1158-P: Genetic Dissection of a Vagal Neurocircuit for Blood Glucose Regulation.

Neurons of the hindbrain's dorsal motor nucleus of the vagus (DMV) in the hindbrain control key physiological functions related to diabetes, including pancreatic hormone secretion and food passage through the GI tract. Different subtypes of DMV neurons, or "functional units," are thought to mediate distinct physiological roles. However, a lack of definition and access to these subtypes has greatly limited what is known about them. Thus, there is much to learn about the nature of the DMV neurons controlling insulin release and gastric motility, how they function, and how they can be targeted to treat diabetes. To gain traction on this issue, we began by classifying DMV neuron subtypes based on their gene expression, using high-throughput single-nuclei RNA-seq in a mouse model. Our analysis revealed seven, molecularly-distinct subtypes of DMV neurons, two of which were respectively marked by their expression of the genes Calb2 and Grp. Fluorescence in situ hybridization revealed that Calb2 DMV neurons and Grp DMV neurons occupy different subregions of the DMV, suggesting they may innervate different parts of the digestive system. To investigate this, we stained the axons of Calb2 DMV neurons and Grp DMV neurons and imaged them in optically cleared stomach and pancreas from mouse. These studies revealed that Calb2 DMV neurons innervate pancreas but not stomach, whereas Grp DMV neurons innervate neither organ. To then determine whether Calb2 DMV neurons control pancreas endocrine function, we used intersectional optogenetics to stimulate Calb2 DMV neurons while assessing blood glucose levels in vivo. Preliminary data indicate that activating Calb2 DMV neurons causes a rapid and substantial decrease in blood glucose levels. Together our results not only identify Calb2 DMV neurons as pancreas afferents that can lower blood glucose, but reveal a "labeled line" logic to the organization of vagal motor neurons, in which genetically-distinct neuron subtypes innervate different digestive organs to control their function. Disclosure: N. J. Conley: None. C. Li: None. J. Campbell: None. Funding: American Diabetes Association/Pathway to Stop Diabetes (1-18-INI-14 to J.C.) [ABSTRACT FROM AUTHOR]