Direct synaptic contacts on the myenteric ganglia of the rat stomach from the dorsal motor nucleus of the vagus

The myenteric ganglia regulate not only gastric motility but also secretion, because a submucous plexus is sparsely developed in the rodent stomach. We have examined whether the neurons of the dorsal motor nucleus of the vagus (DMV) have direct synaptic contacts on the myenteric ganglia and the ultrastructure of the vagal efferent terminals by using wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). The myenteric ganglia of the rat were composed of four types of neurons, i.e., small, medium-sized, large, and elongated neurons. The average numbers of axosomatic terminals per profile were 2.0 on the small neurons, 3.1 on the medium-sized neurons, 1.2 on the large neurons, and 4.2 on the elongated neuron. More than half of the axosomatic terminals contained round vesicles and formed asymmetric synaptic contacts on the small, medium-sized, and large neurons. About 80% of the axosomatic terminals on the elongated neurons contained pleomorphic vesicles and formed asymmetric synaptic contacts. When WGA-HRP was injected into the DMV, many anterogradely labeled terminals were found around the myenteric neurons. The labeled terminals were large (3.16 +/- 0.10 microm) and contacted exclusively the somata. Most of them (about 90%) contained round vesicles and formed asymmetric synaptic contacts. Serial ultrathin sections revealed that almost all neurons in a ganglion received projections from the DMV. The vagal axon terminals generally contacted the medium-sized or the elongated neurons, whereas a few labeled terminals contacted the small and the large neurons. The present results indicate that the DMV projects to all types of neurons and that their axon terminals contain mostly round synaptic vesicles and form asymmetric synaptic contacts.     

Ultrastructure of the rostral ventral respiratory group neurons in the ventrolateral medulla of the rat

The neurons in the ventrolateral medulla that project to the spinal cord are called the rostral ventral respiratory group (rVRG) because they activate spinal respiratory motor neurons. We retrogradely labeled rVRG neurons with Fluoro-Gold (FG) injections into the fourth cervical spinal cord segment to determine their distribution. The rostral half of the rVRG was located in the area ventral to the semicompact formation of the nucleus ambiguus (AmS). A cluster of the neurons moved dorsally and intermingled with the palatopharyngeal motor neurons at the caudal end of the AmS. The caudal half of the rVRG was located in the area including the loose formation of the nucleus ambiguus caudal to the AmS. We also labeled the rVRG neurons retrogradely with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) to determine their ultrastructural characteristics. The neurons of the rVRG were medium to large (38.1 x 22.1 microm), oval or ellipsoid in shape, and had a dark cytoplasm containing numerous free ribosomes, rough endoplasmic reticulum (rER), mitochondria, Golgi apparatuses, lipofuscin granules and a round nucleus with an invaginated nuclear membrane. The average number of axosomatic terminals in a profile was 33.2. The number of axosomatic terminals containing round vesicles and making asymmetric synaptic contacts (Gray's type I) was almost equal to those containing pleomorphic vesicles and making symmetric synaptic contacts (Gray's type II). The axodendritic terminals were large (1.55 microm), and about 60% of them were Gray's type I. The rVRG neurons have ultrastructural characteristics, which are different from the palatopharyngeal motor neurons or the prorpiobulbar neurons.     

Immunohistochemical characterization of cardiac vagal preganglionic neurons in the rat

Cardiac vagal preganglionic neurons (CVN) control cardiac activity by negative chronotropic, dromotropic and inotropic effects. We attempted to characterize the distribution and neuronal properties of the CVN by using double labeling with the retrograde tracer cholera toxin B subunit (CTb) and immunohistochemistry for choline acetyltransferase (ChAT), tyrosine hydroxylase (TH), calcitonin gene-related peptide (CGRP) or nitric oxide synthase (NOS). Injection of CTb into the sinoatrial ganglia resulted in many retrogradely labeled of neurons in the dorsal motor nucleus of the vagus (DMV), the compact (AmC), semicompact (AmS), loose (AmL), external (AmE) formations of the nucleus ambiguus, and the intermediate zone (IZ) between DMV and the nucleus ambiguus. Almost all CTb-labeled neurons showed ChAT immunoreactivity in the DMV, AmC, AmS, AmL and IZ, but most of the CTb-labeled neurons showed no ChAT immunoreactivity in the AmE. Most of the CTb-labeled neurons were double-labeled with CGRP immunoreactivity in the AmC, AmS and AmL, but a few double-labeled neurons were found in the DMV, IZ and AmE. A few CTb-labeled neurons were double-labeled with NOS immunoreactivity only in the DMV. No TH-immunoreactive neurons were found among the CVN. These results indicate that there are four kinds of neurons among the CVN: non-cholinergic CVN in the AmE, cholinergic and CGRP-containing CVN in the AmC, AmS and AmL, and cholinergic or cholinergic and NOS-containing CVN in the DMV.     

