Selective alterations in prefrontal cortical GABA neurotransmission in schizophrenia: a novel target for the treatment of working memory dysfunction

The treatment of cognitive impairment in schizophrenia

Cognitive deficits are major contributors to disability in schizophrenia. Many pharmacologic targets have been identified for cognitive enhancing agents, including receptors involved in dopaminergic, glutamatergic, GABAergic, serotonergic and cholinergic neurotransmission. In addition, new approaches to drug development have been directed towards neuroprotection and the facilitation of neuroplasticity. While several pharmacologic agents and cognitive remediation have shown promise in early trials, no treatment has yet demonstrated efficacy in large replication trials. The experience with different pharmacologic targets is reviewed and methodologic issues are discussed with recommendations for future research.

Neocortical excitation/inhibition balance in information processing and social dysfunction

Severe behavioural deficits in psychiatric diseases such as autism and schizophrenia have been hypothesized to arise from elevations in the cellular balance of excitation and inhibition (E/I balance) within neural microcircuitry. This hypothesis could unify diverse streams of pathophysiological and genetic evidence, but has not been susceptible to direct testing. Here we design and use several novel optogenetic tools to causally investigate the cellular E/I balance hypothesis in freely moving mammals, and explore the associated circuit physiology. Elevation, but not reduction, of cellular E/I balance within the mouse medial prefrontal cortex was found to elicit a profound impairment in cellular information processing, associated with specific behavioural impairments and increased high-frequency power in the 30-80 Hz range, which have both been observed in clinical conditions in humans. Consistent with the E/I balance hypothesis, compensatory elevation of inhibitory cell excitability partially rescued social deficits caused by E/I balance elevation. These results provide support for the elevated cellular E/I balance hypothesis of severe neuropsychiatric disease-related symptoms.

Visuospatial working memory deficits in remitted patients with bipolar disorder: susceptibility to the effects of GABAergic agonists

OBJECTIVES

Visuospatial working memory (VSWM) deficit under high working memory (WM) load deserves further investigation as a potential trait marker for bipolar disorder (BPD). However, VSWM performances may depend on basic neurocognitive processes and are possibly compromised by neurocognitive effects of psychotropic medications.

METHODS

A total of 32 remitted BPD patients and 39 healthy controls undertook parametric VSWM tasks and assessments for selective attention, sustained attention, psychomotor speed, mental flexibility, and Wechsler Adult Intelligence Scale-III full IQ. Using a multivariate model and trend analysis and controlling for other basic neurocognitive ability, the effects of mood stabilizers, antipsychotics, GABAergic agonists, and anticholinergics on VSWM performances were explored by post-hoc analysis comparing performances across WM loads between healthy controls and patients treated and not treated with a specific medication.

RESULTS

Remitted BPD patients showed more pronounced performance declines in VSWM performances as WM loads increased, indicating inefficient VSWM processing. The VSWM deficits of remitted patients were independent of their impairments in attentional processes or psychomotor speed. Among the medications, only GABAergic agonists were associated with impaired VSWM performances.

CONCLUSIONS

Remitted BPD patients had WM-load-dependent VSWM processing deficits after controlling for neurocognitive performances. As these deficits were associated with the use of GABAergic agonists, altered GABAergic neurotransmission might be involved with the underlying mechanisms of the impaired VSWM processing of BPD. Since GABAergic agonist use is often continued from the acute to the remitted phase in BPD and might potentially affect the functional recovery, clinicians should be aware of these neurocognitive side effects, even at low dosages. Close monitoring and timely discontinuation of GABAergic agonists is of utmost importance for clinical practice.

Integrative circuit models and their implications for the pathophysiologies and treatments of the schizophrenias

A preponderance of evidence indicates that the heterogeneous group of schizophrenias is accompanied by disturbances in neural elements distributed throughout multiple levels of interconnected cortico-striato-pallido-thalamic circuitry. These disturbances include a substantial loss of, or failure to develop, both cells and/or appropriate cellular connections in regions that include at least portions of the hippocampus, parahippocampal gyrus, entorhinal cortex, amygdala, prefrontal and anterior cingulate cortex, superior and transverse temporal gyri, and mediodorsal, anterior, and pulvinar nuclei of the thalamus; they appear to reflect failures of early brain maturation, that become codified into dysfunctional circuit properties, that in the opinion of this author cannot be "undone" or even predictably remediated in any physiological manner by existing pharmacotherapies. These circuit disturbances are variable across individuals with schizophrenia, perhaps reflecting the interaction of multiple different risk genes and multiple different epigenetic events. Evidence for these complex circuit disturbances has significant implications for many areas of schizophrenia research, and for future efforts toward developing more effective therapeutic approaches for this group of disorders. The conclusion of this chapter is that such future efforts should focus on further developing and refining medications that target nodal or convergent circuit points within the limbic-motor interface, with the goal of constraining the scope and severity of psychotic exacerbations, to be used in concert with systematic rehabilitative psychotherapies designed to engage healthy neural systems to compensate for and replace dysfunctional higher circuit elements. This strategy should be applied in both preventative and treatment settings, and disseminated for community delivery via an evidence-based manualized format. In contrast to alternative treatment strategies that range from complex polypharmacy to gene therapies to psychosurgical interventions, the use of combined medication plus targeted cognitive and behavioral psychotherapy has both common sense and time-tested documented efficacy with numerous other neuropsychiatric disorders.

Reducing prefrontal gamma-aminobutyric acid activity induces cognitive, behavioral, and dopaminergic abnormalities that resemble schizophrenia

BACKGROUND

Perturbations in gamma-aminobutyric acid (GABA)-related markers have been reported in the prefrontal cortex of schizophrenic patients. However, a preclinical assessment of how suppression of prefrontal cortex GABA activity may reflect behavioral and cognitive pathologies observed in schizophrenia is forthcoming.

METHODS

We assessed the effects of pharmacologic blockade of prefrontal cortex GABA(A) receptors in rats on executive functions and other behaviors related to schizophrenia, as well as neural activity of midbrain dopamine neurons.

RESULTS

Blockade of prefrontal cortex GABA(A) receptors with bicuculline (12.5-50 ng) did not affect working memory accuracy but did increase response latencies, resembling speed of processing deficits observed in schizophrenia. Prefrontal cortex GABA(A) blockade did not impede simple discrimination or reversal learning but did impair set-shifting in a manner dependent on when these treatments were given. Reducing GABA activity before the set-shift impaired the ability to acquire a novel strategy, whereas treatment before the initial discrimination increased perseveration during the shift. Latent inhibition was unaffected by bicuculline infusions before the preexposure/conditioning phases, suggesting that reduced prefrontal cortex GABA activity does not impair "learned irrelevance." GABA(A) blockade increased locomotor activity and showed synergic effects with a subthreshold dose of amphetamine. Furthermore, reducing medial prefrontal cortex GABA activity selectively increased phasic burst firing of ventral tegmental area dopamine neurons, without altering the their overall population activity.

CONCLUSIONS

These results suggest that prefrontal cortex GABA hypofunction may be a key contributing factor to deficits in speed of processing, cognitive flexibility, and enhanced phasic dopamine activity observed in schizophrenia.

