Increases in [³H]Muscimol and [³H]Flumazenil Binding in the Dorsolateral Prefrontal Cortex in Schizophrenia Are Linked to α4 and γ2S mRNA Levels Respectively

<div><h3>Background</h3><p>GABA_A receptors (GABA_AR) are composed of several subunits that determine sensitivity to drugs, synaptic localisation and function. Recent studies suggest that agonists targeting selective GABA_AR subunits may have therapeutic value against the cognitive impairments observed in schizophrenia. In this study, we determined whether GABA_AR binding deficits exist in the dorsolateral prefrontal cortex (DLPFC) of people with schizophrenia and tested if changes in GABA_AR binding are related to the changes in subunit mRNAs. The GABA orthosteric and the benzodiazepine allosteric binding sites were assessed autoradiographically using [³H]Muscimol and [³H]Flumazenil, respectively, in a large cohort of individuals with schizophrenia (n = 37) and their matched controls (n = 37). We measured, using qPCR, mRNA of β (β1, β2, β3), γ (γ1, γ2, γ2S for short and γ2L for long isoform, γ3) and δ subunits and used our previous measurements of GABA_AR α subunit mRNAs in order to relate mRNAs and binding through correlation and regression analysis.</p> <h3>Results</h3><p>Significant increases in both [³H]Muscimol (p = 0.016) and [³H]Flumazenil (p = 0.012) binding were found in the DLPFC of schizophrenia patients. Expression levels of mRNA subunits measured did not show any significant difference in schizophrenia compared to controls. Regression analysis revealed that in schizophrenia, the [³H]Muscimol binding variance was most related to α4 mRNA levels and the [³H]Flumazenil binding variance was most related to γ2S subunit mRNA levels. [³H]Muscimol and [³H]Flumazenil binding were not affected by the lifetime anti-psychotics dose (chlorpromazine equivalent).</p> <h3>Conclusions</h3><p>We report parallel increases in orthosteric and allosteric GABA_AR binding sites in the DLPFC in schizophrenia that may be related to a “shift” in subunit composition towards α4 and γ2S respectively, which may compromise normal GABAergic modulation and function. Our results may have implications for the development of treatment strategies that target specific GABA_AR receptor subunits.</p> </div

Regression modelling of the interaction between relevant GABA_AR subunits (α and β) and [³H]Muscimol binding.

<p>Regression modelling of the interaction between relevant GABA_AR subunits (α and β) and [³H]Muscimol binding.</p

Correlations of [³H]Muscimol binding and α4 mRNA subunit expression level in the superficial layers of the DLPFC of control (CON) (n = 37) and schizophrenia (SCZ) (n = 37) cases.

<p>Correlations of [³H]Muscimol binding and α4 mRNA subunit expression level in the superficial layers of the DLPFC of control (CON) (n = 37) and schizophrenia (SCZ) (n = 37) cases.</p

Correlations between [³H]Muscimol binding and α-β GABA_AR subunit mRNAs.

<p>Correlations between [³H]Muscimol binding and α-β GABA_AR subunit mRNAs.</p

Correlations between [³H]Flumazenil binding and α-γ/δ GABA_AR subunit mRNAs.

<p>Correlations between [³H]Flumazenil binding and α-γ/δ GABA_AR subunit mRNAs.</p

Scatter plots presenting the binding values (fmoles/mg tissue equivalent) of [³H]Muscimol (A) and [³H]Flumazenil (B) in control (CON) (n = 37) and schizophrenia (SCZ) (n = 37), in the superficial (surface) and deep layers of the DLPFC.

<p>* = p<0.05 and refers to a significant main effect of diagnosis (schizophrenia>control); # = p<0.001 and refers to a significant main effect of layers (superficial>deep) after two-way ANCOVA. Bars represent the means.</p

Correlations of [³H]Flumazenil binding and γ2S mRNA subunit expression level in the superficial layers of the DLPFC of control (CON) (n = 37) and schizophrenia (SCZ) (n = 37) cases.

<p>Correlations of [³H]Flumazenil binding and γ2S mRNA subunit expression level in the superficial layers of the DLPFC of control (CON) (n = 37) and schizophrenia (SCZ) (n = 37) cases.</p

Summary of Cohort Demographics.

<p>Abbreviations: yrs, years; hrs, hours; PMI, post-mortem interval; RIN, RNA integrity number.</p><p>Average values ± SD for continuous variables are shown.</p>§<p>Schizoaffective.</p

Regression modelling of the interaction between relevant GABA_AR subunits (α, γ and δ) and [³H]Flumazenil binding.

<p>Regression modelling of the interaction between relevant GABA_AR subunits (α, γ and δ) and [³H]Flumazenil binding.</p