Rosemarie Terwilliger

Single-cell genomics is a powerful tool for studying heterogeneous tissues such as the brain. Yet little is understood about how genetic variants influence cell-level gene expression. Addressing this, we uniformly processed single-nuclei, multiomics datasets into a resource comprising >2.8 million nuclei from the prefrontal cortex across 388 individuals. For 28 cell types, we assessed population-level variation in expression and chromatin across gene families and drug targets. We identified >550,000 cell type-specific regulatory elements and >1.4 million single-cell expression quantitative trait loci, which we used to build cell-type regulatory and cell-to-cell communication networks. These networks manifest cellular changes in aging and neuropsychiatric disorders. We further constructed an integrative model accurately imputing single-cell expression and simulating perturbations; the model prioritized ~250 disease-risk genes and drug targets with associated cell types.

Ethanol dependence and tolerance involve perturbation of GABAergic neurotransmission. Previous studies have demonstrated that ethanol treatment regulates the function and expression of GABAA receptors throughout the CNS. Conceivably, changes in receptor function may be associated with alterations of subunit composition. In the present study, a comprehensive (1-12 weeks) ethanol treatment paradigm was used to evaluate changes in GABAA receptor subunit expression in several brain regions including the cerebellum, cerebral cortex, ventral tegmental area (VTA) (a region implicated in drug reward/dependence), and the hippocampus (a region involved in memory/cognition). Expression of alpha 1 and alpha 5 subunits was regulated by ethanol in a region-specific and time-dependent manner. Following 2-4 weeks of administration, cortical and cerebellar alpha 1 and alpha 5 subunits immunoreactivity was reduced. In the VTA, levels of alpha 1 subunit immunoreactivity were significantly decreased after 12 weeks but not 1-4 weeks of treatment. Hippocampal alpha 1 subunit immunoreactivity and mRNA content were also significantly reduced after 12 but not after 4 weeks of treatment. In contrast, alpha 5 mRNA content was increased in this brain region. These data indicate that chronic ethanol administration alters GABAA receptor subunit expression in the VTA and hippocampus, effects that may play a role in the abuse potential and detrimental cognitive effects of alcohol.

Previous studies indicate that corticotropin-releasing factor (CRF) contributes to the anxiety-like and aversive states associated with drug-induced withdrawal. The present study extends this work by analyzing the CRF receptor subtype involved in withdrawal responses. First, the influence of a selective CRF receptor-1 (CRF-R1) antagonist, CP-154,526, on opiate withdrawal behavior was examined. Pretreatment with the CRF-R1 antagonist significantly attenuated several behavioral signs of naltrexone-induced morphine withdrawal, including writhing, chewing, weight loss, lacrimation, salivation, and irritability, measured during the first hour of withdrawal. Next the expression of CRF-R1 was determined as a second measure of the involvement of this receptor in opiate withdrawal. Naltrexone-induced morphine withdrawal resulted in down-regulation of CRF-R1 mRNA in several brain regions, including the frontal cortex, parietal cortex, striatum, nucleus accumbens, and amygdala, but not in the hypothalamus or periaqueductal gray. Expression of CRF-R2, the other major CRF receptor subtype, was not down-regulated significantly by withdrawal in any of the regions examined, although morphine alone significantly increased levels of this receptor subtype. Taken together, the behavioral and receptor regulation findings indicate that CRF-R1 is the primary mediator of the actions of the CRF system on opiate withdrawal, although it is possible that CRF-R2 contributes to the response.