Hippocampal N-acetyl aspartate in unaffected siblings of patients with schizophrenia: a possible intermediate neurobiological phenotype

Proton magnetic resonance spectroscopy of the frontal lobe in schizophrenics: a critical review of the methodology

Schizophrenic patients undergoing proton magnetic resonance spectroscopy show alterations in N-acetyl aspartate levels in several brain regions, indicating neuronal dysfunction. The present review focuses on the main proton magnetic resonance spectroscopy studies in the frontal lobe of schizophrenics. A MEDLINE search, from 1991 to March 2004, was carried out using the key-words spectroscopy and schizophrenia and proton and frontal. In addition, articles cited in the reference list of the studies obtained through MEDLINE were included. As a result, 27 articles were selected. The results were inconsistent, 19 papers reporting changes in the N-acetyl aspartate levels, while 8 reported no change. Methodological analysis led to the conclusion that the discrepancy may be due the following factors: (i) number of participants; (ii) variation in the clinical and demographic characteristics of the groups; (iii) little standardization of the acquisition parameters of spectroscopy. Overall, studies that fulfill strict methodological criteria show N-acetyl aspartate decrease in the frontal lobe of male schizophrenics.

Selective deficit of hippocampal N-acetylaspartate in antipsychotic-naive patients with schizophrenia

BACKGROUND

Studies using proton magnetic resonance spectroscopy in schizophrenia have demonstrated abnormality of N-acetylaspartate but are confounded by the effects of phase of illness and medication. There is mounting evidence that antipsychotic medication influences N-acetylaspartate.

METHODS

A group of first-episode patients who had received no, or minimal, antipsychotic medication was examined at baseline and after 3 months treatment. Normal comparison subjects were examined at the same interval. Ratios of N-acetylaspartate, creatine plus phosphocreatine, and choline-containing compounds in the left prefrontal cortex, hippocampus, and basal ganglia were measured.

RESULTS

The mean duration of symptoms for all patients was 31.6 (SD 26.1) weeks. A significant reduction of hippocampal N-acetylaspartate/creatine plus phosphocreatine was found in the antipsychotic-naive group relative to those previously treated and to controls at baseline (F = 7.3, p <.002). No group differences were found at follow-up.

CONCLUSIONS

Hippocampal N-acetylaspartate/creatine plus phosphocreatine appears to be selectively affected early in the course of illness. The finding of neurochemical differences between treatment naive and previously treated patients confirms the relevance of medication status in proton magnetic resonance spectroscopy studies. Further investigation of the influence of medication at this stage of illness is warranted.

Genetically mediated brain abnormalities in schizophrenia

Schizophrenia is a highly heritable, neurobehavioral disorder; however, the mode of inheritance is complex, and linkage findings have been difficult to replicate. Some consistent linkage findings have emerged on chromosomes 1, 6, 8, 11, 13, 15, and 22. New methods are being developed for candidate gene identification, including the use of neurobiologic phenotypes observed in relatives of persons with schizophrenia. Neuroimaging studies of relatives implicate abnormal hippocampal structure and inefficient prefrontal network functioning, probably representing mild variants of the abnormalities observed in schizophrenia. These characteristics may represent stable markers of vulnerability to schizophrenia, because they are not confounded by effects of antipsychotic drugs or psychosis. Recent studies provide evidence for a small role of the catechol-O-methyltransferase gene on 22q, and the serotonin receptor transporter gene on 17q11-q12 in the development of schizophrenia. Linking genes and brain regions or networks is an important step in identification of the pathophysiology of schizophrenia.

Pathogenesis of schizophrenia: Part I. Symptomatology, cognitive characteristics and brain morphology

The objective of the present study was to provide a pathophysiological model of the development of schizophrenia. The method used was a selective review of recent findings, including those in our own department, concerning the clinical symptoms, cognitive characteristics and morphological brain changes in schizophrenia. A four-syndrome classification was proposed in which 'alienation syndrome' is separated from delusion syndrome. Memory organization deficit in schizophrenia patients was correlated with reduced activation of the left inferior frontal regions. Magnetic resonance imaging and statistical parametric mapping analysis revealed that volume reduction in the temporal lobe was seen in both schizotypal disorder and schizophrenia patients, but schizophrenia patients had additional changes in the medial and dorsolateral frontal regions. In conclusion, a temporo-frontal dual pathology of schizophrenia was suggested.

The BDNF val66met polymorphism affects activity-dependent secretion of BDNF and human memory and hippocampal function

Brain-derived neurotrophic factor (BDNF) modulates hippocampal plasticity and hippocampal-dependent memory in cell models and in animals. We examined the effects of a valine (val) to methionine (met) substitution in the 5' pro-region of the human BDNF protein. In human subjects, the met allele was associated with poorer episodic memory, abnormal hippocampal activation assayed with fMRI, and lower hippocampal n-acetyl aspartate (NAA), assayed with MRI spectroscopy. Neurons transfected with met-BDNF-GFP showed lower depolarization-induced secretion, while constitutive secretion was unchanged. Furthermore, met-BDNF-GFP failed to localize to secretory granules or synapses. These results demonstrate a role for BDNF and its val/met polymorphism in human memory and hippocampal function and suggest val/met exerts these effects by impacting intracellular trafficking and activity-dependent secretion of BDNF.

