine) to placebo. Neuropsychological tests will be used to assess cognitive functioning, and will be administered at baseline and at the end of the study. The study will provide new information on the efficacy of d-cycloserine and glycine for both persistent primary and secondary negative symptoms and its effect on cognitive functioning.

DESCRIPTION: (provided by applicant) Phencyclidine (PCP) is a major clinical psychotogenic agent and drug of abuse. PCP and other dissociative anesthetics induce their unique behavioral effects by blocking neurotransmission mediated at the N-methyl-D-aspartate (NMDA)-type glutamate receptor. In addition to the main agonist-binding site for glutamate, the NMDA receptor complex contains multiple co-agonist/modulatory sites, including a strychnine-insensitive glycine-binding site. In rodents, stimulation of the glycine site reverses PCP-induced hyperactivity, whereas in humans glycine and similar agents (e.g., D-serine, D-cyCloserine) ameliorate PCP psychosis-like symptoms of schizophrenia. In CNS glycine levels in the immediate vicinity of NMDA receptors are maintained at low, subsaturating doses by the action of colocalized glycine transporters. Therefore, inhibition of glycine uptake, rather than administration of large doses of glycine, may be a preferred method for elevating glycine levels in the immediate vicinity of NMDA receptors. This is an application for continuation of a project initiated in 1982 to investigate mechanisms underlying PCP induced psychosis. This cycle of the project with investigate effects of subchronic PCP administration in animal models of schizophrenia. Specific measures to be studied include: 1. PCP-induced potentiation of amphetamine-stimulated dopamine release in prefrontal cortex and striatum; 2. PCP-induced disruption of prepulse inhibition and neurophysiological deficits, similar to those observed in schizophrenia; and 3. PCP-induced behavioral deficits in social interaction models. Projects will also continue ongoing investigations into effectiveness of glycinergic agents, including glycine site agonists (e.g.. glycine, D-serine) and glycine transport inhibitors (GTIs) in reversing PCP-induced behavioral, neurochemical and neurophysiological deficits in animals. Effects of glycinergic agents will be compared to those of typical/atypical antipsychotics. The overall goals of the project are 1) to evaluate the potential utility of glycine agonists/GTIs in the treatment of PCP psychosis and PCP psychosis-like symptoms of schizophrenia, and 2) to develop animal models sensitive to the non-dopaminergic, as well as dopaminergic, consequences of PCP-induced NMDA receptor blockade.

DESCRIPTION (provided by applicant): This is a application for a Shared Instrumentation Grant to permit purchase of MR-compatible high-density ERP recording systems to permit combined event-related potential (ERP) and magnetic resonance imaging (MRI) experiments. Over the past decade, there have been remarkable breakthroughs in the ability to analyze cognition-related brain activity using functional MRI and high-density ERP recording. fMRI possess high spatial resolution but low temporal resolution. In contrast. ERP possess millisecond level temporal resolution but low spatial resolution. Thus, ERP and fMRI provides complementary information regarding neurophysiological bases of normal and abnormal cognition. NKI currently houses research dedicated 3T and 7T MR systems for human and animal experiments, respectively, along with high-density recording human and animal ERP recording laboratories. Multiple projects are now in progress utilizing parallel MR and ERP recordings, demonstrating convergence between the two methodologies. Clinical projects have demonstrated impaired sensory processing in schizophrenia related to abnormal information processing at the level of primary auditory cortex, and impaired visual ERP generation related to dysfunction of lateral occipital (LO) cortex as well as dorsal stream visual regions. Parallel intracortical recordings in animals have confirmed generator locations and identified underlying neurophysiological mechanisms. ERP and MRI data are presently being acquired in separate sessions in parallel. The proposed equipment would permit ERP data recording during simultaneous MR acquisition. This will greatly enhance efficiency of data acquisition and will substantially decrease variance due to state changes between sessions. The equipment will also permit monitoring of background EEG during both human and animal studies. Software is requested for state-of-the-art ERP dipole mapping and ERP/MRI co-registration.

DESCRIPTION OF THE PROGRAM (provided by applicant): Persistent negative and cognitive symptoms are a primary cause of chronic disability and poor long-term outcome in schizophrenia. Phencylidine (PCP) and other antagonists of N-methyl-D-aspartate (NMDA)-mediated neurotransmission induce symptoms and cognitive deficits that closely resemble those of schizophrenia, indicating a potentially critical role of NMDA receptors in the etiopathology of primary negative symptoms. NMDA receptors are modulated in vivo by glycine and D-serine, which bind to a modulatory site of the NMDA receptor complex. Clinical trials with NMDA/glycine site agonists have yielded highly encouraging clinical data. This CDDG application will focus on development of D-serine as an effective treatment for persistent negative symptoms and cognitive dysfunction in schizophrenia, in collaboration with Rexim Corporation, a major manufacturer of D-serine and other amino acids for the pharmaceutical industry. The application consists of two projects. Project 1 will consist of PK/PD, dose-finding and subsequent double-blind treatment studies at NKI involving patients, with chronic schizophrenia, and investigating D-serine effects on persistent negative symptoms and cognitive dysfunction. Project 2 will consist of a collaborative multicenter trial of D-serine treatment of the schizophrenia prodrome to be conducted at Yale University and Zucker Hillside Hospital. Together these projects will validate treatment targets for NMDA agonists in general and D-serine in particular and will encourage continued clinical development.

