False-positive artifacts of tracer strategies distort autonomic connectivity maps

Enkephalin immunoreactivity and messenger RNA in a discrete projection from the nucleus of the solitary tract to the nucleus ambiguous in the rat

Previous work described in the rat a circumscribed, partly somatostatinergic, interneuronal projection from the esophageal afferent part of the nucleus of the solitary tract (NTSc) to esophageal motor neurons in the compact formation of the nucleus ambiguous (NAcf: Cunningham and Sawchenko, J Neurosci 9:1668, 1989). In the present study, axonal transport, immunohistochemical and in situ hybridization histochemical techniques were used to determine whether enkephalin (ENK), a peptide known to be expressed in a number of somatostatin-containing medullary cell groups, is also expressed in the projection from the NTSc to the NAcf. The results may be summarized as follows: 1) cells immunoreactive (IR) for prepro-enkephalin (ppENK)-derived peptides were found in the NTSc in colchicine-pretreated animals; in untreated animals, a dense ENK-IR terminal field was observed in the NAcf: sections stained with antisera against dynorphin-related peptides showed sparse staining in both regions; 2) signal indicating the presence of ppENK messenger RNA (mRNA) was found over the NTSc, including over a majority of cells identified using a retrograde tracing technique as projecting to the region of the NAcf; the signal for ppENK mRNA signal was greater than that for prepro-somatostatin (ppSS) in the NTSc; 3) a combined anterograde tracing-immunohistochemical technique demonstrated a strong correspondence between the distribution of inputs from the NTS to the NAcf, and the distribution of endogenous ENK-IR varicosities; in addition, leucine (L)-ENK-IR was found in an appreciable number of varicosities in the NAcf that had been anterogradely labeled from the NTSc; 4) unilateral electrolytic lesions of the rostromedial NTS, which included the central subnucleus, virtually eliminated ENK-IR in the ipsilateral NAcf, while staining on the contralateral side was unaffected. Taken together, these studies provide evidence that ppENK- and ppSS-derived peptides are expressed in the pathway from the NTSc to the NAcf, a pathway thought to play a role in the reflex control of esophageal peristalsis.

Localization of cardiac parasympathetic preganglionic neurons in the medulla oblongata of pigeon, Columba livia: a study using fragment C of tetanus toxin

The binding fragment of tetanus toxin, fragment C, was injected into several different regions of the pigeon heart. Retrogradely and/or transneuronally labeled cardiomotor parasympathetic preganglionic neurons were found in two separate nuclei within the medulla oblongata. The majority of fragment C-immunolabeled cells was confined to the caudal division of the nucleus ambiguus. This nuclear region is likely to be homologous to the ventrolateral nucleus of the external formation of the nucleus ambiguus in mammals. A smaller fraction (10-30%) of fragment C-positive cardiomotor preganglionic neurons were localized within a restricted portion of the ventrolateral subnucleus of the dorsal motor nucleus of the vagus nerve. This dual cardiac representation in an avian is very similar to the organization established in several mammalian species, and suggests that the brainstem organisation of cardiac parasympathetic efferents is evolutionarily stable across avians and mammals.

Representation of the cecum in the lateral dorsal motor nucleus of the vagus nerve and commissural subnucleus of the nucleus tractus solitarii in rat

Motor fibers of the accessory celiac and celiac vagal branches are derived from the lateral columns of the dorsal motor nucleus of the vagus nerve. These branches also contain sensory fibers that terminate within the nucleus of the tractus solitarii. This study traces the innervation of the intestines by using the tracer cholera toxin-horseradish peroxidase. In 53 rats, the tracer was injected into either the stomach, duodenum, jejunum, terminal ileum, cecum, or ascending colon. With all cecal injections, prominent retrograde labeling of cell bodies occurred bilaterally in the lateral columns of the dorsal motor nucleus of the vagus nerve above, at, and below the level of the area postrema. Dendrites of laterally positioned neurons projected medially and rostrocaudally within the dorsal motor nucleus of the vagus nerve and dorsomedially into both the medial subnucleus and parts of the commissural subnucleus of the nucleus of the tractus solitarii. Sensory terminal labeling occurred in the dorsolateral commissural subnucleus at the level of the rostral area postrema and the medial commissural subnucleus caudal to the area postrema. Additionally, there was sensory terminal labeling within a small confined area of the dorsomedial zone of the nucleus of the tractus solitarii immediately adjacent to the fourth ventricle at a level just anterior to the area postrema. Stomach injections labeled motoneurons of the medial column of the entire rostrocaudal extent of the dorsal motor nucleus of the vagus nerve and a sensory terminal field primarily in the subnucleus gelatinosus, with less intense labeling extending caudally into the medial and ventral commissural subnuclei. Dendrites of gastric motoneurons project rostrocaudally and mediolaterally within the dorsal motor nucleus of the vagus nerve and dorsolaterally within the nucleus of the tractus solitarii. They are most pronounced at the level of the rostral area postrema where many dendrites course dorsolaterally terminating primarily within the subnucleus gelatinosus. Injections of the duodenum labeled a small number of the cells within the medial aspects of the dorsal motor nucleus of the vagus nerve. Jejunal, ileal, and ascending colon injections labeled cells sparsely within the lateral aspects of the dorsal motor nucleus of the vagus nerve bilaterally. No afferent terminal labeling was evident after injection of these areas of the bowel.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent innervation of the gallbladder in the cat, studied by the horseradish peroxidase method

