Reduced gamma-amino butyric acid and elevated Glu/Gln complex in the anterior cingulate cortex of medicated schizophrenic patients
Pui Wai Chiu1, Queenie Chan2, Sai-yu Lui3, Karen Shee Yueng Hung3, Raja Rizal Azman Raja Aman4, Raymond Chor Kiu Chan5, Pak Chung Sham6, Eric Fuk Chi Cheung3, Richard A Edden7, and Henry Ka Fung Mak1

1Diagnostic Radiology, The University of Hong Kong, Hong Kong, Hong Kong, 2Philips Healthcare, Hong Kong, Hong Kong, Hong Kong, 3Institute of Mental Health, Castle Peak Hospital, Hong Kong, Hong Kong, 4Biomedical Imaging, University of Malaya, Kuala Lumpur, Malaysia, 5Neuropsychology and Applied Cognitive Neuroscience Laboratory, Chinese Academy of Sciences, Beijing, China, People's Republic of, 6Psychiatry, The University of Hong Kong, Hong Kong, Hong Kong, 7Radiology and Radiological Sciences, Johns Hopkins University, Baltimore, MD, United States

Synopsis

Gamma-amino butyric acid (GABA) is thought to play an important role in the pathophysiology of schizophrenia. The anterior cingulate cortex (ACC) has been reported to exhibit functional and morphological abnormalities in schizophrenic patients compared to healthy controls(HC). In this pilot study, absolute concentrations of GABA([GABA]abs) and Glx([Glx]abs) were measured in the ACC of 9 schizophrenic patients and 14 HC at 3.0T. Significant lower [GABA]abs level in ACC of schizophrenic patients might provide evidence of abnormalities in GABAergic neurotransmission in schizophrenia. Significant positive correlation between [Glx]abs and positive symptoms subscale might indicate Glx level is specific for positive symptoms in ACC.

Purpose

One of the plausible mechanisms of schizophrenia is the so-called “gamma-amino butyric acid (GABA)-ergic origin hypothesis”, which originates from the hypofunction of N-methyl-D-aspartate (NMDA)-type of glutamate (Glu) receptor.1 GABA, which is produced from Glu, is the chief inhibitory neurotransmitter and is thought to play an important role in the pathophysiology of schizophrenia.2 In vivo GABA can be measured non-invasively by proton magnetic resonance spectroscopy (1H-MRS), but unambiguous detection of GABA cannot be accomplished by conventional pulse sequences due to the overlapping of resonance peaks of GABA with other detectable metabolites. Yet, with the advent of technology, a MEGA-PRESS pulse sequence was developed to detect GABA.3 Glu, on the other hand, is the most importantly excitatory neurotransmitter in the brain, whereas Gln is the precursor and reaction product of Glu in the Glu/Gln cycle. Glx (summation of Glu and Gln) could access the entire brain pool of Glu and Gln. The anterior cingulate cortex (ACC) has been reported to exhibit morphological change in schizophrenia and activation deficits during cognitive tasks. More importantly, a prior study reported that levels of glutamic acid decarboxylase (GAD), which is a key enzyme in GABA synthesis, was found to be significantly reduced in schizophrenic patients compared with healthy controls (HC).4 In this pilot study, absolute concentrations of GABA, Glx, and other metabolites including N-acetyl-aspartate (NAA), choline (Cho) and creatine (Cr), were measured in the ACC of 9 medicated schizophrenic patients and 14 HC using 1H-MRS at 3T.

Methods

9 schizophrenic patients who were effectively treated on a stable medication regimen (mean age=26.89±6.03 years; 5M4F; treatment duration ranging from 2-34 months) were recruited in this study. Of the 9 schizophrenic patients, 6 of them were of positive schizophrenia. 14 HC (mean age=27.64±5.93 years, 8M6F) were also recruited. All subjects underwent MR scan using 3.0T Achieva TX scanner, Philips Healthcare. MEGA-PRESS (TR/TE = 2000/68 ms; 320 signal averages) was used as volume selection method with single voxel of 3x3x3cm3 placed in the ACC for GABA measurement. PRESS (TR/TE = 2000/39 ms) with 2x2x2cm3 voxel placed in the ACC was also used for measurement of other metabolites, i.e. Glx, NAA, Cho, and Cr. GABA was measured and quantified using internal water as reference by GANNET 2.0 (Figure 1). Glx, NAA, Cho, and Cr were measured and quantified with cerebrospinal fluid normalization using internal water as reference by QUEST in jMRUI (4.0). Two-sample t-test was used to investigate any differences in metabolite concentrations between schizophrenic patients and HC. Pearson correlation coefficient (r) was calculated to assess the correlation between metabolite concentrations and Positive and Negative Syndrome Scale (PANSS) subscales scores within the schizophrenic patients. SPSS version 20.0 was used for statistical analysis and level of significance was set at 0.05.

