Schizophrenia Research Forum - A Catalyst for Creative Thinking

GABA Receptor Drug for Schizophrenia Is Put Through Its Paces

7 November 2008. A pilot clinical trial of an experimental drug that selectively targets a subtype of γ-aminobutyric acid (GABA) receptor to treat cognition in schizophrenia has shown enough promise to warrant further study, according to a report published online October 15 in the American Journal of Psychiatry. Researchers led by David Lewis of the University of Pittsburgh present evidence that the drug, MK-0777, is well tolerated in a short trial and may improve performance in subjects with schizophrenia on some tests of cognition and memory. They note, however, that the study was too small to provide robust statistical evidence of cognitive improvement. In support of continuing this line of study, the authors also report preliminary evidence suggesting that the drug increased frontal cortical γ band (30-80 Hz) activity in subjects with schizophrenia during a cognitive task.

Indirect evidence for abnormalities in GABAergic neurotransmission in schizophrenia has been reported by a number of researchers (see, e.g., SRF related news story). One hypothesis that Lewis's group has focused on suggests that working memory deficits in schizophrenia can be traced in part to a subset of prefrontal cortex GABAergic interneurons that fail to synthesize and release enough GABA (see Lewis interview). Among the compensatory responses, there is postulated to be an upregulation of the GABAA receptors in postsynaptic pyramidal neurons, especially receptors containing the α2 subunit. Lewis and colleagues suggest that working memory in schizophrenia might be improved by giving this compensatory response a helping hand using a positive allosteric modulator that boosts GABA's effects at GABAA receptors containing the α2 subunit.

In their current study, Lewis, and colleagues at the University of Pittsburgh and the University of California, Davis, used the experimental benzodiazepine-like drug MK-0777, developed by Merck & Co., because it is relatively selective for receptors containing the α2 subunit, while avoiding those containing the α1 subunit. This would avoid the sedation caused by benzodiazepine drugs, which bind indiscriminately to GABAA receptors.

During the four-week, randomized, double-blind, placebo-controlled trial of 15 men with schizophrenia, there was no effect of the study drug on symptoms, as assessed with the Brief Psychiatric Rating Scale. However, MK-0777 improved performance on several cognitive tests (N-back, X Continuous Performance Test, and Preparing to Overcome Prepotency), but only on the delayed memory domain of the Repeatable Battery of the Assessment of Neuropsychological Status (RBANS) (p = 0.04).

The authors suggest that a large clinical trial might help to determine whether statistically non-significant improvements in other domains of the RBANS represent real clinical benefits or perhaps are due solely to practice effects (see SRF related news story). However, they also suggest the possibility that neuropsychological test batteries such as the RBANS may not be sensitive enough, and "[i]f a drug has its effect on one specific cognitive system (e.g., prefrontal-dependent cognitive control functions regulating working memory and response inhibition), then more fine-grained cognitive measures that target those specific functions (e.g., the N-back task and AX Continuous Performance Test) may provide a more sensitive approach to measuring drug effects."

Coauthors Raymond Cho and Cameron Carter of UC Davis have reported previously that people with schizophrenia have reduced γ band oscillations, measured by electroencephalography, in prefrontal cortex during the Preparing to Overcome Prepotency Task, a measure of cognitive control (see SRF related news story). In the current study, they report trends indicating a "normalization" of this deficit by the experimental drug, but firm conclusions from these data could not be derived from the small sample.—Hakon Heimer.

Reference:
Lewis DA, Cho RY, Carter CS, Eklund K, Forster S, Kelly MA, Montrose D. Subunit-Selective Modulation of GABA Type A Receptor Neurotransmission and Cognition in Schizophrenia. Am J Psychiatry. 2008 Oct 15. [Epub ahead of print] Abstract

Comments on News and Primary Papers
Comment by:  Robert McCarley
Submitted 7 November 2008
Posted 7 November 2008