Following injection of horseradish peroxidase (HRP) into the wall of the gallbladder of cats, HRP-positive cells were found bilaterally in dorsal root ganglia T2-L3 (T2-L2, and T3-L2/L3 also observed in a few cats) and nodose ganglia. In about 33% of animals labelled cells were also distributed in cervical dorsal root ganglia C5-C7. Labelled cells were more frequently localized on the right side than the left. There was no apparent change in numbers of labelled cells in the nodose ganglion (NG) on either side following greater and lesser splanchnicotomy or section of the right phrenic nerve or removal of the celiac ganglion. After severing both the greater and lesser splanchnic nerves unilaterally, numbers of labelled afferent cells from the gallbladder in dorsal root ganglia (DRGs) significantly decreased on the ipsilateral side but there was no change in the pattern of distribution contralaterally. After section of the right phrenic nerve, labelled cells were not found in ipsilateral cervical ganglia. That some afferent fibers from the gallbladder travel via the phrenic nerves, particularly on the right side, may be a supplementary mechanism in the generation of referred pain in gallbladder disease. The splanchnic nerves are the main, but not the only pathway for afferent fibers from the gallbladder.

The target specificity of the extrinsic innervation of the rat small intestine

The target specificity of the extrinsic innervation of the rat small intestine was examined by simultaneously injecting the proximal and distal small intestine with either wheat germ agglutinin-horseradish peroxidase (HRP) or fast blue. The number of single- and double-labeled cells in the nodose, dorsal root and coeliac-superior mesenteric ganglia and the dorsal motor nucleus of the vagus were counted and expressed as percentages of total labeled cells. Cells containing both HRP and Fast blue projected to both regions of the intestine. We found that the nodose and mesenteric ganglia contained significantly fewer double-labeled neurons (approximately 3 and 9% respectively) than the dorsal motor nucleus (19%) or dorsal root ganglion (20%). Presumably, a large number of double-labeled afferent or efferent neurons would limit the ability of a given component of the extrinsic innervation to control the activity of restricted regions of the small intestine (but might be important in overall regulation of intestinal function). In a separate series of experiments we examined the topography of neurons in the dorsal motor nucleus of the vagus labeled with HRP injection into either the proximal or distal small intestine. Both of these injections labeled neurons in the entire rostro-caudal extent of the nucleus, though approximately 75% of the cells were located between 720 microns caudal and 720 microns rostral to the obex. Cells in the rostral regions were found primarily in the lateral pole of the nucleus, whereas caudal regions contained labeled cells in both the medial and lateral poles.

Neonatal infraorbital nerve transection in the rat: comparison of effects on substance P immunoreactive primary afferents and those recognized by the lectin Bandierea simplicifolia-I

Retrograde tracing, immunocytochemical, and histochemical methods were used to determine the manner in which different classes of trigeminal (V) ganglion cells respond to transection of their axons during infancy. Retrograde tracing with true blue (TB), histochemistry using the plant lectin Bandieraea simplicifolia-I (BS-I), and immunocytochemistry using an antiserum directed against substance P (SP) were carried out in the V ganglion and V brainstem complex of normal adult rats. In the adult V ganglion, 11.9 +/- 1.9% of the cells that sent axons into the infraorbital nerve (ION) contained SP-like immunoreactivity (SPLI) and 26.9 +/- 3.6% bound the lectin BS-I. Only 2.7 +/- 1.6% of ION cells were labelled by both the SP antiserum and BS-I. Transection of the ION on the day of birth had very different effects upon primary afferent neurons containing SPLI and those labelled by BS-I. We have previously shown that such lesions result in a significant expansion of the portion of SpC innervated by primary afferents containing SPLI and we have also provided data consistent with the proposal that ganglion cells recognized by an antiserum directed against SP are more likely than other primary afferent neurons to survive neonatal axotomy. In the present study, combination of retrograde tracing with TB and lectin binding histochemistry showed that cells recognized by BS-I were selectively lost after neonatal ION transection. Only 14.2 +/- 4.4% of the ION ganglion cells that projected into this nerve at the time of the lesion and that survived neonatal axotomy were BS-I positive when the animals reached adulthood. Neonatal ION transection also resulted in a permanent reduction in the density of BS-I binding in SpC. Bandieraea simplicifolia-I binding in the brainstem ipsilateral to the damaged nerve was almost completely gone within 1 day of the nerve transection and recovered only partially by the time the rats were 2 months of age. In alternate sections tested with the SP antiserum, there was a slight reduction in the density of SPLI in the deafferented SpC on postnatal days 4 and 5, but this change never approached that observed for BS-I binding.