Results

Absolute concentration of GABA ([GABA]abs) was found to be significantly lower (p = 0.043) in schizophrenic patients (1.63 ± 0.20 mM) compared with HC (1.80 ± 0.14 mM), while absolute concentration of Glx ([Glx]abs) was found to be significantly higher (p = 0.022) in schizophrenic patients (13.98 ± 5.75 mM) compared with HC (9.77 ± 2.28 mM) (Figure 2). Within the 9 schizophrenic patients, [Glx]abs revealed a significant positive correlation with PANSS positive symptom subscale (r = 0.725, p = 0.027), but no significant correlation was found between [GABA]abs and PANSS positive or negative symptom subscales. In addition, the schizophrenic patients’ [GABA]abs and [Glx]abs has no significant correlation but a negative trend (r = -0.592, p = 0.093) was found.

Discussion

In this study, significant lower [GABA]abs level in the ACC of schizophrenic patients might provide evidence of abnormalities in GABAergic neurotransmission in schizophrenia. This finding might further complement the reduced levels of GAD shown in a prior study as GAD is an enzyme essential for GABA synthesis from Glu.1 Elevations of [Glx]abs in schizophrenic patients might probably reflect the dysfunction of NMDA receptors. We postulated that the elevated [Glx]abs might be due to increase in Glu in the synaptic cleft owing to a paucity or hypofunctioning of NMDA receptors.1 Although the behavioral effects of NMDA receptor hypofunction include both positive and negative symptoms,5 the significant positive correlation between [Glx]abs and PANSS positive subscale might indicate Glx level is specific for positive symptoms in the ACC, while lack of significant correlation between GABA and negative symptoms might be due to a limited number of negative schizophrenic patients in our study.

Conclusion

This pilot study provided evidence of abnormalities in GABAergic neurotransmission in schizophrenia in the ACC. Glx level might be specific for positive symptoms in schizophrenia.

Acknowledgements

No acknowledgement found.

References

1. Nagazawa K, Zsiros V, Jiang Z, et al. GABAergic interneuron origin of schizophrenia pathophysiology. Neuropharmacology. 2012;62: 1574-1583.

2. Wassef A, Baker J, Kochan LD. GABA and schizophrenia: a review of basic science and clinical studies. J. Clin. Psychopharmacol. 2003;23(6):601–640.

3. Edden RA, Barker PB. Spatial effects in the detection of gamma-aminobutyric acid: improved sensitivity at high fields using inner volume saturation. Magn Reson Med. 2007;58:1276–1282.

4. Woo TUW, Walsh JP, Benes FM. Density of Glutamic Acid Decarboxylase 67 Messenger RNA-Containing Neurons That Express the N-Methyl-D-Aspartate Receptor Subunit NR2A in the Anterior Cingulate Cortex in Schizophrenia and Bipolar Disorder. Arch Gen Psychiatry. 2004;61(7):649–657.

5. Buchanan RW, Javitt DC, Marder SR, et al. The Cognitive and Negative Symptoms in Schizophrenia Trial (CONSIST): the efficacy of glutamatergic agents for negative symptoms and cognitive impairments. Am J Psychiatry 2007;164(10):1593-1602.

Figures

Figure 1. (a) Position of voxel placed in the anterior cingulate cortex for GABA measurement using MEGA-PRESS. (b) GABA quantification using GANNET.

Figure 2. Scatter plots of (a) [GABA]abs, and (b) [Glx]abs, in schizophrenic patients and healthy controls.



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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