Analysis of gaba-ergic interneuron markers in the anterior and posterior cingulate cortex of subjects diagnosed with bipolar disorder and schizophrenia
Krolewski DM, Kumar V, Waselus M, Myers RM, Lee FS, Barchas JD, Schatzberg AF, Bunney WE, Akil H, Watson SJ Jr
Society for Neuroscience. 2018.
Bipolar disorder (BP) and Schizophrenia (SZ) represent clinically distinct psychiatric illnesses yet are thought to display overlapping features such as alterations in mood and information processing by cortical gamma-aminobutyric acid (GABA)-ergic interneurons. For example, BP and SZ postmortem analyses reveal deficits in classic interneuron-related molecular markers including glutamic acid decarboxylase 67 (GAD67), calcium-binding proteins, and neuropeptide expression in several cortical regions. It should be noted that similar investigation of the anterior cingulate (ACg) and posterior cingulate (PCg) cortices have largely focused on the ACg of SZ subjects with effects highlighting diminished GAD67, parvalbumin (PV) and somatostatin (SST) mRNA. In contrast, potential abnormalities regarding the orchestration of GABA-ergic interneuronal networks are less understood in the ACg and PCg of BP subjects. Considering the ACg and PCg differentially contribute to behaviors linked to control of emotion and memory-based evaluative process, respectively, prospective gene expression changes may also generate new anatomical correlates. Therefore, the aim of the present study is to quantify and compare the relative distribution of GAD67 mRNA transcripts as well as those demarcating distinct GABA-ergic interneuron subpopulations that utilize differential synaptic contacts with pyramidal neurons. More specifically, we chose to examine PV (cell body, axon initial segment), SST (dendrites), and vasoactive intestinal peptide ((VIP); other interneurons)) in the ACg and PCg of both BP and SZ subjects. To achieve this, we performed in situ hybridization (ISH) using radiolabeled cRNA probes applied to 10 ɥm fresh-frozen ACg and PCg sections from control (n=16), SZ (n=19), and BP (n=19) subjects. With quantitation currently ongoing, preliminary results indicate similar SST and VIP mRNA layer-expression patterns within the ACg and PCg of controls while PV intensity level seems to depend on ACg subregion (BA24a vs. BA24b and BA24c). To better characterize distinct cingulate-localized interneuron subpopulations, we have developed complementary cDNA probes suitable for fluorescent ISH (FISH) to visualize the degree of specific mRNA colocalization. Moreover, we also look to illuminate the 3-dimensional neuroanatomical relationships between interneurons using CLARITY and iDISCO brain transparency methods. The results of these experiments will serve to further elucidate the underpinnings of GABA-ergic interneuron function in the ACg and PCg of patients diagnosed with BP and SZ. Support: The Pritzker Neuropsychiatric Disorder Research Consortium