Reduced Glutamate Decarboxylase 65 Protein Within Primary Auditory Cortex Inhibitory Boutons in Schizophrenia

Abstract

Background Schizophrenia is associated with perceptual and physiological auditory processing impairments that may result from primary auditory cortex excitatory and inhibitory circuit pathology. High-frequency oscillations are important for auditory function and are often reported to be disrupted in schizophrenia. These oscillations may, in part, depend on upregulation of gamma-aminobutyric acid synthesis by glutamate decarboxylase 65 (GAD65) in response to high interneuron firing rates. It is not known whether levels of GAD65 protein or GAD65-expressing boutons are altered in schizophrenia. Methods We studied two cohorts of subjects with schizophrenia and matched control subjects, comprising 27 pairs of subjects. Relative fluorescence intensity, density, volume, and number of GAD65-immunoreactive boutons in primary auditory cortex were measured using quantitative confocal microscopy and stereologic sampling methods. Bouton fluorescence intensities were used to compare the relative expression of GAD65 protein within boutons between diagnostic groups. Additionally, we assessed the correlation between previously measured dendritic spine densities and GAD65-immunoreactive bouton fluorescence intensities. Results GAD65-immunoreactive bouton fluorescence intensity was reduced by 40% in subjects with schizophrenia and was correlated with previously measured reduced spine density. The reduction was greater in subjects who were not living independently at time of death. In contrast, GAD65-immunoreactive bouton density and number were not altered in deep layer 3 of primary auditory cortex of subjects with schizophrenia. Conclusions Decreased expression of GAD65 protein within inhibitory boutons could contribute to auditory impairments in schizophrenia. The correlated reductions in dendritic spines and GAD65 protein suggest a relationship between inhibitory and excitatory synapse pathology in primary auditory cortex.

MEG—measured auditory steady-state oscillations show high test–retest reliability: A sensor and source-space analysis

“…Reduced 40 Hz ASSRs in these disorders is consistent with findings of altered cellular parameters affecting E/I balance (Hashimoto et al, 2008;Moyer et al, 2012;Sweet et al, 2009;2007), supporting the potential clinical utility of the ASSR-paradigm in translational research.…”

Altered Glutamate Protein Co-Expression Network Topology Linked to Spine Loss in the Auditory Cortex of Schizophrenia

“…We have previously observed decreased GAD65(82) in the Al of SCZ patients. These decreases, measured at layer 3 inhibitory boutons, were much greater than those observed in whole tissue homogenates(82), suggesting that alterations to other proteins observed in the present study may be greater within specific neuronal microdomain. We also observed differences in expression of the ubiquitin/proteasome pathway proteins UCHL1 and PSMA1, which have previously been implicated in SCZ(83).…”

Loss of Microtubule-Associated Protein 2 Immunoreactivity Linked to Dendritic Spine Loss in Schizophrenia

“…2), operationalized as phalloidin mask objects that overlapped (≥ 1 voxel) with a spinophilin-IR mask object. Spine density (N v ) and number (N) in cohort 1 were calculated as previously described with minor modification (39, 40): $$N_v≔\frac{{\overline{t}}_{w{Q}^{-}}}{h}·\frac{\sum true(Q_i^{-}·w_{i}true)}{BA·a·\sum true(P_i·w_{i}true)}$$ Where a is the area of the counting frames, $Q_i^{-}$ is the count of dendritic spines within the i th block, P i is the count of the associated points hitting the region of interest in the i th block, h = disector height (see supplemental methods for additional details), BA is the cryostat block advance (50 µm for cohort 1 and 60 µm for cohort 2, t̅ wQ − is the block-and-number-weighted mean section thickness calculated using this formula: $${\overline{t}}_{w{Q}^{-}}≔\frac{\sum true(t_j·q_j^{-}·w_{i}true)}{\sum true(q_j^{-}·w_{i}true)}$$ where t j is the local section thickness measured centrally in the j th sampling frame and $q_j^{-}$ is the corresponding count of dendritic spines in the j th frame. w i is the block weight—i.e.…”

“…either 1 or 1/3. The number of spines was estimated as the product of previously determined deep layer 3 volumes in these subjects (17, 39, 40) and the N v calculated in the above equation, represented here: $$N≔N_v·V_{\text{deep layer}3}$$ Because for cohort 2, sections adjacent to the mapping sections were sampled, calculation of N v and N were as above but omitting the block weighting (46). …”