The central organization of the vagus nerve innervating the stomach of the rat

Inhibition of gastric acid secretion by stress: a protective reflex mediated by cerebral nitric oxide

Moderate somatic stress inhibits gastric acid secretion. We have investigated the role of endogenously released NO in this phenomenon. Elevation of body temperature by 3 degrees C or a reduction of 35 mmHg (1 mmHg = 133 Pa) in blood pressure for 10 min produced a rapid and long-lasting reduction of distension-stimulated acid secretion in the rat perfused stomach in vivo. A similar inhibitory effect on acid secretion was produced by the intracisternal (i.c.) administration of oxytocin, a peptide known to be released during stress. Intracisternal administration of the NO-synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) reversed the antisecretory effect induced by all these stimuli, an action prevented by intracisternal coadministration of the NO precursor, L-arginine. Furthermore, microinjection of L-NAME into the dorsal motor nucleus of the vagus nerve reversed the acid inhibitory effects of mild hyperthermia, i.v. endotoxin, or i.c. oxytocin, an action prevented by prior microinjection of L-arginine. By contrast, microinjection of L-NAME into the nucleus tractus solitarius failed to affect the inhibitory effects of hyperthermia, i.v. endotoxin, or i.c. oxytocin. Immunohistochemical techniques demonstrated that following hyperthermia there was a significant increase in immunoreactivity to neuronal NO synthase in different areas of the brain, including the dorsal motor nucleus of the vagus. Thus, our results suggest that the inhibition of gastric acid secretion, a defense mechanism during stress, is mediated by a nervous reflex involving a neuronal pathway that includes NO synthesis in the brain, specifically in the dorsal motor nucleus of the vagus.

Use of animal models in peptic ulcer disease

Considerable progress has been made in the understanding of the formation of gastric erosions by the use of animals. The role of gastric acid secretion in their pathogenesis has been clarified. Gastric erosions are associated with the presence of acid in the stomach and slow gastric contractions. With several different experimental procedures, the animal's body temperature falls; preventing the fall averts erosions. A fall in body temperature or exposure to cold are associated with the secretion of thyrotropin-releasing hormone (TRH), and both increased and decreased concentration of corticotropin-releasing factor (CRH) in discrete regions of rat brains. Thyrotropin-releasing hormone when injected into specific sites in the brain produces gastric erosions and increases acid secretion and slow contractions, whereas CRH has the opposite effects. One of the major sites of interaction of the two peptides is in the dorsal motor complex of the vagus nerve. Thyrotropin-releasing hormone increases serotonin (5-HT) secretion into the stomach. Serotonin counter-regulates acid secretion and slow contractions. Many other peptides injected into discrete brain sites stimulate or inhibit gastric acid secretion.

The dorsal vagal complex of the ferret: anatomical and immunohistochemical studies

To further the understanding of gastrointestinal function in this species, and in particular to advance our own work concerning central emetic pathways, the cytoarchitecture and the distribution of eight neurochemicals were studied in the ferret dorsal vagal complex (DVC; area postrema, nucleus of the solitary tract [nTS] and dorsal motor nucleus of the vagus). The cytoarchitectural features of this region in the ferret were similar to those seen in other species; however, the ferret possesses a particularly large and distinct subnucleus gelatinosus of the nTS. Dense calcitonin gene-related peptide-immunoreactivity was found in the gelatinous, interstitial and commissural subnuclei of the nTS, with lesser amounts in other regions of the DVC. Enkephalin-immunoreactivity of varying densities was found throughout the DVC. Moderate to dense galanin-immunoreactivity was observed throughout the DVC, with the exception of the subnucleus gelatinosus of the nTS, from which it was virtually absent. Dense neuropeptide Y-immunoreactivity was observed in the subnucleus gelatinosus and interstitial subnucleus, with moderate staining in other regions of the DVC. Neurotensin immunoreactivity was very sparse or absent. Immunoreactivity for serotonin was sparsely distributed throughout the DVC. Moderate somatostatin-immunoreactivity was observed over a large portion of the DVC, but was virtually absent from the gelatinosus and interstitial subnuclei. Substance P immunoreactivity was observed throughout the DVC and was particularly dense in the dorsal/dorsolateral subnucleus and the dorsal aspects of the medial and commissural subnuclei. In terms of its cytoarchitecture the DVC of the ferret is more similar to the cat than the rat, especially with regard to the area postrema and the subnucleus gelatinosus of the nTS. The distribution of neuroactive substances was largely similar to other species; however, differences were present particularly in patterns of immunoreactivity for enkephalin, serotonin, neuropeptide Y and somatostatin.

Ultrastructural characterization of pharyngeal and esophageal motoneurons in the nucleus ambiguus of the rat

The viscerotopic organization of the upper alimentary tract has been established in the nucleus ambiguus, but there is little information about the morphology of the individual neurons innervating the pharynx and esophagus. We studied the ultrastructure of pharyngeal (PH), cervical esophageal (CE), and subdiaphragmatic esophageal (SDE) motoneurons labeled by retrogradely transported wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) in the compact formation of the nucleus ambiguus. WGA-HRP was injected into the lower pharynx, or the cervical and subdiaphragmatic esophagus of male rats. The retrogradely labeled PH neurons in the rostral portion of the compact formation were large (26.1 x 50.1 microns, 906.7 microns2), polygonal, and contained well-developed cell organelles with a round nucleus. Subsurface cisterns connected with rough endoplastic reticulum were often present near the postsynaptic membrane. Both CE and SDE neurons in the compact formation were medium-sized, round or oval, and contained well-developed cell organelles, although the SDE neuron was significantly larger than the CE neuron (24.9 x 33.6 microns, 593.0 microns2 in the SDE neuron, and 19.5 x 30.2 microns, 440.3 microns2 in the CE neuron). The average number of axosomatic terminals in a sectional plane was largest in PH neurons (29.0), smaller in CE neurons (7.9), and smallest in SDE neurons (4.2). The number of axosomatic terminals containing round vesicles (Gray's type I) was almost equal to that of terminals containing pleomorphic vesicles (Gray's type II) in PH and CE neurons, but there were few Gray's type II axosomatic terminals in SDE neurons. Desmosome-like junctions at somato-somatic or somato-dendritic apposition were often present in the area surrounding SDE neurons. There were also small unlabeled neurons (9.5 x 18.1 microns, 131.8 microns2) in the compact formation of the nucleus ambiguus. The small neurons contained poorly developed cell organelles and an irregular shaped nucleus with invaginated nuclear membrane, and had no Nissl bodies. These results indicate that PH neurons have the characteristics of somatic motoneurons, and that CE and SDE neurons are similar to visceral motoneurons.

Distribution of bombesin-like immunoreactivity in the nucleus of the solitary tract and dorsal motor nucleus of the rat and human: colocalization with tyrosine hydroxylase

Bombesin is a peptide neurotransmitter/neuromodulator with important autonomic and behavioral effects that are mediated, at least in part, by bombesin-containing neurons and nerve terminals in the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus (DMV). The distribution of bombesin-like immunoreactive nerve terminals/fibers and cell bodies in relation to a viscerotopically relevant subnuclear map of this region was studied by using an immunoperoxidase technique. In the rat, bombesin fiber/terminal staining was heavy in an area that included the medial subnucleus of the NTS and the DMV over their full rostral-caudal extent. Distinctly void of staining were the gelatinous, central, and rostral commissural subnuclei and the periventricular area of the NTS, regions to which gastric, esophageal, cecal, and colonic primary afferents preferentially project. The caudal commissural and dorsal subnuclei had light bombesin fiber/terminal staining, as did the intermediate, interstitial, ventral, and ventrolateral subnuclei. With colchicine pretreatment, numerous cell bodies were stained in the medial and dorsal subnuclei, with fewer neurons in the caudal commissural, intermediate, interstitial, ventral, and ventrolateral subnuclei. Bombesin-like immunoreactive neurons were found in numerous other areas of the brain, including the ventrolateral medulla, the parabrachial nucleus, and the medial geniculate body. In the human NTS/DMV complex, the distribution of bombesin fiber/terminal staining was very similar to the rat. In addition, occasional bombesin-like immunoreactive neurons were labeled in a number of subnuclei, with clusters of neurons labeled in the dorsal and ventrolateral subnuclei. Double immunofluorescence studies in rat demonstrated that bombesin colocalizes with tyrosine hydroxylase in neurons in the dorsal subnucleus of the NTS. Bombesin does not colocalize with tyrosine hydroxylase in any other location in the brain. In conclusion, the distribution of bombesin in the NTS adheres to a viscerotopically relevant map. This is the anatomical substrate for the effects of bombesin on gastrointestinal function and satiety and its likely role in concluding a meal. The anatomic similarities between human and rat suggest that bombesin has similar functions in the visceral neuraxis of these two species. Bombesin coexists with catecholamines in neurons in the dorsal subnucleus, which likely mediate, in part, the cardiovascular effects of bombesin.

