Abstract

Spatial transcriptomics reveal basal differences in immediate early gene profiles associated with temperament: studies in a rat model of emotional reactivity

Waselus M, Hebda-Bauer EK, Dai M, Meng F, Akil H, Watson SJ
51st Annual Meeting of the Society for Neuroscience. 2022.

The selectively-bred lines of high- and low-responder rats (bHR and bLR, respectively) model two temperamental phenotypes representing both contrasting emotionality and reactivity to the environment. These include differences in exploratory locomotion, propensity to self-administer drugs of abuse, and anxiety-like behaviors. Using anatomical methods such as in situ hybridization, we have implicated several specific transcripts and brain regions in these behavioral differences. But these classical anatomical tools allow only a finite number of genes to be examined in any given brain structure or subject. Yet, expression profiling (e.g. RNAseq) reveals profound differences between the lines across a large number of transcripts. To better link gene expression regulation with neural circuitry and behavioral outcomes, we relied on an anatomically precise expression profiling approach to capture basal gene expression differences in a regionally defined manner. Spatial transcriptomics solutions such as Visium developed by 10X Genomics combine RNAseq with spatial registration to provide a global picture of RNA expression with anatomical specificity. As a proof of principle, we examined a set of immediate early genes to determine whether there are differences in basal expression between the bHR and bLR lines. Brains from the 68th generation of our selective breeding colony were used to examine bHR/bLR differences in gene expression in an upper quadrant of the adult rat brain which included the dorsal hippocampus. One section per “condition” (bred line x sex) was collected from a bHR and bLR family per slide, allowing each slide to function as its own independent study. Adjacent sections were collected on a second slide to serve as a technical replicate, and a second bHR and bLR family was included as a biological replicate. While extensive gene expression differences were noted between the lines, our gene list focused on prototypical immediate early genes (IEGs; e.g., Arc, Fos, zif-268) as well as other genes known to show time-dependent responses to growth factor activation (Tullai, et al., 2007). While bHRs exhibited a higher basal expression of immediate early genes in the brain vs. bLR rats, fewer differences between lines were found at later timepoints. These findings are relevant to the bHR/bLR lines given well-established differences in response to psychostimulants such as cocaine, and the effects of psychostimulants on IEGs. Thus, the unbiased investigation of bHR/bLR brain differences using the Visium platform promises to be a valuable tool for elucidating differences in gene expression and enables more refined anatomical queries in the future.