This paper is further evidence of an important and laudable new trend in schizophrenia psychopharmacology: namely the development and test of compounds on the basis of their relationship to circuit abnormalities, evidence derived from postmortem, genetic, and animal model studies. The authors based their choice of MK-0777 for test in schizophrenia on evidence for decreased cortical GABA neurotransmission onto pyramidal neurons at receptors having the α2 subunit, and other evidence pointing to the GABA-pyramidal neuron interaction as important in cognition and in generation of γ band oscillations. In this add-on, double-blind placebo study, the Ns were underpowered and more subjects need to be studied to be certain about clinical effects. However, one test, the Preparing to Overcome Prepotency Test (POP), had significant improvements in response latency and showed concomitant improvement in increased frontal γ band activity induced during the task, although not meeting the criterion for statistical significance. POP requires subjects either to “go with the flow” (indicated by a green light) and respond in the same direction as an arrow, or when cued by a red light to “go upstream” and point in the opposite direction, a test previously used in the Cho et al. 2006 PNAS paper and found to be accompanied by increased induced γ band oscillations.

γ band activity has justifiably attracted considerable attention, since there is mounting evidence of its relevance to human cognition as well as to basic neuroscience studies of neuronal assembly communication. Its important basis in the GABA cortical neuronal interaction with pyramidal cells makes it especially fascinating in schizophrenia. However, an important caution light was recently flashed by Yuval-Greenberg et al. in an article in Neuron (2008) in which they presented strong evidence that apparent increases or decreases in the “induced γ band oscillations” (those not temporally linked to a response or stimulus) could be the result of the eye muscle activation associated with small saccadic eye movements, “a saccadic spike potential” that could be confused with γ band oscillations. The Yuval-Greenberg article appeared too late for the authors to discuss in the present paper, but its implications for future work using induced γ are important. For studies of induced γ, we all will have to begin using eye movement measures sensitive to mini-saccades. Those of us who measure γ phase-locked to measureable events, such as sensory stimuli or responses, appear to be off the hook since we condition on known events, unlike conditions where induced γ is measured.

References:

Cho RY, Konecky RO, Carter CS. Impairments in frontal cortical gamma synchrony and cognitive control in schizophrenia. Proc Natl Acad Sci U S A. 2006 Dec 26;103(52):19878-83. Abstract

Yuval-Greenberg S, Tomer O, Keren AS, Nelken I, Deouell LY. Transient induced gamma-band response in EEG as a manifestation of miniature saccades. Neuron. 2008 May 8;58(3):429-41. Abstract

View all comments by Robert McCarley

Comments on Related News


Related News: Asynchrony and the Brain—Gamma Deficits Linked to Poor Cognitive Control

Comment by:  Richard Deth
Submitted 14 December 2006
Posted 15 December 2006

Schizophrenia is associated with dopaminergic dysfunction, impaired gamma synchronization and impaired methylation. It is therefore of interest that the D4 dopamine receptor is involved in gamma synchronization (Demiralp et al., 2006) and that the D4 dopamine receptor uniquely carries out methylation of membrane phospholipids (Sharma et al., 1999). A reasonable and unifying hypothesis would be that schizophrenia results from a failure of methylation to adequately support dopamine-stimulated phospholipid methylation, leading to impaired gamma synchronization. Synchronization in response to dopamine can provide a molecular mechanism for attention, as information in participating neural networks is able to bind together to create cognitive experience involving multiple brain regions.

View all comments by Richard Deth

Related News: Asynchrony and the Brain—Gamma Deficits Linked to Poor Cognitive Control

Comment by:  Fred Sabb
Submitted 12 January 2007
Posted 12 January 2007
  I recommend the Primary Papers

Cho and colleagues find patients with schizophrenia showed a reduction in induced gamma band activity in the dorsolateral prefrontal cortex compared to healthy control subjects during a behavioral task that is known to challenge cognitive control processes. Importantly, the induced gamma band activity was correlated with better performance in healthy subjects, and negatively correlated with higher disorganization symptoms in patients with schizophrenia. These findings help explain previous post-mortem evidence of disruptions in thalamofrontocortical circuits in these patients.