A twin study of genetic contributions to hippocampal morphology in schizophrenia

Our goal was to establish whether altered hippocampal morphology represents a trait marker for genetic vulnerability in schizophrenia. We outlined the hippocampi on high-resolution MR images obtained from matched samples of control and discordant monozygotic and dizygotic co-twins (N = 40 pairs). Hippocampal measures were used in statistical tests specifically designed to identify disease-associated genetic and nongenetic influences on morphology. 3D surface average maps of the hippocampus were additionally compared in biological risk groups. Smaller hippocampal volumes were confirmed in schizophrenia. Dizygotic affected co-twins showed smaller left hippocampi compared to their healthy siblings. Disease-associated effects were not present between monozygotic discordant co-twins. Monozygotic, but not dizygotic, unaffected co-twins exhibited smaller left hippocampi compared to control twins, supporting genetic influences. Surface areas and posterior volumes similarly revealed schizophrenia and genetic liability effects. Results suggest that hippocampal volume reduction may be a trait marker for identifying individuals possessing a genetic predisposition for schizophrenia.

Understanding predisposition to schizophrenia: toward intervention and prevention

OBJECTIVE

Early intervention to prevent schizophrenia is one of the most important goals of schizophrenia research. However, the field is not yet ready to initiate trials to prevent prodromal or psychotic symptoms in people who are at risk for developing the disorder. In this paper, we consider some of the major obstacles that must be studied before prevention strategies become feasible.

METHOD AND RESULTS

One of the most important hurdles is the identification of a syndrome or set of traits that reflects a predisposition to schizophrenia and that might provide potential targets for intervention. In a recent reformulation of Paul Meehl's concept of schizotaxia, we integrate research findings obtained over the last 4 decades to propose a syndrome with meaningful clinical manifestations. We review the conceptualization of this syndrome and consider its multidimensional clinical expression. We then describe preliminary research diagnostic criteria for use in adult, nonpsychotic, first-degree relatives of patients diagnosed with schizophrenia, based on negative symptoms and neuropsychological deficits. We follow this with evidence supporting the validity of the proposed syndrome, which mainly includes social dysfunction and response to a low dosage of one of the newer antipsychotic medications.

CONCLUSIONS

Continued progress toward the eventual initiation of prevention strategies for schizophrenia will include sustained efforts to validate the traits reflecting a predisposition to develop the disorder (for example, schizotaxia), follow-up studies to confirm initial findings, and the identification of potentially useful preventive interventions.

Finding susceptibility genes for developmental disorders of speech: the long and winding road

Finding susceptibility genes for complex disorders is the next major challenge facing genetics researchers. The purpose of this paper is to stimulate creative thinking about the gene-finding process for developmental speech disorders (DSDs), specifically disorders of articulation/phonology and stuttering. The paper will begin with a review of existing behavioral genetic studies of these phenotypes. This will be followed by a discussion of roadblocks that may impede the molecular study of DSDs, research that is in very early stages of development. As a third objective, the small number of molecular genetic studies of DSDs that have been published or presented will be described. The paper concludes with a discussion of research strategies that may maximize the success of molecular studies of speech phenotypes. It will be argued that progress will most likely be enhanced if theories about biological systems and processes can be used to narrow the search for candidate susceptibility genes.

LEARNING OUTCOMES

The reader will be introduced to findings and conceptual issues that relate to the behavioral and molecular genetic investigation of DSDs. After completing this paper, readers should be able to (a) identify key epidemiological findings for the three speech phenotypes that were discussed (DAS, speech delay, and stuttering); (b) summarize the findings of the behavioral genetic studies of speech disorders that were presented; (c) identify four specific challenges that may impede future molecular genetic studies of these phenotypes; (d) describe the methodological sequence that led to the discovery of the FOXP2 gene; and (e) summarize the two research strategies that were presented to potentially reduce sample heterogeneity for future molecular genetics research.

Neuroimaging studies of the hippocampus in schizophrenia

Three neuroimaging techniques, morphometric neuroimaging, magnetic resonance spectroscopy, and functional neuroimaging, have provided evidence for abnormal hippocampal structure and function in schizophrenia. Hippocampal volume reduction is now one of the most consistent structural abnormalities found in schizophrenia: it is present at the onset of the illness and, to a lesser degree, in first-degree relatives of schizophrenic probands. Decreased levels of N-acetyl-aspartate point towards a cellular basis of such volume changes. Functional neuroimaging studies have demonstrated abnormal levels of hippocampal activity at rest, during the experience of auditory hallucinations, and during the performance of memory retrieval tasks. These results of neuroimaging studies complement evidence from post-mortem and behavioral studies, which have found regionally specific abnormalities of the hippocampus and of memory function in schizophrenia.

