The central distribution of the cervical vagus nerve and gastric afferent and efferent projections in the rat

The medullary distribution of afferent fibers and cells of origin of the cervical vagal trunk and of the vagal innervation of the stomach have been studied using the anterograde and retrograde transport of horseradish peroxidase (HRP). Injections of HRP were made into the cervical vagus nerve, the stomach wall, the proximal small intestine, or the peritoneal cavity. Two to four days following the injections, the rats were perfused and the medullae oblongatae and nodose ganglia were processed using the tetramethyl benzidine method. Cervical vagus nerve injections of HRP resulted in heavy anterograde labeling in the ipsilateral nucleus of the tractus solitarius (NTS) and the commissural nucleus. Lighter labeling was seen in these regions on the contralateral side, but did not extend as far rostrally in the NTS. Labeling was also seen in the area postrema. Retrogade labeling of somata was present in the ipsilateral side in the nodose ganglion, throughout the whole extent of the dorsal motor nucleus of the vagus, much of the nucleus ambiguus and in rostral levels of the cervical spinal cord. After stomach injections, labeling indicative of afferent fibers was observed bilaterally in the dorsomedial and medial portions of the NTS and in the commissural nucleus. Labeled efferent fibres arose from neurons in the dorsal motor nucleus of the vagus, nucleus ambiguus and the cervical spinal cord. Retrogradely labeled somata were found bilaterally, throughout the rostrocaudal length of the dorsal motor nucleus in all cases with stomach injections. In some, but not all cases, labeled somata were seen bilaterally in compact areas within the nucleus ambiguus, particularly rostrally. Control injections of HRP into the intestinal wall and peritoneal cavity indicated that the stomach was the primary source of afferent and efferent labeling in the medulla following subdiaphragmatic injections.     

The renal afferent pathways in the rat: a pseudorabies virus study

Retrograde tract tracing studies have indicated that dorsal root ganglion cells from T₈ to L₂ innervate the rat's left kidney. Electrophysiology studies have indicated that putative second-order sympathetic afferents are found in the dorsal horn at spinal segments T₁₀ to L₁ in laminae V–VII. Here, the spread of pseudorabies virus through renal sensory pathways was examined following 2–5 days post-infection (PI) and the virus was located immunocytochemically using a rabbit polyclonal antibody. Two days PI, dorsal root ganglion neurons (first-order sympathetic afferents) were infected with PRV. An average of 1.2, 0.8, 2.1 and 4.4% of the infected dorsal root ganglion neurons were contralateral to the injected kidney at spinal segments T₁₀, T₁₁, T₁₂ and T₁₃, respectively. Four days PI, infected neurons were detected within laminae I and II of the dorsal horn of the caudal thoracic and upper lumbar spinal cord segments. The labeling patterns in the spinal cord are consistent with previous work indicating the location of renal sympathetic sensory pathways. The nodose ganglia were labeled starting 4 days PI, suggesting the involvement of parasympathetic sensory pathways. Five days PI, infected neurons were found in the nucleus tractus solitarius. In the present study, it was unclear whether the infected neurons in the nucleus tractus solitarius are part of sympathetic or parasympathetic afferent pathways or represent a convergence of sensory information. Renal denervation prevented the spread of the virus into the dorsal root ganglia and spinal cord. Sectioning the dorsal roots from T₁₀–L₃ blocked viral spread into the spinal cord dorsal horn, but did not prevent infection of neurons in dorsal root ganglion nor did it prevent infection of putative preganglionic neurons in the intermediolateral cell column. The present results indicated that renal afferent pathways can be identified after pseudorabies virus infection of the kidney. Our results suggest that renal afferents travel in sympathetic and parasympathetic nerves and that this information may converge at the NTS.     

