Spatial Transcriptomics of Supraoptic Nucleus and Paraventricular Nucleus of the Hypothalamus in the Adult Rat

Purpose: Magnocellular neurosecretory cells (MNCs) in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus release oxytocin (OXY) and arginine vasopressin (AVP) into the peripheral circulation, playing a key role in the regulation of body fluid homeostasis. Transcriptomics of MNCs have been studied; however, the data lack spatial context important for better understanding physiological functions of genes. Our study leverages spatially-resolved transcriptomics to address this limitation. Methods: 10x Genomics' Visium Spatial Gene Expression was used to obtain spatially-resolved gene expression data for SON and PVN of an adult male Sprague-Dawley rat. Briefly, the workflow includes: 1) sample preparation (section, mount, stain, and image tissue), 2) cDNA library preparation, 3) sequencing, and 4) analysis/data visualization. Results: Gene cluster analysis successfully differentiated myelinated fiber tracts from nuclei and identified several distinct neuronal populations. Clusters overlaying fiber tracts contain glia-specific markers (e.g., Mbp and Gfap), and those overlaying SON and PVN regions contain neuron-specific markers (e.g., Syn1 and Nrgn). SON clustered with magnocellular PVN, while parvocellular PVN was a different cluster. Differential expression analysis of these two clusters revealed relevant genes for the distinct regions and neuronal subpopulations in the top 20 globally distinguishing genes (e.g., Avp and Oxt for SON and magnocellular PVN cluster and Trh for parvocellular PVN cluster). Conclusions: This data allows us to obtain whole transcriptomic data without sacrificing morphological context. Future spatial transcriptomic studies will investigate transcriptomics of MNCs related to sex differences and disease models that can potentially inform pathophysiology.