Projections to the alimentary canal from the dopaminergic neurons in the dorsal motor nucleus of the vagus of the rat

The motility of the alimentary canal is regulated not only by neurons that contain acetylcholine or adrenaline, but also by nonadrenergic noncholinergic neurons. There are many neurons containing dopamine in the dorsal motor nucleus of the vagus (DMV). We examined the projections of these dopaminergic neurons to the alimentary canal with double-labeling immunohistochemistry for tyrosine hydroxylase (TH) and the retrograde tracer cholera toxin subunit b following its injection into the subdiaphragmatic esophagus, the cardia, the pylorus, the duodenum, the jejunum, and the ascending colon. Almost all double-labeled neurons were found in the half of the DMV caudal to the area postrema. In the caudal half of the DMV, about 58% of the TH-immunoreactive neurons projected to the cardia, about 36% projected to the pylorus, and about 28% projected to the subdiaphragmatic esophagus. Only a few TH-immunoreactive neurons projected to the duodenum, the jejunum, or the ascending colon. As a whole, less than 10% of the neurons in the DMV that projected to the alimentary canal showed TH-like immunoreactivity. These results suggest that some of the dopaminergic neurons in the DMV might regulate the activities of the stomach and the subdiaphragmatic esophagus.     

Ultrastructural single- and double-label immunohistochemical studies of substance P-containing terminals and dopaminergic neurons in the substantia nigra in pigeons.

The vast majority of striatonigral projection neurons in pigeons contain substance P (SP), and the vast majority of SP-containing fibers terminating in the substantia nigra arise from neurons in the striatum. To help clarify the role of striatonigral projection neurons, we conducted electron microscopic single- and double-label immunohistochemical studies of SP+ terminals and/or dopaminergic neurons (labeled with either anti-dopamine, DA, or anti-tyrosine hydroxylase, TH) in pigeons to determine: (1) the synaptic organization of SP+ terminals, (2) the synaptic organization of TH+ perikarya and/or dendrites, and (3) the synaptic relationship between SP+ terminals and TH+ neurons in the substantia nigra. Tissue single-labeled for SP revealed numerous SP+ terminals contacting thin unlabeled dendrites in the substantia nigra, but few SP+ terminals were observed contacting perikarya or large-diameter dendrites. SP+ terminals contained round, densely packed, clear vesicles, and often contained one or more dense-core vesicles. Synaptic junctions between SP+ terminals and their targets were more often symmetric (86%) than asymmetric. In tissue single-labeled for DA, we observed few terminals contacting DA+ perikarya, whereas terminals contacting DA+ dendrites were more abundant. Terminals contacting DA+ structures comprised at least four different morphologically distinct types based on the morphology of the clear synaptic vesicles and the type of synaptic junction. One type of terminal contained round clear vesicles and made symmetric synapses, and thus resembled the predominant type of SP+ terminal. The second type contained round clear vesicles and made asymmetric synapses, the third type contained medium-size pleomorphic clear vesicles and made symmetric synapses, and the fourth type contained small pleomorphic clear vesicles and made symmetric synapses. The presence of contacts between SP+ terminals and dopaminergic dendrites in the substantia nigra was directly demonstrated in tissue double-labeled for SP (by the peroxidase-antiperoxidase procedure, or PAP, with diaminobenzidine) and TH (by either the silver-intensified immunogold procedure or the PAP procedure with benzidine dihydrochloride). SP+ terminals commonly contacted thin TH+ dendrites in the substantia nigra, but few SP+ terminals contacted large-diameter TH+ dendrites or perikarya. Synapses between SP+ terminals and TH+ neurons were always symmetric. TH+ dendrites also were contacted by terminals not labeled for SP, which were more abundant than were SP+ terminals. Non-TH+ neurons were also contacted by both SP+ terminals and non-SP+ terminals.(ABSTRACT TRUNCATED AT 400 WORDS)     

