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.

Double labeling of vagal preganglionic and sympathetic postganglionic fibers in celiac ganglion, superior mesenteric arteries and myenteric plexus.

Sympathetic efferents regulate the "fight-or-flight" response and sympathetic and vagal fibers have been suggested to retrogradely and centrally spread pathogens associated with Parkinson's disease. To examine the arrangement of the vagal and sympathetic motor fibers in the celiac ganglion (CG), gastrointestinal tract, and along the superior mesenteric artery and its sub-branches, we double-labeled the vagal efferents by injecting Dextran-Texas Red into the dorsal motor nucleus of the vagus and the sympathetic postganglionics with tyrosine hydroxylase immunohistochemistry in male Sprague-Dawley rats (n = 18). The laser scanning confocal microscope was used for image analysis. Vagal nerve endings were densely distributed around the CG neurons, and the right CG received more. Vagal and sympathetic efferent endings formed various ring or string shapes that tangled closely in the myenteric plexus of the forestomach, duodenum, jejunum and ileum. Vagal and sympathetic efferents coursed within the same nerve bundles before reaching the myenteric plexus, had in-apposition varicosities, and ran parallel with the superior mesenteric artery and its sub-branches. Although a complete sympathetic tracing and an incomplete tracing and/or damage to the vagal preganglionic neurons may lead to a sampling bias, the sympathetic innervations in the blood vessels and myenteric plexus are stronger than in the vagus. The in-apposition innervation varicosities of the vagal and sympathetic efferents within the same nerve bundles and in the myenteric plexus of the gut with complex innervation patterns may offer a network to automatically control gastrointestinal functions and an infection route of the Parkinson's disease between the autonomic efferent endings.

Abdominal vagal afferent pathways and their distributions of intraganglionic laminar endings in the rat duodenum.

We examined abdominal vagal afferents (n = 33) and the distributions of their intraganglionic laminar endings (IGLEs) in the duodenum. Rats (male, Sprague-Dawley) received a partial subdiaphragmatic vagotomy that spared a single branch. Wheat germ agglutinin-horseradish peroxidase (0.5-1.0 µl) was injected into the nodose ganglion ipsilateral to the vagotomized side. We observed that the hepatic branch does not project to the stomach, that the accessory celiac and celiac branches course along the celiac artery and innervate the intestines, and that the left nodose afferents innervate predominantly the duodenum. The hepatic branch innervates the duodenum via the "hepatoduodenal" subbranch and has the densest IGLE distribution in both the dorsoventral and the rostrocaudal extensions of the first 4-cm segment. Both gastric branches have two subbranches that innervate the duodenum; the "lesser curvature" subbranches follow the lesser curvature artery and may join the "hepatoduodenal" subbranch, whereas the "pyloric" subbranches run through the antrum and pylorus to reach the proximal duodenum. Moreover, the subbranches of ventral and dorsal gastric branches innervate more in the ventral and dorsal parts of the duodenum, respectively, and have more IGLEs in the rostral region than in the caudal. A posteriori comparisons indicate that, in the first-centimeter segment, the ventral gastric branch has significantly more IGLEs, whereas, in the third- and fourth-centimeter segments, the hepatic branch has more IGLEs. The finding that three different vagal branches innervate the duodenum with different densities of afferent endings might indicate a viscerotopic receptive field that coordinates digestive functions in feeding.