Brainstem origins and projections of the cervical and abdominal vagus in the golden hamster: a horseradish peroxidase study

Effect of estrogen on vagal afferent projections to the brainstem in the female

The effects of 17β-estradiol (E) on the distribution and density of brainstem projections of small or large diameter primary vagal afferents were investigated in Wistar rats using transganglionic transport of wheat germ agglutinin- (WGA; preferentially transported by non-myelinated afferent C-fibers; 2%), or cholera toxin B-subunit- (CTB, 5%; preferentially transported by large myelinated afferent A-fibers) conjugated horseradish peroxidase (HRP) in combination with the tetramethylbenzidine method in age matched ovariectomized (OVX) only or OVX and treated with E (OVX+E; 30 pg/ml plasma) females for 12 weeks. Additionally, these projections were compared to aged matched males. Unilateral microinjection of WGA-HRP into the nodose ganglion resulted in dense anterograde labeling bilaterally, with an ipsilateral predominance in several subnuclei of the nucleus of the solitary tract (NTS) and in area postrema that was greatest in OVX+E animals compared to OVX only and males. Moderately dense anterograde labeling was also observed in paratrigeminal nucleus (PAT) of the OVX+E animals. CTB-HRP produced less dense anterograde labeling in the NTS complex, but had a wider distribution within the brainstem including the area postrema, dorsal motor nucleus of the vagus, PAT, the nucleus ambiguus complex and ventrolateral medulla in all groups. The distribution of CTB-HRP anterograde labeling was densest in OVX+E, less dense in OVX only females and least dense in male rats. Little, if any, labeling was found within PAT in males using either WGA-or CTB-HRP. Taken together, these data suggest that small, non-myelinated (WGA-labeled) and large myelinated (CTB-labeled) diameter vagal afferents projecting to brainstem autonomic areas are differentially affected by circulating levels of estrogen. These effects of estrogen on connectivity may contribute to the sex differences observed in central autonomic mechanisms between gender, and in females with and without estrogen.

Suppression of noise-induced hyperactivity in the dorsal cochlear nucleus following application of the cholinergic agonist, carbachol

Increased spontaneous firing (hyperactivity) is induced in fusiform cells of the dorsal cochlear nucleus (DCN) following intense sound exposure and is implicated as a possible neural correlate of noise-induced tinnitus. Previous studies have shown that in normal hearing animals, fusiform cell activity can be modulated by activation of parallel fibers, which represent the axons of granule cells. The modulation consists of a transient excitation followed by a more prolonged period of inhibition, presumably reflecting direct excitatory inputs to fusiform cells and an indirect inhibitory input to fusiform cells from the granule cell-cartwheel cell system. We hypothesized that since granule cells can be activated by cholinergic inputs, it might be possible to suppress tinnitus-related hyperactivity of fusiform cells using the cholinergic agonist, carbachol. To test this hypothesis, we recorded multiunit spontaneous activity in the fusiform soma layer (FSL) of the DCN in control and tone-exposed hamsters (10 kHz, 115 dB SPL, 4h) before and after application of carbachol to the DCN surface. In both exposed and control animals, 100 μM carbachol had a transient excitatory effect on spontaneous activity followed by a rapid weakening of activity to near or below normal levels. In exposed animals, the weakening of activity was powerful enough to completely abolish the hyperactivity induced by intense sound exposure. This suppressive effect was partially reversed by application of atropine and was usually not associated with significant changes in neural best frequencies (BF) or BF thresholds. These findings demonstrate that noise-induced hyperactivity can be pharmacologically controlled and raise the possibility that attenuation of tinnitus may be achievable by using an agonist of the cholinergic system.

