Central connections of the lingual-tonsillar branch of the glossopharyngeal nerve and the superior laryngeal nerve in lamb

Effect of peripherally and cortically evoked swallows on jaw reflex responses in anesthetized rabbits

This study aimed to investigate whether the jaw-opening (JOR) and jaw-closing reflexes (JCR) are modulated during not only peripherally, but also centrally, evoked swallowing. Experiments were carried out on 24 adult male Japanese white rabbits. JORs were evoked by trigeminal stimulation at 1 Hz for 30 s. In the middle 10 s, either the superior laryngeal nerve (SLN) or cortical swallowing area (Cx) was simultaneously stimulated to evoke swallowing. The peak-to-peak JOR amplitude was reduced during the middle and late 10-s periods (i.e., during and after SLN or Cx stimulation), and the reduction was dependent on the current intensity of SLN/Cx stimulation: greater SLN/Cx stimulus current resulted in greater JOR inhibition. The reduction rate was significantly greater during Cx stimulation than during SLN stimulation. The amplitude returned to baseline 2 min after 10-s SLN/Cx stimulation. The effect of co-stimulation of SLN and Cx was significantly greater than that of SLN stimulation alone. There were no significant differences in any parameters of the JCR between conditions. These results clearly showed that JOR responses were significantly suppressed, not only during peripherally evoked swallowing but also during centrally evoked swallowing, and that the inhibitory effect is likely to be larger during centrally compared with peripherally evoked swallowing. The functional implications of these results are discussed.

Distribution of Fos-Like Immunoreactivity, Catecholaminergic and Serotoninergic Neurons Activated by the Laryngeal Chemoreflex in the Medulla Oblongata of Rats

The laryngeal chemoreflex (LCR) induces apnea, glottis closure, bradycardia and hypertension in young and maturing mammals. We examined the distribution of medullary nuclei that are activated by the LCR and used immunofluorescent detection of Fos protein as a cellular marker for neuronal activation to establish that the medullary catecholaminergic and serotoninergic neurons participate in the modulation of the LCR. The LCR was elicited by the infusion of KCl-HCl solution into the laryngeal lumen of adult rats in the experimental group, whereas the control group received the same surgery but no infusion. In comparison, the number of regions of Fos-like immunoreactivity (FLI) that were activated by the LCR significantly increased in the nucleus of the solitary tract (NTS), the vestibular nuclear complex (VNC), the loose formation of the nucleus ambiguus (AmbL), the rostral ventral respiratory group (RVRG), the ventrolateral reticular complex (VLR), the pre-Bötzinger complex (PrBöt), the Bötzinger complex (Böt), the spinal trigeminal nucleus (SP5), and the raphe obscurus nucleus (ROb) bilaterally from the medulla oblongata. Furthermore, 12.71% of neurons with FLI in the dorsolateral part of the nucleus of the solitary tract (SolDL) showed tyrosine hydroxylase-immunoreactivity (TH-ir, catecholaminergic), and 70.87% of neurons with FLI in the ROb were serotoninergic. Our data demonstrated the distribution of medullary nuclei that were activated by the LCR, and further demonstrated that catecholaminergic neurons of the SolDL and serotoninergic neurons of the ROb were activated by the LCR, indicating the potential central pathway of the LCR.

Ponto-medullary nuclei involved in the generation of sequential pharyngeal swallowing and concomitant protective laryngeal adduction in situ

Both swallowing and respiration involve postinspiratory laryngeal adduction. Swallowing-related postinspiratory neurons are likely to be located in the nucleus of the solitary tract (NTS) and those involved in respiration are found in the Kölliker-Fuse nucleus (KF). The function of KF and NTS in the generation of swallowing and its coordination with respiration was investigated in perfused brainstem preparations of juvenile rats (n = 41). Orally injected water evoked sequential pharyngeal swallowing (s-PSW) seen as phasic, spindle-shaped bursting of vagal nerve activity (VNA) against tonic postinspiratory discharge. KF inhibition by microinjecting isoguvacine (GABAA receptor agonist) selectively attenuated tonic postinspiratory VNA (n = 10, P < 0.001) but had no effect on frequency or timing of s-PSW. KF disinhibition after bicuculline (GABAA receptor antagonist) microinjections caused an increase of the tonic VNA (n = 8, P < 0.01) resulting in obscured and delayed phasic s-PSW. Occurrence of spontaneous PSW significantly increased after KF inhibition (P < 0.0001) but not after KF disinhibition (P = 0.14). NTS isoguvacine microinjections attenuated the occurrence of all PSW (n = 5, P < 0.01). NTS bicuculline microinjections (n = 6) resulted in spontaneous activation of a disordered PSW pattern and long-lasting suppression of respiratory activity. Pharmacological manipulation of either KF or NTS also triggered profound changes in respiratory postinspiratory VNA. Our results indicate that the s-PSW comprises two functionally distinct components. While the primary s-PSW is generated within the NTS, a KF-mediated laryngeal adductor reflex safeguards the lower airways from aspiration. Synaptic interaction between KF and NTS is required for s-PSW coordination with respiration as well as for proper gating and timing of s-PSW.

The generation of pharyngeal phase of swallow and its coordination with breathing: interaction between the swallow and respiratory central pattern generators

Swallowing and breathing utilize common muscles and an anatomical passage: the pharynx. The risk of aspiration of ingested material is minimized not only by the laryngeal adduction of the vocal folds and laryngeal elevation but also by the precise coordination of swallows with breathing. Namely, swallows: (1) are preferentially initiated in the postinspiratory/expiratory phase, (2) are accompanied by a brief apnea, and (3) are often followed by an expiration and delay of the next breath. This review summarizes the expiratory evidence on the brainstem regions comprising the central pattern generator (CPG) that produces the pharyngeal stage of swallow, how the motor acts of swallowing and breathing are coordinated, and lastly, brainstem regions where the swallowing and respiratory CPGs may interact in order to ensure "safe" swallows.

Water drinking-related muscle contraction induces the pressor response via mechanoreceptors in conscious rats

Water drinking is known to induce the pressor response. The efferent pathway in this response involves sympathoexcitation, because the pressor response was completely abolished by ganglionic blockade or an α(1)-adrenergic antagonist. However, the afferent pathway in this response has not been identified. In the present study, we hypothesized that water itself stimulates the upper digestive tract to induce the pressor response, and/or drinking-related muscle contraction induces the pressor response via mechanoreceptors. To examine this hypothesis, we evaluated the pressor response induced by spontaneous or passive water drinking in conscious rats. Since the baroreflex modulates and obscures the pressor response, the experiments were conducted using rats with sinoaortic denervation. The pressor response was not suppressed by 1) transient oral surface anesthesia using lidocaine, 2) bilateral denervation of the glossopharyngeal nerve and sensory branch of the superior laryngeal nerve, or 3) denervation of the tunica adventitia in the esophagus. However, the pressor response was significantly suppressed (by -52%) by intravenous gadolinium chloride administration. Electrical stimulation of the hypoglossal nerve induced the pressor response, which was significantly suppressed (by -57%) by intravenous gadolinium chloride administration and completely abolished by severing the distal end of this nerve. These results indicate that afferent signals from mechanoreceptors in drinking-related muscles are involved in the water drinking-induced pressor response.