Increased schedule-induced polydipsia in the rat following subchronic treatment with MK-801

Primary polydipsia, defined as excessive fluid intake not explained by medical causes, has been reported to occur in over 20% of chronically ill psychiatric inpatients and is especially common in schizophrenic populations. We tested the hypothesis that in an animal model of schizophrenia-like symptoms (subchronic injections of MK-801, 0.5 mg/kg twice daily for 7 days) an increase in the acquisition of schedule-induced polydipsia (SIP) will occur. Young adult, male rats acquired SIP when food-restricted and placed on a non-contingent fixed-time 1-min food schedule. In comparison with saline-treated control animals, subchronic MK-801 treatment significantly increased SIP. These findings suggest an animal model of polydipsia associated with schizophrenia in humans.

Thinking glutamatergically: changing concepts of schizophrenia based upon changing neurochemical models

Clinical concepts of mental illness have always been modulated by underlying theoretical considerations. For the past fifty years, schizophrenia has been considered primarily a disease of dopaminergic neurotransmission. Although this conceptualization has helped greatly in explaining the clinical effects of psychostimulants and guiding the clinical use of both typical and atypical antipsychotics, it has nevertheless shaded how we look at the disorder from both a pathophysiological and therapeutic perspective. For example, most explanatory research in schizophrenia has focused on dopamine-rich regions of the brain, with little investigation of regions of the brain that are relatively dopamine poor. Starting approximately twenty years ago, an alternative formulation of schizophrenia was proposed based upon actions of the "dissociative anesthetic" class of psychotomimetic agents, including phencyclidine (PCP), ketamine and various designer drugs. These compounds induce psychosis by blocking neurotransmission at N-methyl-D-aspartate (NMDA)-type glutamate receptors, suggesting an alternative model for pathogenesis in schizophrenia. As opposed to dopamine, the glutamatergic system is widely distributed throughout the brain and plays a prominent role in sensory processing as well as in subsequent stages of cortical analysis. Glutamatergic theories of schizophrenia, thus, predict that cortical dysfunction will be regionally diffuse but process specific. In addition, NMDA receptors incorporate binding sites for specific endogenous brain compounds, including the amino acids glycine and D-serine and the redox modulator glutathione, and interact closely with dopaminergic, cholinergic and γ-aminobutyric acid (GABA)-ergic systems. Glutamatergic theories, thus, open new potential approaches for treatment of schizophrenia, most of which are only now entering clinical evaluation.

N-methyl-d-aspartate (NMDA) receptor dysfunction or dysregulation: the final common pathway on the road to schizophrenia?

Schizophrenia is a severe mental disorder associated with a characteristic constellation of symptoms and neurocognitive deficits. At present, etiological mechanisms remain relatively unknown, although multiple points of convergence have been identified over recent years. One of the primary convergence points is dysfunction of N-methyl-d-aspartate (NMDAR)-type glutamate receptors. Antagonists of NMDAR produce a clinical syndrome that closely resembles, and uniquely incorporates negative and cognitive symptoms of schizophrenia, along with the specific pattern of neurocognitive dysfunction seen in schizophrenia. Genetic polymorphisms involving NMDAR subunits, particularly the GRIN2B subunit have been described. In addition, polymorphisms have been described in modulatory systems involving the NMDAR, including the enzymes serine racemase and d-amino acid oxidase/G72 that regulate brain d-serine synthesis. Reductions in plasma and brain glycine, d-serine and glutathione levels have been described as well, providing potential mechanisms underlying NMDAR dysfunction. Unique characteristics of the NMDAR are described that may explain the characteristic pattern of symptoms and neurocognitive deficits observed in schizophrenia. Finally, the NMDAR complex represents a convergence point for potential new treatment approaches in schizophrenia aimed at correcting underlying abnormalities in synthesis and regulation of allosteric modulators, as well as more general potentiation of pre- and post-synaptic glutamatergic and NMDAR function.

Subchronic phencyclidine in rats: alterations in locomotor activity, maze performance, and GABA(A) receptor binding

Phencyclidine (PCP), an antagonist at the N-methyl-D-aspartate subtype of ionotropic glutamatergic receptors, decreases gamma-aminobutyric acid (GABA)ergic inhibition, suggesting that changes in GABAergic receptor function underlie behavioral and cognitive deficits resulting from repeated administration of PCP. To test this hypothesis, male Sprague-Dawley rats treated with PCP (4.5 mg/kg, intraperitoneal, twice a day for 7 consecutive days) or saline were tested in behavioral and cognitive tasks 7 days after injections. The PCP group showed increased amphetamine (1.5 mg/kg)-stimulated locomotor activity, and exhibited a greater number of errors in the double Y-maze memory task, when compared with controls. Subchronic PCP treatment increased [H]muscimol-binding sites and decreased affinity for [H]muscimol binding in frontal cortex, hippocampus, and striatum in comparison with controls. There were no changes in the expression of glutamic acid decarboxylase or the GABA membrane transporter protein. These data show that subchronic PCP administration induces an impaired performance of a previously learned task and an enhanced response to amphetamine in the rat. The observed changes in GABAA receptors in the rat brain are consistent with the notion that alterations in GABAergic receptor function contribute to the behavioral and cognitive impairments associated with repeated exposure to PCP.

Modeling the positive symptoms of schizophrenia in genetically modified mice: pharmacology and methodology aspects

In recent years, there have been huge advances in the use of genetically modified mice to study pathophysiological mechanisms involved in schizophrenia. This has allowed rapid progress in our understanding of the role of several proposed gene mechanisms in schizophrenia, and yet this research has also revealed how much still remains unresolved. Behavioral studies in genetically modified mice are reviewed with special emphasis on modeling psychotic-like behavior. I will particularly focus on observations on locomotor hyperactivity and disruptions of prepulse inhibition (PPI). Recommendations are included to address pharmacological and methodological aspects in future studies. Mouse models of dopaminergic and glutamatergic dysfunction are then discussed, reflecting the most important and widely studied neurotransmitter systems in schizophrenia. Subsequently, psychosis-like behavior in mice with modifications in the most widely studied schizophrenia susceptibility genes is reviewed. Taken together, the available studies reveal a wealth of available data which have already provided crucial new insight and mechanistic clues which could lead to new treatments or even prevention strategies for schizophrenia.

Prepulse inhibition and genetic mouse models of schizophrenia

Mutant mouse models related to schizophrenia have been based primarily on the pathophysiology of schizophrenia, the known effects of antipsychotic drugs, and candidate genes for schizophrenia. Sensorimotor gating deficits in schizophrenia patients, as indexed by measures of prepulse inhibition of startle (PPI), have been well characterized and suggested to meet the criteria as a useful endophenotype in human genetic studies. PPI refers to the ability of a non-startling "prepulse" to inhibit responding to the subsequent startling stimulus or "pulse." Because of the cross-species nature of PPI, it has been used primarily in pharmacological animal models to screen putative antipsychotic medications. As techniques in molecular genetics have progressed over the past 15 years, PPI has emerged as a phenotype used in assessing genetic mouse models of relevance to schizophrenia. In this review, we provide a selected overview of the use of PPI in mouse models of schizophrenia and discuss the contribution and usefulness of PPI as a phenotype in the context of genetic mouse models. To that end, we discuss mutant mice generated to address hypotheses regarding the pathophysiology of schizophrenia and candidate genes (i.e., hypothesis driven). We also briefly discuss the usefulness of PPI in phenotype-driven approaches in which a PPI phenotype could lead to "bottom up" approaches of identifying novel genes of relevance to PPI (i.e., hypothesis generating).