Thematic review series: adipocyte biology. Sympathetic and sensory innervation of white adipose tissue

During our study of the reversal of seasonal obesity in Siberian hamsters, we found an interaction between receptors for the pineal hormone melatonin and the sympathetic nervous system (SNS) outflow from brain to white adipose tissue (WAT). This ultimately led us and others to conclude that the SNS innervation of WAT is the primary initiator of lipid mobilization in these as well as other animals, including humans. There is strong neurochemical (norepinephrine turnover), neuroanatomical (viral tract tracing), and functional (sympathetic denervation-induced blockade of lipolysis) evidence for the role of the SNS in lipid mobilization. Recent findings suggest the presence of WAT sensory innervation based on strong neuroanatomical (viral tract tracing, immunohistochemical markers of sensory nerves) and suggestive functional (capsaicin sensory denervation-induced WAT growth) evidence, the latter implying a role in conveying adiposity information to the brain. By contrast, parasympathetic nervous system innervation of WAT is characterized by largely negative neuroanatomical evidence (viral tract tracing, immunohistochemical and biochemical markers of parasympathetic nerves). Functional evidence (intraneural stimulation and in situ microdialysis) for the role of the SNS innervation in lipid mobilization in human WAT is convincing, with some controversy regarding the level of sympathetic nerve activity in human obesity.

White adipose tissue lacks significant vagal innervation and immunohistochemical evidence of parasympathetic innervation

Converging evidence indicates that white adipose tissue (WAT) is innervated by the sympathetic nervous system (SNS) based on immunohistochemical labeling of a SNS marker (tyrosine hydroxylase [TH]), tract tracing of WAT sympathetic postganglionic innervation, pseudorabies virus (PRV) transneuronal labeling of WAT SNS outflow neurons, and functional evidence from denervation studies. Recently, WAT para-SNS (PSNS) innervation was suggested because local surgical WAT sympathectomy (sparing hypothesized parasympathetic innervation) followed by PRV injection yielded infected cells in the vagal dorsomotor nucleus (DMV), a traditionally-recognized PSNS brain stem site. In addition, local surgical PSNS WAT denervation triggered WAT catabolic responses. We tested histologically whether WAT was parasympathetically innervated by searching for PSNS markers in rat, and normal (C57BL) and obese (ob/ob) mouse WAT. Vesicular acetylcholine transporter, vasoactive intestinal peptide and neuronal nitric oxide synthase immunoreactivities were absent in WAT pads (retroperitoneal, epididymal, inguinal subcutaneous) from all animals. Nearly all nerves innervating WAT vasculature and parenchyma that were labeled with protein gene product 9.5 (PGP9.5; pan-nerve marker) also contained TH, attesting to pervasive SNS innervation. When Siberian hamster inguinal WAT was sympathetically denervated via local injections of catecholaminergic toxin 6-hydroxydopamine (sparing putative parasympathetic nerves), subsequent PRV injection resulted in no central nervous system (CNS) or sympathetic chain infections suggesting no PSNS innervation. By contrast, vehicle-injected WAT subsequently inoculated with PRV had typical CNS/sympathetic chain viral infection patterns. Collectively, these data indicate no parasympathetic nerve markers in WAT of several species, with sparse DMV innervation and question the claim of PSNS WAT innervation as well as its functional significance.

Excitatory amino acid neurotransmission in the primary gustatory nucleus of the goldfish Carassius auratus

The vagal lobe in goldfish is a laminated structure in the midmedulla responsible for processing vagal gustatory input from the oropharynx. The anatomical arrangement of the vagal lobe is conducive to an in vitro slice preparation for investigating the physiology and pharmacology of primary gustatory fibers. Postsynaptic population responses (N2 and N3) were evoked from sensory layers of the vagal lobe following stimulation of the incoming vagal fibers. Application of 100 microM kynurenic acid, a broad spectrum glutamate receptor antagonist, abolished or significantly decreased the evoked responses. These results indicate that excitatory amino acids are the neurotransmitter at the first relay in the taste pathway in the central nervous system.