A light and electron microscopic study of the dorsal motor nucleus of the vagus nerve in the cat

The morphology of the dorsal motor nucleus of the vagus nerve (DMV) in the cat was studied with the aid of light and electron microscopy. In frozen sections stained by the Kluver-Barrera method or stained to show retrograde labeling in the DMV following injections of horseradish peroxidase (HRP) in the cervical vagus nerve and the stomach wall a range of sizes of DMV neurons was observed but it was not possible to distinguish separate types. In contrast, two distinct types of neurons, one medium-sized and the other small, were identified with the light microscope in Golgi-Cox and 1-μm Epon sections and with the electron microscope in ultrathin sections. The medium-sized neurons had a range of sizes but generally measured 18 × 25 μm and possessed three to four proximal dendrites which branched two or three times. Spines were observed occasionally on the soma and on dendrites. These neurons contained a well-developed cytoplasm and a noninvaginated round to oval nucleus. The small neurons generally measured 9 × 14 μm and were round or slightly elongated in shape. Their dendritic processes were fewer and thinner than those of the medium-sized neurons and extended for shorter lengths. Their soma contained scanty cytoplasm and an invaginated nucleus. The medium-sized neurons outnumbered the small neurons by more than three to one but both neuronal types were distributed evenly throughout the nucleus. The medium-sized neurons seemed to correspond in size to the parasympathetic efferent neurons of the viscera as indicated by the HRP studies. Axosomatic synapses on both types of neurons and axodendritic synapses were observed in the DMV. Terminals containing mainly small clear round vesicles and making asymmetrical contact with the postsynaptic membrane were involved in the majority of synapses on both the soma and dendrites. Terminals containing predominantly pleomorphic vesicles and making symmetrical contact with the postsynaptic membrane were also common, comprising up to one-third of all synapses observed. Serial sections revealed that most synaptic terminals contained varying numbers of large (75–110 nm) dense-cored vesicles. Smaller dense-cored vesicles (45–55 nm) were sometimes observed, often close to the area of synaptic contact. Terminals 1–2 μm in diameter which contacted dendrites 1–3 μm in diameter formed the most common synaptic combination throughout the rostral to caudal extent of the DMV. No distinct regional differences were observed with respect to distribution of synaptic types.     

Localization of the neurons active during paradoxical (REM) sleep and projecting to the locus coeruleus noradrenergic neurons in the rat

Locus coeruleus (LC) noradrenergic neurons are active during wakefulness, slow their discharge rate during slow wave sleep, and stop firing during paradoxical sleep (PS). A large body of data indicates that their inactivation during PS is due to a tonic GABAergic inhibition. To localize the neurons responsible for such inhibition, we first examined the distribution of retrogradely and Fos double-immunostained neurons following cholera toxin b subunit (CTb) injection in the LC of control rats, rats selectively deprived of PS for 3 days, and rats allowed to recover for 3 hours from such deprivation. We found a significant number of CTb/Fos double-labeled cells only in the recovery group. The largest number of CTb/Fos double-labeled cells was found in the dorsal paragigantocellular reticular nucleus (DPGi). It indeed contained 19% of the CTb/Fos double-labeled neurons, whereas the ventrolateral periaqueductal gray (vlPAG) contained 18.3% of these neurons, the lateral paragigantocellular reticular nucleus (LPGi) 15%, the lateral hypothalamic area 9%, the lateral PAG 6.7%, and the rostral PAG 6%. In addition, CTb/Fos double-labeled cells constituted 43% of all the singly CTb-labeled cells counted in the DPGi compared with 29% for the LPGi, 18% for the rostral PAG, and 10% or less for the other structures. Although all these populations of CTb/Fos double-labeled neurons could be GABAergic and tonically inhibit LC neurons during PS, our results indicate that neurons from the DPGi constitute the best candidate for this role.     