The central projections of the laryngeal nerves in the rat

The larynx serves respiratory, protective, and phonatory functions. The motor and sensory innervation to the larynx controlling these functions is provided by the superior laryngeal nerve (SLN) and the recurrent laryngeal nerve (RLN). Classical studies state that the SLN innervates the cricothyroid muscle and provides sensory innervation to the supraglottic cavity, whereas the RLN supplies motor innervation to the remaining intrinsic laryngeal muscles and sensory innervation to the infraglottic cavity, but recent data suggest a more complex anatomical and functional organisation. The current neuroanatomical tracing study was undertaken to provide a comprehensive description of the central brainstem connections of the axons within the SLN and the RLN, including those neurons that innervate the larynx. The study has been carried out in 41 adult male Sprague-Dawley rats. The central projections of the laryngeal nerves were labelled following application of biotinylated dextran amines onto the SLN, the RLN or both. The most remarkable result of the study is that in the rat the RLN does not contain any afferent axons from the larynx, in contrast to the pattern observed in many other species including man. The RLN supplied only special visceromotor innervation to the intrinsic muscles of the larynx from motoneurons in the nucleus ambiguus (Amb). All the afferent axons innervating the larynx are contained within the SLN, and reach the nucleus of the solitary tract. The SLN also contained secretomotor efferents originating from motoneurons in the dorsal motor nucleus of the vagus, and special visceral efferent fibres from the Amb. In conclusion, the present study shows that in the rat the innervation of the larynx differs in significant ways from that described in other species.

Sensory input pathways and mechanisms in swallowing: a review

Over the past 20 years, research on the physiology of swallowing has confirmed that the oropharyngeal swallowing process can be modulated, both volitionally and in response to different sensory stimuli. In this review we identify what is known regarding the sensory pathways and mechanisms that are now thought to influence swallowing motor control and evoke its response. By synthesizing the current state of research evidence and knowledge, we identify continuing gaps in our knowledge of these mechanisms and pose questions for future research.

Extensive reorganization of primary afferent projections into the gustatory brainstem induced by feeding a sodium-restricted diet during development: less is more

Neural development is especially vulnerable to environmental influences during periods of neurogenesis and rapid maturation. In fact, short periods of environmental manipulations confined to embryonic development lead to significant changes in morphology and function. A guiding principal emerging from studies of sensory systems is that experimentally induced effects are most dramatic in higher neural levels (e.g., cortex) and primarily involve postnatal synaptic refinements. In contrast to other sensory systems, the gustatory system is particularly susceptible to the effects of deprivation much earlier and with profound changes evident in the brainstem. Here we show that feeding pregnant rats a custom diet featuring a low-sodium content for 9 d before the tongue appears in the fetus produces extensive restructuring of the gustatory brainstem. Rats born to mothers fed the custom diet from embryonic day 3 (E3) to E12 have terminal field volumes of the greater superficial petrosal, chorda tympani, and glossopharyngeal nerves at adulthood that are expanded as much as 10 times beyond that found in rats fed a standard rat chow. The widespread alterations are not attributable to increased numbers of nerve cells, increased target size, or obvious changes in peripheral taste function. Moreover, we show that the limited period of feeding the custom diet has much larger effects than if rats were fed the diet to postweaning ages. Our results suggest that early periods of altered experience, especially during nucleus of the solitary tract neurogenesis, leads to a restructuring of the gustatory brainstem, which in turn may impact the control of sensory and homeostatic processes.

Ultrastructure and synaptology of the paratrigeminal nucleus in the rat: primary pharyngeal and laryngeal afferent projections

The paratrigeminal nucleus (PTN) receives primary afferent projections from the aerodigestive tract and orofacial regions and plays a role in the integration of visceral and somatic information. This study describes the fine structure of the rat PTN and the synaptology of primary afferent projections from the pharynx and larynx. Injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) or cholera toxin-HRP (CT-HRP) were made into the wall of the pharynx or larynx to label primary afferent axon terminals. Light microscopic observations demonstrated that afferent axons terminated bilaterally in overlapping fields in the PTN. Electron microscopic observations of the PTN revealed that there were three distinct classes of neurons, based on morphology and axosomatic contacts. The most abundant neurons, Type 1, were fusiform in shape and received very few or no axosomatic contacts. Type 2 neurons contained prominent Nissl substance (rough endoplasmic reticulum) and few axosomatic contacts, while Type 3 neurons had many axosomatic synapses. Terminals containing round, clear vesicles and forming asymmetric contacts (round asymmetric, RA) with dendrites were the predominant synaptic type in the PTN. Primary afferent terminals from the pharynx and larynx were of the RA type and formed synaptic contacts with small-diameter (<1 microm) dendrites. Visceral primary afferent inputs from the pharynx and larynx overlap with trigeminal somatic afferents in the PTN and have similar synaptic morphology. The results support the concept that the PTN provides an anatomical substrate for mediating viscerovisceral and somatovisceral reflexes via efferent connections with autonomic centers in the brainstem.

Proyecciones centrales del nervio laríngeo superior de la rata

Laryngeal nerves contain the fibres that control the laryngeal function. On the rat, the studies on the functional components and the real origin of the fibres conveyed by the superior laryngeal nerve (SLN) are few. No one of such works were developed using biotinylated dextrane amines (BDA), a powerful tool for tracing neural pathways. The aim of our study was to identify by using BDA, in the rat, the nuclei of real origin of the fibres of the SLN, knowing in this way the functional components of this nerve. The study has been developed in 11 adult male Sprague-Dawley rats, applying the BDA into the damaged SLN. The results obtained in all the animals shown that the rat SLN carries efferent fibres originated within the ipsilateral nucleus ambiguous (NA) and dorsal nucleus of the vagus (DNV), and that afferent fibres reach the tractus solitari and the nucleus tractus solitari. So, in the rat, the SLN seems to convey efferent fibres from the NA and DNV and, probably, all the laryngeal afferent fibres.

Functional and morphological organization of the nucleus tractus solitarius in the fictive cough reflex of guinea pigs

Projection of the superior laryngeal nerve (SLN) afferent fibers into the nucleus tractus solitarius (NTS) was investigated using a fluorescent tracer in guinea pigs. High density of fluorescence was detected in the ipsilateral NTS extending from 0.5 mm caudal to 1.2 mm rostral to the obex. At coronal slices, the fluorescent granules, lines and patches were located in the interstitial, medial and dorsal regions of NTS. Fluorescence was also found in the dorsal region of contralateral commissural NTS. Microstimulation of the rostral NTS, which corresponded to the region showing the strong fluorescence, induced an increase in the inspiratory discharge of phrenic nerve that was immediately followed by a large burst discharge of the iliohypogastric nerve in decerebrate, paralyzed and artificially ventilated guinea pigs. This serial response of the two nerves was identical to that induced by electrical stimulation of the SLN. Intravenous injection of codeine suppressed both NTS and SLN-induced responses. The SLN-induced response was inhibited by microinjection of codeine into the ipsilateral NTS and abolished by lesion of the ipsilateral NTS. These results suggest that the NTS has an integrative function in production of cough reflex and is possible sites of action of central antitussive agents.

Water stimulation of the posterior oral cavity induces inhibition of gastric motility

The response of gastric motility to the administration of water and saline in the larynx and epiglottis was investigated in urethan-chloralose anesthetized rats. Administration of water inhibited motility of the distal stomach, but 0.15 M NaCl did not induce the inhibitory response. Bilateral sectioning of the superior laryngeal nerve (SLN) abolished the inhibitory response induced by water. Bilateral cervical vagotomies abolished the inhibitory responses, although spinal transection did not affect the inhibitory response. These inhibitory responses have been observed in immobilized animals. The degree of inhibition by water and hypotonic saline was negatively correlated with the sodium concentration. In contrast, the degree of inhibition to hypertonic saline was positively correlated with the sodium concentration. The proximal stomach also showed a reduction in intragastric pressure in response to the administration of water. These findings suggest that water-responsive afferent neurons in the SLN suppress gastric motility via the vagal efferent nerve.

