Selective brain-to-gut communication via transcriptionally-defined vagus-to-enteric neuron circuits - Parasympathetic control of gastrointestinal (GI) physiology, from distal esophagus to proximal colon, is carried out by preganglionic neurons located in the hindbrain dorsal motor nucleus of the vagus (DMV). In addition to being responsible for CNS control of the gut, they also provide the efferent motor arms for GI vago (sensory)- vagal (motor) reflexes that coordinate gut function. DMV neurons do not directly cause GI responses, but instead they do so by synaptically engaging and activating downstream “postganglionic” enteric neurons (ENs) which then release either acetylcholine (ACh) or nitric oxide (NO) and/or various neuropeptides. To account for the vast array of temporally-, spatially- and functionally-precise GI responses, it is widely believed that highly specific DMV-to-EN circuits (motor units) must exist, with their specificity being due to different DMV neurons projecting to different parts of the gut, and within a given part of the gut, different DMV neurons selectively targeting functionally distinct enteric neurons. Despite extensive evidence supporting the existence of such highly selective DMV-to-EN motor circuits, they are presently “hidden from view” and can’t be studied. This is because the means for uncovering and selectively manipulating them are lacking – and this is the case for all mammalian species. The overall goal of this proposal is to address this problem by leveraging the transcriptional diversity of DMV and EN neuron subtypes and the genetic tractability of a model organism (the mouse), to create the first-ever detailed roadmap of mammalian DMV neuron subtype to gut EN subtype communication. Confirming the existence of such highly specific circuits and showing the feasibility of this approach, we recently created a single nuclei RNA-seq (snRNA-seq) atlas of different DMV neurons and then, by employing neuron subtype-specific gene marker-recombinase mice, we showed that two DMV subtypes marked by Cck or Pdyn, respectively, project exclusively to the distal stomach where they differentially engage Chat (ACh-releasing) versus Nos1 (NO-releasing) ENs (Tao J., et al., Neuron, 2021). This proposal greatly expands upon this prior study: a) by mapping and manipulating the projections of all DMV neuron subtypes: 5 that project to different parts of the stomach, 1 to intestine, 1 to pancreas and 1 likely to the lower esophageal sphincter, and b) by linking each of these DMV subtypes to their unique downstream transcriptionally-defined EN subtypes. To facilitate the latter, in preliminary studies we’ve created a snRNA-seq atlas of stomach ENs, discovering 7 subtypes of cholinergic ENs, 6 subtypes of nitrergic ENs and one novel “peptidergic” EN (atlases for intestine EN subtypes already exist). Motivated by: a) the likely existence of highly specific DMV-to-EN circuits and b) the clear transcriptional diversity of DMV and EN subtypes, this grant proposes the following Aims to create the first-ever detailed map of DMV subtype to EN subtype communication and function. Aim 1: To create a transcriptional atlas of stomach EN subtypes, and probe projections / functions. Aim 2: To map DMV subtype à end organ EN subtype circuits, and study their function.