Spinal and vagal influences on the responses of rat solitary nucleus neurons to stimulation of uterus, cervix and vagina

Neurons in the rat solitary nucleus (NTS) respond to mechanical stimulation of the uterine horn, cervix and vagina [7]. The present study examined how these responses were affected by bilateral vagotomy and/or T10-T12 spinal transection for 12 single NTS neurons recorded in 12 rats anesthetized with halothane/nitrous oxide. Spinal transections eliminated all responses. Vagotomies eliminated responses only to uterine horn stimulation and either reduced the excitatory or enhanced the inhibitory responses to cervix and vaginal stimuli. These results suggest that NTS neuronal responses to cervix and vaginal stimulation depend upon input from the spinal dorsal horn and are facilitated by vagal input, whereas responses to uterine horn stimulation may require both spinal and vagal input.     

Axonal transport of neurotrophins by visceral afferent and efferent neurons of the vagus nerve of the rat

The receptor-mediated axonal transport of [¹²⁵I]-labeled neurotrophins by afferent and efferent neurons of the vagus nerve was determined to predict the responsiveness of these neurons to neurotrophins in vivo. [¹²⁵I]-labeled neurotrophins were administered to the proximal stump of the transected cervical vagus nerve of adult rats. Vagal afferent neurons retrogradely transported [¹²⁵I]neurotrophin-3 (NT-3), [¹²⁵I]nerve growth factor (NGF), and [¹²⁵I]neurotrophin-4 (NT-4) to perikarya in the ipsilateral nodose ganglion, and transganglionically transported [¹²⁵I]NT-3, [¹²⁵I]NGF, and [¹²⁵I]NT-4 to the central terminal field, the nucleus tractus solitarius (NTS). Vagal afferent neurons showed minimal accumulation of [¹²⁵I]brain-derived neurotrophic factor (BDNF). In contrast, efferent (parasympathetic and motor) neurons located in the dorsal motor nucleus of the vagus and nucleus ambiguus retrogradely transported [¹²⁵I]BDNF, [¹²⁵I]NT-3, and [¹²⁵I]NT-4, but not [¹²⁵I]NGF. The receptor specificity of neurotrophin transport was examined by applying [¹²⁵I]-labeled neurotrophins with an excess of unlabeled neurotrophins. The retrograde transport of [¹²⁵I]NT-3 to the nodose ganglion was reduced by NT-3 and by NGF, and the transport of [¹²⁵I]NGF was reduced only by NGF, whereas the transport of [¹²⁵I]NT-4 was significantly reduced by each of the neurotrophins. The competition profiles for the transport of NT-3 and NGF are consistent with the presence of TrkA and TrkC and the absence of TrkB in the nodose ganglion, whereas the profile for NT-4 suggests a p75 receptor-mediated transport mechanism. The transport profiles of neurotrophins by efferent vagal neurons in the dorsal motor nucleus of the vagus and nucleus ambiguus are consistent with the presence of TrkB and TrkC, but not TrkA, in these nuclei. These observations describe the unique receptor-mediated axonal transport of neurotrophins in adult vagal afferent and efferent neurons and thus serve as a template to discern the role of specific neurotrophins in the functions of these visceral sensory and motor neurons in vivo. J. Comp. Neurol. 393:102–117, 1998. Published 1998 Wiley-Liss, Inc.

1 This article is a US government work and, as such, is in the public domain in the United States of America.

     

Observations on the afferent and efferent organization of the vagus nerve and the innervation of the stomach in the squirrel monkey