[unreadable] DESCRIPTION (provided by applicant): Phencyclidine (PCP) is a major clinical psychotogenic agent and drug of abuse. PCP and other dissociative anesthetics (e.g. ketamine) induce their unique behavioral effects by blocking neurotransmission mediated at the N-methyl-D-aspartate (NMDA)-type glutamate receptor. In addition to the main agonist binding site for glutamate, the NMDA receptor complex contains multiple co-agonist/modulatory sites, including a strychnine-insensitive glycine binding site. In rodents, stimulation of the glycine site reverses PCP-induced hyperactivity, whereas in humans glycine and similar agents (e.g. D-serine) ameliorate PCP psychosis-like symptoms of schizophrenia. In CNS, glycine and D-serine levels in the immediate vicinity of NMDA receptors are maintained at low, subsaturating doses by the action of colocalized amino acid transporters. Over the past grant cycle, we have demonstrated that inhibitors of glycine transport significantly antagonized neurochemical effects of PCP, both in vitro and in vivo. Further, we have demonstrated the existence of novel transporters which may serve as additional treatment targets, as well as significant interactions between NMDA and GABA-B systems. Finally, we have shown that subchronic PCP administration induces persistent neurophysiological and neuroanatomical changes that may account for chronic cognitive deficits following prolonged abuse and may also serve as an animal model for investigating similar deficits in schizophrenia. Over the upcoming project cycle, we will continue to investigate effects of subchronic continuous treatment and compare these effects with those obtained following subchronic intermittnet or acute perinatal treatment. Neurochemical, neurophysiological and neuroanatomic paradigms will be used to compare consequences of persistent exposure to NMDA antagonists to deficits observed in schizophrenia, as well as the ability of NMDA/glycine-site agonists to reverse these changes. Plain Language: Schizophrenia and substance abuse are both major public health concerns. This project seeks to develop new understandings of effects of drugs of abuse such as PCP and Ketamine in the brain, and seeks to develop new treatments for schizophrenia by searching for drugs that counteract the effect of PCP and ketamine in rodents. [unreadable] [unreadable] [unreadable]

PROJECT SUMMARY/ABSTRACT: Schizophrenia (Sz) is associated with psychotic symptoms that remain partially or fully refractory to standard antipsychotic medications for most patients. All marketed antipsychotics primarily work through blocking dopamine D2 receptors. Despite robust effectiveness in preclinical models, alternative, glutamatergic approaches for treatment development have not yet led to FDA approved medications. A major barrier to effective glutamatergic treatment development is the absence of validated measures for functional target engagement that can identify effective compounds and guide dose selection. The present project seeks to refine ketamine-induced pharmacoBOLD (phBOLD) as target engagement biomarker for development of metabotropic glutamate (mGluR2/3) agonists. The combination of aims will permit future studies using phBOLD to identify potential candidates for glutamate-based interventions, permit target engagement studies within Sz and explore the mechanisms of dopamine and glutamate in psychosis. As part of the recently completed NIMH multicenter FAST-PS initiative, we have evaluated ketamine-induced phBOLD in healthy volunteers (HV). In an initial HV study, we demonstrated that ketamine induces a robust, highly significant increase in phBOLD response. More recently, using this assay we have demonstrated that the dose of an mGluR2/3 agonist (POMA) used in the prior clinical studies (80 mg) did not lead to significant inhibition of ketamine-induced phBOLD or symptomatic response in HV, suggesting that prior negative clinical results may have resulted from inadequate dosing. By contrast, at doses ~4x higher than those used in the negative clinical trials, evidence of behavioral target engagement was observed, underscoring the need for in vivo clinical biomarkers. In parallel studies of of a more recently developed mGluR2/3 agonist (TS-134), we demonstrated showed evidence of both behavioral ( and phBOLD pre-post target engagement. In addition, TS- 134 suppressed ketamine induced phBOLD known to be integral for dopaminergic function. Aims of the present project are as follows. Under Aim 1, we will titrate the ketamine dose downward in HV in order to identify doses that produce reduced psychotomimetic effects, but nevertheless sufficiently robust (d=1.5) phBOLD effects to permit detection of mGluR2/3 agonist effect. We will then evaluate the degree to which still-lower doses of ketamine nevertheless produce sufficient phBOLD response (d=1.5) to enable target engagement testing in Sz patients. Finally, we will evaluate the relative sensitivity of different doses of ketamine to TS-134 in HV in order to determine optimal target effect sizes for future target engagement studies in Sz. In parallel, we evaluate the sensitivity of the dopamine system to NMDAR antagonism, along with the relationship of ketamine phBOLD, 1H MRS and a proxy measure of dopamine synthesis capacity using neuromelanin.