Effect of superior laryngeal nerve transection on pharyngeal muscle contraction timing and sequence of activity during eating and stimulation of the nucleus solitarius in dogs

The effect of unilateral or bilateral transection of the superior laryngeal nerve on the electromyographic activity in the hyopharyngeal, thyropharyngeal, and cricopharyngeal muscles was studied in 10 dogs during eating and during unilateral electrical stimulation of the solitary nucleus. In all groups of dogs, after unilateral or bilateral transection, there were some swallowing actions in which the sequence of activity in the pharyngeal muscles was disturbed during eating and during stimulation of the solitary nucleus. In the dogs in which the transection was unilateral, this fraction was 18% in the ipsilateral muscles during eating and 7% in the contralateral muscles. After bilateral transection it was 8% in the left muscles and 16% in the right muscles. The fractions were not significantly different when swallowing was evoked by stimulation of the solitary nucleus. Swallowing actions having a normal sequence of activity in these dogs were compared with those in a group of eight dogs in which the superior laryngeal nerves were intact. Contraction timing was not significantly different during eating, but during stimulation of the solitary nucleus the timing was significantly shorter than in the dogs with intact nerves. It was concluded that superior laryngeal nerve transection modulates the central pattern generator for pharyngeal swallowing in dogs.

Central control of the cardiovascular and respiratory systems and their interactions in vertebrates

This review explores the fundamental neuranatomical and functional bases for integration of the respiratory and cardiovascular systems in vertebrates and traces their evolution through the vertebrate groups, from primarily water-breathing fish and larval amphibians to facultative air-breathers such as lungfish and some adult amphibians and finally obligate air-breathers among the reptiles, birds, and mammals. A comparative account of respiratory rhythm generation leads to consideration of the changing roles in cardiorespiratory integration for central and peripheral chemoreceptors and mechanoreceptors and their central projections. We review evidence of a developing role in the control of cardiorespiratory interactions for the partial relocation from the dorsal motor nucleus of the vagus into the nucleus ambiguus of vagal preganglionic neurons, and in particular those innervating the heart, and for the existence of a functional topography of specific groups of sympathetic preganglionic neurons in the spinal cord. Finally, we consider the mechanisms generating temporal modulation of heart rate, vasomotor tone, and control of the airways in mammals; cardiorespiratory synchrony in fish; and integration of the cardiorespiratory system during intermittent breathing in amphibians, reptiles, and diving birds. Concluding comments suggest areas for further productive research.

Pharyngeal branch of the vagus nerve carries intraepithelial afferent fibers in the cat pharynx: an elucidation of the origin and central and peripheral distribution of these components

The presence of a sensory component in the pharyngeal branch of the vagus nerve (PhB), including its peripheral distribution and central projection, was studied by denervation and tracer experiments in the cat. The distribution of nerve fibers immunoreactive to protein gene product 9.5, a sensitive neuronal marker; calcitonin gene-related peptide; and substance P in the pharyngeal epithelium was analyzed in both intact animals and animals subjected to partial denervation by means of sectioning two of the three nerve trunks, the glossopharyngeal nerve, the superior laryngeal nerve, and the PhB, while leaving one intact. The results of this study show that the glossopharyngeal nerve and superior laryngeal nerve carry nerve fibers to the pharyngeal epithelium rostral and caudal to the middle level of the epiglottis, respectively, whereas the PhB carries nerve fibers to the mesopharyngeal epithelium. Tracer experiments, by applying wheat germ agglutinin-horseradish peroxidase to the PhB, demonstrated retrogradely labeled primary sensory neurons in the jugular ganglion and transganglionic labeling of terminals in the interstitial subnucleus of the nucleus of the tractus solitarius. These results indicate that the PhB contains a sensory component that originates from the jugular ganglion, innervates the mesopharyngeal epithelium, and projects to the nucleus of the tractus solitarius.

Distribution and origin of the intraepithelial nerve fibres in the feline pharyngeal mucosa

Sensory inputs from the pharynx play an important role in initiation of the swallowing reflex and in feedback control of motor activities. Using an immunohistochemical technique and denervation procedures, we examined the distribution and origin of the intraepithelial nerve fibres in the feline pharyngeal mucosa to clarify the role of the afferent nerve in swallowing. The posterior pillar was very densely innervated, and the posterior and lateral walls of the mesopharynx had a moderate nerve density. In contrast, the base of the tongue, the vallecula, the pharyngeal surface of the epiglottis, and the pyriform sinus had only a few nerve fibres. The epithelium of the rostral and caudal portions of the pharyngeal mucosa were innervated by the glossopharyngeal nerve and superior laryngeal nerve, respectively, with a borderline at the middle level of the epiglottis. A portion of the intraepithelial nerve fibres in the lateral and posterior walls of the mesopharynx originated from the pharyngeal branch of the vagus nerve. It is hypothesized that the intraepithelial nerve fibres that exist in densely innervated areas are related to the initiation of the swallowing reflex induced by stimulation of the pharyngeal mucosa.

Association of leptin receptor (OB-Rb), NPY and GLP-1 gene expression in the ovine and murine brainstem

Appetite-related neuropeptide systems have not been studied extensively in the ruminant, although there have been a number of recent studies of the hypothalamus. Since some leptin signaling is integrated in the rodent brainstem, and leptin modulates neuropeptidergic activity, we now describe leptin receptor (long splice variant, OB-Rb), neuropeptide Y (NPY) and glucagon-like peptide-1 (GLP-1) gene expression in the ovine brainstem. Leptin receptor mRNA was localized to the spinal trigeminal tract and nucleus, nucleus of the solitary tract (NTS), area postrema and dorsal motor nucleus of the vagus. NPY gene expression was abundant in the ovine medulla, occurring in two bilateral 'bands' that encompassed the NTS region and ran ventrolaterally. GLP-1 mRNA was confined largely to the NTS. The distribution of OB-Rb mRNA overlapped with that of NPY and GLP-1 gene expression, suggesting the possibility of interaction between leptin and these brainstem neuropeptide systems. However, in an extension of earlier work, co-expression studies in the murine brainstem revealed only a small number of neurons that expressed both NPY and leptin receptor mRNA, despite the widespread and abundant expression of the former. Thus the majority of NPY synthesis in the brainstem may not be directly regulated by leptin. The sheep brainstem had similar anatomical distribution of OB-Rb, NPY and GLP-1 gene expression to the rodent, consistent with a role for this region in peripheral leptin feedback signaling and brainstem-hypothalamo communication.

Crossing inputs of the superior laryngeal nerve afferents to medullary swallowing-related neurons in the cat

To understand the neural mechanism for generation of synchronous activity on both sides during swallowing, we examined the convergence of inputs from the bilateral superior laryngeal nerves (SLNs) in the urethane-anesthetized cat medulla and we also examined the changes in swallowing outputs after a longitudinal brain-stem split in decerebrate cats. Twenty-six (31%) of 84 swallowing-related neurons (SRNs) that were oligosynaptically activated by ipsilateral SLN stimulation and recorded mostly in the reticular formation received contralateral inputs, which were confirmed by orthodromic spike responses (n = 16) or were detected as subliminal facilitatory or inhibitory inputs (n = 10) using conditioning-test stimuli. The rate of convergence of inputs from bilateral SLNs in these SRNs was significantly higher than that (4%) in the SRNs that were regarded as sensory-relay neurons in the nucleus tractus solitarius (NTS). The SRNs receiving signals from the contralateral SLN were located diffusely from the NTS and the adjacent reticular formation to the nucleus ambiguus (NA) and the reticular formation dorso-medial to the NA. A midsagittal split from 3 mm caudal to 6 mm rostral to the obex could change symmetrical swallowing to unilateral swallowing. Thus the crossing projections to the contralateral SRNs appear to contribute to symmetrical swallowing.

Effect of stimulating peripheral and central neural pathways on pharyngeal muscle contraction timing during swallowing in dogs

The effect of stimulating peripheral and central neural pathways on the electromyographic activity in the hyopharyngeal, thyropharyngeal, and cricopharyngeal muscles was studied in eight dogs during 1) eating, 2) unilateral electrical stimulation of the superior laryngeal nerve, and 3) unilateral electrical stimulation of the solitary nucleus. The duration of pharyngeal swallowing was significantly shorter during eating than during stimulation of the solitary nucleus in the anesthetized dog (mean difference 127 ms, SEM 9, n = 15). The duration of pharyngeal swallowing was significantly shorter during eating than during stimulation of the superior laryngeal nerve in the awake dog (mean difference 84 ms, SEM 13, n = 9). The duration of pharyngeal swallowing during stimulation of the superior laryngeal nerve under anesthesia was significantly shorter than during stimulation of the solitary nucleus under anesthesia (mean difference 58 ms, SEM 18, n = 9). The difference in duration of pharyngeal swallowing during stimulation of the superior laryngeal nerve between the awake state and during anesthesia was not significant (mean 19 ms, SEM 14, n = 9). It was concluded that stimulation of peripheral and central neural pathways resulted in different pharyngeal muscle contraction timing during swallowing in dogs.