Horseradish peroxidase was injected into the cervical vagus nerve or stomach wall of adult squirrel monkeys. Following cervical vagus nerve injections, labelled afferent fibres were present in the tractus solitarius and labelled fibres and terminals were present in medial and lateral parts of the nucleus of the tractus solitarius (NTS) ipsilaterally. Afferent labelling was also seen in the ipsilateral commissural nucleus and in the area postrema. Labelling was present contralaterally in caudal levels of the medial parts of the NTS, in the commissural nucleus, and in the area postrema. Afferent projections to the ipsilateral pars interpolaris of the spinal trigeminal nucleus and to the substantia gelatinosa of the C1 segment of the spinal cord were also labelled. Following injections of HRP into the anterior and posterior stomach walls, the tractus solitarius was labelled bilaterally. Afferent labelling was concentrated bilaterally in the dorsal parts of the medial division of the NTS, i.e., in the subnucleus gelatinosus, and in the commissural nucleus. The regions of NTS immediately adjacent to the tractus solitarius were largely unlabelled. Injections of HRP into the cervical vagus nerve resulted in heavy retrograde labelling of neurons in the ipsilateral dorsal nucleus of the vagus (DMX) and in the nucleus ambiguus (NA). In addition a few neurones were labelled in the intermediate zone between these two nuclei. Retrogradely labelled neurons were also present in the nucleus dorsomedialis in the rostral cervical spinal cord and in the spinal nucleus of the accessory nerve. Injections of HRP into the left cricothyroid muscle in two cases resulted in heavy retrograde labelling of large neurons in the left NA. Following stomach wall injections of HRP retrograde labelling of neurons was seen throughout the rostrocaudal and mediolateral extent of the DMX; there was no apparent topographical organization of the projection. In these cases, a group of labelled smaller neurons was found lying ventrolateral to the main part of the NA through its rostral levels. This study in a primate indicates that a large vagal afferent projection originates in the stomach wall and terminates primarily in the subnucleus gelatinosus of the NTS and in the commissural nucleus with a distribution similar to that described previously in studies in several subprimate mammalian species. The present results and those of other studies suggest some degree of segregation of visceral input within different subnuclei of the NTS.(ABSTRACT TRUNCATED AT 400 WORDS)     

Immunohistochemical and biochemical analysis of serotonin and substance P colocalization in the nucleus tractus solitarii and associated afferent ganglia of the rat

In a previous study of afferent projections to the nucleus tractus solitarii (NTS), it was shown that over half of the retrogradely-labelled neurons in the nucleus raphe pallidus contained serotonin-immunoreactivity and over half of these neurons contained substance P-immunoreactivity, suggesting that these two putative neurotransmitters are colocalized in NTS-afferent neurons. The objectives of the present study were to 1) directly determine if varicosities in the NTS, the area postrema (AP), and the dorsal motor nucleus of the vagus nerve (DMN) do contain both transmitters, 2) determine if primary afferent neurons in the nodose and pretrosal ganglia might also colocalize serotonin and substance P, and 3) quantify the amount of substance P that is contained in serotonergic varicosities in the NTS. Distributions and colocalization of substance P and serotonin in the NTS were studied using dual-color immunohistochemistry, while the quantity of substance P in serotonergic varicosities was assessed by radioimmunoassay (RIA) using micropunches from the NTS of 5,7-dihydroxytryptamine-(5,7 DHT-) and vehicle-treated rats. Varicosities that contained both serotonin- and substance P-immunoreactivity were found in the NTS, the DMN, and the AP. Double-labelled varicosities were common in the NTS and DMN (i.e., qualitatively similar to the density seen in the hypoglossal nucleus and in the ventral horn of the cervical spinal cord); however, the vast majority of the varicosities in these autonomic areas only displayed immunoreactivity for one or the other of these transmitters. This paucity of doubly-labelled varicosities, in comparison to the number of singly-labelled varicosities, was reflected in the lack of a significant decrease in substance P levels as determined by RIA of micropunches taken from caudal and intermediate levels of the NTS in 5,7 DHT- and vehicle-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Vagal neurons and pathways to the rat's lower viscera: An electrophysiological study

The vagal pathways to the rat's pancreas are anatomically difficult to describe. A stimulation/recording technique has been used on various segments of the vagus to trace vagal pathways to the lower viscera, and a microelectrode recording technique to locate vagal neurons of origin in the brain stem's dorsal motor nucleus (DMX). The two main pathways (right cervical vagus to dorsal celiac branch and left cervical vagus to ventral celiac branch) are supplemented by two accessory ones where each cervical vagus gives some fibers to its contralateral homologue at the diaphragmatic level. These pathways consist almost exclusively of C-fibers. Neurons of origin of the dorsal vagal trunk fibers have been identified by the collision test and occupy the caudal half of the DMX; those of the dorsal celiac branch fibers originate from the medial part of that area.     

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. © 1996 Wiley-Liss, Inc.     

