Alterations of membrane phospholipid metabolism in patients with schizophrenia assessed by phosphorus magnetic resonance spectroscopy

Applications of Magnetic Resonance Spectroscopy to Psychiatry

The inaccessibility of the human brain to biochemical studies has historically challenged the ability of in vestigators to elucidate the pathophysiology of psychiatric syndromes. Magnetic resonance spectroscopy (MRS) now provides a noninvasive means of assessing neurochemistry in vivo. Since the first application of the technique to the study of the human brain, many new advances have been made. This new technology broadens the applications of the MRS. The major principles of the technique and compounds currently available for study are discussed in this article. A brief review of current and future applications of the technology to the field of psychiatry are discussed. NEUROSCIENTIST 5:192-196, 1999

Event-related potential correlates of impaired visuospatial working memory in schizophrenia

Previous studies have reported that patients with schizophrenia demonstrate impaired performance during working memory (WM) tasks. The current study aimed to determine whether WM impairments in schizophrenia are accompanied by reduced slow wave (SW) activity during on-line maintenance of mnemonic information. Event-related potentials were obtained from patients with schizophrenia and well controls as they performed a visuospatial delayed response task. On 50% of trials, a distractor stimulus was introduced during the delay. Compared with controls, patients with schizophrenia produced less SW memory negativity, particularly over the right hemisphere, together with reduced frontal enhancement of SW memory negativity in response to distraction. The results indicate that patients with schizophrenia generate less maintenance phase neuronal activity during WM performance, especially under conditions of distraction.

Intrinsic excitatory connections in the prefrontal cortex and the pathophysiology of schizophrenia

Working memory, a fundamental cognitive process that is disturbed in schizophrenia, appears to depend upon the sustained activity of specific populations of neurons in the prefrontal cortex. Understanding the neural mechanism(s) that may contribute to the sustained activity of these neurons represents a critical step in predicting the types of alterations in prefrontal circuitry that may be present in schizophrenia, and in determining how such alterations may contribute to the cognitive symptoms of this disorder. This article reviews recent findings which suggest that intrinsic horizontal connections among pyramidal neurons in layer 3 of the dorsolateral prefrontal cortex may provide a critical anatomical substrate for working memory processes, and that alterations in these connections may account for the observations of disturbed working memory, adolescence-related onset of clinical features, and certain pathological changes in the prefrontal cortex of subjects with schizophrenia.

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.

Frontal lobe in vivo (31)P-MRS reveals gender differences in healthy controls, not in schizophrenics

Phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS) has gained much interest in schizophrenia research in recent years since it allows the non-invasive measurement of high-energy phosphates and phospholipids in vivo. However, until now only differences in metabolite concentrations between certain brain areas of schizophrenic patients and healthy controls have been examined. We investigated the influence of gender on the concentrations of different phosphorus compounds. For this purpose, well-defined volumes in the frontal lobe of 32 healthy controls and 51 schizophrenic in-patients were examined with an image selected in vivo spectroscopy (ISIS) sequence on a whole-body scanner at 1.5 T. Healthy females exhibited increased values of inorganic phosphate (P(i)) and decreased values of phosphocreatine (PCr) in comparison to their male counterparts. In schizophrenic patients such gender differences were not present. Thus, the results can be interpreted in the sense that frontal energy demanding processes are enhanced in female compared to male healthy volunteers; schizophrenia seems to reduce these gender differences.

Altered GABA neurotransmission and prefrontal cortical dysfunction in schizophrenia

Dysfunction of the dorsolateral prefrontal cortex appears to be a central feature of the pathophysiology of schizophrenia, and this dysfunction may be related to alterations in gamma aminobutyric acid (GABA) neurotransmission. Determining the causes and consequences of altered GABA neurotransmission in schizophrenia, and the relationship of these changes to other abnormalities in prefrontal cortical circuitry, requires an understanding of which of the multiple subpopulations of cortical GABA neurons are affected. The chandelier class of GABA neurons, especially those located in the middle layers of the prefrontal cortex (PFC), have been hypothesized to be preferentially involved in schizophrenia because they 1) receive direct synaptic input from dopamine axons, 2) exert powerful inhibitory control over the excitatory output of layer 3 pyramidal neurons, and 3) undergo substantial developmental changes during late adolescence, the typical age of onset of schizophrenia. Consistent with this hypothesis, the axon terminals of chandelier neurons, as revealed by immunoreactivity for the GABA membrane transporter, are reduced substantially in the middle layers of the PFC in schizophrenic subjects. This alteration appears to be selective for the chandelier class of GABA neurons and for the disease process of schizophrenia. These findings provide insight into the pathophysiologic mechanisms underlying prefrontal cortical dysfunction in schizophrenia, and they reveal new targets for therapeutic intervention in this illness.

Multiple regression analysis of relationship between frontal lobe phosphorus metabolism and clinical symptoms in patients with schizophrenia

We investigated the differences among diagnostic types of 36 schizophrenic patients in the brain phosphorus metabolism in the frontal lobe. We performed phosphorus-31 magnetic resonance spectroscopy (31P-MRS) in the frontal region in patients with schizophrenia of the catatonic (n = 4), disorganized (n = 8), paranoid (n = 10) and undifferentiated (n = 14) types. In the disorganized type, the PME level was significantly decreased compared to those in the other three types, while the phosphodiester (PDE) level tended to be higher, although not significantly, than those in the other types. Using multiple regression analysis, we investigated whether or not the clinical symptoms were correlated with the brain phosphorus metabolism. An increased motor retardation factor score was significantly correlated with decreased PME level, whereas more severe emotional withdrawal and blunted affect were associated with increased PDE level. These results suggest that altered membrane phospholipid metabolism in the frontal region may be associated with negative symptoms and that schizophrenia of the disorganized type is associated with more severe negative symptoms and may present more severe brain abnormalities compared to the other types.