These findings tie together several different previously identified phenotypes into a unifying story. The ability to link phenotypes across translational research domains is paramount to understanding complex neuropsychiatric diseases like schizophrenia. Cho and colleagues provide an excellent example for connecting evidence from symptom rating scales with behavioral, neural systems and neurophysiological data. Although not specifically addressed by the authors, these data may have important implications for understanding the neural basis of thought disorder as well. Hopefully, these findings will provide a frame-work for examining more informed and specific phenotypes relevant to schizophrenia.

View all comments by Fred Sabb

Related News: Genetics, Expression Profiling Support GABA Deficits in Schizophrenia

Comment by:  Karoly Mirnics, SRF Advisor
Submitted 26 June 2007
Posted 26 June 2007

The evidence is becoming overwhelming that the GABA system disturbances are a critical hallmark of schizophrenia. The data indicate that these processes are present across different brain regions, albeit with some notable differences in the exact genes affected. Synthesizing the observations from the recent scientific reports strongly suggest that the observed GABA system disturbances arise as a result of complex genetic-epigenetic-environmental-adaptational events. While we currently do not understand the nature of these interactions, it is clear that this will become a major focus of translational neuroscience over the next several years, including dissecting the pathophysiology of these events using in vitro and in vivo experimental models.

View all comments by Karoly Mirnics

Related News: Genetics, Expression Profiling Support GABA Deficits in Schizophrenia

Comment by:  Schahram Akbarian
Submitted 26 June 2007
Posted 26 June 2007
  I recommend the Primary Papers

The three papers discussed in the above News article are the most recent to imply dysregulation of the cortical GABAergic system in schizophrenia and related disease. Each paper adds a new twist to the story—molecular changes in the hippocampus of schizophrenia and bipolar subjects show striking differences dependent on layer and subregion (Benes et al), and in prefrontal cortex, there is mounting evidence that changes in the "GABA-transcriptome" affect certain subtypes of inhibitory interneurons (Hashimoto et al). The polymorphisms in the GAD1/GAD67 (GABA synthesis) gene which Straub el al. identified as genetic modifiers for cognitive performance and as schizophrenia risk factors will undoubtedly spur further interest in the field; it will be interesting to find out in future studies whether these genetic variants determine the longitudinal course/outcome of the disease, treatment response etc etc.

View all comments by Schahram Akbarian

Related News: Antipsychotics and Cognition: Practice Makes Perfect Confounder

Comment by:  Richard Keefe
Submitted 12 October 2007
Posted 12 October 2007

As stated in the CATIE and CAFÉ neurocognition manuscripts, it is possible that the small improvements in neurocognitive performance following randomization to one of the antipsychotic treatments in these studies are due solely to practice effects or expectation biases. This statement is affirmed by the excellent recent study by Goldberg et al. in which improvements in cognitive performance were almost identical in magnitude to the practice effects found in healthy controls. While these data may be perhaps disappointing to the hope that second-generation medications improve cognition, they may also suggest that cognitive performance is less recalcitrant to change than previously expected.

In the context of a double-blind study design, the degree of cognitive enhancement observed for each treatment group is a function of three major variables: treatment effect, placebo effect, and practice effect. In studies of antipsychotic medications without a placebo control group, practice and placebo effects in schizophrenia cannot be disentangled from treatment effects. They also cannot be disentangled from each other. Recent data from a double-blind study comparing the effects of donepezil hydrochloride and placebo in a highly refined sample of 226 patients with schizophrenia stabilized while taking second-generation antipsychotics suggested that patients taking placebo had neurocognitive effect size improvements (0.22 SD after being tested twice over 6 weeks; 0.45 SD after the third assessment at 12 weeks) on the same test battery used in the CATIE and CAFÉ studies, suggesting a practice or placebo effect (Keefe et al., Neuropsychopharmacology, in press) consistent with the improvements reported in the CATIE and CAFÉ treatment studies. These cognitive improvements are in contrast to test-retest data collected in patients with schizophrenia tested with the MATRICS Consensus Cognitive Battery (MCCB; Nuechterlein et al., in press) and the Brief Assessment of Cognition in Schizophrenia (BACS; Keefe et al., 2004), which showed very little practice effects. The contrast of the data from these test-retest studies that did not involve the initiation of new treatments with cognitive improvements following the initiation of antipsychotic treatment or placebo suggests that attribution biases beyond simple practice effects may be at work.