A fully automated method for tissue segmentation and CSF-correction of proton MRSI metabolites corroborates abnormal hippocampal NAA in schizophrenia

In this report, we describe the implementation and application of a fully automated segmentation routine using SPM99 algorithms and MATLAB for clinical Magnetic Resonance Spectroscopic Imaging (MRSI) studies. By segmenting high-resolution 3-D image data and coregistering the results to the spatial localizer slices of a spectroscopy examination, the program offers the possibility to easily calculate segmentation maps for a large variety of MRSI experiments. The segmented data are corrected for the individual point-spread function, slice and VOI profiles for measurement sequences with selective pulses as well as for the chemical shifts of different metabolites. The new method was applied to investigate discrete hippocampal metabolite abnormalities in a small sample of schizophrenic patients in comparison to healthy controls (15 patients, 15 controls). Only after correction was the N-acetyl-aspartate (NAA) signal significantly lower in patients compared to controls. No differences were found for the corrected signals from the creatine/phosphocreatine (Cr) or choline-containing compounds (Ch). These results are in good agreement with neuropathological and previous MR spectroscopy studies of the hippocampus in schizophrenic patients.

An integration of schizophrenia with schizotypy: identification of schizotaxia and implications for research on treatment and prevention

The liability to schizophrenia (schizotaxia) is associated with deficits in a variety of domains, including negative symptoms and neuropsychological deficits, even in the absence of psychosis or pre-psychotic prodromal symptoms. Conceptually, this view of schizotaxia is similar to negative schizotypy (i.e., schizotypal personality disorder minus the positive symptoms). It is broader than DSM-IV schizotypal personality disorder (SPD), however, in that more relatives of patients with schizophrenia show core symptoms of schizotaxia than meet the diagnostic criteria for SPD. Three lines of evidence support the validity of schizotaxia. First, evidence of concurrent validation was obtained by showing that schizotaxic subjects were more impaired than non-schizotaxic subjects on a variety of independent clinical scales. Second, schizotaxic subjects showed higher levels of negative symptoms on the Structured Interview for Schizotypy than non-schizotaxic subjects, but did not differ on positive symptoms. Third, subjects who met predetermined criteria for schizotaxia (i.e., negative symptoms and neuropsychological deficits) showed positive effects following treatment with low doses of risperidone (0.25-2.0 mg). Thus, clinical deficits in schizotaxia may be identifiable, and to a significant extent, reversible. Implications for the conception of schizotypy and the prevention of schizophrenia will be discussed.

Concurrent validation of schizotaxia: a pilot study

BACKGROUND

Many first-degree relatives of patients with schizophrenia show deficits in clinical, neuropsychological, neurobiological and social domains, in the absence of psychosis. We recently reformulated Meehl's concept of schizotaxia to conceptualize the liability to schizophrenia, and we proposed preliminary criteria based on the presence of negative symptoms and neuropsychological deficits. Here we investigate the concurrent validity of schizotaxia by comparing a group of subjects who met criteria for schizotaxia with a group who did not on independent measures of clinical function, and on lifetime rates of selected comorbid psychiatric disorders.

METHODS

Twenty-seven adults who were first-degree, biological relatives of patients with schizophrenia were evaluated for schizotaxia based on our predetermined criteria involving negative symptoms and neuropsychological deficits. Subjects also received portions of the Diagnostic Interview for Genetic Studies, the Structured Interview for Schizotypy, the Family Interview for Genetic Studies, the DSM-IV Global Assessment of Functioning, the Physical Anhedonia Scale, the Social Adjustment Scale and the Symptom Checklist-90-Revised. Subjects who met criteria for schizotaxia were compared with those who did not on each of the clinical measures, and on their rates of comorbid DSM-IV psychiatric diagnoses.

RESULTS

Eight subjects met criteria for schizotaxia, and 19 did not. Subjects with schizotaxia showed significantly lower levels of function on each of the clinical scales. Differences in comorbid psychiatric diagnoses were not significant, although the rate of lifetime substance abuse diagnoses in the schizotaxic group (50%) approached levels that are often seen in schizophrenia.

CONCLUSIONS

These findings provide the first evidence of concurrent validation for a proposed syndrome of schizotaxia. They are also consistent with the view that the vulnerability to schizophrenia may be defined, at least partially, although larger studies to assess both the concurrent and predictive validity of schizotaxia will be required to confirm these results.

Advances in schizophrenia

Recent studies into the etiology of schizophrenia have yielded both promising leads and disappointing dead ends, indicating the multifactored and complex nature of the disorder. The focus has subsequently shifted back to refining the phenotype and identifying clinical and biological subtypes. Recent technological breakthroughs in genomics and proteomics hold promise for advancing our understanding of the molecular pathophysiology of schizophrenia.