Synaptic interaction of vagal afferents and catecholaminergic neurons in the rat nucleus tractus solitarius

Combined radioautography and immunocytochemistry were used to define the ultrastructure and synaptic relations between vagal sensory afferents and catecholaminergic (CA) neurons of the A2 group located within the nucleus tractus solitarius (NTS) of rat brain. The vagal afferents were radioautographically labeled by tritiated amino acids anterogradely transported from the nodose ganglion. Immunocytochemical labeling for tyrosine hydroxylase (TH) served for the identification of catecholaminergic neurons. The radiographically labeled axons seen by light microscopy were widely distributed throughout the more caudal NTS. The reduced silver grains were more densely distributed within the NTS located homolateral to the injected nodose ganglion. The radioautographically labeled processes were localized in regions containing catecholaminergic neurons as indicated by immunoreactivity for TH. Electron microscopic analysis of the medial NTS at the level of the obex demonstrated that the reduced silver grains were localized within axon terminals. The radioautographically labeled terminals were 2-3 microns in diameter, contained numerous small, clear and a few large, dense vesicles, and formed predominately axodendritic synapses. Many of the recipient dendrites contained immunoreactivity for TH. In rare instances, vagal afferents formed synaptic appositions with both TH-labeled and unlabeled axon terminals and neuronal soma. This study provides the first ultrastructural evidence that the catecholaminergic neurons within the NTS receive direct synapses from sensory neurons in the nodose ganglion.     

Ultrastructural examination of enkephalin and substance P input to cholinergic neurons within the rat neostriatum.

Enkephalin and substance P-containing inputs to cholinergic perikarya were examined in the rat neostriatum using an ultrastructural immunocytochemical double-labeling protocol. Sections of rat neostriatum were double-labeled for either choline acetyltransferase (ChAT) and substance P or ChAT and enkephalin using silver intensified colloidal gold and peroxidase as labels. Regions containing both ChAT-positive neurons and peroxidase reaction product were identified in the light microscope prior to sectioning for electron microscopy. Substance P-containing terminals which contained round synaptic vesicles and made symmetrical synaptic contacts were commonly observed in the neostriatum. Substance P synapses onto ChAT-positive perikarya and dendrites were frequently observed: up to 5 synaptic contacts were observed onto a ChAT-positive dendrite. Enkephalin labeling was also seen in a population of axon terminals containing round synaptic vesicles and exhibiting symmetrical synaptic specializations. In contrast to substance P-containing terminals, relatively few synaptic contacts were observed onto ChAT-positive labeled perikarya and dendrites although enkephalin-labeled terminals were seen in frequent contact with perikarya and dendrites of unlabeled spiny neurons. Since enkephalin and substance P are contained within different populations of striatal spiny neurons, the results of the present study suggest that these two types of neurons differ in their intrinsic striatal connections.     

Synaptic remodeling in the nucleus ambiguus following vagal-hypoglossal nerve anastomosis in the cat

We reported recently the occurrence of a massive and selective elimination of synaptic boutons on motoneurons in the dorsal motor nucleus of the vagus (DMV) in the cat following vagal-hypoglossal nerve anastomosis (VHA) [J. Comp. Neurol. 458 (2003) 195]. This study was aimed to explore the synaptic reorganization in the other major nucleus associated with the vagus, namely, the nucleus ambiguus (NA) following the same treatment. In view of the tremendous difference in function, the NA and DMV are considered to be two ideal nuclei for explanatory studies seeking to elucidate how VHA could induce different plasticity of brainstem neurons influenced by the newly reestablished neural pathway. The present results showed that the vagal efferent neurons in the NA had responded to VHA in a different manner compared with those in the DMV. Firstly, the numbers of axon terminals containing round (R), round with dense-cored (R+D), pleomorphic (P) or flattened (F) synaptic vesicles contacting the NA motoneurons were markedly increased at 500-day postoperation, the longest reinnervation interval. The percent increases in the synapse frequency for R, R+D, P and F boutons were 8.6%, 274.4%, 238.3% and 400.0%, respectively. Secondly, the formation of astroglial ensheathment around the motoneurons in the DMV following VHA was not evident in the NA. Another striking difference was the extensive dendritic sprouting of the NA neurons as opposed to the dendritic retraction of the DMV neurons as shown by a significant increase in distal dendrites of NA motoneurons. The different modes of neural remodeling between NA and DMV may be attributed to the unique nature of the two nuclei to structures they normally supply and their different compatibility with the newly innervated target, viz. tongue skeletal musculature.     