Association of substance P and its receptor with efferent neurons projecting to the greater curvature of the rat stomach

Retrograde tracing and immunocytochemistry were used to identify and map the distribution of substance P (SP) and its receptor (NK-1r) associated with gastric motor neurons in the dorsal motor nucleus of the vagus (DMV) in the rat brain stem. The presence of peptide and receptor in surrounding regions within the dorsal vagal complex were also observed. Injection of the retrograde tracer Fluorogold (FG) into the greater curvature of the stomach produced bilateral labelling of neurons within the DMV. The majority of the NK-1r immunoreactivity appeared as an intricate lattice of fibres with a small number of immunoreactive cell bodies. The NK-1r-labelled fibres were detected within the DMV in close association with FG-labelled neurons and in the region between the DMV and nucleus of the solitary tract (NTS). A proportion of FG-labelled neuronal cell bodies were also labelled with NK-1r (7% of total). The greatest density of NK-1r-labelled fibres was observed at the rostral end of the FG-labelled neuron columns in the DMV (close to the IV ventricle) in the region where gastric vagal afferents terminate. Little NK-1r labelling was observed at the caudal end of the FG-labelled neuron tracts adjacent to the central canal. In the coronal plane, the NK-1r-labelled fibres were seen at the edges of the DMV extending into overlying NTS. Substance P was visualized as a dense network of fibres spanning the entire length of the DMV and in close association with FG-labelled neurons. Substance P staining was also detected in the NTS and in the ventral AP. Most of the association between SP/NK-1r immunoreactive fibres was observed within the DMV and at the border between the DMV and NTS. These findings suggest that SP directly regulates a subpopulation of efferent neurons in the DMV which project to the greater curvature of stomach.

Topographic organization of Fos-like immunoreactivity in the rostral nucleus of the solitary tract evoked by gustatory stimulation with sucrose and quinine

Fos immunohistochemistry was used to elucidate the pattern of activation elicited by two qualitatively and hedonically distinct taste stimuli, sucrose and quinine, within the first-order gustatory relay, the rostral division of the nucleus of the solitary tract. Compared to unstimulated controls, both sucrose and quinine elicited significant increases in Fos-like immunoreactivity in the rostral central subnucleus, the region of the rostral solitary nucleus that receives the densest primary afferent input. Within the rostral central subnucleus, neurons that exhibited Fos-like immunoreactivity following quinine stimulation were concentrated medially, but neurons that exhibited Fos-like immunoreactivity following sucrose stimulation were distributed more evenly along the mediolateral axis. Despite their differential distribution, sucrose- and quinine-activated neurons also demonstrated notable intermingling. Further, the chemotopic arrangement was only partially consistent with what would be predicted if chemotopy was merely an outcome of orotopy. Our results suggest that a rough chemotopy characterizes the organization of taste responses in the nucleus of the solitary tract, and that the topographic pattern of taste afferent terminations in this nucleus is related to their chemosensitivity as well as to their peripheral spatial distribution.

Motoneuron development after deafferentation. I. dorsal rhizotomy does not alter growth in the spinal nucleus of the bulbocavernosus (SNB)

The spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN) are sexually dimorphic motor nuclei in the rat lumbar spinal cord. During postnatal development, SNB and DLN motoneurons grow substantially in measures of soma size, dendritic length, and radial dendritic extent. SNB motoneurons exhibit a biphasic pattern of dendritic growth, where there is an initial period of exuberant growth followed by a period of retraction to mature lengths by 7 weeks. In this experiment, we examined whether primary afferent input to the SNB nucleus was necessary for the normal postnatal growth of SNB motoneurons. We partially deafferented the SNB via unilateral dorsal rhizotomy of lumbosacral dorsal roots in male rats at 1 week of age. Using cholera toxin horseradish peroxidase (BHRP) to visualize SNB motoneurons, we examined SNB motoneuron morphology at 4 and 7 weeks of age. SNB motoneurons in rhizotomized males developed normally; measures of dendritic length in rhizotomized males were typically exuberant at 4 weeks of age, and declined significantly to mature lengths by 7 weeks of age. In addition, dorsal rhizotomy did not alter the development of SNB motoneuron soma size or radial dendritic extent. These results are discussed in reference to sensorimotor connections in the SNB, the extent of the deafferentation, and dendrodendritic interactions.

Vagal control of digestion: modulation by central neural and peripheral endocrine factors

Vago-vagal reflex control circuits in the dorsal vagal complex of the brainstem provide overall coordination over digestive functions of the stomach, small intestine and pancreas. The neural components forming these reflex circuits are under significant descending neural control. By adjusting the excitability of the different components of the reflex, alterations in digestion control can be produced by the central nervous system. Additionally, the dorsal vagal complex is situated within a circumventricular region without an effective "blood-brain barrier". As a result, vago-vagal reflex circuitry is also exposed to humoral influences which profoundly alter digestive functions by acting directly on brainstem neurons. Behavioral and endocrine physiological observations suggest that this "humoral afferent pathway" may significantly alter the regulation of food intake.

Time course of the induction of VGF mRNA in the dorsal vagal complex in rats with cysteamine-induced peptic ulcers

The time course of induction of VGF mRNA in the dorsal vagal complex of the medulla oblongata was investigated in rats with duodenal ulcer induced with cysteamine by in situ hybridization histochemistry. In control rats, weak VGF mRNA signals were detected in a few neurons in the nucleus tractus solitarii and dorsal motor nucleus of vagus. After the cysteamine administration (450 mg/kg, s.c.), VGF mRNA signals began to increase after 3 h, reached at peak level at 12 h, and decreased slightly at 24 h, but remained high after 48 h. The time course of duodenal ulcer score was absent at 3 h, very low at 6 h, about grade 1 at 12 h, and grade 2 or more at 24 and 48 h. The present results support the hypothesis that the increase of the central neuronal activity of the vagus nerve precedes ulcer generation in the duodenum.

Relationships between the morphology and function of gastric- and intestine-sensitive neurons in the nucleus of the solitary tract

This study employed single cell recording and intracellular iontophoretic injection techniques to characterize and label gastric- and/or intestine-sensitive neurons in the rat nucleus of the solitary tract (NST). It was possible to divide our sample of NST neurons into three broad groups based on their response to increased intra-gastric and intra-duodenal pressure. Group 1 cells (N = 14) were excited by duodenal distention but were not responsive to gastric stimulation. Most of these intestine-sensitive neurons exhibited a delayed tonic response to the stimulus. Group 2 neurons (N = 13) were excited by gastric distention but were not sensitive to distention of the duodenum. The typical Group 2 neuron evidenced a rapid, phasic response to the distention stimulus. Group 3 neurons (N = 29) responded to both gastric and duodenal stimulation. We found that the Group 2 neurons had greater dendritic length and more dendritic branch segments than the Group 1 or Group 3 neurons. Most of the Group 1 neurons were found in the subpostremal/commissural region of the NST, while the majority of the Group 2 neurons were in the gelatinous subnucleus and a disproportionate number of the Group 3 neurons were located in the medial subnucleus. The results of this investigation demonstrate that 1) there are relationships between the morphology and physiology of distention-sensitive neurons in the NST, and 2) there are distinct functional differences between the gelatinous, medial and commissural subnuclei of this nucleus.

Role of dorsal motor nucleus of vagus in gastric function and mucosal damage induced by ethanol in rats

Experimental evidence indicates that the autonomic nervous system, especially the cholinergic pathway modulates the mucosal defensive mechanism and affects mucosal damage in the stomach. The present study investigated the role of the dorsal motor nucleus of vagus (DMV) in gastric function and its influences on ethanol-induced mucosal damage in pentobarbitone-anesthetized rats. Electrolytic lesion of the DMV as compared with sham operation and lesions of other brain areas, eg, nucleus reticular gigantocellularis and cuneate nucleus, reduced the basal gastric mucosal blood flow (GMBF) and also the blood flow after ethanol administration. The same operation did not affect the acid secretion either in the basal state or during the ethanol treatment period. Lesions at the caudal half of the DMV produced a bigger depression of GMBF when compared with lesion at the rostral half. In the sham-operated rats, ethanol induced severe hemorrhagic lesions in the gastric glandular mucosa, and this was significantly potentiated by lesions at the DMV, especially in the caudal half. The present findings indicate that acute DMV damage at the caudal half markedly affects the GMBF but not the acid secretion. The action on GMBF may contribute to the aggravation of ethanol-induced gastric damage in rats. These data reinforce the idea that the central vagal pathway, especially the caudal half of the DMV, plays a significant role in the modulation of GMBF, which in turn affects the integrity of gastric mucosal barrier.