Brainstem origin of the efferent components of the cervical vagus nerve in the house musk shrew, Suncus murinus

The brainstem origin of the efferent neurons of the vagus nerve in the house musk shrew, an animal species which has been recently used in researches on emesis, was studied using the retrograde tracing method. The vagus nerve was exposed and cut at the mid-cervical level below the nodose ganglion. Horseradish peroxidase was applied to the proximal end of the cut nerve. The brainstem was sectioned and processed histochemically with the tetramethylbenzidine method. The horseradish peroxidase injection into the vagus nerve resulted in heavy retrograde labelling of neurons in the ipsilateral dorsal motor nucleus of the vagus nerve and ambigual nuclear complex. Labelled neurons in the dorsal motor nucleus of the vagus nerve, constituting approximately 80% of the total labelled neurons, formed a longitudinal column whose length varied from 3.4 to 3.8 mm. Half of labelled neurons in this nucleus were found at the level between the area postrema and 0.6 mm rostral to it. The ambigual nuclear complex was made up of two major longitudinal divisions; the dorsal division corresponded to the ambiguus nucleus and the ventral division was identified as the external formation of the ambiguus nucleus. Our results suggest that in the Suncus murinus the neuroanatomical feature of the dorsal motor nucleus of the vagus nerve is similar to those of other mammals, but ambigual nuclear complex must be somewhat different between mammals.

Brainstem topology of the vagal motoneurons projecting to the esophagus and stomach in the house musk shrew, Suncus murinus

The central origin of vagal efferents innervating the esophagus and stomach in the house musk shrew, Suncus murinus, was studied using the retrograde tracing technique. The animals were perfused with fixative 48-72 h after HRP injection and sections were processed by HRP histochemistry. HRP application into the gastroesophagus resulted in bilateral labelling of neurons in the dorsal motor nucleus of the vagus nerve (DMX) and ambiguous nucleus (AN). Labelled neurons in the DMX were observed from all regions except from the cervical esophagus, while ones in the AN were seen from the esophagus and cardia. The more labelled neurons were observed on the right DMX from subdiaphragmatic esophagus, cardia, lesser curvature and ventral corpus, while on the left DMX from the dorsal corpus labelled neurons in the longitudinal extent of the DMX were generally located at the dorsal and dorsomedial part, and those in the middle part were scattered. Labelled neurons in the AN were located restricted in the rostral part. Our results suggest that in the Suncus murinus the rostrocaudal site-specific localization within the DMX was not found, but it was prominent in the AN. In addition, while the majority of neurons which supply the esophagus and stomach were located in the DMX, only a small number was found in the AN.

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).

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.

The central localization of the vagus nerve in the ferret (Mustela putorius furo) and the mink (Mustela vison)

The location of vagal preganglionic neurones (VPN) has been determined in nine ferrets (Mustela putorius furo) and seven mink (M. vison) using neuronal tract-tracing techniques employing horseradish peroxidase (HRP) and wheat-germ agglutinin conjugated HRP (WGA-HRP) mixtures injected into the nodose ganglion of the vagus nerve. Labelled VPN were located ipsilaterally in the dorsal motor nucleus of the vagus (DmnX), nucleus ambiguus (nA), and reticular formation (rf) of the medulla oblongata. In four of the ferrets, labelled VPN were also identified in the nucleus dorsomedialis (ndm) and the nucleus of the spinal accessory nerve (nspa). In a single mink a few labelled cells were observed in the ndm but no labelled VPN were found in the nspa. Labelling of afferent components of the vagus nerve was seen in two ferrets and two mink with the best labelling obtained following an injection of an HRP/WGA-HRP mixture into the nodose ganglion. Labelled afferents were observed to cross the ipsilateral spinal trigeminal tract (SpV) before entering the tractus solitarius (TS) in regions separate from the motor axons which exit the medulla in separate fasicles. Sensory terminal fields were identified bilaterally in the nucleus of the tractus solitarius (nTS) in both species and bilaterally in the area postrema (ap) of the ferret; however, the contralateral labelling was sparse in comparison to the densely labelled ipsilateral nTS/ap. Maximal terminal labelling was seen in regions just rostral and caudal to obex in both species.