Nucleus of the tractus solitarius projections to the olfactory tubercle: An HRP study

Labelled cells were found in the nucleus of the tractus solitarius (NTS) after horseradish peroxidase injections in the olfactory tubercle (OT) of the rat. These results suggest a direct pathway from the NTS to the OT. The importance of this pathway in a neural circuit related to autonomic functions is discussed.     

Efferent and collateral organization of paratrigeminal nucleus projections: An anterograde and retrograde fluorescent tracer study in the rat

The paratrigeminal nucleus (PTN) receives primary visceral afferent projections through cranial nerves IX and X and somatic afferent projections through cranial nerve V and dorsal roots as far caudally as C7. Pressure injections of the anterograde tracer tetramethylrhodamine dextran into the PTN in the rat resulted in bilateral labeling in the nucleus of the tractus solitarius, dorsal motor nucleus of the vagus nerve, and parabrachial nucleus. Anterograde labeling in the parabrachial nucleus was strongest in the external medial, external lateral, and ventral lateral subnuclei. Anterograde labeling was also found in the contralateral paratrigeminal nucleus, lamina I of the spinal trigeminal nucleus subnucleus caudalis, and ventroposteromedial nucleus of the thalamus. The collateral organization of PTN neurons was demonstrated by injecting different fluorescent retrograde tracers into the terminal fields of PTN projections as determined by the anterograde tracing experiments. Double-labeled neurons were found in the paratrigeminal nucleus following all combinations of injection sites. The most prominent PTN efferent projections and the most highly collateralized were to the nucleus of the tractus solitarius and parabrachial nucleus. The efferent and collateral connections of the paratrigeminal nucleus may provide a neuroanatomical substrate for integrating convergent visceral and somatic afferent information used to modulate autonomic function and behavior related to thermoregulation, nociception, and gustation. J. Comp. Neurol. 402:93–110, 1998. © 1998 Wiley-Liss, Inc.     

Prenatal ontogeny of substance P-like immunoreactivity in the nucleus tractus solitarii and dorsal motor nucleus of the vagus nerve of the human fetus: an immunocytochemical study

By using immunocytochemical method, the prenatal ontogeny of substance P-like immunoreactivity (SP-LI) was demonstrated in the dorsal motor nucleus of the vagus nerve (nX) and the nucleus tractus solitarii (nTS) of the human fetus at fetal age (menstruation age) of 11.5 weeks to 40 weeks. The time of initial appearance of SP-LI in the human brainstem nTS was between the fetal age 11.5 weeks and 16 weeks. At fetal age 16 weeks, the nTS showed moderate density of SP-LI fibers and terminals in subnucleus dorsalis of the nTS and nX. While the fetus grew, the density of SP-LI in the human fetus brainstem nTS and nX increased gradually from fetal age 16 weeks to 40 weeks. According to the Nissl staining, at fetal age 23 weeks, the nTS of human fetus can be subdivided into dorsal, medial, dorsolateral, ventrolateral and ventral gelatinosus subnuclei. The cytoarchitectonic subdivisions of human fetus nTS is in good agreement with the results obtained by immunocytochemical staining. These findings indicated that substance P (SP) might play an important role in the development of human brainstem nX, nTS, their related cranial nerves, and in their functional establishment during the pranatal period.     

Connections of a vagal communicating branch in the ferret I. Pathways and cell body location

In contrast to most other species, ferrets possess a single communicating branch connecting the dorsal and ventral vagal trunks immediately rostral to the diaphragm. This branch is being used in physiological studies of gastrointestinal function and emesis. However, the fibre routes which pass through this branch are not known. In this study, the afferent and efferent pathways within this supradiaphragmatic vagal communicating branch of the ferret were studied through the use of the horseradish peroxidase (HRP) tracing technique. The region of the branch was exposed using a thoracotomy and HRP crystals were applied to one of the following: (A) the ventral end of the communicating branch, (B) the dorsal end of the communicating branch, (C) the distal end of the dorsal vagal trunk rostral to the communicating branch or (D) the distal end of the ventral vagal trunk rostral to the communicating branch. Following a 72 hour survival period, the animals were reanaesthetized and perfused. The superior cervical and nodose ganglia and the brain stem were processed using the tetramethylbenzidine method. Following application of HRP to the cut ventral end of the communicating branch, labelled cell bodies were found in the left and right nodose ganglia and in the left dorsal motor nucleus of the vagus. After HRP application to the cut dorsal end of the communicating branch, labelled cells were found in the left and right nodose ganglia. No HRP containing cell bodies were found following HRP application to the cut distal end of either the dorsal or the ventral vagal trunk. These results indicate that several afferent pathways exist within the branch, although only one consistently labelled efferent pathway was found.     

