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The versatility of somatosensation arises from heterogenous human dorsal root ganglion (DRG) neurons. The critical information to decipher their functions, i.e., the soma transcriptome, is lacking due to technical difficulties. Here we developed a novel approach to isolate individual human DRG neuron somas for deep RNA sequencing (RNA-seq). On average, >9000 unique genes per neuron were detected, and 16 neuronal types were identified. Cross-species analyses revealed that touch-, cold-, and itch-sensing neuronal types were relatively conserved, while the pain-sensing neurons displayed marked divergence. Soma transcriptomes of human DRG neurons predicted novel functional features, which were confirmed using single-cellin vivoelectrophysiological recordings. These results support a close relationship the between physiological properties of human sensory afferents and molecular profiles uncovered by the single-soma RNA-seq dataset. In summary, by conducting single-soma RNA-seq of human DRG neurons, we generated an unprecedented neural atlas for human somatosensation.

Summary Sensory functions of the vagus nerve are critical for conscious perceptions and for monitoring visceral functions in the cardio-pulmonary and gastrointestinal systems. Here, we present a comprehensive identification, classification, and validation of the neuron types in the neural crest (jugular) and placode (nodose) derived vagal ganglia by single-cell RNA sequencing (scRNA-seq) transcriptomic analysis. Our results reveal major differences between neurons derived from different embryonic origins. Jugular neurons exhibit fundamental similarities to the somatosensory spinal neurons, including major types, such as C-low threshold mechanoreceptors (C-LTMRs), A-LTMRs, Aδ-nociceptors, and cold-, and mechano-heat C-nociceptors. In contrast, the nodose ganglion contains 18 distinct types dedicated to surveying the physiological state of the internal body. Our results reveal a vast diversity of vagal neuron types, including many previously unanticipated types, as well as proposed types that are consistent with chemoreceptors, nutrient detectors, baroreceptors, and stretch and volume mechanoreceptors of the respiratory, gastrointestinal, and cardiovascular systems., Graphical Abstract, Highlights • A comprehensive molecular identification of neuronal types in vagal ganglion complex • Prdm12+ jugular ganglion neurons share features with spinal somatosensory neurons • Phox2b+ viscerosensory nodose neurons are molecularly versatile and highly specialized • Nodose neuron types are consistent with chemo-, baro-, stretch-, tension-, and volume-sensors, Visceral sensory neurons are necessary for the control of organ functions, but knowledge on the complexity of neuron types involved is missing. Kupari et al. molecularly identify jugular and nodose ganglion neurons and find a large diversity of neuron types that are consistent with the numerous sensory functions of the vagus nerve.

Distinct types of dorsal root ganglion sensory neurons may have unique contributions to chronic pain. Identification of primate sensory neuron types is critical for understanding the cellular origin and heritability of chronic pain. However, molecular insights into the primate sensory neurons are missing. Here we classify non-human primate dorsal root ganglion sensory neurons based on their transcriptome and map human pain heritability to neuronal types. First, we identified cell correlates between two major datasets for mouse sensory neuron types. Machine learning exposes an overall cross-species conservation of somatosensory neurons between primate and mouse, although with differences at individual gene level, highlighting the importance of primate data for clinical translation. We map genomic loci associated with chronic pain in human onto primate sensory neuron types to identify the cellular origin of human chronic pain. Genome-wide associations for chronic pain converge on two different neuronal types distributed between pain disorders that display different genetic susceptibilities, suggesting both unique and shared mechanisms between different pain conditions.

The neuroanatomical basis behind acupuncture practice is still poorly understood. Here we used intersectional genetic strategy to ablate NPY(+) noradrenergic neurons and/or adrenal chromaffin cells. Using endotoxin-induced systemic inflammation as a model, we found that electroacupuncture stimulation (ES) drives sympathetic pathways in somatotopy- and intensity-dependent manners. Low intensity ES at hindlimb regions drives the vagal-adrenal axis, producing anti-inflammatory effects that depend on NPY(+) adrenal chromaffin cells. High intensity ES at the abdomen activates NPY(+) splenic noradrenergic neurons via the spinal-sympathetic axis; these neurons engage incoherent feedforward regulatory loops via activation of distinct adrenergic receptors (ARs), and their ES-evoked activation produces either anti- or pro-inflammatory effects due to disease state-dependent changes in AR profiles. The revelation of somatotopic organization and intensity dependency in driving distinct autonomic pathways could form a road map for optimizing stimulation parameters to improve both efficacy and safety in using acupuncture as a therapeutic modality.

Summary Vagal sensory neurons relay viscero- and somatosensory information from within the body and play a key role in maintaining physiological homeostasis. We recently characterized the diversity of vagal sensory neurons in the mouse using a single-cell transcriptomics approach. Here, we provide an in-depth protocol for the extraction of mouse vagal ganglia and the production of high-quality single-cell suspensions from this tissue. This effective protocol can also be applied for use with other peripheral and central neuron populations with few modifications. For complete details on the use and execution of this protocol, please refer to Kupari et al. (2019)., Graphical Abstract, Highlights • An in-depth protocol for the extraction of mouse vagal ganglia • Production of high-quality single-cell suspensions of mouse vagal ganglia • This protocol can also be applied to other peripheral and central neuron populations, Vagal sensory neurons relay viscero- and somatosensory information from within the body and play a key role in maintaining physiological homeostasis. We recently characterized the diversity of vagal sensory neurons in the mouse using a single-cell transcriptomics approach. Here, we provide an in-depth protocol for the extraction of mouse vagal ganglia and the production of high-quality single-cell suspensions from this tissue. This effective protocol can also be applied for use with other peripheral and central neuron populations with few modifications.