Synaptic microcircuitry of tyrosine hydroxylase-containing neurons and terminals in the striatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated monkeys

A population of tyrosine hydroxylase (TH)-containing neurons that is up-regulated after lesion of the nigrostriatal dopaminergic pathway has been described in the primate striatum. The goal of this study was to examine the morphology, synaptology, and chemical phenotype of these neurons and TH-immunoreactive (-ir) terminals in the striatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated rhesus monkeys. TH-ir perikarya were small (10-12 microm), displayed nuclear invaginations, and received very few synaptic inputs. On the other hand, TH-containing dendrites were typically large in diameter (>1.0 microm) and received scarce synaptic innervation from putative excitatory and inhibitory terminals forming asymmetric and symmetric synapses, respectively. More than 70% of TH-positive intrastriatal cell bodies were found in the caudate nucleus and the precommissural putamen, considered as the associative functional territories of the primate striatum. Under 10% of these cells displayed calretinin immunoreactivity. TH-ir terminals rarely formed clear synaptic contacts, except for a few that established asymmetric axodendritic synapses. Almost two-thirds of TH-containing boutons displayed gamma-aminobutyric acid (GABA) immunoreactivity in the striatum of parkinsonian monkeys, whereas under 5% did so in the normal striatum. These findings provide strong support for the existence of a population of putative catecholaminergic interneurons in the associative territory of the striatum in parkinsonian monkeys. Their sparse synaptic innervation raises interesting issues regarding synaptic and nonsynaptic mechanisms involved in the regulation and integration of these neurons in the striatal microcircuitry. Finally, the coexpression of GABA in TH-positive terminals in the striatum of dopamine-depleted monkeys suggests dramatic neurochemical changes in the catecholaminergic modulation of striatal activity in Parkinson's disease.     

Origin of noradrenergic afferents to the shell subregion of the nucleus accumbens: anterograde and retrograde tract-tracing studies in the rat

The nucleus accumbens (NAcc) can be subdivided into `core' and `shell' based on anatomical connections and histochemical markers. Previous studies have demonstrated dopamine-β-hydroxylase immunoreactive (DBH-ir) fibers in the NAcc shell, but the source of these noradrenergic (NE) afferents has not been determined. Therefore, we have investigated in detail the anatomy of NE afferents to this subregion. Dual immunohistochemistry for DBH and substance P demonstrated numerous DBH-ir fibers in the caudal NAcc shell. Neurons projecting to the NAcc were identified with Fluoro-Gold (FG) or cholera toxin B (CTb) retrograde tracing and tyrosine hydroxylase (TH) immunohistochemistry. Single- and double-labeled neurons were observed in the A2 and A1 NE cell groups following FG injections into the caudal NAcc shell. Numerous FG and CTb single-labeled neurons were found in the rostral locus coeruleus (LC), subcoeruleus and pericoerulear dendritic region, with an occasional double-labeled neuron in the LC. Few labeled neurons were seen in the brainstem after FG injections into the NAcc core, consistent with the lack of DBH-ir in this subterritory. To confirm these results, injections of Phaseolus vulgaris leucoagglutinin or biotinylated dextran amine were made into the LC or nucleus tractus solitarius (NTS). Virtually no labeled fibers were observed in the NAcc following injections into central LC. However, fibers were observed in the NAcc shell after injections in the NTS. These results indicate that the primary source(s) of NE afferents to the NAcc shell is the A2 region of the NTS, with lesser contributions from A1 and LC.     

Organization of central adrenergic pathways: I. Relationships of ventrolateral medullary projections to the hypothalamus and spinal cord

We studied the organization of projections from the C1 adrenergic and A1 noradrenergic cell groups in the ventrolateral medulla (VLM) to the hypothalamus and the spinal cord by using a combination of retrograde transport of fluorescent tracers and immunocytochemistry. Three issues were addressed. Neurons in the VLM that stain immunohistochemically for phenylethanolamine N-methyltransferase (PNMT) have been assumed to be adrenergic. However, the presence of PNMT-immunoreactive neurons in the hypothalamus that do not stain for tyrosine hydroxylase (TH) prompted us to re-evaluate the VLM by an elution-restaining immunohistochemical procedure. We confirmed that nearly all of the rostral medullary PNMT-immunoreactive neurons also stained for TH. By contrast, in the caudal medulla, very few TH-positive neurons stained for PNMT. Neurons of the C1 group in the rostral VLM project both to the thoracic spinal cord and to the hypothalamus. To determine whether individual C1 neurons send collaterals to the hypothalamus and spinal cord, we injected different-colored fluorescent dyes (diamidino yellow or fast blue) into the thoracic spinal gray matter and either the median preoptic (MnPO) or paraventricular (PVH) nuclei of the hypothalamus. Very few double-labeled neurons were found in the VLM, indicating that hypothalamic and spinal cord projections arise from almost completely independent populations of cells. Approximately half of the neurons projecting to the spinal cord from rostral VLM were not immunoreactive for TH or PNMT, indicating that a substantial part of this projection is noncatecholaminergic. The MnPO and the PVH both receive extensive catecholaminergic inputs from the VLM. We also used fluorescent retrograde tracers to determine whether individual VLM neurons send collaterals to both hypothalamic sites. Approximately 20% of neurons projecting to the MnPO in the rostral two thirds of the VLM also sent collaterials to the PVH, nearly all of these neurons being TH-positive. The collateralization of the VLM catecholaminergic projection to the hypothalamus may provide an anatomical substrate for integration of fore-brain participation in cardiovascular regulation. In contrast, the adrenergic projection from the VLM to the intermediolateral column of the spinal cord arises from a separate population of neurons.     

