Alterations of muscarinic and GABA receptor binding in the posterior cingulate cortex in schizophrenia

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Abstract

The posterior cingulate cortex (PCC), a key component of the limbic system, has been implicated in the pathology of schizophrenia because of its sensitivity to NMDA receptor antagonists. Recent studies have shown that the PCC is dysfunctional in schizophrenia, and it is now suspected to be critically involved in the pathogenesis of schizophrenia. Studies also suggest that there are abnormalities in muscarinic and GABAergic neurotransmission in schizophrenia. Therefore, in the present study we used quantitative autoradiography to investigate the binding of [3H]pirenzepine, [3H]AF-DX 384 and [3H]muscimol, which respectively label M1/4 and M2/4 muscarinic and GABAA receptors, in the PCC of schizophrenia and control subjects matched for age and post-mortem interval. The present study found that [3H]pirenzepine binding was significantly decreased in the superficial (− 24%, p = 0.002) and deep (− 35%, p < 0.001) layers of the PCC in the schizophrenia group as compared with the control group. In contrast, a dramatic increase in [3H]muscimol binding was observed in the superficial (+ 112%, p = 0.001) and deep layers (+ 100%, p = 0.017) of the PCC in the schizophrenia group. No difference was observed for [3H]AF-DX 384 binding between the schizophrenia and control groups. The authors found a significant inverse correlation between [3H]pirenzepine binding in the deep cortical layers and [3H]muscimol binding in the superficial layers (rho =  0.732, p = 0.003). In addition, negative correlations were also found between age and [3H]pirenzepine binding in both superficial and deep cortical layers (rho =  0.669 p = 0.049 and rho =  0.778, p = 0.014), and between age of schizophrenia onset and [3H]AF-DX 384 binding (rho =  0.798, p = 0.018). These results for the first time demonstrated the status of M1/M4, M2/M4 and GABAA receptors in the PCC in schizophrenia. Whilst the exact mechanism causing these alterations is not yet known, a possible increased acetylcholine and down regulated GABA stimulation in the PCC of schizophrenia is suggested.

Introduction

The posterior cingulate cortex (PCC), part of the corticolimbic system, is a brain area involved in memory, spatial orientation, and monitoring of eye movements (Vogt et al., 1992). Functional MRI data have shown that the PCC is a site of pathology in schizophrenia, as demonstrated by: 1) impaired posterior cingulate cortex functionality in a semantic task which relates to verbal memory deficits that are frequently observed in schizophrenia patients (Tendolkar et al., 2004); 2) an inability of schizophrenia patients to produce an increase in blood flow to the posterior cingulate in response to a recognition memory test, compared to healthy volunteers (Crespo-Facorro et al., 2001); and 3) a reduction in metabolic rate and volume in this region in schizophrenia patients compared to the controls (Haznedar et al., 2004, Mitelman et al., 2004). Furthermore, animal studies have shown that NMDA antagonists can selectively damage the PCC (Olney and Farber, 1995), and that this damage can be attenuated by gamma-aminobutyric acid A (GABAA) receptor agonists as well as anticholinergic drugs such as scopolamine and benztropine (Olney et al., 1991). This suggests that the muscarinic and GABAergic systems may play a role in NMDA antagonist-induced neurotoxicity in the PCC.

Muscarinic receptors are associated with cognition, attention, memory and motor control (Hyde and Crook, 2001), functions that are altered in schizophrenia. There are 5 muscarinic cholinergic receptors and all are G-protein coupled. Muscarinic receptors of the M1 subtype are primarily localised postsynaptically and are the most abundant of the muscarinic receptors in the cortex (Volpicelli and Levey, 2004). In contrast, M2 receptors are predominantly located presynaptically at the axonal terminals of the cholinergic neurons, where they inhibit acetylcholine release (Mash et al., 1985). M4 receptors have been shown to be postsynaptic in the cortex (Billard et al., 1995). Recently our group and others have found reduced M1 and M2 receptor binding in a region-specific manner in schizophrenia (Crook et al., 1999, Crook et al., 2000, Crook et al., 2001, Dean et al., 1996, Dean et al., 2004, Deng and Huang, 2005, Katerina et al., 2004, Zavitsanou et al., 2005).

GABA is the major inhibitory neurotransmitter in the brain. There are two receptors that mediate GABA neurotransmission in the brain; GABAA and GABAB. GABAA receptors are ligand gated chloride ion channels (Steiger and Russek, 2004). GABA was originally implicated in schizophrenia when low cerebrospinal fluid GABA levels were found in schizophrenia patients (van Kammen et al., 1980). Since then, studies have continued to provide strong evidence of GABAergic hypofunction in the schizophrenia brain. Decreased mRNA expression of the 67 kDa isoform of glutamate decarboxylase (GAD67), the enzyme responsible for synthesizing GABA, has been reported in the dorsolateral prefrontal cortex in schizophrenia (Akbarian et al., 1995), and reductions in GABA in nucleus accumbens and thalamus have also been found in schizophrenia (Perry et al., 1979). Furthermore, reductions in GABA uptake sites have been reported in prefrontal cortex, amygdala, and hippocampus in schizophrenia (Reynolds et al., 1990, Simpson et al., 1989).

In view of the above evidence, the present study examined the hypothesis that muscarinic and GABA receptors are altered in the posterior cingulate cortex in schizophrenia. Using quantitative autoradiography, we compared the binding of [3H]pirenzepine, [3H]AF-DX 384, and [3H]muscimol to M1/4, M2/4 and GABAA receptors in the posterior cingulate cortex of schizophrenia subjects and matched controls.