SMS 201-995-induced stimulation of gastric acid secretion via the dorsal vagal complex and inhibition via the hypothalamus in anaesthetized rats

1. SMS 201-995, a somatostatin analogue which interacts with highest affinities at somatostatin receptor subtypes 5 > 2 > or = 3, was microinjected into selective brain sites and its influence on pentagastrin (10 micrograms kg-1 h-1, i.v.)-stimulated gastric acid secretion was investigated in rats anaesthetized with urethane. Gastric acid secretion was measured by flushing the stomach with saline through a gastric cannula every 10 min. 2. SMS 201-995 microinjected into the dorsal vagal complex (DVC, 7, 15, 30 and 60 ng) dose-dependently increased pentagastrin-stimulated gastric acid secretion. The peak acid response was reached within 20 min and returned to basal level 50 min post-injection. SMA 201-995 (30 ng) microinjected into the surrounding area or the central amygdala did not modify pentagastrin-stimulated acid secretion. 3. SMS 201-995 injected into the lateral ventricle (i.c.v., 100, 200, or 300 ng), paraventricular nucleus (PVN) or lateral hypothalamus (LH) (7.5, 15, or 30 ng) dose-dependently inhibited pentagastrin-stimulated gastric acid secretion. SMS 201-995 (30 ng) microinjected into the area surrounding the PVN or LH did not modify the acid secretion response to pentagastrin. 4. Vagotomy prevented the effects of SMS 201-995 (30 ng) microinjected into the DVC and LH. 5. Spinal cord transection abolished the inhibitory action of SMS 201-995 (30 ng) microinjected into the PVN but not the LH. 6. These results demonstrate that SMS 201-995 acts in the DVC to enhance and in the LH and PVN to inhibit pentagastrin-stimulated gastric acid secretion. The action is mediated through vagal (DVC, LH)or spinal (PVN) pathways. The site specific pattern of acid responses to SMS 201-995 may be linked to the distribution of receptor subtypes at these sites that convey the different biological actions of somatostatin.

Fos-like immunoreactivity in vagal and hypoglossal nuclei in different feeding states: a quantitative study

This study characterized the distribution of Fos-like immunoreactivity (FLI) in three hindbrain nuclei: dorsal motor nucleus of the vagus (DMN), nucleus of the solitary tract (NST) and hypoglossal nucleus (HG) in response to eating or activation of specific components of feeding behavior. The degree of FLI was quantified by automated image analysis software that provided an efficient and sensitive method for counting the number of cells labelled with Fos antibody. Ingestion, and anticipation, of a meal both increased FLI in the DMN and HG, but not in the NST. Sham feeding 1 M sucrose was a more potent stimulus for FLI activation in DMN and NST than combined oral plus gastric/postingestive stimulation provided by real feeding the same food. The results indicate that the physiological stimulus of eating is sufficient to elicit FLI in the hindbrain and that specific components of the feeding act, especially oral stimulation provided by sham feeding, can activate FLI. The results suggest further that, under specific experimental conditions, gastric and/or postgastric stimulation may decrease FLI in the NST and DMN.

Nitric oxide-synthesising neurons in the central subnucleus of the nucleus tractus solitarius provide a major innervation of the rostral nucleus ambiguus in the rabbit

We describe an intramedullary nitric oxide synthase (NOS) neural pathway that projects from the nucleus tractus solitarius (NTS) to the rostral nucleus ambiguus (NA) in the rabbit. With the use of NADPH diaphorase histochemistry and NOS immunohistochemistry, a compact group of NOS-positive perikarya was identified in the central subnucleus of the NTS dorsomedial to the tractus solitarius and rostral to the obex. A dense network of NOS terminals was seen in the rostral NA. We investigated whether NOS terminals in the NA derive from NOS perikarya in the central NTS and whether the central NOS pathway links esophageal afferents and efferents. In some rabbits, the central NTS was unilaterally lesioned. In others, Phaseolus vulgaris-leucoagglutinin (PHA-L) was injected into the central NTS, or cholera toxin-gold was injected into the NA, or cholera toxin-horseradish peroxidase (HRP) was injected into the wall of the esophagus. The medulla was subsequently processed to demonstrate PHA-L, cholera toxin-gold, HRP, and NOS reactivity. Seven days after the NTS lesion, we observed a marked decrease in the density of NOS terminals in the ipsilateral NA. After injection of PHA-L into the central NTS, a dense group of PHA-L fibres was seen in the rostral NA, principally ipsilaterally. Afferent fibres from the esophagus were found around the NOS cell bodies in the central NTS, and many of these NOS neurons were double labeled with cholera toxin-gold after injection of this tracer into the NA. NOS terminals were found around NA neurons that were retrogradely labelled from the esophagus. We conclude that the NOS neurons in the central NTS act as interneurons in a central pathway connecting esophageal afferents and efferents.

Immunocytochemical localization of the renal neutral and basic amino acid transporter in rat adrenal gland, brainstem, and spinal cord

A neutral and basic amino acid transporter (NBAT) cloned from rat kidney was recently localized to enteroendocrine cells and enteric neurons. We used an antibody directed against a synthetic peptide representing a putative extracellular domain of NBAT to determine whether this transporter was also present in other endocrine and neural tissues, including rat adrenal gland, brainstem, and spinal cord. Abundant, highly granular labeling for NBAT was observed in the cytoplasm of chromaffin and ganglion cells in the adrenal medulla. A small population of intensely labeled varicose processes was also seen in both the cortex and the medulla of the adrenal gland. More numerous, intensely labeled varicose processes were detected in brainstem and spinal cord nuclei, including the locus coeruleus, rostral ventrolateral medulla, nuclei of the solitary tract, dorsal motor nucleus of the vagus, and intermediolateral cell column of the thoracic spinal cord. Significant perikaryal labeling for NBAT was only detected in brainstem and spinal cord following intraventricular colchicine treatment, which increased the number, distribution, and intensity of NBAT-immunolabeled cells. These NBAT-immunoreactive perikarya were most numerous in the locus coeruleus, rostral ventrolateral medulla, nuclei of the solitary tract, and raphe nuclei. Ultrastructural examination of the nuclei of the solitary tract of normal rats showed that NBAT was localized predominantly to axon terminals. Within these labeled terminals, NBAT was associated with large dense core vesicles and discrete segments of plasma membrane. The observed localization of NBAT suggests that this renal specific amino acid transporter subserves a role as a vesicular or plasmalemmal transporter in monoamine-containing cells, including chromaffin cells and autonomic neurons.

Pancreatic polypeptide microinjection into the dorsal motor nucleus inhibits pancreatic secretion in rats

BACKGROUND/AIMS

Pancreatic polypeptide (PP), a hormone released from the pancreas, inhibits pancreatic secretion in vivo but not in vitro, suggesting that the inhibitory action of PP on pancreatic secretion is indirect. Circulating PP in physiological concentrations binds to specific receptors in the dorsal vagal complex in the brainstem. Therefore, the hypothesis of this study was that PP acts centrally and inhibits pancreatic secretion by modulating vagal tone.

METHODS

The effects of microinjection of PP into the dorsal motor nucleus on 2-deoxy-D-glucose-stimulated and cholecystokinin octapeptide (CCK-8)-stimulated pancreatic secretion were examined in urethane-anesthetized rats.

RESULTS

Microinjection of PP to the dorsal motor nucleus but not brainstem sites outside it inhibited 2-deoxy-D-glucose-stimulated pancreatic flow and protein output. CCK-8-stimulated pancreatic protein output was inhibited by PP in the dorsal motor nucleus in dose-dependent and site-specific manners. The inhibitory effect of PP on CCK-8-stimulated protein output was eliminated by vagotomy.

CONCLUSIONS

The results suggest that PP acts in the dorsal motor nucleus to modulate vagal tone on the pancreas, thereby inhibiting pancreatic secretion. This study shows for the first time that the dorsal motor nucleus is involved in central feedback inhibition of the exocrine pancreas.