Afferent projections of the cervical vagus and nodose ganglion in the dog

The distribution within the brain stem of the afferent projections of the cervical vagus and the nodose ganglion was studied with horseradish peroxidase (HRP) and HRP-wheat germ agglutinin conjugate. Two to eight days after application of tracer into the cervical vagosympathetic trunk or the nodose ganglion the brain stems and ganglia were perfused and processed by the tetramethyl benzidine method. Vagal afferent fibers entered the lateral medulla as a distinct bundle spatially separate from the vagal efferent rootlets which were caudal and ventral to the afferents. Labeled axons in the solitary tract began to enter the nucleus tractus solitarii (nTS) 4.5 mm anterior to obex and were seen throughout the ipsilateral nTS as far as 3.5 mm caudal to obex. Label density varied within the nTS, with heaviest labeling in the dorsal and dorsolateral portions. Label was also seen in the ipsilateral area postrema (ap) and dorsal motor nucleus of the vagus. Labeled fibers crossed in the commissural portions of ap and nTS to enter the contralateral ap and nTS.     

The distribution of the cat''s carotid sinus nerve afferent and efferent cell bodies using the horseradish peroxidase technique

The location of both afferent and efferent carotid sinus nerve (CSN) cell bodies in the cat has been determined using the horseradish peroxidase (HRP) technique. Following a limited exposure of the central cut end of the CSN to HRP, labeled sensory ganglion cells were found in both the petrosal and superior ganglia of the IXth cranial nerve. An average of 387 in the former and 16 cells in the latter ganglion were labeled.

Retrogradely labeled neurons were found only within the ipsilateral medulla. These cells were both round and spindle shaped and had an average somal diameter of 19 μm. The number of these CSN efferent cell bodies ranged from 1 to a maximum of 20 in a given animal. They were found in both the nucleus parvocellularis and the retrofacial nucleus. In 8 cases axonal labeling was observed. Axons generally projected dorsomedially from the ventrolateral medulla.     

Neuropeptide Y-immunoreactive perikarya and nerve terminals in the rat medulla oblongata: relationship to cytoarchitecture and catecholaminergic cell groups

The aim of this study was to examine details of the distribution of neuropeptide Y (NPY)-immunoreactive perikarya and nerve terminals in the medulla oblongata in relation to cytoarchitectonically and functionally distinct catecholaminergic regions. The immunoperoxidase method was combined with Nissl staining to determine nuclear boundaries of transmitter-identified nerve cell bodies and to examine the relationship between populations of NPY-immunoreactive neurons and catecholaminergic cell groups (A1, A2, C1, C2, and C3) in serial sections. Previous studies using immunofluorescence have described the existence of NPY catecholaminergic immunoreactive nerve cell bodies in the brainstem. No information is currently available with regard to details of the distribution of these peptidergic neurons and nerve terminals in the functional subnuclear units of the medulla oblongata. In this study we have delineated the anatomical association of NPY immunoreactivity with cardiovascular function. Neuropeptide Y-immunoreactive neurons were found located in close association with noradrenergic neurons of the A1 cell group in the caudal ventrolateral medulla oblongata, where they were usually found located dorsal to the lateral reticular nucleus (LRt). A second population of NPY-immunoreactive neurons was found located medial to the A1 cell group in the ventral subdivision of the reticular nucleus of the medulla (MdV). Neuropeptide Y-immunoreactive neurons in the rostral medulla were found located in regions corresponding to the principal distribution of adrenergic neurons in the C1, C2, and C3 cell groups. In the dorsomedial medulla (A2 region) NPY-immunoreactive neurons were localized in the area postrema (ap) and in a number of subnuclei of the nucleus of the tractus solitarius (nTS), i.e., the dorsal parasolitary region (dPSR), the dorsal strip (ds), the periventricular region (PVR), and the ventral parasolitary region (vPSR). The location of NPY-immunoreactive perikarya and nerve terminals in the dorsal subnuclei of the nTS, i.e., the dPSR and ds, is of particular significance, since this distribution corresponds with the location of small adrenergic neurons as well as with the site of termination of aortic and carotid sinus nerve afferent fibers. NPY-immunoreactive neurons in the dorsomedial medulla are ideally situated for receiving monosynaptic input from baroreceptor afferents and could play a key role in the central integration of cardiovascular reflexes.     