Schizophrenia

To provide the most effective care for this difficult patient population, it is helpful to remember that patients with schizophrenia have disease-intrinsic limitations that limit their ability to participate in their care. These limitations are symptoms of a disease and not volitional. For the physician to substitute for these deficits, a certain degree of flexibility as well as the willingness to use unorthodox interventions is necessary. Good medical care is as important for the patient with schizophrenia as for any other patient.

Gray matter-changes and correlates of disease severity in schizophrenia: a statistical parametric mapping study

Voxel-based morphometry has recently been used successfully to detect gray matter volume reductions in schizophrenic patients. The aim of the present study was to confirm the findings on gray-matter changes and to complement these by applying the methodology to CSF-differences. Also, we wanted to determine whether a correlation exists between a clinically defined parameter of disease severity and brain morphology in schizophrenic patients. We investigated 48 schizophrenic patients and compared them with 48 strictly age- and sex-matched controls. High-resolution whole-brain MR-images were segmented and analyzed using SPM99. In a further analysis, the covariate effect of the global assessment of functioning-score (GAF) was calculated. Main findings were (i) left-dominant frontal, temporal, and insular GM-reductions and (ii) GM-increases in schizophrenic patients in the right basal ganglia and bilaterally in the superior cerebellum; (iii) CSF-space increases in patients complementary to some GM-reductions; (iv) a correlation between the GAF-score and local GM-volume in the left inferior frontal and inferior parietal lobe of schizophrenic patients. This study confirms and extends some earlier findings on GM-reduction and detected distinct GM-increases in schizophrenic patients. These changes were corroborated by complementary CSF-increases. Most importantly, a correlation could be established between two particular gray matter-regions and the overall disease severity, with more severely ill patients displaying a local GM-deficit. These findings may be of potentially large importance for both the future interpretation and design of neuroimaging studies in schizophrenia and the further elucidation of possible pathophysiological processes occurring in this disease.

An association between reduced interhemispheric EEG coherence in the temporal lobe and genetic risk for schizophrenia

Previous studies have suggested that schizophrenic patients show resting changes such as frequency-slowing and decreased coherence in the frontal and temporal area. We sought to determine whether these findings are also found in clinically unaffected siblings of schizophrenics and estimate heritability by calculating relative risk. We investigated two independent data sets: (1) from the NIMH St. Elisabeth's campus (59 schizophrenics, 76 unaffected siblings and 32 unrelated normal controls) and (2) from the NIH-campus (Bethesda) (59 schizophrenics, 90 unaffected siblings and 26 unrelated normal controls). We computed power spectra and coherence on the first data set and then tried to replicate the results on the second data set. Power spectrum analysis suggested that schizophrenics are cortically hypoactivated, whereas in unaffected siblings, a tendency for hyperactivation was found. In contrast, spectral coherences (0.5-5Hz) were reduced in both data sets in the temporal lobe areas in schizophrenics and in their unaffected siblings. Changes were most pronounced for the interhemispheric coherence linking both posterior temporal lobe areas. Relative risk calculations (lambda(S)) ranged between 3.7 and 9.8, depending on phenotype definition. Thus, while power spectrum EEG abnormalities may be state-dependent, reduced coherence as a possible measure of neuronal synchronization is familial and potentially a heritable trait related to genetic risk for schizophrenia.