Monosynaptic input from Leu5-enkephalin-immunoreactive terminals to vagal motor neurons in the nucleus ambiguus: comparison with the dorsal motor nucleus of the vagus

Vagal motor neurons in the rat dorsal motor nucleus of the vagus (DMN) are known to receive direct synaptic input from enkephalin-containing terminals. We examined 1) whether the vagal motor neurons within the nucleus ambiguus (NA) also received monosynaptic input from enkephalin-immunoreactive terminals and 2), if so, whether their ultrastructural relations differed from those in the DMN. In both regions, terminals containing Leu5-enkephalin-like immunoreactivity (LE-LI) were examined in relation to motor neurons identified by retrograde transport of wheat germ-agglutinated horseradish peroxidase (WGA-HRP) applied to the cut end of the cervical vagus nerve in single sections of the medulla oblongata of adult rats. By light microscopy, the most significant overlap between varicose processes with LE-LI and WGA-HRP-containing neurons was seen in the rostral compact portion of the NA and the DMN at the level of the obex. Thus, only these regions were examined by electron microscopy. The most distinguishing ultrastructural feature of WGA-HRP-labeled neurons in the NA compared to the DMN was their higher incidence of nonsynaptic appositions with other neurons. In both the NA and the DMN, terminals with LE-LI formed primarily symmetric synapses on smaller (presumably distal) dendrites; many of these dendrites, as well as most target perikarya, contained WGA-HRP. Additionally, in the compact portion of the NA compared to the DMN 1) multiple LE-labeled terminals more frequently contacted single perikarya or dendrites and 2) single terminals with LE-LI more commonly showed two contacts or active zones and contained more abundant LE-immunoreactive large (80-100 nm) dense-core vesicles (dcvs). In contrast to small (40-50 nm), clear vesicles, which were usually aggregated near active zones, the immunoreactive dcvs were usually located near glial processes distal to these zones. These results indicate that enkephalin immunoreactivity is intensely localized to dcvs within terminals that may have direct inhibitory (symmetric synapses) actions on vagal motor neurons in both the compact portion of the NA and the DMN. Moreover, because numbers of dcvs and active zones have been equated with synaptic strength, our findings suggest enhanced potencies of enkephalin-immunoreactive terminals in the compact portion of the NA. Our findings support a prominent role for enkephalin in the coordinated activity of esophageal motor neurons located in the compact portion of the NA.

Localization of nitric oxide synthase in the brain stem neural circuit controlling esophageal peristalsis in rats

BACKGROUND/AIMS

The central subnucleus of the nucleus of the solitary tract has been implicated in central reflex control of esophageal peristalsis. This study determined the presence of nitric oxide synthase in the brain stem circuit controlling esophageal peristalsis by combining transsynaptic retrograde tract tracing with pseudorabies virus and nicotinamide adenine dinucleotide phosphate diaphorase (NADPH) histochemistry.

METHODS

Virus was injected into the esophagus of 10 of 15 rats. After 60-63 hours, brain sections were processed for viral immunofluorescence and NADPH histochemistry.

RESULTS

Fluorescent neuronal labeling was limited to the compact formation of the nucleus ambiguus and the central subnucleus of the nucleus of the solitary tract. Most fluorescence-labeled neurons in the central subnucleus stained positively for NADPH (double labeled). In the compact formation, there were almost no double-labeled neurons; however, NADPH-stained terminals surrounded fluorescence-labeled motoneurons.

CONCLUSIONS

NO synthase is present in premotor neurons of the central subnucleus of the nucleus of the solitary tract that innervate esophageal motoneurons in the compact formation of the nucleus ambiguus. NADPH staining in both somata and terminals of esophageal premotor neurons suggests that NO is involved in neurotransmission in the central subnucleus and at the site of synaptic contact between esophageal premotor neurons and motoneurons in the compact formation of the nucleus ambiguus.

Cell types in the rostral nucleus of the solitary tract

The rostral subdivision of the nucleus of the solitary tract (rNST) is not laminated or otherwise organized into clearly segregated cell types. Although a variety of experimental approaches have yielded a wealth of information, the definition of cell types in this nucleus has been difficult, as reflected in the sometimes contradictory literature on morphological cell typing. The present review discusses how rNST neurons have been classified in the past and adds to the evidence that distinct neuron types exist in this nucleus. Consistencies in the literature, as well as inconsistencies among studies, are discussed. Furthermore, we have included a summary of our own results that help provide additional data relevant to cell typing. The definition of cell types in other central nervous system nuclei has helped our understanding of the organization of these nuclei and our understanding of the relationships between the morphology and function of neurons. It is hoped that this synthesis of the extant literature will facilitate the many ongoing efforts to correlate neuronal morphology and physiology in the gustatory system.

Evidence against a hemodynamic role for serotonin in the dorsal motor nucleus of the vagus

This study was performed to investigate the potential role of serotonin (5-HT) in the dorsal motor nucleus of the vagus (dmnX) in regulating peripheral hemodynamics. Microinjections (5 or 25 nmol in 50 nl) of the monoaminergic neurotransmitter were made into the dorsomedial medulla of the urethaneanesthetized rat during continuous recording of femoral arterial blood pressure. Heart rate was extracted electronically from the pressure waveform. Discrete injections of 5-HT placed directly in the dmnX were found to be entirely without effect on peripheral hemodynamics. In contrast, injections placed in the solitary tract nucleus, lying immediately above the dmnX, were found to have profound depressor and bradycardic effects, while the immediately subjacent hypoglossal nucleus appeared to contain both depressor and unresponsive sites. These findings cast doubt on the involvement of serotonin in the dmnX in the regulation of cardiovascular hemodynamics.

Caudal raphe-dorsal vagal complex peptidergic projections: role in gastric vagal control

Subpopulations of raphe pallidus (Rpa) and raphe obscurus (Rob) neurons containing TRH, serotonin (5-HT), and substance P contribute projections to the dorsal vagal complex (DVC). Activation of Rpa and Rob neurons induces a vagal cholinergic-dependent stimulation of gastric secretory and motor function and modulates resistance of the gastric mucosa to gastric injury in rats and cats. The caudal raphe nuclei-DVC pathways containing TRH/5-HT are involved in mediating cold-induced vagal stimulation of gastric function and erosion formation. These results suggest that Rpa/Rob-DVC projections containing TRH/5-HT may be an important pathways in the medullary regulation of vagal activity to the viscera.

Innervation of the larynx, pharynx, and upper esophageal sphincter of the rat

We identified a 'semicircular' compartment of the rat thyropharyngeus muscle at the pharyngoesophageal junction and used the glycogen depletion method to determine how the fibers of this muscle (as well as all others of the pharynx and larynx) are innervated by different cranial nerve branches. The semicircular compartment appears anatomically homologous to the human cricopharyngeus muscle, an important component of the upper esophageal sphincter. While we found very little overlap in the muscle targets of the pharyngeal, superior laryngeal and recurrent laryngeal nerves within the pharynx and larynx, the semicircular muscle receives a dual, interdigitating innervation from two vagal branches: the pharyngeal nerve and a branch of the superior laryngeal nerve we call the dorsal accessory branch. After applying horseradish peroxidase to either of these two nerves, we compared the distribution and number of cells labeled in the brainstem. The dorsal accessory branch conveys a more heterogeneous set of efferent fibers than does the pharyngeal nerve, including the axons of pharyngeal and esophageal motor neurons and parasympathetic preganglionic neurons. The observed distribution of labeled motor neurons in nucleus ambiguus also leads us to suggest that the semicircular compartment is innervated by two subsets of motor neurons, one of which is displaced ventrolateral to the main pharyngeal motor column. This arrangement raises the possibility of functional differences among semicircular compartment motor neurons correlated with the observed differences in brainstem location of cell bodies.

Structure and function of gustatory neurons in the nucleus of the solitary tract. I. A classification of neurons based on morphological features

Prior investigations in other laboratories have provided convincing evidence that the neurons of the rostral nucleus of the solitary tract (rNST) can be grouped according to their physiological response properties or morphologic features. The present study is based on the premise that the response properties of gustatory neurons are related to, and perhaps governed by, their morphology and connectivity. In this first phase of our ongoing investigation of structure-function relationships in the rNST of the rat, we have used intracellular injection of neurobiotin to label individual physiologically characterized gustatory neurons. A total of 63 taste-sensitive neurons were successfully labeled and subjected to three-dimensional quantitative and qualitative analysis. A cluster analysis using six morphologic features (total cell volume, soma area, mean segment length, swelling density, spine density, and number of primary dendrites) was used to identify six cell groups. Subsequent analyses of variance and posthoc comparisons verified that each of these six groups differed from all others with respect to at least one variable, so each group was "typified" by at least one of the six morphologic features. Neurons in group A were found to be the smallest neurons in the sample. The cells in group B had small somata and exhibited the highest swelling density of any group. Group C neurons were distinguished by dendrites with long, spine-free branches. These dendrites were significantly longer than those of any other group except Group F. The neurons in group D had more primary dendrites than any other group. Group E neurons possessed dendrities with the lowest swelling density but the most spines of any group. The cells in group F were the largest neurons in our sample and possessed the largest somata of any group. Thus overall cell size and density of dendritic spines and swellings were found to be particularly important variables in this classification scheme. Our preliminary results suggest that the number and density of dendritic spines (as well as other morphologic features) may be related to a given neuron's most effective stimulus, indicating that it will indeed be possible to use the criteria established in the present investigation to derive structure-function relationships for gustatory neurons in the rNST.

