Vagal and spinal afferent mapping of rat and human hearts in health and disease - The sensory system of the heart protects it from insult or injury but their overactivation and dysfunction are deleterious for cardiac function. However, the phenotypes of cardiac afferents, the regions they innervate, and the visceral reflexes they evoke are poorly documented. Associating specific afferent systems in terms of fiber type and neurochemical phenotype relative to the region they innervate and their sensory modality would inform future strategies to selectively modulate their activity for therapeutic gain in disease. To better understand the structural and functional roles of these afferent nerves, we will map both the vagal and spinal innervation of healthy and diabetic (Type 2) hearts with high resolution in rats. In addition, we will phenotypically and functionally distinguish mechanosensitive from nociceptive cardiac afferent neurons. Furthermore, we will adapt our techniques in animals to study diabetes-induced remodeling of nociceptive afferent innervation in the human hearts. Finally, we will integrate these anatomical mapping and functional data onto 3D heart scaffold models. In rats, 1) we will first inject tracers into the heart to retrogradely identify the afferent neurons in the vagal nodose ganglion (VNG) and dorsal root ganglion (DRG). 2) We will inject tracers into the VNG and DRG to anterogradely label vagal and spinal afferent innervation of the heart. 3) We will utilize double immunohistochemical (IHC) labeling of two mechanosensitive markers (Piezo 1 and Piezo 2) and two nociceptive markers (CGRP and TRPV1) in tracer-injected rats to identify the different types and topographical distributions of VNG and DRG afferent axons. 4) Using these distribution maps, we will characterize and compare the cardiopulmonary reflex responses evoked from VNG and DRG heart-projecting neurons in response to physiological mechanical and noxious stimuli. 5) With our novel mapping tool, the topographical anatomical innervation and functional data will be integrated into 3D heart scaffolds for a structure-function map. 6) We will assess laterality preferences of VNG and DRG neurons, and sexual dimorphism and this data will also be integrated into the scaffold. For rats, we hypothesize that the VNG and DRG have different types of sensory neurons with distinct afferent distribution patterns and receptive fields. Moreover, the left and right VNG and DRG will have different afferent maps (laterality differences). Males and females may also have different innervation maps (sex differences). For diabetic rats and humans, we hypothesize that diabetes desensitizes/degenerates nociceptive afferents because pain is not well sensed by patients (silent myocardial infarction). Deliverable: For the first time, we will produce comprehensive topographical anatomical and functional maps of the vagal and spinal afferent innervation of the healthy and diabetic hearts on a novel digitized 3D heart scaffold. This will establish a foundation for an afferent heart- brain atlas, accelerate the understanding of cardiac functions and diabetes-induced remodeling, and the development of new approaches to treat cardiac and interoceptive disorders, especially in diabetic patients.