A review of MRI findings in schizophrenia

After more than 100 years of research, the neuropathology of schizophrenia remains unknown and this is despite the fact that both Kraepelin (1919/1971: Kraepelin, E., 1919/1971. Dementia praecox. Churchill Livingston Inc., New York) and Bleuler (1911/1950: Bleuler, E., 1911/1950. Dementia praecox or the group of schizophrenias. International Universities Press, New York), who first described 'dementia praecox' and the 'schizophrenias', were convinced that schizophrenia would ultimately be linked to an organic brain disorder. Alzheimer (1897: Alzheimer, A., 1897. Beitrage zur pathologischen anatomie der hirnrinde und zur anatomischen grundlage einiger psychosen. Monatsschrift fur Psychiarie und Neurologie. 2, 82-120) was the first to investigate the neuropathology of schizophrenia, though he went on to study more tractable brain diseases. The results of subsequent neuropathological studies were disappointing because of conflicting findings. Research interest thus waned and did not flourish again until 1976, following the pivotal computer assisted tomography (CT) finding of lateral ventricular enlargement in schizophrenia by Johnstone and colleagues. Since that time significant progress has been made in brain imaging, particularly with the advent of magnetic resonance imaging (MRI), beginning with the first MRI study of schizophrenia by Smith and coworkers in 1984 (Smith, R.C., Calderon, M., Ravichandran, G.K., et al. (1984). Nuclear magnetic resonance in schizophrenia: A preliminary study. Psychiatry Res. 12, 137-147). MR in vivo imaging of the brain now confirms brain abnormalities in schizophrenia. The 193 peer reviewed MRI studies reported in the current review span the period from 1988 to August, 2000. This 12 year period has witnessed a burgeoning of MRI studies and has led to more definitive findings of brain abnormalities in schizophrenia than any other time period in the history of schizophrenia research. Such progress in defining the neuropathology of schizophrenia is largely due to advances in in vivo MRI techniques. These advances have now led to the identification of a number of brain abnormalities in schizophrenia. Some of these abnormalities confirm earlier post-mortem findings, and most are small and subtle, rather than large, thus necessitating more advanced and accurate measurement tools. These findings include ventricular enlargement (80% of studies reviewed) and third ventricle enlargement (73% of studies reviewed). There is also preferential involvement of medial temporal lobe structures (74% of studies reviewed), which include the amygdala, hippocampus, and parahippocampal gyrus, and neocortical temporal lobe regions (superior temporal gyrus) (100% of studies reviewed). When gray and white matter of superior temporal gyrus was combined, 67% of studies reported abnormalities. There was also moderate evidence for frontal lobe abnormalities (59% of studies reviewed), particularly prefrontal gray matter and orbitofrontal regions. Similarly, there was moderate evidence for parietal lobe abnormalities (60% of studies reviewed), particularly of the inferior parietal lobule which includes both supramarginal and angular gyri. Additionally, there was strong to moderate evidence for subcortical abnormalities (i.e. cavum septi pellucidi-92% of studies reviewed, basal ganglia-68% of studies reviewed, corpus callosum-63% of studies reviewed, and thalamus-42% of studies reviewed), but more equivocal evidence for cerebellar abnormalities (31% of studies reviewed). The timing of such abnormalities has not yet been determined, although many are evident when a patient first becomes symptomatic. There is, however, also evidence that a subset of brain abnormalities may change over the course of the illness. The most parsimonious explanation is that some brain abnormalities are neurodevelopmental in origin but unfold later in development, thus setting the stage for the development of the symptoms of schizophrenia. Or there may be additional factors, such as stress or neurotoxicity, that occur during adolescence or early adulthood and are necessary for the development of schizophrenia, and may be associated with neurodegenerative changes. Importantly, as several different brain regions are involved in the neuropathology of schizophrenia, new models need to be developed and tested that explain neural circuitry abnormalities effecting brain regions not necessarily structurally proximal to each other but nonetheless functionally interrelated. (ABSTRACT TRUNCATED)

Neurochemical investigation of the schizophrenic brain by in vivo phosphorus magnetic resonance spectroscopy

Abnormal phospholipid metabolisms may play important roles in the pathophysiology of schizophrenia. Phosphorus magnetic resonance spectroscopy (31P-MRS) offers a new method for studying phosphorus-related metabolism in vivo. A decrease in the level of phosphomonoesters (PME) and an increase in the level of phosphodiesters (PDE) has been demonstrated in the prefrontal lobe of neuroleptic-naive schizophrenic patients. Most of the studies in medicated schizophrenic patients have shown decreased PME and/or increased PDE. The decreased PME in the frontal lobe appears to be associated with negative symptoms and poor working memory performance. 1H-decoupled 31P-MRS revealed a reduction in the phosphocholine element of PME and an elevation in the mobile phospholipids of PDE in the prefrontal region of medicated schizophrenic patients. PDE were elevated in the temporal lobes of neuroleptic-naive schizophrenic patients, and this increase was partially normalized by haloperidol administration. Data about the temporal lobes of medicated schizophrenic patients have not been consistent. Except for the reduction in the adenosine triphosphate (ATP) in the basal ganglia and the correlation between the increase in the frontal lobe phosphocreatine (PCr) and negative symptomatology, data related to changes in high-energy phosphates are contradictory. No consensus on the effect of neuroleptics on phosphorus metabolites has been achieved. Methodological problems inherent in 31P-MRS may have contributed to the confusion in understanding available data. Future directions of MRS studies are suggested in the last section of the paper.

The timing of neurodevelopmental abnormality in schizophrenia: an integrative review of the neuroimaging literature

In this paper we will review recent neuroimaging research in schizophrenia, with an aim to critically evaluate several recent proposals concerning the nature and the timing of the neuroanatomic abnormalities underlying the disorder. Specifically, enlargement of cerebrospinal fluid spaces, deficits in cortical gray matter, and reduced volume of mesiotemporal structures have all been reported in patients in the first episode of schizophrenia, their first-degree relatives, and individuals with schizotypal personality disorder, supporting the possibility that these abnormalities reflect a genetically mediated neurodevelopmental disorder. These findings from the empirical literature will be synthesized from the perspective of dual cytoarchitectonic trends theory of neurodevelopment, as well as in relation to current conceptions of the schizophrenia prodrome. We believe that the evidence shows that sufficient groundwork has been laid to begin longitudinal neuroimaging studies of adolescents at clinical risk for schizophrenia, in order to more definitively determine the pathophysiology of the disorder. Such information could have significant implications in terms of understanding the prediction, treatment, and ultimately the prevention of schizophrenia.