The internal organization of the human solitary nucleus

The present study examines the topography and cytoarchitecture of the solitary nucleus (Sol). Three human medulla oblongatae were serially sectioned and alternate sections were reacted for the enzyme acetylcholinesterase or stained with cresyl violet. The 10 component subnuclei of Sol were identified on the basis of their acetylcholinesterase reactivity and cytoarchitecture. These subnuclei are the paracommissural, commissural, gelatinosus, medial, ventral, ventrolateral, dorsal, dorsolateral, intermediate, and interstitial. Cytoarchitecturally, Sol is characterised by an abundance of small cells of varied morphology but also features some medium to large cells as well as pigmented neurons which are differentially distributed across the subnuclei. From spaced serial sections, the outlines of the subnuclei and the entire Sol were used to create three-dimensional computer reconstructions to display the position and extent of each component subnucleus. Our results show that the internal architecture of the human solitary nucleus is similar to that of rodents and carnivores, though there are some notable species differences.

GABA-like immunoreactivity in the gustatory zone of the nucleus of the solitary tract in the hamster: light and electron microscopic studies

The distribution of GABA-like immunoreactive (GABA-LI) somata was studied in the gustatory zone of the nucleus of the solitary tract (NST) in the hamster in order to identify putative inhibitory circuitry in gustatory processing. Immunoreactive somata were located throughout the gustatory NST, in accordance to the distribution of large and small types of neurons as determined in previous morphometric studies. Consequently, GABA-LI somata were mostly found in the dorsal two-thirds of the gustatory zone. Such somata were mostly ovoid in shape and possessed somal areas that averaged 85.5 +/- 2.8 microns 2 (12.7 x 8.4 microns). A narrow range of somal areas (50-125 microns 2) suggested a single functional group. At the electron microscopic level, 18% of the neurons encountered were immunoreactive and their nuclei always possessed deeply invaginated boundaries. This morphological feature indicated that GABA-LI neurons are smaller members of the most common class of neurons within the gustatory NST. Because GABA is often implicated as the neurotransmitter of small inhibitory local circuit neurons, these findings indicate a possible inhibitory aspect to the processing of taste information at the level of the first relay in the brainstem.

Fine distribution of substance P-like immunoreactivity in the dorsal nucleus of the vagus nerve in cats

The ultrastructure of substance P (SP)-immunoreactive elements in the cat dorsal motor nucleus of the vagus nerve was examined using pre- and post-embedding immunocytochemical procedures. Substance P-like immunoreactivity was observed in axon terminals and axon fibres which were mostly unmyelinated. Quantitative data showed that at least 16% of axon terminals contained SP. Their mean diameter was larger than that of their non-immunoreactive counterparts. Most (83%) SP-containing terminals were seen to contact dendrites but some were observed adjoining soma or entirely embedded in the cytoplasm of vagal neurons (4.5%). Only 0.5% were observed to contact soma of internuerons. A few immunoreactive axon terminals (4%) were observed in contact with non-immunoreactive axon terminals. Round agranular vesicles and numerous dense core vesicles were visible in most SP-containing axon terminals (84.6%). The immunogold procedure showed the preferential subcellular location of SP to be dense core vesicles. In 32.4% of cases, SP-containing terminals were involved in synaptic contacts that were generally of the asymmetrical Gray type 1 and mainly apposed dendrites. The theoretical total of synaptic contacts was 74.5% and this suggests the existence of weak non-synaptic SP innervation involving approximately 25% of SP-containing axon terminals. No axo-axonic synapses were observed in the dorsal vagal nucleus. These results support the hypothesis that SP found in the dorsal vagal nucleus originates partly from vagal afferents and is involved in direct modulation of visceral functions mediated by vagal preganglionic neurons.