Local and commissural neuropeptide-containing projections of the nucleus of the solitary tract to the dorsal vagal complex in the pigeon

The neuropeptide content of neurons of the nucleus of the solitary tract (NTS), which have local and commissural projections to the dorsal motor nucleus of the vagus (DMNX) and to NTS, were demonstrated in the pigeon (Columba livia) by using a combined fluorescein-bead retrograde-transport-immunofluorescence technique. The specific peptides studied were bombesin, cholecystokinin, enkephalin, galanin, neuropeptide Y, neurotensin, and substance P. Perikarya immunoreactive for bombesin were located in medial tier subnuclei of NTS and the caudal NTS. Most galanin- and substance P-immunoreactive cells were found in subnucleus medialis ventralis. Cells immunoreactive for neuropeptide Y were found in the medial tier of NTS and in the lateral tier, especially in subnucleus lateralis dorsalis intermedius. The majority of enkephalin- and neurotensin-immunoreactive cells were found centrally in subnuclei medialis dorsalis and medialis intermedius. Cells immunoreactive for cholecystokinin were located in subnuclei lateralis dorsalis pars anterior, medialis superficialis, and the caudal NTS. Based on the presence of retrogradely labeled cells, numerous neurons of the medial tier of NTS, but extremely few lateral tier NTS neurons, had projections to the ipsilateral and contralateral DMNX and NTS. The number of retrogradely labeled NTS cells was always greater ipsilaterally than contralaterally. The percentages of peptide-immunoreactive NTS cells that projected to the ipsilateral and contralateral DMNX were in the ranges of 29-61% and 10-48%, respectively. The percentages of peptide-immunoreactive NTS cells that projected to the contralateral NTS ranged from 13 to 60%. Peptide-immunoreactive NTS cells that have local and commissural projections to DMNX and NTS may act as interneurons in vagovagal reflex pathways and in the integration of visceral sensory and forebrain input to NTS and DMNX.

Pituitary adenylate cyclase-activating polypeptide-like immunoreactivity in autonomic regulatory areas of the rat medulla oblongata

Pituitary adenylate cyclase-activating polypeptide-like immunoreactivity (PACAP-LI) was mapped immunohistochemically in the rat medulla oblongata. We found the majority of perikarya with PACAP-LI in the visceral areas of the solitary nucleus, dorsal motor vagal nucleus, nucleus ambiguus, ventrolateral medulla, ventral medullary surface, and caudal raphe nuclei. Medium densities of labeled fibers were detected in the area postrema, solitary nucleus, dorsal vagal and raphe pallidus nuclei. Our morphological data support the hypothesis that PACAP is a central regulator of visceral functions.

Effects of microinjection of kainic acid into the nucleus tractus solitarius on fluid and NaCl absorption across the jejunum

Effects of bilateral chemical inactivation of the nucleus tractus solitarius (NTS) by microinjection of kainic acid (KA) on fluid and NaCl absorption across the jejunum were examined in anesthetized Sprague-Dawley rats. Jejunal fluid and NaCl absorption was measured in a jejunal loop before and after the microinjection of artificial cerebrospinal fluid (aCSF) or KA into the NTS. Net fluid and NaCl absorption was not altered by a microinjection of aCSF. However, net fluid (from 1.12 +/- 0.07 to 1.66 +/- 0.06 ml/30 min) and NaCl (Na+ from 164.5 +/- 10.1 to 243.3 +/- 7.1 muEq/30 min; and Cl- from 175.9 +/- 7.5 to 260.8 +/- 6.5 muEq/30 min) absorption was significantly increased by the chemical inactivation of the NTS. To examine the efferent mechanism of the increased net absorption induced by the NTS inactivation, mesenteric nerve activity (MNA) was measured before and after the inactivation of the NTS. MNA was significantly increased by 165.9 +/- 74.2% after the bilateral inactivation of the NTS. Furthermore, absorption experiments were conducted in rats with pretreatment of atropine (acetylcholine-antagonist) or yohimbine (specific alpha 2-antagonist). In atropine treated rats, net jejunal absorption was significantly increased by the inactivation of the NTS. However, the increase in net absorption induced by the inactivation of the NTS was completely abolished by pretreatment with yohimbine. These results suggest that the NTS has a tonic suppression on jejunal absorption through alpha 2-adrenergic mechanism.

Differential effects of dihydrotestosterone and estrogen on the development of motoneuron morphology in a sexually dimorphic rat spinal nucleus

The rat lumbar spinal cord contains a sexually dimorphic motor nucleus, the spinal nucleus of the bulbocavernosus (SNB), whose motoneurons innervate perineal muscles involved in copulatory reflexes. Dendritic development of SNB motoneurons is biphasic and androgen dependent. During the first 4 postnatal weeks, SNB dendrites grow exuberantly, and subsequently retract to mature lengths by 7 weeks of age. After early postnatal castration, SNB dendrites fail to grow, and testosterone replacement restores this growth. In other systems, testosterone and its metabolites, dihydrotestosterone and estrogen, are important for somatic and neural sexual differentiation. The purpose of the present study was to examine the effects of castration and dihydrotestosterone or estrogen replacement on the growth of SNB motoneuron somata and dendritic arbors. Male rat pups were castrated on postnatal (P) day 7 and treated daily with either dihydrotestosterone propionate (DHTP; 2 mg) or estradiol benzoate (EB; 100 micrograms) until P28 or P49. By using cholera toxin horseradish peroxidase (BHRP) histochemistry, the soma size, dendritic length, dendritic extent, and arbor area of BHRP-labeled SNB motoneurons were measured and analyzed. Both DHTP and EB treatment supported the initial exuberant growth of SNB dendrites through P28, but EB treatment was ineffective in maintaining mature, adult lengths at P49. The possible sites of hormone action and functional implications of these hormonal treatments are discussed.

Microinjection of thyrotropin-releasing hormone in the paraventricular nucleus of the hypothalamus stimulates gastric contractility

Changes in gastric contractility following microinjection of thyrotropin-releasing hormone (TRH) into the paraventricular nucleus of the hypothalamus (PVN) were examined in fasted, urethane-anesthetized rats. Gastric contractility was measured with extraluminal force transducers and analysed by computer. Unilateral and bilateral PVN microinjections of TRH (0.5 and 1.0 microgram) significantly increased the force index of gastric contractions from 0 to 60 min postinjection, when compared with animals microinjected with 0.1 microgram TRH, 0.1% BSA or TRH (0.5 and 1.0 microgram TRH) in sites adjacent to the PVN. The gastric force index was also significantly elevated from 61 to 120 min postinjection in rats receiving bilateral PVN microinjections of TRH (0.5 and 1.0 microgram). Peak gastric responses occurred within 10-20 min postinjection and represented an approximately eight-fold increase over basal values. In the remaining groups, the force index was not significantly altered from preinjection values. The excitatory action of TRH (1.0 microgram) on gastric contractility was completely abolished by subdiaphragmatic vagotomy. These results suggest that TRH acts within the PVN to stimulate gastric contractility via vagal-dependent pathways.

Dendritic architecture of hypoglossal motoneurons projecting to extrinsic tongue musculature in the rat

The tracer, cholera toxin-horseradish peroxidase, was used to determine the dendritic architecture and organization of hypoglossal motoneurons in the rat. In 22 animals, the tracer was injected unilaterally into either the geniohyoid, genioglossus, hyoglossus, or styloglossus muscle. Within the hypoglossal nucleus, motoneurons innervating the extrinsic tongue muscles were functionally organized. Geniohyoid and genioglossus motoneurons were located within the ventrolateral and ventromedial subnuclei, respectively, while hyoglossus and styloglossus motoneurons were located within the dorsal subnucleus. Motoneurons located in all subnuclear divisions were found to have extensive dendrites that extended laterally into the adjacent reticular formation and medially to the ependyma. Less extensive extranuclear dendritic projections were found in the dorsal vagal complex and median raphe. Prominent rostrocaudal and mediolateral dendritic bundling was evident within the ventral subnuclei and dorsal subnucleus, respectively. Dendritic projections were also found extending inter- and intrasubnuclearly with a distinct pattern for each muscle. These data suggest that the varied and extensive dendritic arborizations of hypoglossal motoneurons provide the potential for a wide range of afferent contacts for, and interactions among, motoneurons that could contribute to the modulation of their activity. Specifically, the prominent dendritic bundling may provide an anatomic substrate whereby motoneurons innervating a specific muscle receive and integrate similar afferent input and are thus modulated as a functional unit. In contrast, the extensive intermingling of both inter- and intrasubnuclear dendrites within the hypoglossal nucleus may provide a mechanism for the coordination of different muscles, acting synergistically or antagonistically to produce a tongue movement.