The role of the gastric and hepatic vagus in voluntary alcohol intake

The present study investigated a possible role for neural signals sent from the liver and stomach to the brain in the regulation of alcohol intake. Experiment 1 showed that gastric vagotomy (GVX) reduced the intake of 3% alcohol and 6% alcohol, while water intake was increased. This effect was not due to an alteration in pharmacokinetics, although an alteration in taste function could not be ruled out. Angiotensin II reduced the intake of 6% alcohol and stimulated the intake of water similarly in both GVX and sham groups. In Experiment 2 rats were subjected to hepatic vagotomy or sham laparotomy and then offered a choice between an alcohol solution and tap water for 40 min each day. Although hepatic vagotomy (HVX) did not alter the intake of 3% alcohol or water, 6% alcohol intake was significantly reduced. Angiotensin II decreased 6% alcohol intake and increased water intake similarly in both groups. These experiments indicated that interrupting information from the liver and stomach to the brain by selective gastric and hepatic vagotomy can decrease voluntary alcohol intake. Since vagal afferent nerves are thought to participate in the control of food intake, the present findings support the hypothesis that the "food-like" qualities of alcohol, i.e., calories and taste, can contribute to the regulation of alcohol intake.

Thyrotropin-releasing hormone-immunoreactive nerve terminals synapse on the dendrites of gastric vagal motoneurons in the rat

Thyrotropin-releasing hormone stimulates vagally mediated gastric acid secretion and motility by an undefined central mechanism in the rat. The present study sought to determine the anatomical basis for this stimulatory effect by examining the ultrastructural relationship of nerve terminals immunoreactive for thyrotropin-releasing hormone with the dendrites of gastric vagal motoneurons. A light and electron microscopic double immunostaining technique was employed using the beta subunit of unconjugated cholera toxin as a neural tracer. Cholera toxin (50 microliters, 0.25%) was injected into the ventral stomach musculature in five rats. After 72 hours' survival, animals were sacrificed by transcardiac perfusion fixation. Retrogradely transported cholera toxin was immunocytochemically localized in vagal gastric motoneurons and their dendrites in the dorsal motor nucleus of the vagus and nucleus of the solitary tract, alone or in combination with the immunocytochemical localization of thyrotropin-releasing hormone. Ultrastructural analysis of double-labeled material revealed thyrotropin-releasing hormone-immunoreactive nerve terminals making asymmetric synaptic contacts on the retrogradely labeled dendrites of vagal gastric motoneurons. Nerve terminals immunoreactive for thyrotropin-releasing hormone also made asymmetric and symmetric synaptic contacts with unlabeled dendrites of undetermined perikaryal origin. In addition, nonsynaptic varicosities immunoreactive for thyrotropin-releasing hormone were frequently observed in the vagal nuclei. The synaptic contacts between thyrotropin-releasing hormone-immunoreactive nerve terminals and vagal gastric motoneuronal dendrites provide one possible basis for the profound stimulatory effect of central thyrotropin-releasing hormone on gastric vagal motor activity.

Central neural control of esophageal motility: a review

We review recent studies on the central neural control of esophageal motility, emphasizing the anatomy and chemical coding of esophageal pathways in the spinal cord and medulla. Sympathetic innervation of the proximal esophagus is derived primarily from cervical and upper thoracic paravertebral ganglia, whereas that of the lower esophageal sphincter and proximal stomach is derived from the celiac ganglion. In addition to noradrenaline, many sympathetic fibers in the esophagus contain neuropeptide Y (NPY), and both noradrenaline and NPY appear to decrease blood flow and motility. Preganglionic neurons innervating the cervical and upper thoracic ganglia are located at lower cervical and upper thoracic spinal levels. The preganglionic innervation of the celiac ganglion arises from lower thoracic spinal levels. Both acetylcholine (ACh) and enkephalin (ENK) have been localized in sympathetic preganglionic neurons, and it has been suggested that ENK acts to pre-synaptically inhibit ganglionic transmission. Spinal afferents from the esophagus are few, but have been described in lower cervical and thoracic dorsal root ganglia. A significant percentage contain calcitonin gene-related peptide (CGRP) and substance P (SP). The central distribution of spinal afferents, as well as their subsequent processing within the spinal cord, have not been addressed. Medullary afferents arise from the nodose ganglion and terminate peripherally both in myenteric ganglia, where they have been postulated to act as tension receptors, and, to a lesser extent, in more superficial layers. Centrally, these afferents appear to end in a discrete part of the nucleus of the solitary tract (NTS) termed the central subnucleus. The transmitter specificity of the majority of these afferents remains unknown. The central subnucleus, in turn, sends a dense and topographically discrete projection to esophageal motor neurons in the rostral portion of the nucleus ambiguous (NA). Both somatostatin-(SS) and ENK-related peptides have been localized in this pathway. Finally, motor neurons from the rostral NA innervate striated portions of the esophagus. In addition to ACh, these esophageal motor neurons contain CGRP, galanin (GAL), N-acetylaspartylglutamate (NAAG), and brain natriuretic peptide (BNP). The physiological effect of these peptides on esophageal motility remains unclear. Medullary control of smooth muscle portions of the esophagus have not been thoroughly investigated.