Central distribution and peripheral functional properties of afferent and efferent components of the superior laryngeal nerve: morphological and electrophysiological studies in the rat

The central distribution of the afferent and efferent components of the superior laryngeal nerve (SLN), which in the rat is ramified into the three branches of the rostral branch (R.Br), middle branch (M.Br), and caudal branch (C.Br), was examined after application of horseradish peroxidase conjugated with wheat germ agglutinin (HRP-WGA) to the proximal cut end of each branch. In addition, the afferent and efferent neural activities of each branch were recorded to investigate the functional properties. The present study provided several new findings as to the distribution of each branch and the functional properties of the SLN. The following conclusions were drawn: 1) the R.Br, containing only afferent fibers projecting to the ipsilateral lateral region of the nucleus of the solitary tract (NST), extends between slightly below the obex and the region approximately 0.6 mm rostral from the obex, and it corresponds to the interstitial subnucleus of the NST; 2) the M.Br, innervating the cricothyroid muscle, contains only efferent fibers originating ipsilaterally from the motoneurons localized within the ambiguus nucleus (Amb) and in the area ventrolateral to the Amb; and 3) the C.Br, which innervates the inferior pharyngeal constrictor muscle, contains both efferent and afferent fibers. HRP-WGA-labeled cells are distributed within both the Amb and the dorsal motor nucleus of the vagus nerve, ipsilateral to the injection site. Afferent proprioceptive fibers project to the ipsilateral interstitial subnucleus of the NST. The present results provide evidence that each branch of the SLN has distinctive functional properties and contributes to the laryngeal functions.

The sites of origin and termination of afferent and efferent components in the lingual and pharyngeal branches of the glossopharyngeal nerve in the Japanese monkey (Macaca fuscata)

Afferent and efferent components in the lingual and pharyngeal branches of the glossopharyngeal nerve (Li and Ph) of the Japanese monkey (Macaca fuscata) were examined. After injecting wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) unilaterally into the central cut end of the Li and Ph, or into the stylopharyngeal muscle, labeled neuronal cell bodies and terminal labeling were observed in the medulla oblongata, peripheral ganglia of the glossopharyngeal and vagus nerves, and cervical ganglia of the sympathetic trunk. The following conclusions were deduced from the results. The Li contains efferent fibers from the inferior salivatory nucleus, and superior cervical ganglion. The afferent fibers in the Li are composed mainly of peripheral processes of ganglion neurons in the superior and petrous ganglia of the glossopharyngeal nerve, and additionally of those of ganglion neurons in the jugular ganglion of the vagus nerve. The afferent fibers in the Li terminate mainly in the lateral division of the nucleus of the solitary tract, and additionally in the dorsal aspect of the lateral marginal region of the interpolar spinal trigeminal nucleus. The Ph is mainly composed of efferent fibers from the ambiguous nucleus and superior cervical ganglion; only a small number of afferent fibers from the sensory ganglia of the glossopharyngeal and vagus nerves are contained in the Ph. Stylopharyngeal motoneurons are distributed in the retrofacial part of the ambiguous nucleus.

Distribution and synaptology of glossopharyngeal afferent nerve terminals in the nucleus of the solitary tract of the hamster

The distribution and synaptology of the afferent fibers of the glossopharyngeal nerve (IXN) in the hamster were studied by using horseradish peroxidase (HRP) histochemistry visualized with light and electron microscopy. Crystals of HRP were applied to the trunk of IXN in the vicinity of the petrosal ganglion. The densest IXN afferent label was distributed within the nucleus of the solitary tract (nst), just caudal to but overlapping with the area of termination of the facial nerve. Labeled IXN fibers extended rostrally to the principal trigeminal nucleus and caudally to the cervical spinal cord. There was significant labeling within the spinal trigeminal complex; the area postrema and the medullary reticular formation contained some labeled fibers. Ultrastructurally, the synaptic arrangements of anterogradely labeled IXN fibers were examined in the nst. Quantitative measures were taken of the area, maximum diameter, perimeter, and vesicles of labeled endings and the length of their synaptic junctions with dendritic processes. These endings were compared to comparable endings in control material and to published descriptions of VIIth nerve afferent terminals in the hamster nst. The synaptic relations of IXN afferent endings were predominantly with dendritic spines and shafts. The majority (86.6%) of IXN afferent endings were with dendritic processes that were not in apparent contact with other, unlabeled processes. Only 13.4% of IXN synaptic relationships were with dendritic processes that were also contacted by unlabeled vesicle-containing processes. This is in contrast to 31.2% of facial nerve afferent endings in the nst which make synaptic contact with such processes. There were more direct synaptic contacts between facial endings and unlabeled vesicle-containing processes (26.1%) than between IXN endings and unlabeled vesicle-containing processes (1.3%). Thus, unlike the glomerular-like endings of the gustatory fibers of the VIIth nerve, less complex relations appeared to characterize IXN synapses in the nst. These differences were related to the differential physiology of gustatory fibers in the VIIth nerve and IXN.

An anterograde-retrograde labeling study of the carotid sinus nerve of the Japanese monkey (Macaca fuscata)

The sites of origin and termination of efferent and afferent fibers in the carotid sinus nerve (CSN) were investigated in the Japanese monkey. After application of a mixture of horseradish peroxidase (HRP) and wheat germ aggulutinin-conjugated HRP to the central cut end of the CSN, sensory ganglion neurons were labeled in the jugular ganglion of the vagus nerve, as well as in the superior and petrosal ganglia of the glossopharyngeal nerve. Many sympathetic ganglion neurons were also labeled retrogradely in the superior cervical ganglion. In the brain, many labeled terminals were seen ipsilaterally in the lateral division of the nucleus of the solitary tract (NST). A few neuronal cell bodies were also labeled ipsilaterally in a reticular region dorsomedial to the caudal one-third of the facial nucleus. The results indicate that the CSN of the Japanese monkey is composed mainly of afferent fibers terminating in the NST, that the afferent fibers in the CSN originate not only from the superior and petrosal ganglia of the glossopharyngeal nerve but also from the jugular ganglion of the vagus nerve, and that efferent fibers contained in the CSN arise from the medullary reticular formation and superior cervical ganglion.

Studies on nerves of the upper respiratory tract in the ferret and the mink

The central localization of the superior laryngeal nerve (SLN), recurrent laryngeal nerve (RLN) and pharyngeal nerve (PHAR) in the ferret (Mustela putorius furo) and mink (Mustela vision) was determined by neuronal tract tracing techniques. The anterograde transport of horseradish peroxidase (HRP)/wheat germ aggluttinin conjugated HRP mixtures (WGA-HRP) revealed afferent fibres of the SLN projecting ipsilaterally in the tractus solitarius (TS) before terminating in the ipsilateral nucleus of the tractus solitarius (nTS). In both mustelids large concentrations of terminal reaction product were observed in the dorsal/dorsolateral and medial subnuclei of the nTS; however, at levels near obex significant projections of the SLN to the interstitial subnucleus were also observed. Caudal to obex, sparse terminal labelling was identified bilaterally in the nucleus commissuralis (n com). There were no labelled afferent projections of the SLN to the spinal trigeminal complex in either mustelid; neither was afferent terminal reaction product detected in the medulla oblongata following labelling of the RLN (in either the ferret or the mink) or PHAR (in the ferret). Projection of the SLN to areas of the nTS associated with upper airway functions, like swallowing and respiration, suggest a substantial role for this nerve in the initiation and control of airway reflexes. Extensive labelling of the nucleus ambiguus (nA) was revealed following HRP/WGA-HRP application to the PHAR, RLN and SLN and there was some evidence of a topographical arrangement of neuronal cell bodies in the nA, relative to the different nerves, in the ferret. In the case of the SLN, retrogradely labelled cells were also identified in the dorsal motor nucleus of the vagus (DmnX), nTS and reticular formation (rf). Electrical stimulation of the SLN produced periods of apnoea/ataxic breathing in both mustelids. As well as respiratory effects, stimulation of the SLN often caused bradycardia in the mink, but not in the ferret, in which heart rate generally remained unchanged. This difference did not reflect anatomical differences in the central localization of the SLN.