Dye-coupling between vagal motoneurones within the compact region of the adult rat nucleus ambiguus, in-vitro

The electrophysiological and morphological characteristics of vagal motoneurones lying within the compact region of the nucleus ambiguus were investigated in thin coronal slices of the adult rat medulla utilising intracellular recording techniques. The majority of neurones were found to be silent, displaying no underlying synaptic activity or oscillations in membrane potential. Intracellular dye-filling demonstrated that the neurones had multipolar cell bodies, with 2-8 major dendrites, each branching up to 4 times and extending up to 200 microns from the cell body. The existence of dye-coupling between adjacent neurones was shown in 30% of cells investigated. This evidence suggests a possible mechanism for the provision of synchronous activity within groups of vagal motoneurones, a process essential for the control of deglutination.

The subnuclear distribution of 5-HT3 receptors in the human nucleus of the solitary tract and other structures of the caudal medulla

The distribution of 5-HT3 receptors was examined in the human medulla using [3H]LY278584, a highly selective 5-HT3 receptor antagonist. The highest density of 5-HT3 receptors was found in the substantia gelatinosus subnucleus of nucleus of the solitary tract (NTS) throughout its rostrocaudal extent, followed by the dorsal subnucleus, the area postrema (AP), the commissural subnucleus, the medial subnucleus, and in an arc corresponding to the pars gelatinosus of the spinal trigeminal nucleus (nSp5). The distribution of 5-HT3 receptors in the brain may help explain some of the reported CNS activities of 5-HT3-selective drugs. The anti-emetic and antinociceptive activities of 5-HT3 antagonists may be mediated by receptors in sensory areas of the brainstem.

The relationship of efferent projections from the area postrema to vagal motor and brain stem catecholamine-containing cell groups: an axonal transport and immunohistochemical study in the rat

The area postrema has been implicated as a major station for the processing of visceral sensory information, involved primarily in eliciting rapid homeostatic responses to fluid and nutrient imbalances. Yet the precise relationship of efferent projections from the area postrema to medullary motor and relay nuclei involved in such functions remains unclear. In this study, axonal transport and immunohistochemical techniques were used to investigate the relationship of efferent projections from the area postrema to vagal motor neurons and medullary catecholamine-containing cell groups in the rat. The results may be summarized as follows: (1) The area postrema gives rise to dense inputs to the commissural and medial parts of the nucleus of the solitary tract. Many of these projections are intimately associated with catecholamine-containing neurons in the A2 and C2 cell groups, including a particularly prominent input to a caudally placed cluster of adrenergic neurons (the C2d cell group) in the dorsal aspect of the medial part of the nucleus of the solitary tract. (2) The area postrema provides a dense input to the external lateral part of the parabrachial nucleus. (3) The area postrema does not project significantly to vagal motor neurons in either the dorsal motor nucleus or the nucleus ambiguus, although the possibility for inputs to distal dendrites of dorsal vagal motor neurons cannot be excluded. (4) En route to the parabrachial nucleus, axons of area postrema neurons traverse the regions of the A1, C1 and A5 cell groups, although these fibers make few arborizations, suggesting little functional contact. Together, these results suggest that sensory information received by the area postrema is dispatched to a restricted set of neurons in the commissural, medial, and dorsal parts of the nucleus of the solitary tract, most probably including catecholamine-containing cells in the A2, C2, and C2d cell groups, and to the external lateral portion of the parabrachial nucleus. The targets of area postrema projections are, in turn, in a position to effect adaptive changes in the activities of hypothalamic neurosecretory neurons, vagal motor neurons, and limbic forebrain regions in response to perturbations in fluid and nutrient homeostasis.

Intracisternal thyrotropin-releasing hormone-induced vagally mediated gastric protection against ethanol lesions: central and peripheral mechanisms

The vagus is involved in mediating gastric cytoprotection and adaptive cytoprotection. However, the central and peripheral mechanisms through which the vagus expresses its action are still poorly known. Medullary thyrotropin-releasing hormone (TRH) plays an important role in the vagal regulation of gastric function. The stable TRH analogue, RX 77368, micro-injected into the cisterna magna or the dorsal motor nucleus (DMN) of the vagus at a dose that did not influence gastric acid secretion prevented gastric injury induced by intragastric administration of 60% ethanol in conscious or urethane-anaesthetized rats. The cytoprotective action of TRH is mediated through vagal cholinergic release of prostaglandin E2 (PGE2). Prostaglandin E2 action is unrelated to changes in gastric mucosal blood flow (GMBF). In addition, other peripheral mechanisms involve calcitonin gene-related peptide (CGRP) contained in capsaicin sensitive afferent fibres and nitric oxide, both of which mediate the associated increase in GMBF induced by intracisternal injection of RX 77368. These data indicate that medullary TRH induces vagally mediated gastric protection against ethanol lesions. Its action is expressed through the muscarinic dependent release of PGE2 and nitric oxide, and efferent function of capsaicin-sensitive afferent fibres releasing CGRP.

Morphology and projections of neurobiotin-labeled nucleus tractus solitarii neurons recorded in vitro

The suitability of the anterograde tracer neurobiotin to provide information about the morphology and projections of extracellularly or intracellularly recorded medial nucleus tractus solitarii (nTS) neurons was evaluated in horizontally oriented rat dorsal medulla in vitro slices. After responsiveness to angiotensin (Ang) II, substance P (SP), and L-glutamate was evaluated, neurons were labeled by electrophoresis of neurobiotin at the recording site. Extracellular application (2 microA for 2 min) produced discrete injection sites (40-70 microns) with a small group of labeled neurons. Ejections into the solitary tract documented that the tracer was not taken up by axons traversing the injection site. Neuronal perikarya, primary and secondary dendrites, and axons exhibited a dense Golgi-like appearance, with well-defined dendritic spines and axonal varicosities. Dendritic or axonal processes could be followed for more than 1 mm from the cell soma in a 50 microns thick section, documenting the horizontal architecture of the medial nTS. Intracellular electrophoresis filled the soma, primary and secondary dendrites, and axons of neurons characterized for responsiveness to peptides, L-glutamate and solitary tract stimulation. The location within the nTS and axonal projections of neurons responsive to Ang II and SP appeared to differ from those of cells responsive to Ang II and L-glutamate. Thus, either extracellular or intracellular application of neurobiotin in the in vitro slice can reveal differences in axonal or dendritic targets of neuronal subgroups responsive to different neurotransmitters or peptides and provide evidence for the likely autonomic significance of the neurons.

The central connections of the vagus nerve in the ferret

The vagus nerve mediates emesis due to gastric irritation. The central representation of the vagus in the ferret was studied to establish how the nerve is connected to areas important in the regulation of emesis. In a series of 10 ferrets, WGA-HRP injections (10 microliters) were made into the nodose ganglion. After 24-48 h, animals were reanesthetized and perfused transcardially. A block extending from the pons to upper cervical spinal cord was cut at 50 microns and sections reacted. Nodose ganglion injections of WGA-HRP produced labeling of vagal preterminal segments in the ipsilateral dorsal vagal complex including all subnuclei of the solitary complex where the medial and subgelatinous subnuclei received the densest input, the area postrema (AP), which contained a modest amount of terminal label, and the dorsal motor nucleus of the vagus (DMX). Contralateral terminal label, quantitatively much less, was similarly distributed except that within the solitary complex it was limited to the medial and subgelatinous subnuclei. Retrogradely labeled cells formed ipsilateral dorsomedial and ventrolateral columns, corresponding, respectively, to the DMX and the nucleus ambiguus (including retrofacial and retroambiguus).

