Abstract

Cholecystokinin and vasoactive intestinal peptide mRNA differences in the frontal pole cortex of schizophrenia and bipolar disorder subjects

Krolewski DM, Kumar V, Waselus M, Medina A, Foltz M, Myers RM, Lee FS, Barchas JD, Bunney BG, Bunney WE, Akil H, Watson SJ
52nd Annual Meeting of Society for Neuroscience. 2023.

Background: Gene expression of cholecystokinin peptide (CCK) and vasoactive intestinal peptide (VIP) profile specific subpopulations of inhibitory GABA-ergic interneurons. CCK basket cells primarily synapse around excitatory pyramidal cell bodies whereas VIP types are well known to form disinhibitory circuits through connections with other GABA interneurons. The physiological dysfunction of these interneurons has been previously represented by mRNA reductions in the dorsolateral prefrontal and orbital frontal cortices of schizophrenia (SZ) and bipolar disorder (BPD) postmortem patients (Fung et al., 2010, 2014). Our laboratory has used qPCR to investigate gene expression in the less well studied frontopolar cortex; a region linked to multiple functions including those related to emotion, nociception, and pain. The results uncovered a number of altered GABA-related genes in psychiatric disorders (Medina et al., 2023). To expand on these findings, we conducted a preliminary quantitative analysis of CCK and VIP mRNA in the frontopolar tissue of healthy controls (CTR), SZ, and BPD subjects by cortical layer. Methods: Frontopolar cortex from all diagnoses were obtained from the Brain Donor Program, University of California, Irvine. All samples had zero agonal factors and met stringent criteria for pH and PMI. Hybridization chain-reaction (HCR) fluorescent in situ hybridization (FISH) was performed on 30µm-thick fresh-frozen cryosections. Images were captured on an Olympus Fluoview 3000 with CCK+ and VIP+ cells quantified as stitched z-plane stacks with Amira and ImageJ software. Results: Our preliminary study, CTR (n=5), SZ (n=4), BPD (n=5), showed several notable findings. 1) The mean number of CCK+ cells in CTRs was similar in layers II-V, but considerably lower in layer VI. 2) Across all individual layers, BPD subjects displayed the lowest mean number of CCK+ cells vs. CTRs. 3) VIP+ cells were more numerous in layers II-IV of CTRs, but appreciably less in layers V/VI. 4) Across all layers, the mean number of VIP+ cells was lower in SZ vs. CTR, but even more so in BPD. 5) Although CCK and VIP interneurons are thought to be mostly separate populations, we did find about 12% overlap. The latter was most apparent in layers II-IV. Conclusion: Given the promising results of our preliminary analysis of CCK+ and VIP+ interneurons in the frontopolar cortex, we are currently processing HCR-FISH for CTR, SZ, and BPD subjects to complement these findings (totaling n=16/group). These data will allow for more complete understanding of cortical layer-based interneuron differences and thus the pathology of such networks in psychiatric disorders.