The neonatal ventral hippocampal lesion as a heuristic neurodevelopmental model of schizophrenia

Traditionally, animal models of schizophrenia were predominantly pharmacological constructs focused on phenomena linked to dopamine and glutamate neurotransmitter systems, and were created by direct perturbations of these systems. A number of developmental models were subsequently generated that allowed testing of hypotheses about the origin of the disease, mimicked a wider array of clinical and neurobiological features of schizophrenia, and opened new avenues for developing novel treatment strategies. The most thoroughly characterized (approximately 100 primary research articles) is the neonatal ventral hippocampal lesion (NVHL) model, which is the subject of this review. We highlight its advantages and limitations, and how it may offer clues about the extent to which positive, negative, cognitive, and other aspects of schizophrenia, including addiction vulnerability, represent inter-related pathophysiological mechanisms.

Animal models for schizophrenia via in utero gene transfer: understanding roles for genetic susceptibility factors in brain development

Genetic disturbances of brain development may underlie the pathophysiology of schizophrenia. Recent advances in molecular neurobiology suggest that some genetic risk factors for schizophrenia have multiple roles in various brain regions depending on the developmental stage. Furthermore, these factors are likely to act synergistically or epistatically in common molecular pathways, possibly contributing to disease pathology. Thus, a technique that can manipulate the expression of more than one gene simultaneously in animal models is necessary to address such molecular pathways. To produce such animal models, in utero gene transfer technique is one useful method. Given that plasmid-based cell-type-specific and inducible gene expression systems are now available, combining these technologies and in utero gene transfer opens a new window to examine the functional role of genetic risk factors for schizophrenia by conducting multiple-gene targeting in a spatial and temporal manner. The utility of animal models produced by in utero gene transfer will also be expected to be evaluated in terms of functional and behavioral outcomes after puberty, which may be associated with schizophrenia pathology.

Schizophrenia; from structure to function with special focus on the mediodorsal thalamic prefrontal loop

OBJECTIVE

To describe structural and biochemical evidence from postmortem brains that implicates the reciprocal connections between the mediodorsal thalamic nucleus and the prefrontal cortex in cognitive symptoms of schizophrenia.

METHOD

The estimation of the regional volumes and cell numbers was obtained using stereological methods. The biochemical analyses of molecular expression in postmortem brain involve quantitative measurement of transcripts and proteins by in-situ (RNA) or Western blot/autoradiography in brains from patients with schizophrenia and comparison subjects.

RESULTS

Stereological studies in postmortem brain from patients with schizophrenia have reported divergent and often opposing findings in the total number of neurons and volume of the mediodorsal (MD) thalamic nucleus, and to a lesser degree in its reciprocally associated areas of the prefrontal cortex. Similarly, quantitative molecular postmortem studies have found large inter-subject and between-study variance at both the transcript and protein levels for receptors and their interacting molecules of several neurotransmitter systems in these interconnected anatomical regions. Combined, large variation in stereological and molecular studies indicates a complex and heterogeneous involvement of the MD thalamic-prefrontal loop in schizophrenia.

CONCLUSION

Based on a considerable heterogeneity in patients suffering from schizophrenia, large variation in postmortem studies, including stereological and molecular postmortem studies of the MD thalamus and frontal cortex, might be expected and may in fact partly help to explain the variable endophenotypic traits associated with this severe psychiatric illness.

Steady state responses: electrophysiological assessment of sensory function in schizophrenia

Persons with schizophrenia experience subjective sensory anomalies and objective deficits on assessment of sensory function. Such deficits could be produced by abnormal signaling in the sensory pathways and sensory cortex or later stage disturbances in cognitive processing of such inputs. Steady state responses (SSRs) provide a noninvasive method to test the integrity of sensory pathways and oscillatory responses in schizophrenia with minimal task demands. SSRs are electrophysiological responses entrained to the frequency and phase of a periodic stimulus. Patients with schizophrenia exhibit pronounced auditory SSR deficits within the gamma frequency range (35-50 Hz) in response to click trains and amplitude-modulated tones. Visual SSR deficits are also observed, most prominently in the alpha and beta frequency ranges (7-30 Hz) in response to high-contrast, high-luminance stimuli. Visual SSR studies that have used the psychophysical properties of a stimulus to target specific visual pathways predominantly report magnocellular-based deficits in those with schizophrenia. Disruption of both auditory and visual SSRs in schizophrenia are consistent with neuropathological and magnetic resonance imaging evidence of anatomic abnormalities affecting the auditory and visual cortices. Computational models suggest that auditory SSR abnormalities at gamma frequencies could be secondary to gamma-aminobutyric acid-mediated or N-methyl-D-aspartic acid dysregulation. The pathophysiological process in schizophrenia encompasses sensory processing that probably contributes to alterations in subsequent encoding and cognitive processing. The developmental evolution of these abnormalities remains to be characterized.

GABA(A) receptors and their associated proteins: implications in the etiology and treatment of schizophrenia and related disorders

Gamma-aminobutyric acid type A (GABA(A)) receptors play an important role in mediating fast synaptic inhibition in the brain. They are ubiquitously expressed in the CNS and also represent a major site of action for clinically relevant drugs. Recent technological advances have greatly clarified the molecular and cellular roles played by distinct GABA(A) receptor subunit classes and isoforms in normal brain function. At the same time, postmortem and genetic studies have linked neuropsychiatric disorders including schizophrenia and bipolar disorder with GABAergic neurotransmission and various specific GABA(A) receptor subunits, while evidence implicating GABA(A)R-associated proteins is beginning to emerge. In this review we discuss the mounting genetic, molecular, and cellular evidence pointing toward a role for GABA(A) receptor heterogeneity in both schizophrenia etiology and therapeutic development. Finally, we speculate on the relationship between schizophrenia-related disorders and selected GABA(A) receptor associated proteins, key regulators of GABA(A) receptor trafficking, targeting, clustering, and anchoring that often carry out these functions in a subtype-specific manner.

Subplate neurons: crucial regulators of cortical development and plasticity

The developing cerebral cortex contains a distinct class of cells, subplate neurons, which form one of the first functional cortical circuits. Subplate neurons reside in the cortical white matter, receive thalamic inputs and project into the developing cortical plate, mostly to layer 4. Subplate neurons are present at key time points during development. Removal of subplate neurons profoundly affects cortical development. Subplate removal in visual cortex prevents the maturation of thalamocortical synapse, the maturation of inhibition in layer 4, the development of orientation selective responses in individual cortical neurons, and the formation of ocular dominance columns. In addition, monocular deprivation during development reveals that ocular dominance plasticity is paradoxical in the absence of subplate neurons. Because subplate neurons projecting to layer 4 are glutamatergic, these diverse deficits following subplate removal were hypothesized to be due to lack of feed-forward thalamic driven cortical excitation. A computational model of the developing thalamocortical pathway incorporating feed-forward excitatory subplate projections replicates both normal development and plasticity of ocular dominance as well as the effects of subplate removal. Therefore, we postulate that feed-forward excitatory projections from subplate neurons into the developing cortical plate enhance correlated activity between thalamus and layer 4 and, in concert with Hebbian learning rules in layer 4, allow maturational and plastic processes in layer 4 to commence. Thus subplate neurons are a crucial regulator of cortical development and plasticity, and damage to these neurons might play a role in the pathology of many neurodevelopmental disorders.

Spatio-temporal EEG waves in first episode schizophrenia

OBJECTIVE

Schizophrenia is characterized by a deficit in context processing, with physiological correlates of hypofrontality and reduced amplitude P3b event-related potentials. We hypothesized an additional physiological correlate: differences in the spatio-temporal dynamics of cortical activity along the anterior-posterior axis of the scalp.