Effect of portal infusion of hypertonic saline on neurons in the dorsal motor nucleus of the vagus in the rat

Effects of hepatoportal osmo-receptive (or sodium-receptive) afferents on neurons within the dorsal motor nucleus of the vagus (DMV) were investigated electrophysiologically in urethane-chloralose anesthetized rats. Responses of 56 spontaneously active neurons to antidromic stimulation of the ventral trunk of the subdiaphragmatic vagus were recorded in the left DMV. Among them, 35 neurons were inhibited by electrical stimulation of the hepatic branch of the vagus nerve (inhibitory neurons), except two neurons that were slightly excited. Effects of portal infusion of 3.6% NaCl were examined on 26 inhibitory neurons. Sixteen neurons increased their discharge rates and one neuron decreased its discharge rate in response to portal infusion of hypertonic saline. Thirty-five right DMV neurons responded to electrical stimulation of the dorsal trunk of the subdiaphragmatic vagus were inhibited by electrical stimulation of the hepatic branch of the vagus. Four neurons were excited by this stimulation. Relatively smaller number of neurons (5 out of 22 inhibitory neurons) increased their discharge rates in response to portal infusion of hypertonic saline. In conclusion, the response of DMV neuron observed in this experiment was characterized by increasing the frequency of spike discharges in response to portal infusion of hypertonic saline. However, these neurons were inhibited by electrical stimulation of the hepatic branch of the vagus nerve. These results suggest that the hepatoportal osmo-receptive afferents may be conveyed to the DMV via inhibitory synapses.

Nucleus of the solitary tract and dorsal motor nucleus of the vagus nerve of the pigeon: localization of peptide and 5-hydroxytryptamine immunoreactive fibers

The distribution of peptide and serotonin fibers in the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus nerve (DMNX) in the pigeon (Columba livia) was investigated immunocytochemically. This information was correlated with the viscerotopic organization of the nuclei and with central NTS circuitry to suggest the role of the neurochemical containing fibers in the regulation of organ function. The distribution of fibers containing cholecystokinin (CCK), calcitonin gene-related peptide (CGRP), enkephalin (ENK), neuropeptide Y (NPY), neurotensin (NT), substance P (SP), somatostatin (SS), vasoactive intestinal peptide (VIP), and 5-hydroxytryptamine (5-HT) was determined. Each substance had a distinct distribution within the subnuclei of NTS-DMNX, but certain generalities can be deduced. In the DMNX, fibers immunoreactive for ENK, NT, and SP were found in greatest concentration, while CGRP and 5-HT immunoreactive fibers were the least dense. This suggests that ENK, NT, and SP may have a significant modulatory effect on gastrointestinal functions. In the NTS overall, ENK, NT, SP, and VIP fibers were found in high density, CCK, NPY, SS, and 5-HT fibers were found in moderate density, and CGRP fibers were found in low density. However, some individual NTS subnuclei were found to contain moderate to high concentrations of each of the substances, including CGRP. Fibers containing CCK, ENK, NT, SP, SS, and VIP in the medial dorsal NTS subnuclei may regulate gastroesophageal functions. The caudal part of subnucleus lateralis parasolitarius did not contain most of the substances, which suggests that pulmonary function is not modulated by these neurochemicals. The boundaries of a subnucleus could sometimes be demarcated by a change in density of immunoreactive fibers between adjacent subnuclei. This was particularly evident in NTS subnuclei medialis dorsalis anterior centralis and lateralis parasolitarius, and in DMNX subnucleus posterior dorsalis magnocellularis. The selective distribution of peptide and serotonin immunoreactive fibers in various subnuclei of NTS-DMNX suggests that these substances may be differentially involved in neural circuits that mediate cardiovascular and gastrointestinal functions.

Motoneuron morphology in the dorsolateral nucleus of the rat spinal cord: normal development and androgenic regulation

The rat lumbar spinal cord contains two sexually dimorphic motor nuclei, the spinal nucleus of the bulbocavernosus (SNB), and the dorsolateral nucleus (DLN). These motor nuclei innervate anatomically distinct perineal muscles that are involved in functionally distinct copulatory reflexes. The motoneurons in the SNB and DLN have different dendritic morphologies. The dendrites of motoneurons in the medially positioned SNB have a radial, overlapping arrangement, whereas the dendrites of the laterally positioned DLN have a bipolar and strictly unilateral organization. During development, SNB motoneuron dendrites grow exuberantly and then retract to their mature lengths. In this experiment we determined whether the adult difference in SNB and DLN motoneuron morphology was reflected in different patterns of dendritic growth during normal development. Furthermore, the development of both these nuclei is under androgenic control. In the absence of androgens, SNB dendrites fail to grow; testosterone replacement supports normal dendritic growth. Thus, we also examined the development of DLN dendrites for similar evidence of androgenic regulation. By using cholera toxin-horseradish peroxidase (BHRP) to label motoneurons retrogradely, we measured the morphology of DLN motoneurons in normal males, and in castrates treated with testosterone or oil/blank implants at postnatal day (P) 7, P28, P49, and P70. Our results demonstrate that in contrast to the biphasic pattern of dendritic development in the SNB, dendritic growth in the DLN was monotonic; the dendritic length of motoneurons increased more than 500% between P7 and P70. However, as in the SNB, development of DLN motoneuron morphology is androgen-dependent. In castrates treated with oil/blank implants, DLN somal and dendritic growth were greatly attenuated compared to those of normal or testosterone-treated males. Thus, while androgens are clearly necessary for the growth of motoneurons in both the SNB and DLN, their different developmental patterns suggest that other factors must be involved in regulating this growth.

Regulation of cholecystokinin receptors in the hypothalamus of the rat: reciprocal changes in magnocellular nuclei induced by food deprivation and dehydration

Cholecystokinin (CCK) has been suggested to mediate satiety in a number of non-primate species via its peripheral actions as well as a possible central mechanism involving magnocellular and parvocellular oxytocin release. Quantitative in vitro autoradiography employing [125I]-Bolton-Hunter labelled CCK-8S ([125I]-CCK-8S) was used to examine the distribution and density of CCK receptors in sections of brain from normal rats and rats deprived of food, water or both food and water for 4 days. In food-deprived rats, specific [125I]-CCK-8S binding was reduced by 64 +/- 5% in the hypothalamic supraoptic nucleus (SON) and by 44 +/- 13% in the paraventricular nucleus of the hypothalamus (PVN). In contrast, water deprivation increased binding of [125I]-CCK-8S by 128 +/- 15% in the SON and by 196% +/- 24% in the PVN, while combined food and water deprivation produced smaller increases in both nuclei (30 +/- 5% and 98 +/- 26% in SON and PVN respectively). Changes in receptor density in the PVN appeared to be most prominent in the magnocellular (especially oxytocin-rich) subdivisions. None of the treatments employed produced changes in [125I]-CCK-8S binding in the ventromedial hypothalamic nucleus or the reticular thalamic nucleus. Both CCK-A and CCK-B receptor subtypes were visualized in the nucleus of the solitary tract and the area postrema of normal rats, but levels of binding to both of these subtypes were unaffected by the experimental treatments. These selective alterations demonstrate the plasticity of CCK receptors in the SON and PBN, and are probably associated with changes in the level of neurochemical activity of magnocellular oxytocinergic neurones in these areas. These results, together with reports of changes in the level of CCK synthesis in cells of the SON and PVN after hyperosmotic stimuli, suggest that CCK may act in an autocrine fashion on these neurones and that both CCK receptors and peptide levels are altered in the same direction following cellular activation or inhibition.

Distribution and characterization of tumor necrosis factor-alpha-like immunoreactivity in the murine central nervous system

Tumor necrosis factor-alpha (TNF alpha) is a protein released from macrophages during infection and inflammation. Recent studies suggest that it has several effects within the central nervous system, including generation of fever, enhancement of slow wave sleep, and stimulation of pituitary hormone secretion. We have proposed that TNF alpha may be synthesized by neurons in the CNS and used as a neuromodulator in the pathways involved in the central control of these activities. To test this hypothesis, we have used an antiserum raised against recombinant murine (rm) TNF alpha with an indirect immunoperoxidase technique to stain the murine CNS immunohistochemically. Western blot analysis of mouse brain homogenates revealed one band with electrophoretic mobility identical to that of rmTNF alpha. We identified TNF alpha-like immunoreactive (ir) neurons in the hypothalamus, in the bed nucleus of the stria terminalis, in the caudal raphe nuclei, and along the ventral pontine and medullary surface. TNF alpha ir innervation was widespread within the CNS, particularly in areas involved in autonomic and endocrine regulation, including the hypothalamus, amygdala, bed nucleus of the stria terminalis, parabrachial nucleus, dorsal vagal complex, nucleus ambiguus, and thoracic sympathetic preganglionic cell column. Our data suggest that TNF alpha may serve as a neuromodulator in central pathways involved in the regulation of the autonomic, endocrine and behavioral components of the acute-phase response to inflammation and infection.