Convergence of afferents from the SLN and GPN in cat medullary swallowing neurons

We demonstrated the convergence of information from the pharyngeal and laryngeal mucosa, transmitted by the glossopharyngeal nerve (GPN) and superior laryngeal nerve (SLN), in the nucleus of the tractus solitarius (NTS). First, the distribution of terminals of the GPN and SLN in the NTS was examined by an HPR tracing technique in cats, and the synapse formation of these neurons with NTS neurons was demonstrated by electron microscopy. The HRP-labeled SLN and GPN terminals were localized in a small area of the interstitial subnucleus of the NTS, slightly rostral to the obex, forming synapses with NTS neurons. Next, using extracellular recording in anesthetized cats, we determined whether or not swallowing-related neurons in the medulla oblongata receive peripheral inputs. Convergence of peripheral sensory inputs from the SLN and GPN was observed in more than 80% of the NTS cells. These results suggest that the NTS is not only a sensory-relay nucleus but also integrates information necessary for eliciting protective reflexes of the upper airway, such as swallowing.

Glossopharyngeal evoked potentials in normal subjects following mechanical stimulation of the anterior faucial pillar

The anterior faucial pillar, which is innervated by the glossopharyngeal nerve, is thought to be important in eliciting the pharyngeal swallow in awake humans. Glossopharyngeal evoked potentials (GPEP), elicited by mechanically stimulating this structure, were recorded from 30 normal adults using standard averaging techniques and a recording montage of 16 scalp electrodes. Ten of the subjects experienced a desire to swallow in response to stimulation. Repeatable responses were recorded from all 30 subjects. The GPEPs recorded from the posterior scalp were W-shaped and consisted of P1, N1, P2, N2 and P3 peaks. Mean latencies of P1, N1 and P2 were 11, 16 and 22 msec, respectively, for both left and right pillar stimulation. In contrast, latencies of N2 and P3 varied significantly between left and right pillar stimulation. Mean latencies of N2 and P3 were 27 and 34 msec for left, and 29 and 35 msec for right pillar stimulation. Topographical maps acquired at peak latencies for P1, N1 and P2 revealed consistent asymmetrical voltage distributions between the two hemispheres; the largest responses were recorded from the hemisphere ipsilateral to the side of stimulation. The scalp topography of N2 and P3 varied between male and female subjects as well as between left and right pillar stimulation. These findings support the hypothesis that mechanical stimulation to the anterior faucial pillar alone can elicit repeatable responses from the central nervous system. The integration of this subcortical/cortical activity with that of the medullary swallowing center may play an important role in eliciting the pharyngeal swallow.

Fine structure of taste buds located on the lamb epiglottis

BACKGROUND

Taste buds located on the aryepiglottal folds and laryngeal surface of the epiglottis are the principal receptors responsible for the initiation of the laryngeal chemoreflex. In contrast to the wealth of information available concerning the ultrastructure of oral taste buds, little comparable data exists for taste buds located at the entrance to the larynx. Therefore, the present study was designed to investigate the fine structure of taste buds located on the lamb epiglottis.

MATERIALS

Stained thick and semi-serial thin sections from taste buds located on the lamb epiglottis were examined with light and electron microscopy.

RESULTS

Based on morphological criteria, three types of cells could be identified in the taste bud: Type I, Type II, and basal cells. Both Type I and Type II cells extended into the apical taste pore, but there were differences between these two cell types with regard to nuclear profiles, electron density, and the relative density of ribosomes, apical mitochondria, and rough and smooth endoplasmic reticulum. Basal cells did not extend a process into the taste pore. Nerve processes were observed throughout the taste bud. Synapses were observed between both Type I and Type II cells and nerve fibers. These synapses exhibited membrane thickenings and accumulations of clear and dense-cored vesicles of varying proportions in the taste cell cytoplasm adjacent to membrane specializations.

CONCLUSIONS

The taste buds located on the lamb epiglottis share several structural similarities to taste buds located in the oral cavity and other regions of the pharynx and larynx of many mammalian species. The presence of synapses on both Type I and Type II cells of the lamb epiglottal taste bud suggests that both cell types are involved in laryngeal chemoreception.

Central distribution of substance P, calcitonin gene-related peptide and 5-hydroxytryptamine in vagal sensory afferents in the rat dorsal medulla

The central distribution of vagal afferents in the medulla containing either substance P, calcitonin gene-related peptide or 5-hydroxytryptamine was examined using a double-labelling technique and laser scanning confocal microscopy. Areas of the nucleus tractus solitarii, dorsal motonucleus of the vagus nerve and area postrema were scanned for double-labelled axon profiles. Analysis of this material revealed that all three neurochemicals were contained within the central terminals of vagal nerve sensory neurons. However, the distribution of vagal nerve afferents containing each of these putative transmitters differed. Afferents containing 5-hydroxytryptamine were detected mainly in the areas postrema and the adjacent nucleus tractus solitarii, with a smaller number in the ventral subnuclei of the solitary tract. In contrast afferents containing calcitonin gene-related peptide were found primarily in the medial and commissural regions of the nucleus tractus solitarii. Afferents containing substance P-immunoreactivity were surprisingly few in number and did not appear to be associated with any particular region. These results establish the presence of 5-hydroxytryptamine, substance P and calcitonin gene-related peptide in the central axons of vagal sensory afferents. Furthermore, the differential distribution of afferents immunoreactive for these neurochemicals seen in this study, together with previous demonstrations of the viscerotopic organization of vagal sensory afferents suggests a possible "chemical coding" for individual end organs.

Properties of the lingual and LVP branches of the glossopharyngeal nerve

We investigated the effects of various stimuli on the afferent and efferent branches of the glossopharyngeal nerve in the rat soft palate. One of the sensory components, the lingual branch, responded to tactile stimulation, while the LVP branch responded to stretching of the levator veli palatini muscle. We also obtained physiological and morphological evidence of the existence of muscle spindles in the levator veli palatini muscle and showed that tactile stimulation of the contralateral soft palate and stretching of the contralateral LVP modulated discharges from the motor component of the ipsilateral levator veli palatini muscle. Our results suggest that these receptor units with both sensory and motor efferents may be the main determinants of modulation of respiratory movements in the upper airway by the IXth nerve.