METHODS

This study assessed latency topographies of spatio-temporal waves under task conditions that elicit the P3b. EEG was recorded during separate auditory and visual tasks. Event-related spatio-temporal waves were quantified from scalp EEG of subjects with first episode schizophrenia (FES) and matched controls.

RESULTS

The P3b-related task conditions elicited a peak in spatio-temporal waves in the delta band at a similar latency to the P3b event-related potential. Subjects with FES had fewer episodes of anterior to posterior waves in the 2-4 Hz band compared to controls. Within the FES group, a tendency for fewer episodes of anterior to posterior waves was associated with high Psychomotor Poverty symptom factor scores.

CONCLUSIONS

Subjects with FES had altered global EEG dynamics along the anterior-posterior axis during task conditions involving context update.

SIGNIFICANCE

The directional nature of this finding and its association with Psychomotor Poverty suggest this result is related to findings of hypofrontality in schizophrenia.

Proof-of-concept trial with the neurosteroid pregnenolone targeting cognitive and negative symptoms in schizophrenia

The neurosteroid pregnenolone and its sulfated derivative enhance learning and memory in rodents. Pregnenolone sulfate also positively modulates NMDA receptors and could thus ameliorate hypothesized NMDA receptor hypofunction in schizophrenia. Furthermore, clozapine increases pregnenolone in rodent hippocampus, possibly contributing to its superior efficacy. We therefore investigated adjunctive pregnenolone for cognitive and negative symptoms in patients with schizophrenia or schizoaffective disorder receiving stable doses of second-generation antipsychotics in a pilot randomized, placebo-controlled, double-blind trial. Following a 2-week single-blind placebo lead-in, patients were randomized to pregnenolone (fixed escalating doses to 500 mg/day) or placebo, for 8 weeks. Primary end points were changes in BACS and MCCB composite and total SANS scores. Of 21 patients randomized, 18 completed at least 4 weeks of treatment (n=9/group). Pregnenolone was well tolerated. Patients receiving pregnenolone demonstrated significantly greater improvements in SANS scores (mean change=10.38) compared with patients receiving placebo (mean change=2.33), p=0.048. Mean composite changes in BACS and MCCB scores were not significantly different in patients randomized to pregnenolone compared with placebo. However, serum pregnenolone increases predicted BACS composite scores at 8 weeks in the pregnenolone group (r(s)=0.81, p=0.022). Increases in allopregnanolone, a GABAergic pregnenolone metabolite, also predicted BACS composite scores (r(s)=0.74, p=0.046). In addition, baseline pregnenolone (r(s)=-0.76, p=0.037), pregnenolone sulfate (r(s)=-0.83, p=0.015), and allopregnanolone levels (r(s)=-0.83, p=0.015) were inversely correlated with improvements in MCCB composite scores, further supporting a possible role for neurosteroids in cognition. Mean BACS and MCCB composite scores were correlated (r(s)=0.74, p<0.0001). Pregnenolone may be a promising therapeutic agent for negative symptoms and merits further investigation for cognitive symptoms in schizophrenia.

Decreased glutamic acid decarboxylase(67) mRNA expression in multiple brain areas of patients with schizophrenia and mood disorders

Reduced levels of glutamic acid decarboxylase(67) (GAD(67)), an essential enzyme for GABA synthesis, is one of the most consistent gene expression changes found in the frontal cortex of patients with schizophrenia. Recently this reduction has been shown to extend to other areas including primary sensory, primary motor and anterior cingulate (ACC) cortices. To determine the extent to which additional cortical and subcortical regions may be affected in schizophrenia, we measured the level of GAD(67) mRNA in previously unexplored areas including the orbitofrontal (OFC) and superior temporal (STG) cortices as well as the caudate, putamen, nucleus accumbens, medial dorsal thalamus and anterior thalamus using in situ hybridization. We also examined GAD(67) mRNA levels in all these regions in individuals with bipolar disorder and major depression. ANCOVA comparing GAD(67) mRNA levels in all four diagnostic groups revealed a significant reduction (approximately 30%) in layers III and IV of the OFC of patients with schizophrenia and bipolar disorder. A priori t-tests comparing GAD(67) mRNA levels between the schizophrenia and control groups revealed significant reductions in the ACC, STG, striatum and thalamus. These findings suggest that there may be a widespread reduction in GABA neurotransmission due to a decrease in the synthesis of GAD(67) in subjects with psychiatric disorders. The resulting decrease in inhibitory tone across multiple brain areas may contribute to the psychotic behavior observed in patients with schizophrenia and bipolar disorder.

Disruptions in spatial working memory, but not short-term memory, induced by repeated ketamine exposure

Treatment with non-competitive N-methyl-D-aspartate (NMDA) antagonists such as phencyclidine or ketamine have been shown to induce schizophrenia-like psychotic and cognitive symptoms in humans and animals. However, there have been a number of contradictory findings regarding the effects of repeated treatment with these drugs on working memory in experimental animals. We hypothesized that processes dependent on dopamine transmission in the medial prefrontal cortex (PFC) may be more sensitive to disruption following these treatment. We assessed the effects of repeated treatment with ketamine on working memory performance using a delayed spatial win-shift procedure conducted on a radial-arm maze, dependent on a neural circuit linking hippocampal and dopamine inputs to the medial PFC. Rats were trained on the task prior to drug exposure, after which they were subjected to one of two dosing regimes of ketamine (30 mg/kg twice a day for either 5 or 10 days). After a 10 day withdrawal period, they were re-tested on the task for 15 days. Ketamine treatment for 10 days, but not 5 days, increased the number of errors and days to re-achieve the criterion on the delayed task. However, in a separate group of rats, subchronic ketamine treatment (10 days) did not affect performance of the non-delayed random foraging task, dependent on the hippocampus, but not the PFC. These results indicate that working memory performance assessed with these procedures is sensitive to disruption following repeated exposure to ketamine. Impairments in working memory induced by these treatments are not attributable to dysfunction of motivational, motor, short-term or spatial memory processes. The use of these procedures may prove useful in modeling impairments in this executive function observed in schizophrenia.

Pharmacological cognitive enhancement in schizophrenia

Cognitive impairments in schizophrenia are common and severe. These impairments are also related to functional disability in schizophrenia. As a result, efforts are underway to enhance cognition in schizophrenia through a variety of pharmacological mechanisms. As part of this effort, a designated research design has been developed for this process, through an extensive consensus and validation effort. This paper reviews the methods for pharmacological cognitive enhancement, as well as previous results of efforts in the pharmacological domains. These domains include cholinergic, noradrenergic, serotonergic, glutamatergic, and GABA-ergic mechanisms. While previous results have not been particularly encouraging, there are many challenges that need to be overcome and many of the reasons for past failures may be due to resolvable issues. It is likely that this will be an area of research that will be developing extensively over the next decade and expanding to other conditions as well.