The effect of treatment with antipsychotic drugs on brain N-acetylaspartate measures in patients with schizophrenia

BACKGROUND

The specific intracellular effects of antipsychotic drugs are largely unknown. Studies in animals have suggested that antipsychotics modify the expression of various intraneuronal proteins, but no analogous in vivo data in humans are available. The objective of the present study was to assess whether antipsychotics modify N-acetylaspartate (an intraneuronal marker of neuronal functional integrity) measures in brains of patients with schizophrenia.

METHODS

We used proton magnetic resonance spectroscopic imaging to study 23 patients with schizophrenia (DSM-IV diagnosis) using a within-subject design. Patients were studied twice: once while on a stable regimen of antipsychotic drug treatment (for at least 4 weeks) and once while off medication for at least 2 weeks. Several cortical and subcortical regions were assessed, including the dorsolateral prefrontal cortex and the hippocampal area.

RESULTS

Analysis of variance showed that, while on antipsychotics, patients had significantly higher N-acetylaspartate measures in the dorsolateral prefrontal cortex (p =.002). No other region showed any significant effect of treatment.

CONCLUSIONS

These results indicate that antipsychotic drugs increase N-acetylaspartate measures selectively in the dorsolateral prefrontal cortices of patients with schizophrenia, suggesting that these drugs modify in a regionally specific manner the function of a population of cortical neurons. N-Acetylaspartate measures may provide a useful tool to further investigate the effects of antipsychotics at the intracellular level.

Neural models of schizophrenia

Hallucinations and delusions - two diagnostic features of psychosis shared across the spectrum of heterogeneous schizophrenia constructs - can be described in terms of the pathophysiology of sensory information processing: hallucination is the impaired ability to classify representations as internally or externally generated, while delusion is the immutable linking of representations with each other in the absence of external dependency. The key anatomical systems in higher-order information processing are the cortex, thalamus, basal ganglia, and medial temporal lobe, each of which is modulated by neurotransmitter projection systems. Preliminary evidence, concentrating to date on the dorsolateral prefontal cortex, thalamus, and hippocampal region of the medial temporal lobe, points to neural circuitry dysfunction within and between each system in psychosis. This may account for specific symptoms and associated cognitive deficits such as memory impairment, attention deficit, and language disturbance.

Schizophrenia: vulnerability versus disease

One of the most important trends in the treatment of schizophrenia involves its early diagnosis and intervention. The ultimate goal of research is the prevention of the disorder, A major impediment to the development of prevention strategies, however, is that we do not yet know what the liability for schizophrenia is before the onset of psychosis. Consequently, early treatment attempts are focused on the “prodrome,” which involves the early symptoms of psychosis. In a companion paper, we recently suggested that prevention work should focus not only on the prodrome, but also on “schizotaxia,” which is a clinically meaningful condition that may reflect the vulnerability to schizophrenia in the absence of psychosis. Because schizotaxia can be assessed prior to the prodrome, studies of schizotaxia might lead to more effective prevention programs. We continue the characterization of schizotaxia in this paper by focusing on the etiological roots of schizotaxia, plus its likely neurodevelopmental course, clinical expression, and treatment. Finally, the importance of including neurobiological variables in the conceptualization and eventual diagnosis of schizotaxia is reviewed.

Magnetic resonance spectroscopy in schizophrenia: methodological issues and findings--part II

Magnetic resonance spectroscopy allows investigation of in vivo neurochemical pathology of schizophrenia. "First generation" studies, focusing on phosphorus and proton magnetic resonance spectroscopy, have suggested alterations in membrane phospholipid metabolism and reductions in N-acetyl aspartate in the frontal and temporal lobes. Some discrepancies remain in the literature, perhaps related to the variations in medication status and phase of illness in the patients examined, as well as in magnetic resonance spectroscopy methodology; the pathophysiologic significance of the findings also remains unclear. Technologic advances in magnetic resonance spectroscopy in recent years have expanded the potential to measure several other metabolites of interest such as the neurotransmitters glutamate and gamma-aminobutyric acid and macromolecules such as membrane phospholipids and synaptic proteins. Issues of sensitivity, specificity, measurement reliability, and functional significance of the magnetic resonance spectroscopy findings need to be further clarified. The noninvasive nature of magnetic resonance spectroscopy allows longitudinal studies of schizophrenia both in its different phases and among individuals at genetic risk for this illness. Future studies also need to address confounds of prior treatment and illness chronicity, take advantage of current pathophysiologic models of schizophrenia, and be hypothesis driven.

Proton magnetic resonance spectroscopy of the human brain in schizophrenia

In vivo proton magnetic resonance spectroscopy (1H MRS) has been utilized by neuroimaging laboratories in recent years to reliably measure compounds such as N-acetylaspartate (NAA), choline (Cho), creatine (Cr), and to a lesser extent glutamate and glutamine in the human brain. To date, the most consistently replicated findings in schizophrenia are reduced NAA measures in the hippocampal regions. Since NAA is thought to be a neuronal/axonal marker and a measure of neuronal/axonal integrity, hippocampal NAA reductions have been interpreted as strong evidence for neuronal/axonal loss or dysfunction in this brain region. The evidence for neuronal loss or dysfunction based on NAA is less consistent for the frontal cortex and white matter, temporal cortex, basal ganglia, cingulate region, and thalamus in schizophrenia. Furthermore, there are no consistently replicated findings for choline or creatine alterations in any of the brain regions examined in schizophrenia. Finally, significant technical difficulties make reliable measurement of glutamine and glutamate problematic at the present time.