[The nucleus tractus solitarius: neuroanatomic, neurochemical and functional aspects]

The nucleus tractus solitarii (NTS) has long been considered as the first central relay for gustatory and visceral afferent informations only. However, data obtained during the past ten years, with neuroanatomical, biochemical and electrophysiological techniques, clearly demonstrate that the NTS is a structure with a high degree of complexity, which plays, at the medullary level, a key role in several integrative processes. The NTS, located in the dorsomedial medulla, is a structure of small size containing a limited number of neurons scattered in a more or less dense fibrillar plexus. The distribution and the organization of both the cells and the fibrillar network are not homogeneous within the nucleus and the NTS has been divided cytoarchitectonically into various subnuclei, which are partly correlated with the areas of projection of peripheral afferent endings. At the ultrastructural level, the NTS shows several complex synaptic arrangements in form of glomeruli. These arrangements provide morphological substrates for complex mechanisms of intercellular communication within the NTS. The NTS is not only the site of vagal and glossopharyngeal afferent projections, it receives also endings from facial and trigeminal nerves as well as from some renal afferents. Gustatory and somatic afferents from the oropharyngeal region project with a crude somatotopy within the rostral part of the NTS and visceral afferents from cardiovascular, digestive, respiratory and renal systems terminate viscero-topically within its caudal part. Moreover the NTS is extensively connected with several central structures. It projects directly to multiple brain regions by means of short connections to bulbo-ponto-mesencephalic structures (parabrachial nucleus, motor nuclei of several cranial nerves, ventro-lateral reticular formation, raphe nuclei...) and long connections to the spinal cord and diencephalic and telencephalic structures, in particular the hypothalamus and some limbic structures. The NTS is also the recipient of several central afferent inputs. It is worth to note that most of the structures that receive a direct projection from the NTS project back to the nucleus. Direct projections from the cerebral cortex to the NTS have also been identified. These extensive connections indicate that the NTS is a key structure for autonomic and neuroendocrine functions as well as for integration of somatic and autonomic responses in certain behaviors. The NTS contains a great diversity of neuroactive substances. Indeed, most of the substances identified within the central nervous system have also been detected in the NTS and may act, at this level, as classical transmitters and/or neuromodulators.(ABSTRACT TRUNCATED AT 400 WORDS)

Intramedullary connections of the rostral nucleus of the solitary tract in the hamster

The rostral nucleus of the solitary tract (NST) figures prominently in the gustatory system, giving rise to ascending taste pathways that are well documented. Less is known of the local connections of the rostral NST with sites in the medulla. This study defines the intramedullary connections of the rostral NST in the hamster. Small iontophoretic injections of horseradish peroxidase (HRP), confined to the rostral NST, resulted in Golgi-like filling of axons that exited the NST or that interconnected cytoarchitectonic subdivisions within the NST complex. The NST efferent axons terminated sparsely in the trigeminal, facial and hypoglossal motor nuclei, but axons and endings were heavily distributed in the parvicellular reticular formation ventral to the NST. HRP injections centered in this part of the reticular formation resulted in heavy projections to the orofacial motor nuclei. Intranuclear connections, labelled after NST injections, linked NST subdivisions that receive primary afferent taste inputs to subdivisions involved in (1) projections to the preoromotor reticular formation, (2) projections to swallowing motor neurons, (3) activation of preganglionic parasympathetic neurons, and (4) general viscerosensation. In general, the connections defined in the present study provide anatomical details about the substrate for gustatory-motor and gustatory-visceral interactions.

Primary afferent projections from the upper respiratory tract in the muskrat

The central projections of the ethmoidal, glossopharyngeal, and superior laryngeal nerves were determined in the muskrat by use of the transganglionic transport of a mixture of horseradish peroxidase (HRP) and wheat germ agglutinin (WGA)-HRP. The ethmoidal nerve projected to discrete areas in all subdivisions of the ipsilateral trigeminal sensory complex. Reaction product was focused in ventromedial portions of the principal nucleus, subnucleus oralis, and subnucleus interpolaris. The subnucleus oralis also contained sparse reaction product in its dorsomedial part. Projections were dense to ventrolateral parts of laminae I and II of the rostral medullary dorsal horn, with sparser projections to lamina V. Label in laminae I and V extended into the cervical dorsal horn. A few labeled fibers were followed to the contralateral dorsal horn. The interstitial neuropil of the ventral paratrigeminal nucleus was densely labeled. Extratrigeminal primary afferent projections in ethmoidal nerve cases involved the Kölliker-Fuse nucleus and ventrolateral part of the parabrachial nucleus, the reticular formation surrounding the rostral ambiguous complex, and the dorsal reticular formation of the closed medulla. Retrograde labeling in the brain was observed in only the mesencephalic trigeminal nucleus in these cases. The cervical trunk of the glossopharyngeal and superior laryngeal nerves also projected to the trigeminal sensory complex, but almost exclusively to its caudal parts. These nerves terminated in the dorsal and ventral paratrigeminal nuclei as well as lamina I of the medullary and cervical dorsal horns. Lamina V received sparse projections. The glossopharyngeal and superior laryngeal nerves projected to the ipsilateral solitary complex at all levels extending from the caudal facial nucleus to the cervical spinal cord. At the level of the obex, these nerves projected densely to ipsilateral areas ventral and ventromedial to the solitary tract. Additional ipsilateral projections were observed along the dorsolateral border of the solitary complex. Near the obex and caudally, the commissural area was labeled bilaterally. Labeled fibers from the solitary tract projected into the caudal reticular formation bilaterally, especially when the cervical trunk of the glossopharyngeal nerve received tracer. Labeled fibers descending further in the solitary tract gradually shifted toward the base of the cervical dorsal horn. The labeled fibers left the solitary tract and entered the spinal trigeminal tract at these levels. Retrogradely labeled cells were observed in the ambiguous complex, especially rostrally, and in the rostral dorsal vagal nucleus after application of HRP and WGA-HRP to either the glossopharyngeal or superior laryngeal nerves. In glossopharyngeal nerve cases, retrogradely labeled neurons also were seen in the inferior salivatory nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent projections of the superior and recurrent laryngeal nerves

The central afferent projections of the superior and recurrent laryngeal nerves were investigated in the rat, utilizing the transganglionic transport of WGA-HRP. Labelled superior laryngeal nerve terminal fields were found bilaterally in the interstitial and medial subnuclei of the nucleus tractus solitarii with the ipsilateral being more dense. The distribution of the recurrent laryngeal nerve terminals were similar to that of the SLN with two major differences: the projections were ipsilateral, and there was a marked decrease in the terminal field density. The terminal field density differences were confirmed by quantitatively identifying the labelled ganglion cells of the vagus nerve. These findings accurately delineate the first integrative components in the mediation of the complex laryngeal reflexes.

Subdivisions and neuron types of the nucleus of the solitary tract that project to the parabrachial nucleus in the hamster

The solitary nuclear complex (NST) consists of a number of subdivisions that differ in their cytoarchitectonic features as well as in the amounts of inputs they receive from lingual afferent axons. In this study horseradish peroxidase (HRP) was injected into the parabrachial nucleus (PBN) of the hamster to determine which of these subdivisions contain cells that project to the pons. In the rostral, gustatory division of the NST, the rostral central subdivision contains the greatest number of labelled pontine-projection neurons. The rostral lateral subdivision contains moderate numbers of labelled cells; progressively fewer labelled cells are in the ventral, medial, and dorsal subdivisions. In the caudal, general viscerosensory division of the NST, the caudal central subdivision contains the majority of labelled cells, although fewer than its rostral counterpart. Progressively fewer cells are labelled in the medial, laminar, ventrolateral, and lateral subdivisions; none in the dorsolateral subdivision. Small horseradish peroxidase injections into the pons revealed that cells of the rostral central and rostral lateral subdivisions of the NST project to the medial subdivision of the PBN, predominantly to caudal and ventral parts of the subdivision. Cells of the caudal central and medial subdivisions of the NST project to the central lateral subdivision of the PBN, predominantly to intermediate and rostral-dorsal parts of the subdivision. Outside the NST, cells in the spinal trigeminal nucleus and parvicellular reticular formation were also labelled after PBN injections. Within the rostral central and rostral lateral (gustatory) subdivisions of the NST at least two types of neurons, distinguished on the basis of dendritic and cell body morphology, were labelled after HRP injections that included the medial PBN. Elongate cells have ovoid-fusiform somata and dendrites oriented in the mediolateral plane parallel to primary afferent axons entering from the solitary tract. Stellate cells have triangular or polygonal cell bodies and three to five dendrites oriented in all directions, although one or two often extend mediolaterally. These results indicate that cytoarchitectonic subdivisions of the NST are distinguished by their efferent ascending connections. For each subdivision within the rostral, gustatory NST there is a correlation between the density of lingual inputs it receives and the density of pontine-projection neurons it contains.(ABSTRACT TRUNCATED AT 400 WORDS)