The development of the Purkinje cell in the cerebellar cortex of the opossum

Premotor neurons sending their axons to the trigeminal motor nucleus were observed in the cat by light and electron microscopy after labeling the neurons retrogradely or anterogradely with horseradish peroxidase (HRP). After HRP injection into the trigeminal motor nucleus, retrogradely labeled neurons were seen most frequently in the parvocellular reticular formation bilaterally. Many labeled neurons were also seen contralaterally in the intermediate zone at the rostralmost levels of the cervical cord and its rostral extension into the caudalmost levels of the medulla oblongata. Additionally, some neurons were labeled ipsilaterally in the mesencephalic tri-geminal nucleus, contralaterally in the main sensory trigeminal nucleus and the trigeminal motor nucleus, and bilaterally in the oral and interpolar sub-nuclei of the spinal trigeminal nucleus. Only a few labeled neurons were seen in the confines of the gigantocellular reticular formation. All labeled neurons were small or of medium size; no large neurons were labeled. After HRP injection into the regions around the trigeminal motor nucleus or the parvocellular reticular formation, axodendritic terminals containing HRP granules were found contralaterally within the trigeminal motor nucleus. Some of these labeled terminals were filled with round synap-tic vesicles and others contained pleomorphic synaptic vesicles. The varied morphology of labeled axon terminals was considered to reflect the functional heterogeneity of the premotor neurons for the trigeminal motor nucleus.     

Distribution and synaptic relations of NOS neurons in the dorsal raphe nucleus: A comparison to 5-HT neurons

Anti-nitric oxide synthase antibody was used to study the distribution, cytowchhecture, and synaptic relations of nitric oxide synthase-like immunoreactive neurons in the whole rostral-caudel length of the dorsal raphe nucleus of the rat and compared them with serotonergic neurons. Results showed that the distribution of the nitric oxide synthase in the dorsal raphe nucleus was similar to that of the serotonergic neurons at the rostral part of the dorsal raphe nucleus, including the mediodorsal and the medioventral cell groups, and changed at the middle and caudal parts of the dorsal raphe nucleus. The cytoarchitecture of the nitric oxide synthase-like immunoreactive neurons in the medioventrai cell group of the dorsal raphe nucleus was similar to that of the serotonergic neurons. Similar to the serotonergic neurons there, nitric oxide synthase-like immunoroactive neurons also received synapses from axon terminals that contained round, or flattened vesicles, or both kinds. Different to the serotonergic neurons, the few nitric oxide synthase-like immunoroactive axon terminals that were in this area formed synapses.     

Nucleus of the solitary tract in the C57BL/6J mouse: Subnuclear parcellation,chorda tympani nerve projections,and brainstem connections

