Vagal nerve endings in visceral pleura and triangular ligaments of the rat lung

Using tissue clearing and light sheet fluorescence microscopy for the three-dimensional analysis of sensory and sympathetic nerve endings that innervate bone and dental tissue of mice

Bone and dental tissues are richly innervated by sensory and sympathetic neurons. However, the characterization of the morphology, molecular phenotype, and distribution of nerves that innervate hard tissue has so far mostly been limited to thin histological sections. This approach does not adequately capture dispersed neuronal projections due to the loss of important structural information during three-dimensional (3D) reconstruction. In this study, we modified the immunolabeling-enabled imaging of solvent-cleared organs (iDISCO/iDISCO+) clearing protocol to image high-resolution neuronal structures in whole femurs and mandibles collected from perfused C57Bl/6 mice. Axons and their nerve terminal endings were immunolabeled with antibodies directed against protein gene product 9.5 (pan-neuronal marker), calcitonin gene-related peptide (peptidergic nociceptor marker), or tyrosine hydroxylase (sympathetic neuron marker). Volume imaging was performed using light sheet fluorescence microscopy. We report high-quality immunolabeling of the axons and nerve terminal endings for both sensory and sympathetic neurons that innervate the mouse femur and mandible. Importantly, we are able to follow their projections through full 3D volumes, highlight how extensive their distribution is, and show regional differences in innervation patterns for different parts of each bone (and surrounding tissues). Mapping the distribution of sensory and sympathetic axons, and their nerve terminal endings, in different bony compartments may be important in further elucidating their roles in health and disease.

Evidence of extraganglionic vagal mechanoreceptors in the mouse vagus nerve

Vagal afferent neuronal somas are in the nodose and jugular ganglia. In this study, we identified extraganglionic neurons in whole-mount preparations of the vagus nerves from Phox2b-Cre-ZsGreen transgenic mice. These neurons are typically arranged in small clusters and monolayers along the cervical vagus nerve. Although infrequent, these neurons were sometimes observed along the thoracic and esophageal vagus. We performed RNAscope in situ hybridization and confirmed that the extraganglionic neurons detected in this transgenic mouse strain expressed vagal afferent markers (i.e., Phox2b and Slc17a6) as well as markers that identify them as potential gastrointestinal mechanoreceptors (i.e., Tmc3 and Glp1r). We also identified extraganglionic neurons in the vagus nerves of wild-type mice that were injected intraperitoneally with Fluoro-Gold, thereby ruling out possible anatomical discrepancies specific for transgenic mice. In wild-type mice, extraganglionic cells were positive for peripherin, confirming their neuronal nature. Taken together, our findings revealed a previously undiscovered population of extraganglionic neurons associated with the vagus nerve. Going forward, it is important to consider the possible existence of extraganglionic mechanoreceptors that transmit signals from the abdominal viscera in future studies related to vagal structure and function.

Regulation of breathing by cardiopulmonary afferents

This chapter broadly reviews cardiopulmonary sympathetic and vagal sensors and their reflex functions during physiologic and pathophysiologic processes. Mechanosensory operating mechanisms, including their central projections, are described under multiple sensor theory. In addition, ways to interpret evidence surrounding several controversial issues are provided, with detailed reasoning on how conclusions are derived. Cardiopulmonary sensory roles in breathing control and the development of symptoms and signs and pathophysiologic processes in cardiopulmonary diseases (such as cough and neuroimmune interaction) also are discussed.

Palpation of the Respiratory System in Osteopathic Manual Medicine: From the Trachea to the Lungs

There is a lack of published literature in osteopathic manual medicine on how to perform palpation of the lower respiratory tree such as the trachea, main bronchi, and lungs. Several authors have studied the osteopathic effect and respiratory response of palpation but have failed to demonstrate how to perform palpation of the visceral areas involved in breathing, either in the context of a clinical trial or as a case report. This paper reviews the innervation of these anatomical areas, the mechano-metabolic weight of the passage of fluids and air in the respiratory tract, the anatomical topography, and the movements involved in respiration. Drawing from current knowledge, this article illustrates, for the first time, how to place the hands for an effective osteopathic assessment of the tracheal, bronchial, and pulmonary structures. Understanding how to perform palpation of the lower areas is a fundamental tool in the clinic and potential therapy in osteopathic manual medicine.

