Protein Markers of Neurotransmitter Synthesis and Release in Postmortem Schizophrenia Substantia Nigra

Abstract

The substantia nigra (SN) provides the largest dopaminergic input to the brain, projects to the striatum (the primary locus of action for antipsychotic medication), and receives GABAergic and glutamatergic inputs. This study used western blot analysis to compare protein levels of tyrosine hydroxylase (TH), glutamate decarboxylase (GAD67), and vesicular glutamate transporters (vGLUT1 and vGLUT2) in postmortem human SN in schizophrenia subjects (n = 13) and matched controls (n = 12). As a preliminary analysis, the schizophrenia group was subdivided by (1) treatment status: off medication (n = 4) or on medication (n = 9); or (2) treatment response: treatment resistant (n = 5) or treatment responsive (n = 4). The combined schizophrenia group had higher TH and GAD67 protein levels than controls (an increase of 69.6%, P = 0.01 and 19.5%, P = 0.004, respectively). When subdivided by medication status, these increases were found in the on-medication subjects (TH 88.3%, P = 0.008; GAD67 40.6%, P = 0.003). In contrast, unmedicated schizophrenia subjects had higher vGLUT2 levels than controls (an increase of 28.7%, P = 0.041), but vGLUT2 levels were similar between medicated schizophrenia subjects and controls. Treatment-resistant subjects had significantly higher TH and GAD67 levels than controls (an increase of 121.0%, P = 0.0003 and 58.7%, P = 0.004, respectively). These data suggest increases in dopamine and GABA transmission in the SN in schizophrenia, with a potential relation to treatment and response.

Isoform and protein region abnormalities of dysbindin and copper transporter proteins in postmortem schizophrenia substantia nigra

“…Our sample size was small and as is typical for postmortem investigations, none of our subjects were first-episode and/or antipsychotic-naïve (Schoonover et al 2017; Howes et al 2013). Medication history could affect our results, so we divided the schizophrenia group by treatment status and type to eliminate this confounding variable.…”

“…The work completed in this study was approved by the University of Alabama at Birmingham. The schizophrenia cohort was the same as previously studied (Schoonover et al 2017). Schizophrenia cases (n=15) were matched and compared to normal controls (NC, n=11).…”

“…The SN was blocked as done previously (Schoonover et al 2017). In SN coronal sections, caudal sections were caudal to third nerve rootlets.…”

“…Western blots were used to measure N- and C-terminal ATP7A, ATP7B, extracellular and transmembrane CTR1, and dysbindin 1A and 1B/C protein levels and performed as previously reported (Schoonover et al 2017), with the following exceptions. Samples intended for N-terminal ATP7A assays were not heated to avoid protein aggregation.…”

“…As described previously (Schoonover et al 2017), films were scanned at 600 dpi using a flatbed scanner. Optical densities of the bands were measured using Image J-64 freeware (NIH).…”