Prenatal development of the human nucleus ambiguus during the embryonic and early fetal periods

The ontogenetic development of the nucleus ambiguus was studied in a series of human embryos and fetuses ranging from 3 to 12.5 weeks of menstrual age (4 to 66 mm crown-rump length). They were prepared by Nissl and silver methods. Nucleus ambiguus neuroblasts, whose neurites extend towards and into the IXth and rostral Xth nerve roots, appear in the medial motor column of 4-6-week-old embryos (4.25-11 mm). These cells then migrate laterally (6.5 weeks, 14 mm) to a position near the dorsal motor nucleus of X. At 7 weeks (15 mm), nucleus ambiguus cells begin their migration, which progresses rostrocaudally, into their definitive ventrolateral position. The basic pattern of organization of the nucleus is established in its rostral region at 8 weeks (22.2-24 mm) and extends into its caudal region by 9 weeks (32 mm), when its nearly adult organization is evident. Cells having the characteristics of mature neurons first appear rostrally in the nucleus during the 8.5-9-week period (24.5-32 mm), gradually increase in number, and constitute the entire nucleus at 12.5 weeks (65.5 mm). Definitive neuronal subgroups first appear at 10 weeks (37.5 mm) in the large rostral nuclear region. These features suggest that the human nucleus ambiguus develops along a rostrocaudal temporospatial gradient. Evidence indicates that function of nucleus ambiguus neurons, manifested by fetal reflex swallowing, occurs after the cells migrate into their definitive position, establish the definitive nuclear pattern, and exhibit mature characteristics.

Distribution of postganglionic parasympathetic fibers originating in the pterygopalatine ganglion in the maxillary and ophthalmic nerve branches of the trigeminal nerve; HRP and WGA-HRP study in the guinea pig

The distribution of the postganglionic parasympathetic fibers originating in the pterygopalatine ganglion (PTPG) has been traced in the guinea pig by means of the HRP and WGA-HRP methods. The greatest number of labeled cells were observed when WGA-HRP was injected in the lacrimal gland. After applying HRP to all the ramifications of the maxillary and ophthalmic divisions of the trigeminal nerve, labeled neurons were found in the PTPG. Numerous PTPG fibers were detected in the ethmoidal and sphenopalatine nerves. The presence of PTPG fibers in the supraorbital, infratrochlear, zygomaticotemporal, zygomaticofacial-inferior palpebral, sphenopalatine and infraorbital-superior alveolar nerves has not hitherto been reported in mammals.

Segregation of coarse and fine glossopharyngeal axons in the visceral nucleus of the tractus solitarius of the cat

The projections of coarse and fine axons of the glossopharyngeal (IX) nerve upon the caudal two thirds of the nucleus of the tractus solitarius (NTS) were studied in the cat. These afferents convey the chemo- and baroreceptor activities from the carotid receptors. We applied the Fink-Heimer method on brainstem sections, at different survival times, after a petrosal ganglionectomy. A segregation of fine and coarse fibered components was observed. Degeneration of coarse axons was mostly found in the lateral NTS, while fine fiber degeneration was predominant in regions of the medial and commissural NTS. The injection of WGA-HRP in the different NTS divisions demonstrated that the lateral NTS was mainly innervated by the set of largest neurons of the petrosal ganglion and that the medial and the commissural NTS were innervated by the set of smaller neurons of the ganglia. These results were discussed in relation to cytoarchitecture, myeloarchitecture, distribution of normal axons, and known central connectivity of the different NTS divisions. We concluded that coarse and fine visceral afferents of the IX nerve, which includes the afferents of the carotid body and the carotid sinus, represent different afferent populations that project to particular divisions of the NTS and connect to different central pathways.

Viscerotopic representation of the upper alimentary tract in the rat: sensory ganglia and nuclei of the solitary and spinal trigeminal tracts

The aim of this study was to map the viscerotopic representation of the upper alimentary tract in the sensory ganglia of the IXth and Xth cranial nerves and in the subnuclei of the solitary and spinal trigeminal tracts. Therefore, in 172 rats 0.5-65 microliters of horseradish peroxidase (HRP), wheat germ agglutinin-HRP, or cholera toxin-HRP were injected into the trunks and major branches of the IXth and Xth cranial nerves as well as into the musculature and mucosa of different levels of the upper alimentary and respiratory tracts. The results demonstrate that the sensory ganglia of the IXth and Xth nerves form a fused ganglionic mass with continuous bridges of cells connecting the proximal and distal portions of the ganglionic complex. Ganglionic perikarya were labeled in crude, overlapping topographical patterns after injections of tracers into nerves and different parts of the upper alimentary tract. After injections into the soft palate, pharynx, esophagus, and stomach, anterograde labeling was differentially distributed in distinct subnuclei in the nucleus of the tractus solitarius (NTS). Palatal and pharyngeal injections resulted primarily in labeling of the interstitial and intermediate subnuclei of the NTS and in the paratrigeminal islands (PTI) and spinal trigeminal complex. Esophageal and stomach wall injections resulted in labeling primarily of the subnucleus centralis and subnucleus gelatinosus, respectively. The distribution of upper alimentary tract vagal-glossopharyngeal afferents in the medulla oblongata has two primary groups of components, i.e., a viscerotopic distribution in the NTS involved in ingestive and respiratory reflexes and a distribution coextensive with fluoride-resistant acid-phosphatase-positive regions of the PTI and spinal trigeminal nucleus presumably involved in visceral reflexes mediated by nociceptive or chemosensitive C fibers.

Response characteristics of lamb trigeminal neurons to stimulation of the oral cavity and epiglottis with different sensory modalities

A region of the trigeminal complex located at the border of the subnucleus interpolaris and subnucleus caudalis receives not only trigeminal nerve inputs from the face, tongue and palate, but also afferent terminations from other nerves which innervate the oral cavity and upper airway. To increase our understanding of the types of sensory information relayed to this region of the trigeminal nucleus, we investigated the response characteristics of single neurons to stimulation of the tongue, palate and epiglottis. Receptive field size and location of 83 trigeminal neurons were mapped, and responses to mechanical, thermal and chemical stimuli were recorded. About 90% of the neurons had one receptive field and no convergence between the oral cavity and epiglottis was observed. Furthermore, only about 15% of the trigeminal neurons responded to more than one stimulus modality. A moving mechanical stimulus elicited responses in over 90% of the cells, and 84% responded to moving and punctate mechanical stimuli. These mechanosensitive neurons generally exhibited rapidly adapting responses. Thermal and chemical stimuli were relatively ineffective. Cooling a receptor surface most often produced excitation, and warming inhibition. Responses to chemical stimuli were only observed for salts at high concentrations. These results suggest that, like oral cavity information relayed by the trigeminal nerve, afferent terminations in the trigeminal nucleus from other nerves subserving the oral cavity and upper airway function to relay mechanical sensory information.(ABSTRACT TRUNCATED AT 250 WORDS)

Gustatory innervation in the rabbit: central distribution of sensory and motor components of the chorda tympani, glossopharyngeal, and superior laryngeal nerves