Test-retest data from patients tested twice within a briefer period than the test interval in the four treatment studies discussed above suggest that schizophrenia patients demonstrate relatively small improvements in executive functions (Keefe et al., 2004; Nuechterlein et al., in press) and the WAIS digit-symbol test (Nuechterlein et al., in press), and medium improvements on tests of verbal memory only when identical versions are repeated (Hawkins and Wexler, 1999; Keefe et al., 2004) but not on tests of verbal fluency (Keefe et al., 2004; Nuechterlein et al., in press). In the donepezil/placebo study, patients who received placebo improved substantially across several cognitive domains. Although not tested directly, this series of results suggests that the magnitude of placebo effects in cognitive enhancement trials may exceed the reported size of practice-related improvements in studies of schizophrenia patients tested twice without the prospect of the initiation of a cognitive intervention.

The greater improvements in cognition found in the context of a placebo-controlled trial could be due to a variety of psychological factors. When a patient enters into a trial or is treated with a medication that is believed to contribute beneficially to cognitive performance, rater bias and expectation bias can have strong effects on performance. Patients who are told that their cognitive abilities might improve may be able to perform better on the test batteries used in the study simply because their expectations become more optimistic. Second, testers who believe that a patient will have cognitive improvement, or hope for such improvement, could administer the tests in a more hopeful, positive manner, which can help the patient raise his or her expectations for performance and thus engage motivational systems that were previously disengaged (Keefe, 2006). Such expectation bias can also lead to inaccuracies in scoring; since many cognitive tests require the use of judgment to determine final scores, hopeful testers are more likely to give the “benefit of the doubt” to patients after they have entered into a study in which the treatment is potentially cognitively enhancing. Third, this same type of expectation could have an impact on the support that a patient receives in his or her community/living situation. If the people who interact regularly with the patient begin looking for better performance on cognitively related tasks, these expectations could become self-fulfilling in that they may raise the confidence and motivation of the patient to perform well on such tasks, including cognitive testing.

The factors associated with improvement during a placebo-controlled trial are indeed complex, and it is difficult to distinguish practice effects from placebo effects. However, the relatively small clinical improvement in test-retest designs without treatment or placebo intervention suggests that any potential practice effects may at least be potentiated by placebo effects.

The implications for this series of results include a methodological caution and a reason for optimism. Regarding the caution, future trials of cognitive-enhancing compounds might need to be designed in such a way that practice and placebo are reduced. Very few treatment studies of patients with schizophrenia have employed a priori methodological strategies to reduce the magnitude of potential practice effects, such as the use of a placebo run-in period with one or more administrations of the cognitive battery prior to randomization. Regarding the optimism, these studies suggest that schizophrenia cognition (perhaps especially when freed from the dampening effects of large doses of high potency medications such as haloperidol) could be more plastic that had been previously assumed; it is possibly as sensitive to experience-dependent learning in schizophrenia patients as healthy controls, and it may benefit from improved psychological expectations. While this is a methodological nuisance for clinical trial designs, it may also reveal an unexpectedly large potential gain for psychological interventions such as cognitive remediation, cognitive-behavioral therapy, and even encouragement.

References:

Goldberg TE, Goldman RS, Burdick KE, Malhotra AK, Lencz T, Patel RC, Woerner MG, Schooler NR, Kane JM, Robinson DG. Cognitive improvement after treatment with second-generation antipsychotic medications in first-episode schizophrenia: Is it a practice effect? Arch Gen Psychiatry. 2007 Oct;64:1115-1122. Abstract

Hawkins KA, Wexler BE (1999). California Verbal Learning Test practice effects in a schizophrenia sample. Schizophr Res 39: 73-78. Abstract

Keefe RSE. Missing the sweet spot: Disengagement in schizophrenia. Psychiatry, 2006; 3: 36-41.