The nucleus of the solitary tract (NST) processes gustatory and related somatosensory information rostrally and general viscerosensory information caudally. To compare its connections with those of other rodents, this study in the C57BL/6J mouse provides a subnuclear cytoarchitectonic parcellation (Nissl stain) of the NST into rostral, intermediate, and caudal divisions. Subnuclei are further characterized by NADPH staining and P2X₂ immunoreactivity (IR). Cholera toxin subunit B (CTb) labeling revealed those NST subnuclei receiving chorda tympani nerve (CT) afferents, those connecting with the parabrachial nucleus (PBN) and reticular formation (RF), and those interconnecting NST subnuclei. CT terminals are densest in the rostral central (RC) and medial (M) subnuclei; less dense in the rostral lateral (RL) subnucleus; and sparse in the ventral (V), ventral lateral (VL), and central lateral (CL) subnuclei. CTb injection into the PBN retrogradely labels cells in the aforementioned subnuclei; RC and M providing the largest source of PBN projection neurons. Pontine efferent axons terminate mainly in V and rostral medial (RM) subnuclei. CTb injection into the medullary RF labels cells and axonal endings predominantly in V at rostral and intermediate NST levels. Small CTb injections within the NST label extensive projections from the rostral division to caudal subnuclei. Projections from the caudal division primarily interconnect subnuclei confined to the caudal division of the NST; they also connect with the area postrema. P2X₂‐IR identifies probable vagal nerve terminals in the central (Ce) subnucleus in the intermediate/caudal NST. Ce also shows intense NADPH staining and does not project to the PBN. J. Comp. Neurol. 522:1565–1596, 2014. © 2013 Wiley Periodicals, Inc.     

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.     

Development of catecholaminergic systems in the spinal cord of the dogfish Scyliorhinus canicula (Elasmobranchs)

The development of catecholamine-synthesizing cells and fibers in the spinal cord of dogfish (Scyliorhinus canicula L.) was studied by means of immunohistochemistry using antibodies against tyrosine hydroxylase (TH). The only TH-immunoreactive (TH-ir) cells already present in the spinal cord of stage 26 embryos were of cerebrospinal fluid-contacting (CSF-c) type. These cells were the first catecholaminergic neurons of the dogfish CNS. The number of these TH-ir cells increased very considerably in later embryos and adult dogfish. In later embryos (stage 33; prehatching), faintly TH-ir non-CSF-contacting neurons were observed in the ventral horn throughout most of the spinal cord. In adult dogfish, some non-CSF-contacting TH-ir cells were observed ventral or lateral to the central canal. In the rostral spinal cord, the catecholaminergic neurons observed in dorsal regions were continuous with caudal rhombencephalic populations. Numerous TH-ir fibers were observed in the spinal cord of later embryos and in adults, both intrinsic and descending from the brain, innervating many regions of the cord including the dorsal and ventral horns. In addition, some TH-ir fibers innervated the marginal nucleus of the spinal cord. The early appearance of catecholaminergic cells and fibers in the embryonic spinal cord of the dogfish, and the large number of these elements observed in adults, suggests an important role for catecholamines through development and adulthood in sensory and motor functions.     

A1 catecholamine cell group: Fine structure and synaptic input from the nucleus of the solitary tract

Preembedding immunoperoxidase staining methods were used to characterize tyrosine hydroxylase-immunoreactive (TH-ir) elements in the caudal ventrolateral medulla, and to determine the extent to which neurons of the A1 cell group are directly innervated by projections of the nucleus of the solitary tract (NTS). TH-ir neurons in the A1 region were medium-sized and multipolar. They possessed rounded nuclei with infrequent invaginations, well-developed Golgi apparati, high cytoplasmic densities of mitochondria, and a low to moderate tendency for rough endoplasmic reticulum (RER) to align in parallel stacks. A1 cell bodies were commonly juxtaposed to TH-positive and TH-negative neurons, myelinated profiles, glia and /or vascular elements, but close membrane appositons were only seen with glial elements. Synaptic input to A1 neurons was predominantly asymmetric, provided virtually exclusively by non-TH-ir terminals, and directed principally to dendritic shafts; A1 somata are relatively sparsely innervated. In a second experiment, silver-intensified immunogold localization of TH-ir was combined with immunoperoxidase labeling for anterogradely transported Phaseolus vulgaris-leucoagglutinin (PHA-L), following tracer injections in the caudal aspect of the medial division of the NTS. These experiments revealed a small proportion of PHA-L-labeled axon terminals that made asymmetric contacts with dendritic shafts of TH-ir neurons. These results suggest that the fine structure and synaptic input of A1 neurons are somewhat distinct from that of rostrally situated C1 catecholamine cells. In addition, while they document a direct NTS-A1 projection that may participate in the interoceptive control of vasopressin secretion, the bulk of ventrolaterally directed projections from the caudomedial NTS contact noncatecholaminergic elements in the A1 region, some of which may correspond to so-called depressor neurons implicated in the baroreflex control of sympathetic outflow and vasopressin secretion. © 1995 Willy-Liss, Inc.