Neonatal ventral hippocampal lesions in male and female rats: effects on water maze, locomotor activity, plus-maze and prefrontal cortical GABA and glutamate release in adulthood

Schizophrenia is characterized by diverse behavioural and neurochemical abnormalities that may be differentially expressed in males and females. Male rats with neonatal ventral hippocampal lesions (nVHL) have commonly demonstrated behavioural and neurochemical abnormalities similar to those in schizophrenia. Fewer studies have used female rats. We investigated the hypothesis that male and female nVHL rats will demonstrate behavioural abnormalities accompanied by decreased GABA and l-glutamate release in the prefrontal cortex (PFC). On postnatal day (P) 7 rats received VH injections of ibotenate (3.0 microg/0.3 microl/side; n=18) or saline (n=21) or no injections (n=22). On P56, rats began water-maze, locomotor activity and elevated plus maze testing, and were then sacrificed for potassium-evoked GABA and l-glutamate release from PFC slices. nVHL rats showed impaired performance in water maze acquisition and match-to-sample tasks, increased spontaneous and amphetamine-induced locomotor activity and increased percent open-arm time. These behavioural changes were similar in males and females. These effects were accompanied by significantly reduced potassium-evoked l-glutamate release in male and female nVHL rats relative to controls, and non-significantly lower GABA release. Findings support the notion that behavioural abnormalities in post-pubertal male and female nVHL rats are associated with decreases in PFC neurotransmitter release.

Towards a neurodevelopmental model of clinical case formulation

Rapid advances in molecular genetics and neuroimaging over the last 10 to 20 years have been a catalyst for research in neurobiology, developmental psychopathology, and translational neuroscience. Methods of study in psychiatry, previously described as "slow maturing," now are becoming sufficiently sophisticated to more effectively investigate the biology of higher mental processes. Despite these technologic advances, the recognition that psychiatric disorders are disorders of neurodevelopment, and the importance of case formulation to clinical practice, a neurodevelopmental model of case formulation has not yet been articulated. The goals of this article, which is organized as a clinical case conference, are to begin to articulate a neurodevelopmental model of case formulation, to illustrate its value, and finally to explore how clinical psychiatric practice might evolve in the future if this model were employed.

Selecting paradigms from cognitive neuroscience for translation into use in clinical trials: proceedings of the third CNTRICS meeting

This overview describes the goals and objectives of the third conference conducted as part of the Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia (CNTRICS) initiative. This third conference was focused on selecting specific paradigms from cognitive neuroscience that measured the constructs identified in the first CNTRICS meeting, with the goal of facilitating the translation of these paradigms into use in clinical trials contexts. To identify such paradigms, we had an open nomination process in which the field was asked to nominate potentially relevant paradigms and to provide information on several domains relevant to selecting the most promising tasks for each construct (eg, construct validity, neural bases, psychometrics, availability of animal models). Our goal was to identify 1-2 promising tasks for each of the 11 constructs identified at the first CNTRICS meeting. In this overview article, we describe the on-line survey used to generate nominations for promising tasks, the criteria that were used to select the tasks, the rationale behind the criteria, and the ways in which breakout groups worked together to identify the most promising tasks from among those nominated. This article serves as an introduction to the set of 6 articles included in this special issue that provide information about the specific tasks discussed and selected for the constructs from each of 6 broad domains (working memory, executive control, attention, long-term memory, perception, and social cognition).

Multifunctional pharmacotherapy: what can we learn from study of selective serotonin reuptake inhibitor augmentation of antipsychotics in negative-symptom schizophrenia?

Many patients suffering from major psychiatric disorders do not respond adequately to monotherapy and require additional drugs. To date, there are no objective guidelines for deciding which combination may be effective, and the choice is based on previous clinical experience and on trial and error. Even when combination drugs are effective, the biochemical mechanisms responsible for the value-added effect are unknown. Understanding the mechanism of such synergism may provide a rational basis for choosing drug combinations and for developing more effective drugs. In schizophrenia, negative symptoms respond poorly to antipsychotics, but may improve when these are augmented with selective serotonin reuptake inhibitors (SSRI). This augmenting effect cannot be explained by summating the pharmacological effects of the individual drugs. We proposed that the study of SSRI augmentation can serve as a window to understanding the biochemical mechanisms of clinically effective drug synergism. In a series of studies we identified unique biochemical effects of the combination, different from each individual drug, and proposed that some of these are involved in mediating the clinical effect. Here we review some of the findings and propose that the mechanism of action involves regionally selective modulation of the GABA system. The evidence indicates that the SSRI antidepressant-antipsychotic combination may be a useful paradigm for studying therapeutically effective synergistic drug interactions in schizophrenia. Although as yet limited in scope, the findings of definable molecular targets for synergistic SSRI-antipsychotic interaction provide new directions to inform future research and provide novel bio-molecular targets for drug development.

Subunit-selective modulation of GABA type A receptor neurotransmission and cognition in schizophrenia

OBJECTIVE

Deficits in working memory and cognitive control in schizophrenia are associated with impairments in prefrontal cortical function, including altered gamma band oscillations. These abnormalities are thought to reflect a deficiency in the synchronization of pyramidal cell activity that is dependent, in part, on gamma-aminobutyric acid (GABA) neurotransmission through GABA type A (GABA(A)) receptors containing alpha(2) subunits. The authors conducted a proof-of-concept clinical trial designed to test the hypothesis that a novel compound with relatively selective agonist activity at GABA(A) receptors containing alpha(2) subunits would improve cognitive function and gamma band oscillations in individuals with schizophrenia.

METHOD

Participants were male subjects (N=15) with chronic schizophrenia who were randomly assigned to receive 4 weeks of treatment with the study drug MK-0777, a benzodiazepine-like agent with selective activity at GABA(A) receptors containing alpha(2) or alpha(3) subunits, or a matched placebo in a double-blind fashion. Outcome measures were the Brief Psychiatric Rating Scale (BPRS), Repeatable Battery for the Assessment of Neuropsychological Status, three tests of working memory and/or cognitive control (N-back, AX Continuous Performance Test, and Preparing to Overcome Prepotency), and EEG measures of gamma band oscillations induced during the Preparing to Overcome Prepotency task.

RESULTS

Compared with placebo, the MK-0777 compound was associated with improved performance on the N-back, AX Continuous Performance Test, and Preparing to Overcome Prepotency tasks. The compound was also associated with increased frontal gamma band power during the Preparing to Overcome Prepotency task. No effects of the MK-0777 compound were detected in BPRS or Repeatable Battery for the Assessment of Neuropsychological Status scores, with the exception of improvement on the Repeatable Battery for the Assessment of Neuropsychological Status delayed memory index. The MK-0777 agent was well-tolerated.

CONCLUSIONS

These findings provide preliminary support for the hypothesis that enhanced GABA activity at alpha(2) subunit containing GABA(A) receptors improves behavioral and electrophysiological measures of prefrontal function in individuals with schizophrenia.

The biochemical womb of schizophrenia: A review

The conclusive identification of specific etiological factors or pathogenic processes in the illness of schizophrenia has remained elusive despite great technological progress. The convergence of state-of-art scientific studies in molecular genetics, molecular neuropathophysiology, in vivo brain imaging and psychopharmacology, however, indicates that we may be coming much closer to understanding the genesis of schizophrenia. In near future, the diagnosis and assessment of schizophrenia using biochemical markers may become a "dream come true" for the medical community as well as for the general population. An understanding of the biochemistry/ visa vis pathophysiology of schizophrenia is essential to the discovery of preventive measures and therapeutic intervention.

Maintenance time of sedative effects after an intravenous infusion of diazepam: a guide for endoscopy using diazepam

AIM

To examine whether the sedative effects assessed by psychomotor tests would depend on the cytochrome P450 (CYP) 2C19 genotypes after an infusion regimen of diazepam commonly used for gastrointestinal endoscopy in Japan.

METHODS

Fifteen healthy Japanese volunteers consisting of three different CYP2C19 genotype groups underwent a critical flicker fusion test, an eye movement analysis and a postural sway test as a test for physical sedative effects, and a visual analog scale (VAS) symptom assessment method as a test for mental sedative effects during the 336 h period after the intravenous infusion of diazepam (5 mg).