Changes in dendritic morphology of rat spinal motoneurons during development and after unilateral target deletion

During normal development, motoneuron dendrites in the spinal nucleus of the bulbocavernosus (SNB) grow exuberantly to almost twice their adult length and then retract. In this study, we retrogradely labeled SNB motoneurons with cholera toxin B-conjugated horseradish peroxidase (BHRP) to examine the maturation of SNB dendritic arbors in more detail, particularly with regard to its spatial distribution and reorganization. The number and orientation of SNB motoneuron primary processes did not change over the first ten weeks of life. In contrast, total dendritic length, radial extent and arbor area increased significantly through the first four postnatal weeks and declined thereafter. The declines in length and extent were restricted to particular portions of the arbor, specifically the dorsal, ipsi- and contralateral projections. Estimates of the degree of overlap between the dendritic arbors from both sides of the SNB reflected these changes, with overlap initially increasing and then decreasing as the SNB established its adult dendritic morphology. To determine if dendritic interactions facilitated by this arbor overlap might be involved in regulating the normal retraction of SNB dendrites, we reduced SNB motoneuron numbers unilaterally by target muscle removal on the day of birth. Somal size, number and orientation of primary processes developed normally in unilateral muscle-extirpated animals. The dendritic morphology of surviving SNB motoneurons in unilateral muscle extirpated males was altered, with significant increases in dendritic length, extent and arbor area relative to those of normal males. These results indicate that substantial changes in dendritic organization of SNB motoneurons occur in normal development and may be influenced by interactions between dendrites from the two halves of the SNB.

Localization of the stomach-projecting neurons in the dorsal motor nucleus of the vagus nerve in the guinea pig

The medullary origin of cells of the cervical vagus nerve and the vagal innervation of the stomach in the guinea pig were studied using the retrograde transport of horseradish peroxidase. The horseradish peroxidase was injected into the cervical portion of the vagus nerve, and also into the greater or lesser curvature of the stomach. The animals were perfused with fixative two days after the injection. The medulla oblongata containing the dorsal motor nucleus of the vagus nerve was sectioned and processed histochemically with the tetramethyl benzidine method. The injection of horseradish peroxidase in the cervical vagus nerve resulted in heavy retrograde labelling of neurons in the ipsilateral dorsal motor nucleus and in the nucleus ambiguous. Following the injection of horseradish peroxidase into the greater curvature of the stomach, the stomach-projecting neurons which were bilaterally labelled were localized in the dorsal and dorsolateral part of the dorsal motor nucleus. Although also bilaterally labelled in the dorsal and dorsolateral part of the dorsal motor nucleus, the neurons projecting to the lesser curvature of the stomach were predominantly (approx. 70%) located in the left dorsal motor nucleus. Our study suggests that the parasympathetic preganglionic neurons innervating the greater and lesser curvatures of the stomach are organized viscerotopically in the dorsal motor nucleus in the guinea pig.

Establishment of vagal sensorimotor circuits during fetal development in rats

The differentiation of vagal motor neurons and their emerging central relationship with vagal sensory afferents was examined in fetal rats. To identify peripherally projecting sensory and motor neurons, 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate (DiI) was inserted into the proximal gut or cervical vagus nerve in fixed preparations. At embryonic day (E) 12, labeled vagal sensory neurons are present in the nodose ganglia and a few sensory axons project into the dorsolateral medulla. Central sensory processes become increasingly prevalent between E13 and E14 but remain restricted to the solitary tract. Vagal motor neurons are first labeled at E13, clustered within a region corresponding to the nucleus ambiguus (NA). Additional motor neurons appear to be migrating toward the NA from the germinal zone of the fourth ventricle. Motor neurons in the dorsal motor nucleus of the vagus (DMV) first project to the gut at E14 and have processes that remain in physical contact with the ventricular zone through E16. Sensory axons emerge from the solitary tract at E15 and project medially through the region of the nucleus of the solitary tract (NST) to end in the ventricular zone. A possible substrate for direct vagovagal, sensorimotor interaction appears at E16, when vagal sensory fibers arborize within the DMV and DMV dendrites extend into the NST. By E18, the vagal nuclei appear remarkably mature. These data suggest specific and discrete targeting of vagal sensory afferents and motor neuron dendrites in fetal rats and define an orderly sequence of developmental events that precedes the establishment of vagal sensorimotor circuits.

Localization of tyrosine hydroxylase in neuronal targets and efferents of the area postrema in the nucleus tractus solitarii of the rat

Catecholamines in the nucleus tractus solitarii (NTS) have been implicated in autonomic responses to circulating hormones that act on neurons in the area postrema, the most caudal circumventricular organ in brain. We combined immunoperoxidase labeling of the anterograde tracer, Phaseolus vulgaris leucoagglutinin (PHAL) with immunogold-silver labeling of tyrosine hydroxylase to determine whether this enzymatic marker for catecholamines was present in efferents from the area postrema or their targets in the rat NTS. At survival periods of 10-12 days after PHAL injections into the area postrema, light microscopy revealed numerous varicose processes containing peroxidase reaction product for PHAL in the dorsomedial, medial, and commissural NTS. Some of these labeled processes were located near neuronal perikarya and processes containing immunogold-silver intensified reaction product for tyrosine hydroxylase. Electron microscopy of the commissural and dorsomedial NTS established that the majority of the labeling for PHAL was in axon terminals, whereas immunogold labeling for tyrosine hydroxylase was mainly in soma and dendrites. Only 3 out of 579 PHAL-labeled terminals also contained detectable tyrosine hydroxylase immunoreactivity. Fifty-eight percent (335/579) of the PHAL-labeled terminals formed synapses with recognized symmetric junctions, whereas the remainder lacked synaptic specializations within the examined series of serial sections. Of those PHAL terminals forming recognized symmetric junctions, 22% were on tyrosine hydroxylase-immunoreactive dendrites, 74% on unlabeled dendrites and 4% on unlabeled axon terminals. From a total of 1,250 observed contacts on tyrosine hydroxylase labeled dendrites, 88 (7%) contained PHAL, 9 (< 1%) contained TH, and 1,180 (93%) lacked detectable immunoreactivity and formed primarily symmetric synapses. We conclude that a few catecholamine, but mainly noncatecholamine efferents from the area postrema provide a monosynaptic, and most likely inhibitory input to target neurons both with and without tyrosine hydroxylase immunoreactivity in the dorsomedial and commissural NTS. Synapses between the efferent terminals from the area postrema and tyrosine hydroxylase labeled and unlabeled dendrites as well as unlabeled axons in these specific subnuclei of the NTS suggest multiple sites for modulation of gastric and cardiovascular reflexes in response to circulating peptides.

Bombesin acts in the brain to decrease gastric vagal efferent discharge in rats

The central nervous system action of bombesin to influence basal gastric vagal efferent discharge (GVED) was investigated in urethane-anesthetized rats. Bombesin (62, 620, and 6200 pmol) injected intracisternally (IC) decreased GVED to 78 +/- 10%, 50 +/- 4%, and 43 +/- 3% of preinjection levels, respectively. Bombesin (620 pmol) injected IV also reduced GVED to 36 +/- 6%. Pretreatment with bombesin monoclonal antibody 2A11 completely prevented the decrease in GVED induced by bombesin (620 pmol) given IV but not IC. These data indicate that both IC and IV injections of bombesin decrease basal GVED, and that the inhibitory effect of IC injection represents a central nervous system-mediated action.

The central organization of the vagus nerve innervating the colon of the rat

BACKGROUND

The extent to which the vagus nerve innervates the colon remains controversial.

METHODS

In 29 rats the tracer cholera toxin-horseradish peroxidase was injected into the cecum, the ascending, transverse, or descending colon or the rectum. For comparison, control injections were made into the stomach.

RESULTS

For all areas of colon except the rectum, brainstem motoneuronal labeling was limited to the lateral third of the dorsal motor nucleus of the vagus nerve bilaterally. In contrast, gastric injections resulted in motoneuronal labeling limited to the medial portions of the nucleus. The number of labeled motoneurons was greatest following injection of the cecum, and it significantly decreased for the more distal areas of the colon. Colonic motoneuron dendrites projected into the nucleus of the solitary tract and within the dorsal motor nucleus of the vagus nerve. Sensory afferent terminal labeling was limited to the commissural and medial subnuclei of the nucleus of the solitary tract. For the rectum, sensory and motor labeling was limited to the spinal cord.

CONCLUSIONS

The distribution of labeling within the vagal complex indicates that all regions of the colon, except the rectum, are innervated by the celiac and accessory celiac branches of the vagus nerve.