Vagal baro- and chemoreceptors in middle internal carotid artery and carotid body in rat

The glossopharyngeal nerve, via the carotid sinus nerve (CSN), presents baroreceptors from the internal carotid artery (ICA) and chemoreceptors from the carotid body. Although neurons in the nodose ganglion were labelled after injecting tracer into the carotid body, the vagal pathway to these baro- and chemoreceptors has not been identified. Neither has the glossopharyngeal intracranial afferent/sensory pathway that connects to the brainstem been defined. We investigated both of these issues in male Sprague-Dawley rats (n = 40) by injecting neural tracer wheat germ agglutinin-horseradish peroxidase into: (i) the peripheral glossopharyngeal or vagal nerve trunk with or without the intracranial glossopharyngeal rootlet being rhizotomized; or (ii) the nucleus of the solitary tract right after dorsal and ventral intracranial glossopharyngeal rootlets were dissected. By examining whole-mount tissues and brainstem sections, we verified that only the most rostral rootlet connects to the glossopharyngeal nerve and usually four caudal rootlets connect to the vagus nerve. Furthermore, vagal branches may: (i) join the CSN originating from the pharyngeal nerve base, caudal nodose ganglion, and rostral or caudal superior laryngeal nerve; or (ii) connect directly to nerve endings in the middle segment of the ICA or to chemoreceptors in the carotid body. The aortic depressor nerve always presents and bifurcates from either the rostral or the caudal part of the superior laryngeal nerve. The vagus nerve seemingly provides redundant carotid baro- and chemoreceptors to work with the glossopharyngeal nerve. These innervations confer more extensive roles on the vagus nerve in regulating body energy that is supplied by the cardiovascular, pulmonary and digestive systems.

Axons of Passage and Inputs to Superior Cervical Ganglion in Rat

Wheat germ agglutinin-horseradish peroxidase was injected into the entire (0.8 μL) or partial (rostral or caudal, 0.1-0.3 μL) superior cervical ganglion (SCG) of the rat (male Sprague-Dawley, N = 35) to examine the distribution of neurons in the middle (MCG) and inferior (ICG) cervical ganglion that send axons bypass the SCG. Whole-mounts of the SCG, cervical sympathetic trunk (CST), MCG, ICG, and sections of the brainstem and spinal cord were prepared. With entire SCG tracer injection, neurons were labeled evenly in the MCG (left: 258, right: 121), ICG (left: 848, right: 681), and CST (up to 770). Some neurons grouped in a single bulge just rostral to the MCG, which we termed as the "premiddle cervical ganglion" (pMCG). The left pMCG (120) is larger and has more neurons than the right pMCG (82). Centrally, neurons were labeled in lamina IX of cervical segments (C1: 18%, C2: 46%, C3: 33%, C4: 3%), intermediate zone of thoracic segments (T1: 31%, T2: 35%, T3: 27%, T4: 7%), and intermediate reticular nuclei (96%) and perifacial zone (4%) of brainstem. The rostral and caudal SCG injection selectively labeled neurons mainly in brainstem, C1-C2 and in T1-T2, respectively. Before projecting to their peripheral targets, many neurons in pMCG, MCG and ICG run rostrally within the CST rather than segmentally through the closest rami, from the level of SCG or above. Neurons in pMCG and MCG may have similar or complementary function and those in brainstem may be involved in the vestibulo-autonomic interaction. Anat Rec, 301:1906-1916, 2018. © 2018 Wiley Periodicals, Inc.