Keefe RSE, Malhotra AK, Meltzer H, Kane JM, Buchanan RW, Murthy A, Sovel M, Li, C, Goldman R. Efficacy and safety of donepezil in patients with schizophrenia or schizoaffective disorder: Significant placebo/practice effects in a 12-week, randomized, double-blind, placebo-controlled trial. Neuropsychopharmacology, 2007 [Epub ahead of print]. Abstract

Keefe RSE¸ Goldberg TE, Harvey PD, Gold JM, Poe M, Coughenour L. The Brief Assessment of Cognition in Schizophrenia: Reliability, sensitivity, and comparison with a standard neurocognitive battery. Schizophrenia Research, 2004; 68: 283-297. Abstract

Nuechterlein KH, Green MF, Kern RS, Baade LE, Barch D, Cohen J, Essock S, Fenton WS, Frese FJ, Gold JM, Goldberg T, Heaton R, Keefe RSE, Kraemer H, Mesholam-Gately R, Seidman LJ, Stover E, Weinberger D, Young AS, Zalcman S, Marder SR. The MATRICS consensus cognitive battery: Part 1. Test selection, reliability, and validity. The American Journal of Psychiatry (in press).

View all comments by Richard Keefe

Related News: Antipsychotics and Cognition: Practice Makes Perfect Confounder

Comment by:  Narsimha Pinninti (Disclosure)
Submitted 15 October 2007
Posted 15 October 2007
  I recommend the Primary Papers

This article questions the prevailing notion that antipsychotic medication (particularly second-generation antipsychotics) improve cognitive functioning in individuals with schizophrenia. As the authors rightly note, practice effects should be taken into account before attributing improvements to drug effects.

View all comments by Narsimha Pinninti

Related News: Antipsychotics and Cognition: Practice Makes Perfect Confounder

Comment by:  Saurabh Gupta
Submitted 15 October 2007
Posted 15 October 2007
  I recommend the Primary Papers

I propose that future studies should use computational cognitive assessment tools like CANTAB or CogTest, which have at least two advantages. These tools have multiple similar test modules, so on each testing during one study, participants get a similar but not the same test to assess the same cognitive function. Besides, computational assessment also reduces chances of subjective bias on the part of investigator.

References:

Levaux MN, Potvin S, Sepehry AA, Sablier J, Mendrek A, Stip E. Computerized assessment of cognition in schizophrenia: promises and pitfalls of CANTAB. Eur Psychiatry. 2007 Mar;22(2):104-15. Review. Abstract

View all comments by Saurabh Gupta

Related News: Antipsychotics and Cognition: Practice Makes Perfect Confounder

Comment by:  Sebastian Therman
Submitted 17 October 2007
Posted 17 October 2007

One remedy would be repeated practice over time before the actual baseline, sufficient to reach asymptotic ability. Computerized testing of reaction time measures, short-term memory span, etc. would all be quite cheap and easy to implement, for example, as a weekly session.

View all comments by Sebastian Therman

Related News: Antipsychotics and Cognition: Practice Makes Perfect Confounder

Comment by:  Andrei Szoke
Submitted 1 November 2007
Posted 5 November 2007
  I recommend the Primary Papers

We recently completed a meta-analysis on "Longitudinal studies of cognition in schizophrenia" (to be published in the British Journal of Psychiatry) based on 53 studies providing data for 31 cognitive variables. When enough data were available (19 variables from eight cognitive tests), we compared the results of schizophrenic participants to those of normal controls.

Given the differences in methods and the fact that most of the studies included in our meta-analysis reported results of patients being past their first episode (FE), it is surprising how close our results and conclusions are compared to those of Goldberg et al. In our analysis we found that, with two exceptions (semantic verbal fluency and Boston naming test, which were stable), participants with schizophrenia improved their performances. The improvement was statistically significant for 19 variables (out of 29). However, controls also showed improvement in most of the variables due to the practice effect. A significant improvement (definite practice effect) was present for 10 variables, an improvement that did not reach significance (possible practice effect) was present in six more variables, and three variables showed no improvement. When compared with schizophrenic patients, controls showed similar improvement for 11 variables, significantly more improvement for seven variables (six of them from the “definite practice effect” group, one from the “possible practice effect”) and for one variable less improvement (the Stroop interference score). Thus, these results suggest that for most of the cognitive variables, improvement seen in schizophrenic subjects does not exceed improvement due to the practice effect.