Autoradiographic localization of 5HT1 binding sites in autonomic areas of the rat dorsomedial medulla oblongata.

Serotonin (5HT) binding sites in autonomic portions of the dorsomedial medulla oblongata of the rat were localized using autoradiographic techniques with radioactive ligands that express high affinity for the 5HT1 (3H-5HT), 5HT1A (3H-8OH-DPAT), or 5HT1B (125I-CYP with isoproterenol) receptor subtypes. 5HT1A sites were densely distributed in the nucleus tractus solitarius (NTS), with the highest densities localized to the interstitial subnucleus and the central subnucleus. 5HT1B sites were also found in the NTS, with the highest densities localized to the substantia gelatinosa subnucleus. The dorsal motor nucleus of the vagus nerve and nucleus ambiguus exhibited low densities of 5HT1B sites. However, the nucleus intercalatus, a cerebellar relay nucleus that also contains dendrites of vagal parasympathetic preganglionic neurons and receives autonomic forebrain afferent input, showed very dense 5HT1B sites. The promontorium, paratrigeminal islands, and the dorsomedial portion of the trigeminal nucleus (DM5), which are areas of viscerosomatic integration, exhibited high densities of both 5HT1A and 5HT1B sites. The area postrema contained low levels of both 5HT1A and 5HT1B sites. Visceral deafferentation via cervical vagotomy or nodose ganglionectomy caused a significant decrease in 5HT1A sites in the interstitial subnucleus of the NTS ipsilateral to the lesion. No changes were seen in 5HT1B sites. These studies suggest that 5HT1A and 5HT1B sites are involved in the processing of visceral sensory information in the NTS and associated areas. Based upon viscerotopic organization of the NTS, 5HT1A sites appear preferentially distributed in portions of the NTS that are associated with the coordination of swallowing, respiration, and cardiovascular function, while 5HT1B sites appear preferentially distributed in areas of the NTS associated with gastrointestinal, hepatic, pancreatic, and cardiovascular function. However, since these association were not absolute and there was a great deal of overlap between the two sites, speculation regarding their specific functions in autonomic control must await pharmacological examination.     

Distribution and central projections of primary afferent neurons that innervate the masseter muscle and mandibular periodontium: a double-label study

A double-label strategy was used to determine the distribution and central projections of primary afferent neurons that innervate the periodontium and muscles of mastication in cats. Central injections of either Fast Blue (FB) or a mixture of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) and HRP were made into one of three cytoarchitectonically distinct regions of the spinal trigeminal nucleus. These regions included the subnucleus oralis (Vo), the subnucleus interpolaris (Vi), and the medullary dorsal horn (MDH). In each case, injections were also made into the periodontium of the ipsilateral mandibular teeth or into the ipsilateral masseter muscle. FB injections preceded the peroxidase injections by at least 48 hours and total survival time ranged from 72 to 96 hours. Animals were perfused with phosphate-buffered paraformaldehyde (4%; pH 7.2). Serial frozen sections were made through the brainstem and trigeminal ganglion. Tetramethylbenzidine was used as a chromagen to demonstrate HRP and sections were viewed with brightfield and epifluorescent illumination. Cells containing peripherally injected tracer were observed in the lateral portion of the ganglion and in the mesencephalic nucleus (Vmes). Double-labeled ganglion cells were observed in most cats that received periodontal injections in combination with central injections in the dorsal part of spinal trigeminal nucleus regardless of the rostrocaudal level of the central injection. In the animals that received intramuscular injections, double-labeled ganglion cells were observed only in the animals that received central injections caudal to the Vo. Double-labeled Vmes perikarya were observed in cats that received either intramuscular or periodontal injections in combination with central injections into the MDH and Vo but not in animals that received injections into the Vi. These results demonstrate that ganglion cell periodontal afferents project to the three major rostrocaudal subdivisions of the spinal trigeminal nucleus while ganglion cell muscle afferents have more limited central projections to caudal regions of the nucleus. Masseter and periodontal Vmes afferents also project ot the spinal trigeminal nucleus--specifically, to the Vo and MDH. These findings are consistent with physiological observations regarding the role of periodontal and masseteric afferents in oral and facial reflexes and somesthetic mechanisms.     