RESULTS

The physical sedative effects assessed by the critical flicker test continued for 1 h (t values of 5 min, 30 min and 60 min later: 4.35, 5.00 and 3.19, respectively) and those by the moving radial area of a postural sway test continued for 3 h (t values of 5 h, 30 h, 60 min and 3 h later: -4.05, -3.42, -2.17 and -2.58, respectively), which changed significantly compared with the baseline level before infusion (P<0.05). On the other hand, the mental sedative effects by the VAS method improved within 1 h. The CYP2C19 genotype-dependent differences in the postinfusion sedative effects were not observed in any of the four psychomotor function tests.

CONCLUSION

With the psychomotor tests, the objective sedative effects of diazepam continued for 1 h to 3 h irrespective of CYP2C19 genotype status and the subjective sedative symptoms improved within 1 h. Up to 3 h of clinical care appears to be required after the infusion of diazepam, although patients feel subjectively improved.

Antipsychotic drugs: comparison in animal models of efficacy, neurotransmitter regulation, and neuroprotection

Various lines of evidence indicate the presence of progressive pathophysiological processes occurring within the brains of patients with schizophrenia. By modulating chemical neurotransmission, antipsychotic drugs may influence a variety of functions regulating neuronal resilience and viability and have the potential for neuroprotection. This article reviews the current literature describing preclinical and clinical studies that evaluate the efficacy of antipsychotic drugs, their mechanism of action and the potential of first- and second-generation antipsychotic drugs to exert effects on cellular processes that may be neuroprotective in schizophrenia. The evidence to date suggests that although all antipsychotic drugs have the ability to reduce psychotic symptoms via D(2) receptor antagonism, some antipsychotics may differ in other pharmacological properties and their capacities to mitigate and possibly reverse cellular processes that may underlie the pathophysiology of schizophrenia.

GABA neurons and the mechanisms of network oscillations: implications for understanding cortical dysfunction in schizophrenia

Synchronization of neuronal activity in the neocortex may underlie the coordination of neural representations and thus is critical for optimal cognitive function. Because cognitive deficits are the major determinant of functional outcome in schizophrenia, identifying their neural basis is important for the development of new therapeutic interventions. Here we review the data suggesting that phasic synaptic inhibition mediated by specific subtypes of cortical gamma-aminobutyric acid (GABA) neurons is essential for the production of synchronized network oscillations. We also discuss evidence indicating that GABA neurotransmission is altered in schizophrenia and propose mechanisms by which such alterations can decrease the strength of inhibitory connections in a cell-type-specific manner. We suggest that some alterations observed in the neocortex of schizophrenia subjects may be compensatory responses that partially restore inhibitory synaptic efficacy. The findings of altered neural synchrony and impaired cognitive function in schizophrenia suggest that such compensatory responses are insufficient and that interventions aimed at augmenting the efficacy of GABA neurotransmission might be of therapeutic value.

[Structural and functional brain changes in schizophrenic disorders. Indications of early neuronal developmental disturbances?]

The neurodevelopmental hypothesis of schizophrenia, which was established 30 years ago and discussed controversially for a long time, postulates that pre- and perinatally acting cerebral noxae cause disturbances of corticogenesis in the developing neuronal fibre systems which are essential for later onset of the disease. During recent years the cerebral alterations of schizophrenic patients could be further characterized as area-, layer-, and cell type-specific changes in temporolimbic and frontal regions leading to specific abnormalities of intrinsic and extrinsic connectivity. Animal models allowed for realistic imitations of these structural lesions and for elucidating their functional consequences concerning transmitter systems and behaviour. With modern neuroimaging techniques microstructural changes and alterations in cerebral activation can be exactly demonstrated and related to the specific psychopathologic features of schizophrenia.

Reduced cortical cannabinoid 1 receptor messenger RNA and protein expression in schizophrenia

CONTEXT

Cannabis use is associated with both impaired cognitive functions, including working memory, and an increased risk of schizophrenia. Schizophrenia is characterized by impairments in working memory that are associated with reduced gamma-aminobutyric acid (GABA) neurotransmission in the dorsolateral prefrontal cortex. The cannabinoid 1 receptor (CB1R) is highly expressed in the dorsolateral prefrontal cortex, is contained in the axon terminals of a subpopulation of perisomatic-targeting GABA neurons, and, when activated, suppresses the release of GABA.

OBJECTIVE

To determine the potential relationship between CB1R signaling and altered GABA neurotransmission in schizophrenia by evaluating CB1R messenger RNA (mRNA) and protein expression in the dorsolateral prefrontal cortex.

DESIGN

In situ hybridization and immunocytochemistry techniques were used to examine the cortical levels of CB1R mRNA and protein, respectively.

SETTING

Brain specimens were obtained from autopsies conducted at the Allegheny County Medical Examiner's Office, Pittsburgh, Pennsylvania.

PARTICIPANTS

Postmortem brain specimens from 23 pairs of subjects with schizophrenia and age-, sex-, and postmortem interval-matched comparison subjects, as well as brain specimens from 18 macaque monkeys with long-term exposure to haloperidol, olanzapine, or placebo.

MAIN OUTCOME MEASURES

Optical density measures of CB1R mRNA expression and protein levels and correlations with previously reported glutamic acid decarboxylase 67 and cholecystokinin mRNA measures.

RESULTS

Levels of CB1R mRNA were significantly lower by 14.8% in the subjects with schizophrenia. Similarly, CB1R protein levels, assessed by radioimmunocytochemistry and standard immunocytochemistry, were significantly decreased by 11.6% and 13.9%, respectively. Group differences in CB1R mRNA levels were significantly correlated with those in glutamic acid decarboxylase 67 and cholecystokinin mRNA levels. Expression of CB1R mRNA was not changed in antipsychotic-exposed monkeys, and neither CB1R mRNA levels nor protein levels were affected by potential confounding factors in the subjects with schizophrenia.

CONCLUSIONS

This combination of findings suggests the testable hypothesis that reduced CB1R mRNA and protein levels in schizophrenia represent a compensatory mechanism to increase GABA transmission from perisomatic-targeting cholecystokinin interneurons with impaired GABA synthesis.

Treatment with haloperidol and diazepam alters GABA(A) receptor density in the rat brain

A significant body of data suggests that GABA(A) receptors are altered in the CNS of subjects with schizophrenia. However, subjects with schizophrenia are treated with antipsychotic drugs and, in some cases, antipsychotic drugs and benzodiazepines. It has therefore been suggested that the changes in GABA(A) receptors in the CNS of subjects with schizophrenia are due to such drug treatments. Surprisingly, there appear to be no studies to determine the effect of a combined antipsychotic-benzodiazepine treatment on GABA(A) receptors. We therefore measured both the GABA binding site ([3H]muscimol) and the benzodiazepine binding site ([3H]flumazenil) in the CNS of rats treated with either haloperidol, diazepam or a combination of the two drugs. The main findings of our study are that treatment with diazepam or the combination of diazepam and haloperidol results in regionally selective increases GABA binding sites but treatment with haloperidol alone decreases the GABA binding site in the thalamus but increases these sites in the hypothalamus. By contrast, treatment with diazepam, haloperidol and a combination of the two drugs resulted in widespread decreases in the number of benzodiazepine binding sites in the rat CNS. The notable exception to this outcome was increased numbers of benzodiazepine binding sites in the frontal cortex of rats that had received diazepam. Our data suggests that there are complex changes in the GABA(A) receptor following treatment with haloperidol, diazepam or a combination of these drugs. This outcome may be relevant to the therapeutic benefits of using both drugs in conjunction early in the treatment of a psychotic episode.

