In support of synaptic changes associated with opioid addiction, several genes involved in glutamatergic and GABAergic neurotransmission were altered in individuals with OUD (astrocytes: metabotropic glutamate receptor 5, GRM5, log2FC = −3.13, FDR = 1.06 E −14 and glutamate ionotropic receptor AMPA type subunit 1, GRIA1, log2FC = −1.98, FDR = 2.8 E −8; oligodendrocytes: GABA type A receptor subunit beta1, GABRB1, log2FC = −0.717, FDR = 0.023; microglia: GABA type A receptor subunit gamma 2, GABRG2, log2FC = −1.45, FDR = 0.038). Indeed, we identified several pathways related to various synaptic (e.g., glutamatergic synapse) and immune functions (e.g., TNF-alpha signaling) in gene co-expression network modules unique to MSN subpopulations and microglia (Figs. S10–12; Supplementary Data 1–S18, S19). Together, our cell type-specific findings suggest an interplay between microglial-dependent signaling and synaptic plasticity in OUD, consistent with our previous bulk transcriptomics findings in striatum from individuals with OUD5. With single nuclei resolution, we find the elevation of neuroinflammatory pathways related to microglial activation in OUD is likely due to transcriptional alterations within microglia, rather than pronounced changes in the number of