Section snippets

Post-mortem brain tissue

Human brain tissue from the PCC (left hemisphere) was obtained from the New South Wales Tissue Resource Centre at the University of Sydney. Ethical approval for this study was granted by the University of Wollongong Human Research Ethics Committee (Approval No. HE99/22). Ten male subjects without a known history of psychiatric illness and ten male subjects with a diagnosis of schizophrenia, matched for age and post-mortem interval (PMI), were used in this study (Table 1). Subjects were excluded

Laminar distribution of [3H]pirenzepine, [3H]AF-DX 384, and [3H]muscimol binding in the PCC

Specific binding of [3H]pirenzepine, [3H]AF-DX 384 and [3H]muscimol was observed in all cortical layers of the PCC and was > 95% of total binding for all the three ligands. [3H]pirenzepine appeared to display the highest density of binding sites followed by [3H]AF-DX 384. [3H]muscimol displayed the lowest density of binding sites.

Binding sites labelled by these ligands appeared to have differential distribution patterns among the layers of the PCC. The principal laminar patterns of each ligand

Discussion

The present study investigated the binding of the acetylcholine muscarinic receptor antagonists [3H]pirenzepine and [3H]AF-DX 384, and the GABAA receptor antagonist [3H]muscimol in the PCC of subjects with schizophrenia. These radioligands bind to M1/M4, M2/M4, and GABAA receptors respectively. A significant down-regulation of M1/M4 muscarinic receptors and an upregulation of GABAA receptors was observed in the PCC in schizophrenia. No changes in M2/M4 receptor density were observed between the

Conclusion

In conclusion, the decrease in M1 receptor density and the increase in GABAA receptor density in schizophrenia suggest an involvement of these two systems in the pathology of the PCC in schizophrenia. It is suggested that these changes are the result of increased cortical acetylcholine and decreased cortical GABA. The observed changes may be due to NMDA receptor hypofunction in this region. However, further research is needed to determine the mechanism of these changes, and the examination of a

Acknowledgements

This work was supported by the St. George Foundation, and the Neuroscience Institute of Schizophrenia and Allied Disorders (NISAD) utilising the infrastructure funding from NSW Health. Post-mortem brain tissues were received from the NSW Tissue Resource Centre, which is supported by the University of Sydney, NISAD, National Institute of Alcohol Abuse and Alcoholism and NSW Department of Health. The Beta Imager was provided with funds raised by the Wollongong Lord Mayor's Schizophrenia Awareness

References (53)

  • H. Moore et al.

    Role of accumbens and cortical dopamine receptors in the regulation of cortical acetylcholine release

    Neuroscience

    (1999)
  • T.L. Perry et al.

    Gamma-aminobutyric-acid deficiency in brain of schizophrenic patients

    Lancet

    (1979)
  • M. Piggott et al.

    Comparative distribution of binding of the muscarinic receptor ligands pirenzepine, AF-DX 384, (R,R)-I-QNB and (R,S)-I-QNB to human brain

    J Chem Neuroanat

    (2002)
  • T.J. Raedler et al.

    In vivo olanzapine occupancy of muscarinic acetylcholine receptors in patients with schizophrenia

    Neuropsychopharmacology

    (2000)
  • G.P. Reynolds et al.

    Deficit and hemispheric asymmetry of GABA uptake sites in the hippocampus in schizophrenia

    Biol Psychiatry

    (1990)
  • M.D. Simpson et al.

    Reduced GABA uptake sites in the temporal lobe in schizophrenia

    Neurosci Lett

    (1989)
  • J.L. Steiger et al.

    GABAA receptors: building the bridge between subunit mRNAs, their promoters, and cognate transcription factors

    Pharmacol Ther

    (2004)
  • I. Tendolkar et al.

    Evidence for a dysfunctional retrosplenial cortex in patients with schizophrenia: a functional magnetic resonance imaging study with a semantic-perceptual contrast

    Neurosci Lett

    (2004)
  • D.P. van Kammen et al.

    Schizophrenia: low spinal fluid GABA levels?

    Brain Res Bull

    (1980)
  • M.T. Vilaro et al.

    Muscarinic M2 receptor mRNA expression and receptor binding in cholinergic and non-cholinergic cells in the rat brain: a correlative study using in situ hybridization histochemistry and receptor autoradiography

    Neuroscience

    (1992)
  • L.A. Volpicelli et al.

    Muscarinic acetylcholine receptor subtypes in cerebral cortex and hippocampus

    Prog Brain Res

    (2004)
  • K. Zavitsanou et al.

    M2/M4 muscarinic receptor binding in the anterior cingulate cortex in schizophrenia and mood disorders

    Brain Res Bull

    (2005)
  • K. Zilles et al.

    Quantitative autoradiography of 11 different transmitter binding sites in the basal forebrain region of the rat—evidence of heterogeneity in distribution patterns

    Neuroscience

    (1991)
  • M. Zink et al.

    Differential effects of long-term treatment with clozapine or haloperidol on GABAA receptor binding and GAD67 expression

    Schizophr Res

    (2004)
  • S. Akbarian et al.

    Gene expression for glutamic acid decarboxylase is reduced without loss of neurons in prefrontal cortex of schizophrenics

    Arch Gen Psychiatry

    (1995)
  • American Psychiatric Association, A.P

    Diagnostic and statistical manual of mental disorders: DSM-IV, 4

    (1994)
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