GABAA/Benzodiazepine receptor binding in patients with schizophrenia using [11C]Ro15-4513, a radioligand with relatively high affinity for alpha5 subunit

Dysfunction of the GABA system is considered to play a role in the pathology of schizophrenia. Individual subunits of GABA(A)/Benzodiazepine (BZ) receptor complex have been revealed to have different functional properties. alpha5 subunit was reported to be related to learning and memory. Changes of alpha5 subunit in schizophrenia were reported in postmortem studies, but the results were inconsistent. In this study, we examined GABA(A)/BZ receptor using [(11)C]Ro15-4513, which has relatively high affinity for alpha5 subunit, and its relation to clinical symptoms in patients with schizophrenia. [(11)C]Ro15-4513 bindings of 11 patients with schizophrenia (6 drug-naïve and 5 drug-free) were compared with those of 12 age-matched healthy control subjects using positron emission tomography. Symptoms were assessed using the Positive and Negative Syndrome Scale. [(11)C]Ro15-4513 binding was quantified by binding potential (BP) obtained by the reference tissue model. [(11)C]Ro15-4513 binding in the prefrontal cortex and hippocampus was negatively correlated with negative symptom scores in patients with schizophrenia, although there was no significant difference in BP between patients and controls. GABA(A)/BZ receptor including alpha5 subunit in the prefrontal cortex and hippocampus might be involved in the pathophysiology of negative symptoms of schizophrenia.

Reduced GABAA benzodiazepine receptor binding in veterans with post-traumatic stress disorder

Gamma-aminobutyric acid (GABA(A)) receptors are thought to play an important role in modulating the central nervous system in response to stress. Animal data have shown alterations in the GABA(A) receptor complex by uncontrollable stressors. SPECT imaging with benzodiazepine ligands showed lower distribution volumes of the benzodiazepine-GABA(A) receptor in the prefrontal cortex of patients with post-traumatic stress disorder (PTSD) in one, but not in another study. The objective of the present study was to assess differences in the benzodiazepine-GABA(A) receptor complex in veterans with and without PTSD using [(11)C]flumazenil and positron emission tomography (PET). Nine drug naive male Dutch veterans with deployment related PTSD and seven male Dutch veterans without PTSD were recruited, and matched for age, region and year of deployment. Each subject received a [(11)C]flumazenil PET scan and a structural magnetic resonance imaging scan. Dynamic 3D PET scans with a total duration of 60 min were acquired, and binding in template based and manually defined regions of interest (ROI) was quantified using validated plasma input and reference tissue models. In addition, parametric binding potential images were compared on a voxel-by-voxel basis using statistical parametric mapping (SPM2). ROI analyses using both template based and manual ROIs showed significantly reduced [(11)C]flumazenil binding in PTSD subjects throughout the cortex, hippocampus and thalamus. SPM analysis confirmed these results. The observed global reduction of [(11)C]flumazenil binding in patients with PTSD provides circumstantial evidence for the role of the benzodiazepine-GABA(A) receptor in the pathophysiology of PTSD and is consistent with previous animal research and clinical psychopharmacological studies.

Neurotech for neuroscience: unifying concepts, organizing principles, and emerging tools

The ability to tackle analysis of the brain at multiple levels simultaneously is emerging from rapid methodological developments. The classical research strategies of "measure," "model," and "make" are being applied to the exploration of nervous system function. These include novel conceptual and theoretical approaches, creative use of mathematical modeling, and attempts to build brain-like devices and systems, as well as other developments including instrumentation and statistical modeling (not covered here). Increasingly, these efforts require teams of scientists from a variety of traditional scientific disciplines to work together. The potential of such efforts for understanding directed motor movement, emergence of cognitive function from neuronal activity, and development of neuromimetic computers are described by a team that includes individuals experienced in behavior and neuroscience, mathematics, and engineering. Funding agencies, including the National Science Foundation, explore the potential of these changing frontiers of research for developing research policies and long-term planning.

Cognitive neuroscience-based approaches to measuring and improving treatment effects on cognition in schizophrenia: the CNTRICS initiative

The goal of this article is to discuss ways to further improve the search for potentially procognitive agents that could be used to enhance cognition and functional outcome in schizophrenia. In particular, we focus on the potential advantages to this process of using a contemporary, cognitive neuroscience-based approach to measuring cognitive function in clinical trials of procognitive agents in schizophrenia. These tools include computer-administered tasks that measure specific cognitive systems (such as attention, working memory, long-term memory, cognitive control) as well as the component cognitive processes that comprise these more overarching systems. The advantages of using these tools include the ability to identify and use homologous animal and human models in the drug discovery and testing process and the ability to incorporate noninvasive functional imaging measures into clinical trial contexts at several different phases of the drug development process. However, despite the clear potential advantages to using such methods, a number of barriers exist to their translation from basic science tools to tools for drug discovery. We discuss the development and implementation of a new project, Cognitive Neuroscience Treatment to Improve Cognition in Schizophrenia, designed to identify and overcome these barriers to the translation of cognitive neuroscience measures and methods into regular use in the drug discovery and development process of cognition-enhancing agents for use in schizophrenia.

Molecular targets for treating cognitive dysfunction in schizophrenia

Cognitive impairment is a core feature of schizophrenia as deficits are present in the majority of patients, frequently precede the onset of other positive symptoms, persist even with successful treatment of positive symptoms, and account for a significant portion of functional impairment in schizophrenia. While the atypical antipsychotics have produced incremental improvements in the cognitive function of patients with schizophrenia, overall treatment remains inadequate. In recent years, there has been an increased interest in developing novel strategies for treating the cognitive deficits in schizophrenia, focusing on ameliorating impairments in working memory, attention, and social cognition. Here we review various molecular targets that are actively being explored for potential drug discovery efforts in schizophrenia and cognition. These molecular targets include dopamine receptors in the prefrontal cortex, nicotinic and muscarinic acetylcholine receptors, the glutamatergic excitatory synapse, various serotonin receptors, and the gamma-aminobutyric acid (GABA) system.

Which perspectives can endophenotypes and biological markers offer in the early recognition of schizophrenia?

The early recognition of schizophrenia seems crucial; various studies relate a longer duration-of-untreated-psychosis to a worse prognosis. We give an overview over common psychopathological early recognition instruments (BSABS, CAARMS, SIPS, IRAOS, ERIraos). However, many clinical symptoms of prodromal schizophrenia stages are not sufficiently specific. Thus we review recent contributions of neuroimaging and electrophysiological as well as genetic studies: which new diagnostic perspectives offer endophenotypes (such as P300, P50 sensory gating, MMN, smooth pursuit eye movements; indicating a specific genetic vulnerability) together with a better understanding of schizophrenic pathophysiology (state-dependent biological markers, e.g. aggravated motor neurological soft signs during psychosis) in prodromal schizophrenia when still ambiguous clinical symptoms are present. Several examples (e.g. from COMT polymorphisms to working memory deficits) illustrate more specific underlying neuronal mechanisms behind behavioural symptoms. This way, a characteristic pattern of disturbed cerebral maturation might be distinguished in order to complement clinical instruments of early schizophrenia detection.