Due to poor regenerative capacity of adult kidneys, nephron endowment defined by the nephrogenic program during the fetal period dictates renal and related cardiovascular health throughout life. We show that the neurotropic factor GDNF, which is in clinical trials for Parkinson’s disease, is capable of prolonging the nephrogenic program beyond its normal cessation without increasing the risk of kidney tumors. Our data demonstrates that excess GDNF expands the nephrogenic program by maintaining nephron progenitors and nephrogenesis in postnatal mouse kidneys. GDNF, through its transcriptional targets excreted from the adjacent epithelium, has a major effect on nephron progenitor self-renewal and maintenance; abnormally high GDNF inhibits nephron progenitor proliferation, but lowering its level normalizes the nephrogenic program to that permissive for nephron progenitor self-renewal and differentiation. Based on our results, we propose that the lifespan of nephron progenitors is determined by mechanisms related to perception of GDNF and other signaling levels.

Efferent signals from the vagus nerve are thought to mediate both basal and meal-induced gastric acid secretion, and provide trophic support of the mucosa. However, the underlying mechanisms are incompletely understood. Neurturin, signalling via glial cell line-derived neurotrophic factor (GDNF)-family receptor α2 (GFRα2), is essential for parasympathetic innervation of many target tissues but its role in gastric innervation is unknown. Here we show that most nerve fibres in wild-type mouse gastric mucosa, including all positive for gastrin-releasing peptide, are cholinergic. GFRα2-deficient (KO) mice lacked virtually all cholinergic nerve fibres and associated glial cells in the gastric (oxyntic and pyloric) mucosa but not in the smooth muscle, consistent with the selective expression of neurturin mRNA in the gastric mucosa. 2-Deoxyglucose and hexamethonium failed to affect acid secretion in the GFRα2-KO mice indicating the lack of functional innervation in gastric mucosa. Interestingly, basal and maximal histamine-induced acid secretion did not differ between wild-type and GFRα2-KO mice. Moreover, circulating gastrin levels in both fasted and fed animals, thickness of gastric mucosa, and density of parietal and different endocrine cells were similar. Carbachol-stimulated acid secretion was higher in GFRα2-KO mice, while atropine reduced basal secretion similarly in both genotypes. We conclude that cholinergic innervation of gastric mucosa depends on neurturin-GFRα2 signalling but is dispensable for gastrin secretion and for basal and maximal acid output. Basal acid secretion in the KO mice appears to be, at least partly, facilitated by constitutive activity of muscarinic receptors.

Enteric neurons, unlike sympathetic and sensory neurons that require target-derived neurotrophins for survival, do not undergo classical caspase-3-mediated programmed cell death (PCD) during normal development. Whether parasympathetic neurons in the pancreas, which originate from a subpopulation of enteric nervous system (ENS) precursors, or other parasympathetic neurons undergo PCD during normal mammalian development is unknown. In GFRalpha2-deficient mice, many submandibular and intrapancreatic parasympathetic neurons are missing but whether this is due to increased neuronal death is unclear. Here we show that activated caspase-3 and PGP9.5 doubly positive neurons are present in wild-type mouse pancreas between embryonic day E15 and birth. Thus, in contrast to ENS neurons, intrapancreatic neurons undergo PCD via apoptosis during normal development. We also show that, in GFRalpha2-deficient mice, most intrapancreatic neurons are lost during this late fetal period, which coincides with a period of increased apoptosis of the neurons. Since the percentage of BrdU and Phox2b doubly positive cells in the fetal pancreas and the number of intrapancreatic neurons at E15 were similar between the genotypes, impaired precursor proliferation and migration are unlikely to contribute to the loss of intrapancreatic neurons in GFRalpha2-KO mice. Caspase-3-positive neurons were also found in GFRalpha2-deficient submandibular ganglia around birth, suggesting that parasympathetic neurons depend on limited supply of (presumably target-derived neurturin) signaling via GFRalpha2 for survival.

Despite the variety of physiological and target-related functions, little is known regarding the cellular complexity in the sympathetic ganglion. We explored the heterogeneity of mouse stellate and thoracic ganglia and found an unexpected variety of cell types. We identified specialized populations of nipple- and pilo-erector muscle neurons. These neurons extended axonal projections and were born among other neurons during embryogenesis, but remained unspecialized until target organogenesis occurred postnatally. Target innervation and cell-type specification was coordinated by an intricate acquisition of unique combinations of growth factor receptors and the initiation of expression of concomitant ligands by the nascent erector muscles. Overall, our results provide compelling evidence for a highly sophisticated organization of the sympathetic nervous system into discrete outflow channels that project to well-defined target tissues and offer mechanistic insight into how diversity and connectivity are established during development.