Search for schizophrenia susceptibility genes

Identification of a gene or genes that contribute to the development of schizophrenia, a complex psychiatric disorder, may be possible through genetic linkage analysis. Although to date no single causative gene has been identified, several chromosomal loci have shown positive linkage results and are under investigation as tentative schizophrenia susceptibility loci. Despite such obstacles as locus heterogeneity among sample populations, epistatic inheritance models, and failure to obtain statistical significance in studies, patterns have emerged that focus research efforts on chromosomes 13, 8, 22, and 6 and 10. Initial heterogeneity analyses suggests that identifiable subgroups of the families may not contribute equally to these linkage findings. Findings on several additional chromosomes await further replication. Future progress in the search for schizophrenia susceptibility genes will require collaboration among researchers from both academia and industry.

Magnetic resonance spectroscopy and schizophrenia: what have we learnt?

OBJECTIVE

Magnetic resonance spectroscopy (MRS) has been increasingly used to investigate the in vivo biochemistry of particular regions of the brain in patients with schizophrenia. We review the literature and discuss the theoretical constructs that form the presumed impetus for these studies in light of the current methodological limitations. Future directions are noted.

METHOD

The available published literature in English formed the basis for this review.

RESULTS

The results of 31P-MRS have been interpreted as reflecting a relative increase in cell membrane degradation in prefrontal cortical regions at certain phases of schizophrenia. 1H-MRS studies, though less consistent, provide evidence suggestive of a decrease in neuronal cell mass in the hippocampal region, which supports the findings of volumetric studies. Both groups of MRS studies support a neuro-developmental hypothesis of brain dysfunction in schizophrenia. However, current methodological problems limit the reliable interpretation of MRS data. A clear understanding of the methodology and its reliable interpretation is yet to emerge.

CONCLUSIONS

MRS remains a research instrument that is yet to be fully utilised in schizophrenia research. A few replicated findings are emerging, although the interpretation of these spectroscopic findings needs to be validated.

Familial transmission of risk factors in the first-degree relatives of schizophrenic people

Schizophrenia is a complex illness with multiple pathophysiologic factors that contribute to its psychopathology. One strategy to identify these factors is to observe them in isolation from each other, by characterizing their expression in the relatives of schizophrenic probands. By Mendel's second law, each genetic factor should be independently distributed in a sibship, so that each can be observed by itself, uncomplicated by the general problems of the illness. Such independently distributed phenotypes are obviously useful for genetic analyses; however, they can also be considered together, to model how various brain dysfunctions may combine to produce psychoses. In addition to a sensory gating deficit linked to the alpha 7-nicotinic acetylcholine receptor locus, schizophrenics and their families have a number of other deficits, including decreased hippocampal volume on magnetic resonance images and increased plasma levels of the dopamine metabolite homovanillic acid. Although such research is far from complete, a heuristic model combining a sensory gating deficit, decreased hippocampal neuron capacity, and increased dopaminergic neurotransmission is consonant with current understanding of the neuropsychology of schizophrenia.

Subtype-associated metabolite differences in the temporal lobe in schizophrenia detected by proton magnetic resonance spectroscopy

Brain imaging studies have indicated that the medial temporal lobe functions aberrantly in schizophrenic patients. Both diagnostic subtype and gender may affect functional and morphologic abnormalities in this region. We investigated subtype- and gender-associated differences in metabolites in the left medial temporal lobe in 40 medicated schizophrenic patients by proton magnetic resonance spectroscopy and compared findings with those in 40 healthy control subjects. Peaks corresponding to N-acetylaspartate (NAA), choline-containing compounds (Cho), creatine-phosphocreatine (Cr), and inositol were measured. Schizophrenic patients showed a decrease in the NAA/Cr ratio in the left medial temporal lobe, and patients with the disorganized subtype of illness showed significantly lower NAA/Cr and Cho/Cr ratios than those with paranoid schizophrenia. The NAA/Cr ratio in patients with the undifferentiated subtype also was significantly lower than in the paranoid subtype. No significant associations were observed between metabolite ratios and clinical symptom scores, age at onset of illness, or gender. These findings suggest that patients with the disorganized and undifferentiated subtypes have greater impairments in neuronal integrity or function in the left medial temporal lobe than patients with other subtypes of schizophrenia.