Although rabbits have been used extensively in neurophysiological studies of the gustatory system, there is little information about the anatomical organization of taste in this species. Afferent and efferent central connections of three nerves innervating oral or laryngeal taste buds in the rabbit, including the chorda tympani (CT), the lingual-tonsillar branch of the glossopharyngeal (IX), and the superior laryngeal nerve (SLN), were traced by means of horseradish peroxidase neurohistochemistry. After entering the brainstem, most afferent fibers of CT, IX, and SLN turned caudally in the solitary tract, with fibers of the CT terminating in the nucleus of the solitary tract from 1.0 mm rostral to 3.8 mm caudal to the caudal border of the dorsal cochlear nucleus. There was terminal label from the CT also in the principal trigeminal nucleus. There was terminal label from the CT also in the principal trigeminal nucleus and the oral and intermediate divisions of the spinal trigeminal nucleus. Preganglionic parasympathetic cell bodies of the superior salivatory nucleus were labeled retrogradely in the reticular formation ventral to the rostral pole of the solitary nucleus. Afferent fibers of the IXth nerve terminated in the solitary nucleus from 0.6 mm rostral to 5.0 mm caudal to the caudal border of the dorsal cochlear nucleus. There were also labeled terminals in the principal trigeminal nucleus and in all three divisions of the spinal trigeminal nucleus. Cell bodies composing the inferior salivatory nucleus were labeled in and around the solitary nucleus and subadjacent reticular formation just rostral to the caudal border of the dorsal cochlear nucleus. There were also a few lightly labeled cells within the nucleus ambiguus at its most rostral extent. Afferent fibers of the SLN terminated in the solitary nucleus from 1.2 to 6.8 mm caudal to the dorsal cochlear nucleus. There was also some terminal label in the intermediate and caudal divisions of the spinal trigeminal nucleus. Many cells were retrogradely labeled in the nucleus ambiguus following application of HRP to the SLN and a few cells were labeled in and around the solitary nucleus just caudal to the dorsal cochlear nucleus. These three nerves show an overlapping rostral to caudal distribution of afferent input within the nucleus of the solitary tract that may be related to their gustatory and visceral functions.

Responses of neurons in the lamb nucleus tractus solitarius to stimulation of the caudal oral cavity and epiglottis with different stimulus modalities

Receptors located in the posterior oral cavity and on the epiglottis play an important role in the initiation of upper airway reflexes such as swallowing, gagging, coughing and apnea. Peripheral nerves which innervate these receptor areas terminate in the nucleus tractus solitarius (NTS). We have recorded the responses of 61 neurons in the lamb NTS to stimulation of the caudal tongue, palate and epiglottis with mechanical, chemical and thermal stimuli and mapped receptive field location. Although there was some overlap in the areas of the NTS from which neurons with oral cavity and epiglottal receptive fields could be recorded, a significant difference was observed in the mean recording sites of the two groups of neurons. Neurons with oral cavity receptive fields were located more rostral, lateral and ventral in the NTS than neurons with receptive fields on the epiglottis. Little convergence of sensory input onto single cells in the NTS was observed between the oral cavity and the epiglottis. Only one NTS neuron had a receptive field in both of these receptor areas. In contrast, a large number of neurons with oral cavity receptive fields received input from two receptor areas. These neurons had a receptive field on the tongue which was located directly beneath the receptive field on the palate. Mechanical stimuli were the most effective for neurons with either oral cavity or epiglottal receptive fields and thermal stimuli were the least effective. Neurons which responded to mechanical stimuli responded better to a moving stimulus than to a punctate one, and large increases in the strength of a punctate stimulus were required to elicit significant increases in response frequency. Most NTS neurons responded to more than one of the stimulus modalities. However, a significant difference in the mean number of stimulus modalities which elicited responses was observed between neurons with oral cavity and epiglottal receptive fields. The number of multimodal neurons with epiglottal receptive fields was higher than those with oral cavity receptive fields. The multimodal nature of neurons which responded to epiglottal or oral cavity stimulation combined with their location in reflexogenic areas of the NTS suggests that these neurons could be important in the integration of afferent input from the oral cavity and upper airway. If these NTS neurons are involved in the control of oral and upper airway reflexes it would be important for them to respond to as many of the stimulus cues as possible and the majority of these neurons do just that.

Neuronal architecture of the nucleus of the solitary tract in the hamster

This study provides a scheme for subdividing the nucleus of the solitary tract of the hamster on the basis of cytoarchitectonic criteria, cell measurements, and neuronal cell types identified with the Golgi method. Reduced silver-stained sections revealed the feltlike neuropil that characterizes the nucleus of the solitary tract and were used to define the boundaries of the nuclear complex. Adjacent sections stained for Nissl substance revealed ten subdivisions, each with a characteristic neuronal architecture based on cell sizes, shapes, and packing density. Some subdivisions, e.g., the ventral and medial subnuclei, were identified at all rostrocaudal levels of the nuclear complex, while other subdivisions, e.g., the caudally located dorsolateral and ventrolateral subnuclei, were restricted to particular levels. Golgi preparations were counterstained for Nissl substance, thus allowing dendro- and cytoarchitecture to be compared directly. This material permitted the identification of a number of functionally relevant features of the neuronal constituents of the subdivisions. This approach, employing three cytological methods, has permitted the assembly of a detailed atlas of the nucleus of the solitary tract. The subdivisions of the present atlas have been compared with their likely counterparts identified in previous investigations of the mammalian nucleus of the solitary tract. In order to relate cytoarchitecture with primary afferent termination sites and to define the gustatory-recipient subdivisions, the differential relationships of the subdivisions with lingual afferent projections in the hamster are also described. The present parcellation scheme is intended to facilitate anatomical and physiological investigations of the types of circuits that compose the medullary gustatory and general visceral sensory systems.

Responses of lamb nucleus of the solitary tract neurons to chemical stimulation of the epiglottis

Previous research has shown that applications of chemical stimuli to the epiglottis produced distinct patterns of activity in the lamb superior laryngeal nerve. To determine the response characteristics of second-order neurons, we recorded from single cells in the lamb nucleus of the solitary tract (NST) while stimulating the epiglottis with 0.5 M KCl, NH4Cl, NaCl, LiCl, distilled water, 0.005 M citric acid and 0.01 N HCl. Most neurons responded to more than one of the chemical solutions. The order of effective stimuli was KCl = NH4Cl greater than distilled water greater than HCl greater than citric acid greater than NaCl greater than LiCl. An analysis of the variation in response frequency over time found that different chemical stimuli produced significantly different response patterns in NST neurons. A comparison of the mean neural response profiles of NST neurons and superior laryngeal nerve fibers for each of the stimuli found that only the response profiles elicited by NH4Cl were significantly different. In addition to their responses to chemical solutions, almost one-third of the NST neurons responded to the rinse following application of at least some of the stimuli and 80% of the neurons were excited by mechanical stimulation of the epiglottis with a soft brush. Also, a small number of neurons exhibited a rhythmic response coordinated with respiration. The majority of recording sites were located in areas of the NST linked to swallowing and respiration suggesting that the response patterns of NST neurons elicited by chemical stimulation of receptors on the epiglottis may play a role in upper airway reflexes.

Central projections of the glossopharyngeal and vagal nerves in the channel catfish, Ictalurus punctatus: clues to differential processing of visceral inputs

Transganglionic transport of horseradish peroxidase was used to trace the pattern of medullary terminations of the glossopharyngeal and vagal nerve complex in the channel catfish, Ictalurus punctatus. The glossopharyngeal root terminates centrally in the anterior end of the vagal lobe except for two fascicles that terminate in separate regions of the nucleus intermedius of the facial lobe. Vagal nerve branches innervating regions of the oropharynx terminate in an overlapping, segmental fashion throughout the ipsilateral vagal lobe and the nucleus intermedius of the vagal lobe. The descending branch of the vagus, innervating the abdominal viscera, terminates in the general visceral nucleus and in the nucleus intermedius of the vagal lobe. In addition, abdominal visceral fibers decussate through the commissural nucleus of Cajal and terminate in the general visceral nucleus of the contralateral side. Efferents included in the oropharyngeal and abdominal branches of the vagus also originate from two morphologically separable populations of motor neurons.

The postganglionic parasympathetic fibers originating in the otic ganglion are distributed in several branches of the trigeminal mandibular nerve: an HRP study in the guinea pig

Application of HRP to the proximal stumps of the ramifications of the trigeminal nerve shows that all those belonging to the mandibular branch contain parasympathetic fibers originating in the otic ganglion. The nerve with the largest proportion of these fibers is the auriculotemporal nerve (50-60% of all labeled neurons), while the smallest percentages are found in the lingual nerve and motor root (about 5% each). The presence of otic fibers in the inferior alveolar, mylohyoid, buccal and motor branches of the trigeminal nerve has not hitherto been reported.