Projections between the hypothalamus and the dorsal vagal complex in the cat: An HRP and autoradiographic study

The hypothalamus is known to be intimately involved in the control of autonomic function. This study provides detailed information about pathways between the hypothalamus and the dorsal vagal complex in cat. Injection of horseradish peroxidase into the dorsomedial medulla produced retrograde neuronal labeling in the paraventricular nucleus of the hypothalamus. Injection of 3H-leucine into the paraventricular nucleus produced dense anterograde labeling in the dorsal motor nucleus of the vagus, and lighter labeling in the nucleus of the tractus solitarius, particularly in its medial subnucleus. The subnucleus gelatinous was virtually free of label, except in its medial and lateral portions. Anterograde labeling was distributed bilaterally, with an ipsilateral predominance. Injection of horseradish peroxidase into the area of the paraventricular nucleus produced retrograde neuronal labeling bilaterally in the nucleus of the tractus solitarius and the reticular formation ventrolateral to the dorsal vagal complex. anterograde terminal labeling overlapped the distribution of retrogradely labeled neurons. These findings are compared to those in rat, and discussed in relation to their functional implications.     

The organization of the gastric efferent projections in the brainstem of monkey: An HRP study

Topographic localization of neurons in the dorsal motor nucleus (DMN) of the vagus innervating the stomach and the extent of central decussation of its fibers were investigated in the monkeys after chronic unilateral cervical vagotomy. This study presents findings in regard to the non-topographic representation of the stomach in both DMN and lack of a well-defined decussation of its fibers in the brainstem of monkeys. Reported findings in the rat and cat vis-a-vis our own results in the monkey indicate species difference in the organization of efferent vagal gastric fibers. The evidence of a very small number of HRP-labeled cells in DMN on the vagotomized side after intervals of 2-36 weeks is being reported here, for what we believe to be the first time, and its significance has been discussed.     

Contribution of the vagus nerve to angiotensin II binding sites in the canine medulla

Specific angiotensin II (Ang II) binding sites are present in the dorsal medulla of several species and dose-related cardiovascular effects are produced by microinjection of the peptide into this region. Because the anatomical location of Ang II binding sites in the area postrema (ap), nucleus tractus solitarii (nTS) and dorsal motor nucleus of the vagus (dmnX) coincides with the topography of vagal afferent fibers and efferent motor neurons, the effect of either nodose ganglionectomy or cervical vagotomy on Ang II binding sites in the dorsomedial medulla was investigated in dogs by in vitro receptor autoradiography. Two weeks after unilateral ganglionectomy, there was a marked reduction in the density of specific Ang II binding sites in the ipsilateral ap, nTS and dmnX and an absence of binding sites in the region where vagal afferent fibers course through the rostral medulla. Unilateral cervical vagotomy, which has been shown to spare central processes of afferent fibers, resulted in a loss of binding only in the ipsilateral dmnX. We also show that Ang II binding sites are present in the nodose ganglion and central and peripheral processes of the vagus nerve. The data indicate that medullary Ang II binding sites are associated with both vagal afferent fibers and efferent motor neurons.