New insights on the neuroanatomy of schizophrenia

Recent ideas and research evidence about the neuroanatomy of schizophrenia come to us from diverse sources. These include 1) conventional (magnetic resonance imaging morphometry); 2) novel (diffusion tensor imaging) structural anatomic techniques; 3) information on patterns of anatomic changes from longitudinal anatomic studies; 4) illumination of functional connectivity and pathway anomalies associated with the disorder; 5) family studies on the distribution of anatomic abnormalities within affected and unaffected family members; and 6) anatomic distributions of neurotransmitters and their receptors, as well as their response to drugs used to treat the disorder. Taken together, these new data provide an exciting look at the direction in which the field is headed.

Thalamic and amygdala-hippocampal volume reductions in first-degree relatives of patients with schizophrenia: an MRI-based morphometric analysis

BACKGROUND

Schizophrenia is characterized by subcortical and cortical brain abnormalities. Evidence indicates that some nonpsychotic relatives of schizophrenic patients manifest biobehavioral abnormalities, including brain abnormalities. The goal of this study was to determine whether amygdala-hippocampal and thalamic abnormalities are present in relatives of schizophrenic patients.

METHODS

Subjects were 28 nonpsychotic, and nonschizotypal, first-degree adult relatives of schizophrenics and 26 normal control subjects. Sixty contiguous 3 mm coronal, T1-weighted 3D magnetic resonance images of the brain were acquired on a 1.5 Tesla magnet. Cortical and subcortical gray and white matter and cerebrospinal fluid (CSF) were segmented using a semi-automated intensity contour mapping algorithm. Analyses of covariance of the volumes of brain regions, controlling for expected intellectual (i.e., reading) ability and diagnosis, were used to compare groups.

RESULTS

The main findings were that relatives had significant volume reductions bilaterally in the amygdala-hippocampal region and thalamus compared to control subjects. Marginal differences were noted in the pallidum, putamen, cerebellum, and third and fourth ventricles.

CONCLUSIONS

Results support the hypothesis that core components of the vulnerability to schizophrenia include structural abnormalities in the thalamus and amygdala-hippocampus. These findings require further work to determine if the abnormalities are an expression of the genetic liability to schizophrenia.

Neuropsychiatric dynamics: the study of mental illness using functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) is poised to make significant contributions to the study of neuropsychiatric illnesses. Whatever neural pathology attends such illnesses has proven subtle at best. By identifying predictable, regionally specific deficits in brain function, fMRI can suggest brain regions for detailed cellular analyses, provide valuable in vivo data regarding effective connectivity, provide a means to model the effects of various drug challenge paradigms, and characterize intermediate phenotypes in the search for the genes underlying mental illness. Nonetheless, as promising as fMRI appears to be in terms of its relative safety, repeatability, ability to generate individual brain maps and widespread availability, it is still subject to a number of unresolved conceptual conundrums inherited from earlier neuroimaging work. For example, functional neuroimaging has not generated any pathognomic findings in mental illness, has not established a clear link between neurophysiology and observable behavior, and has not resolved the potential confounds of medication. In this article, we will review the relevant historical background preceding fMRI, address methodological considerations in fMRI, and summarize recent fMRI findings in psychiatry. Finally, fMRI is being used to simplify the complex genetics of neuropsychiatric illness by generating quantitative and qualitative brain phenotypes.

Proton magnetic resonance spectroscopy in schizophrenia

Proton magnetic resonance spectroscopy (MRS) has become an important tool to study in vivo certain biochemical aspects of brain disorders. In the last decade this technique has been applied to the in vivo investigation of pathophysiological aspects of psychiatric disorders, extending knowledge of the related brain alterations. This review will focus on providing some background to clarify technical and biochemical issues and it will describe the studies that have been performed in schizophrenia. The results will be framed in a more general context to highlight what we have learned and what remains to be understood from the application of this technique to schizophrenia.

Cell biology of the hippocampal formation in schizophrenia

The hippocampal formation (HF) has been a centerpiece of neuropathologic investigations of schizophrenia. Numerous MRI studies have demonstrated a slight bilateral reduction in HF volume. Reports of reduced N-acetyl aspartate measured with in vivo proton spectroscopy suggest that neuronal pathology exists. However, morphometric data from postmortem studies have not revealed a clear change in HF size, and recent studies of neuronal number and of cytoarchitecture have been largely negative. Evidence of glial proliferation is consistently absent. The most reproducible positive anatomic finding in postmortem HF has been reduced size of neuronal cell bodies. Studies of gene transcription have provided replicable evidence of decreased expression of mRNAs for synaptophysin, GAP-43, cholecystokinin, and non-NMDA glutamate receptor subunits (GLU R 1 and 2), particularly in CA 3-4. These data about the cellular and molecular biology of the HF in schizophrenia are different from that found in a number of conditions associated with hippocampal damage, including excitotoxicity, epilepsy, alcoholism, Alzheimer's disease, steroid neurotoxicity, and normal aging. Notwithstanding the real possibility that the data are epiphenomena of chronic illness, the findings may implicate a unique cellular defect in schizophrenia--a genetic variation affecting the plasticity of HF circuitry and connectivity. Directions for further research are proposed.