It is interesting to mention that in our analysis only two variables improved significantly more when patients had a change in their medication from first-generation antipsychotics (FGAs) to second-generation antipsychotics (SGAs). These variables were time to complete TMT B and the delayed recall of the Visual Reproduction (from the WMS). In the Goldberg et al. study the only two tests that showed more improvement in schizophrenic subjects than in controls were also the TMT and visual reproduction. Although in our study schizophrenic subjects did not improve more than controls, the two results (Goldberg’s and ours) taken together could be an indirect argument for a differential, specific effect of SGAs on those two (visuo-spatial) tasks. The placebo effect—see the comment by Richard Keefe—could explain why improvement in the study by Goldberg et al. was greater than in our meta-analysis. Studies of effects of changing medication in the opposite direction, from SGAs to FGAs, could contribute to validate or invalidate these hypotheses.

Goldberg et al. suggested that there could be a set of task characteristics that could be used to develop tasks resistant to the practice effect. Our own results are less optimistic as they show that phonemic verbal fluency, despite a very similar format, does not share the “practice resistance” with the semantic verbal fluency. However, we think that there is already a wealth of data that could be used to select the best cognitive tests. An alternative solution is the use of scales and questionnaires for evaluating cognition (that are sensible to the placebo effect but not to the practice effect).

References:

Szoke A, Trandafir A, Dupont M-E, Meary A, Schurhoff F, Leboyer M. Longitudinal studies of cognition in schizophrenia. British Journal of Psychiatry (in press).

View all comments by Andrei Szoke

Related News: Antipsychotics and Cognition: Practice Makes Perfect Confounder

Comment by:  Patricia Estani
Submitted 7 November 2007
Posted 8 November 2007
  I recommend the Primary Papers

Related News: ICOSR 2011—Some Hope for Alleviating Negative Symptoms

Comment by:  Kimberly E. Vanover
Submitted 20 June 2011
Posted 20 June 2011

Thank you for your summary of the presentations from the New Drug Session at ICOSR 2011 on the Schizophrenia Research Forum. The Forum is a helpful and important resource.

I just wanted to clarify your description of ITI-007’s properties at the D2 site. As a dopamine phosphorylation modulator, ITI-007 acts as a pre-synaptic partial agonist and a post-synaptic antagonist with mesolimbic/mesocortical selectivity (Wennogle et al., 2008). In addition to its antagonism of 5-HT2A receptors and unique interaction with D2 receptors, it has affinity for D1 receptors, consistent with partial agonism linked to downstream increases in NMDA NR2B receptor phosphorylation (Zhu et al., 2008), and it is a serotonin reuptake inhibitor (Wennogle et al., 2008). Unfortunately, the short, 10-minute talk during the ICOSR session wasn’t sufficient time to go into the details of the mechanism and supporting preclinical data.

I did notice that a brief description for the mode of action for ITI-007 is listed as “5-HT2A antagonist + dopamine phosphoprotein modulator” with a role in schizophrenia listed as “DA stabilizer + 5hT-T inhibitor” in the Forum’s Drugs in Clinical Trials section. This is a nice, brief way to describe a rather complex mechanism.

References:

Wennogle LP, Snyder GL, Hendrick JP, Vanover KE, Tomesch JT, Li P, O’Callaghan JP, Miller DB, Fienberg AA, Davis RE, Mates S (2008) Unique antipsychotic profile of a novel 5-HT2A receptor antagonist and dopamine receptor protein phosphorylation modulator. Schizophrenia Research 98:Suppl1:15.

Zhu H, Snyder GL, Vanover KE, Rana M, Tsui T, Hendrick JP, Li P, Tomesch J, O’Brien JJ, Guo H, Davis RE, Fienberg AA, Wennogle LP, Mates S (2008) ITI-007: A novel 5-HT2A antagonist and dopamine protein phosphorylation modulator (DPPM) induces a distinct NR2B expression pattern in mouse brain. Program No. 155.14 2008 Neuroscience Meeting Planner. Washington, DC Society for Neuroscience, 2008. Online.

View all comments by Kimberly E. Vanover