Comorbidity implications in brain disease: Neuronal substrates of symptom profiles

The neuronal substrates underlying aspects of comorbidity in brain disease states may be described over psychiatric and neurologic conditions that include affective disorders, cognitive disorders, schizophrenia, obsessive-compulsive disorder, substance abuse disorders as well as the neurodegenerative disorders. Regional and circuitry analyses of biogenic amine systems that are implicated in neural and behavioural pathologies are elucidated using neuroimaging, electrophysiological, neurochemical, neuropharmacological and neurobehavioural methods that present demonstrations of the neuropathological phenomena, such as behavioural sensitisation, cognitive impairments, maladaptive reactions to environmental stress and serious motor deficits. Considerations of neuronal alterations that may or may not be associated with behavioural abnormalities examine differentially the implications of discrete areas within brains that have been assigned functional significance; in the case of the frontal lobes, differential deficits of ventromedial and dorsolateral prefrontal cortex may be associated with different aspects of cognition, affect, remission or response to medication thereby imparting a varying aspect to any investigation of comorbidity.

The anatomy of co-morbid neuropsychiatric disorders based on cortico-limbic synaptic interactions

Many brain disorders appear to involve dysfunctions of aminergic systems. Alterations in dopamine activity may underpin both schizophrenia and the establishment and maintenance of drug dependence while disruption of serotonergic signalling may be crucial in both depression and schizophrenia. The co-existence of nicotine and alcohol abuse with depression and schizophrenia is well-documented as is the particular vulnerability of adolescents. At the same time, a common group of brain structures is increasingly implicated in neuropathological studies. For example, depression may involve a lack of serotonin signalling, particularly in the prefrontal cortex, while in schizophrenia there is evidence for reduced dopamine signalling in the same brain region, co-existing with hyperactivity in the mesolimbic dopamine pathway. Increased dopamine release from the mesolimbic dopamine pathway is also a common factor of drugs of abuse. Furthermore, the control of motivational behaviour and dopamine release is apparently modified by hippocampal and amygdala activity, both brain regions showing pathological changes in schizophrenia and depression. Our work has focused on the intricate synaptic interactions of aminergic terminals and cortical and subcortical neurons in order to unravel the anatomical basis for these disorders and their treatments. We show convergence of dopamine and cortical inputs onto single neurons in the nucleus accumbens, and between different cortical inputs to individual neurons, providing a basis for the gating mechanisms attributed to these interactions. We have also examined local and extrinsic connections in the prefrontal cortex and the basis for regulation of both cortical neurons and midbrain dopamine neurons by serotonin from the raph é nucleus. Together with data concerning subcellular receptor distributions, this information provides a detailed synaptic framework for interpreting behavioural, pharmacological and physiological data and enhances our understanding of possible circuitry underlying comorbidity of disorders such as schizophrenia and depression with drug abuse, information invaluable in the introduction of enhanced therapies.

Deciphering the Disease Process of Schizophrenia: The Contribution of Cortical Gaba Neurons

Schizophrenia is a devastating illness that is manifest through a variety of clinical signs and symptoms. Among these, impairments in certain critical cognitive functions, such as working memory, appear to represent the core features of the disorder. In this chapter, we review the evidence indicating that disturbances in neurotransmission by a subset of GABA neurons in the dorsolateral prefrontal cortex are commonly present in schizophrenia. Despite both pre- and postsynaptic compensatory responses, the resulting pathophysiological process, alterations in the perisomatic inhibitory regulation of pyramidal neurons, underlies a reduced capacity for the synchronization of neuronal activity at gamma frequencies that is required for working memory function. We also discuss several pathogenetic mechanisms that could rise to the alterations in GABA neurotransmission and consider the implication of these findings for therapeutic interventions to improve cognitive function in individuals with schizophrenia.

Alterations in GABAA receptor expression in neonatal ventral hippocampal lesioned rats: Comparison of prepubertal and postpubertal periods

Rats with neonatal ventral hippocampal lesions (NVHL) have been studied as a neurodevelopmental animal model of schizophrenia. NVHL rats exhibit postpubertal emergence of hyperresponsiveness to stress, suggesting increased mesolimbic dopamine (DA) activity. However, previous studies have not yielded clear evidence of this. Disturbances in the gamma-amino-butyric acid (GABA)-ergic system as well as the dopaminergic system are thought to be present in schizophrenia. To determine whether GABA(A) receptors play a role in the abnormal postpubertal behavior in NVHL rats, we compared changes in expression of mRNA of GABA(A) receptor subunits and in [(35)S] t-butylbicyclophosphorothionate ([(35)S] TBPS) binding in the prepubertal and postpubertal periods. Male pups were lesioned with ibotenic acid at postnatal day 7 (PD 7), and in situ hybridization and quantitative autoradiography were then performed. In NVHL rats, alpha1 subunit mRNA expression in prefrontal cortex was decreased at PD 35 (prepubertal period; by 21.7%), but increased at PD 56 (postpubertal period; by 21.4%) when compared with sham controls. beta2 subunit mRNA expression was increased in PFC in the postpubertal period (by 24.3%). beta3 subunit mRNA expression was increased in the caudate-putamen in the postpubertal period (by 37.2%). [(35)S] TBPS binding was increased in PFC only in the postpubertal period (by 17.7%). These findings suggest that dysfunction of the GABAergic system exists in NVHL rats. Furthermore, developmental and regional changes in GABA(A) receptor expression appear to occur in compensation for the attenuation of GABAergic system activity in NVHL rats.

Impairments in frontal cortical gamma synchrony and cognitive control in schizophrenia

A critical component of cognitive impairments in schizophrenia can be characterized as a disturbance in cognitive control, or the ability to guide and adjust cognitive processes and behavior flexibly in accordance with one's intentions and goals. Cognitive control impairments in schizophrenia are consistently linked to specific disturbances in prefrontal cortical functioning, but the underlying neurophysiologic mechanisms are not yet well characterized. Synchronous gamma-band oscillations have been associated with a wide range of perceptual and cognitive processes, raising the possibility that they may also help entrain prefrontal cortical circuits in the service of cognitive control processes. In the present study, we measured induced gamma-band activity during a task that reliably engages cognitive control processes in association with prefrontal cortical activations in imaging studies. We found that higher cognitive control demands were associated with increases in induced gamma-band activity in the prefrontal areas of healthy subjects but that control-related modulation of prefrontal gamma-band activity was absent in schizophrenia subjects. Disturbances in gamma-band activity in patients correlated with illness symptoms, and gamma-band activity correlated positively with performance in control subjects but not in schizophrenia patients. Our findings may provide a link between previously reported postmortem abnormalities in thalamofrontocortical circuitry and alterations in prefrontal activity observed in functional neuroimaging studies. They also suggest that deficits in frontal cortical gamma-band synchrony may contribute to the cognitive control impairments in schizophrenia.

Pharmacological approaches to the management of cognitive dysfunction in schizophrenia

Cognitive dysfunction is a core feature of schizophrenia as deficits that are present in the majority of patients with schizophrenia frequently precede the onset of other symptoms and persist even after other symptoms have been effectively treated. The use of atypical antipsychotics has produced some small improvements, although the need for adjunctive treatment specifically targeting cognitive dysfunction is gaining widespread acceptance. Animal models and some small clinical trials have yielded results that are promising but not definitive. Psychosocial interventions have also met with some success in ameliorating some cognitive limitations. The mixed results of pharmacological interventions are most likely to be as a result of a combination of methodological flaws of many studies, poor outcome measures, dose administration effects and problems with the agents themselves.