The CNS-PNS transitional zone of the rat. Morphometric studies at cranial and spinal levels

The transitional zone is that length of rootlet containing both central and peripheral nervous tissue. The CNS-PNS interface may be defined as the basal lamina covering the intricately interwoven layer of astrocyte processes which forms the CNS surface and which is pierced by axons passing between the CNS and PNS. Study of transitional zone development defines morphologically the growth, relative movement and interaction of central and peripheral nervous tissues as they establish their mutually exclusive territories on either side of the CNS-PNS boundary, and helps to explain the wide variations in the form of the mature transitional zone. Nerve rootlets at first consist of bundles of bare axons. These become segregated by matrices of fine Schwann cell processes peripherally and of astrocyte processes centrally. The latter may prevent Schwann cell invasion of the CNS. Astrocyte processes branch profusely and come to form the principal central nervous tissue component of the transitional zone. Developmental changes in the transitional zone vary markedly between nerves, reflecting differences in its final morphology. Widespread relative movements and migration of CNS and PNS tissues take place during development, so that the central-peripheral interface changes shape and position, commonly oscillating along the proximodistal axis of the rootlet. For example, developing cervical ventral rootlets contain a transient central tissue projection, while that of lumbar ventral rootlets and to a lesser extent that of cervical dorsal rootlets alternately increase and decrease in length. In the developing cochlear nerve, a central tissue projection is present before birth, but regresses somewhat before a marked outgrowth of central nervous tissue along the nerve takes place, which reaches into the modiolus during the first week postnatum. During development, some astrocytic tissue may even break off and migrate distally into the root, giving rise to one or more glial islands within it. During the period immediately preceding birth, Schwann cells come to be present in very large numbers in that part of the rootlet immediately distal to the CNS-PNS interface, the proximal rootlet segment. Here they form prominent sleeves or clusters of closely packed cells which intertwine with and encapsulate one another on the rootlet surface. Such Schwann cell overcrowding in the proximal rootlet segment could result in part from distal overgrowth of the rapidly expanding CNS around axon bundles, which might strip the Schwann cells distally off the bundle segments so engulfed.(ABSTRACT TRUNCATED AT 400 WORDS)

Parabrachial nucleus: neuronal evoked responses to gastric vagal and greater splanchnic nerve stimulation

Unitary responses were recorded extracellularly in the parabrachial nucleus (PBN) in anesthetized cats during electrical stimulation of the 1) gastric branches of the ventral and dorsal vagal trunks which serve the proximal stomach, and 2) left greater splanchnic nerve. The gastric vagally evoked parabrachial responses consisted of phasic single and multiple spike orthodromic discharges, which were bilaterally distributed, with a mean latency of 349 ms (S.D. +/- 38.5). The parabrachial-evoked splanchnic unitary responses had a much shorter latency with a bimodal distribution (mean latencies, 53 and 128 ms, respectively). Convergence of gastric vagal input from the proximal stomach and the left greater splanchnic nerve upon single neurons in the PBN was electrophysiologically demonstrated in 132 units. Eighty-seven percent of the gastric vagally evoked parabrachial unitary responses were inhibited by simultaneous electrical stimulation of the splanchnic nerve. The condition-test paradigm was used to evaluate the time course of the splanchnic inhibition of the gastric vagally evoked parabrachial response. Reciprocal connections between neuronal populations in the nucleus tractus solitarius (NTS) which received gastric vagal input and the PBN were also identified electrophysiologically by direct microstimulation of the former structure. The density and characteristics of the gastric vagal and greater splanchnic input to the PBN suggested that this nucleus receives and processes a substantial amount of visceral afferent input. The PBN may serve as an important site for integrating visceral information governing the proximal stomach and ingestive processes.

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

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

Myelin-axon relationships established by rat vagal Schwann cells deep to the brainstem surface

The central-peripheral transitional zones of rat dorsolateral vagal rootlets are highly complex. Peripheral nervous tissue extends centrally for up to several hundred micrometers deep to the brainstem surface along these rootlets. In some instances this peripheral nervous tissue lacks continuity with the peripheral nervous system (PNS) and so forms an island within the central nervous system (CNS). In conformity with the resulting complexity of the CNS-PNS interface, segments of vagal axons lying deep to the brainstem surface are myelinated by one or more intercalated Schwann cells, contained in peripheral tissue insertions or islands, at either end of which they traverse an astroglial barrier. Intercalated Schwann cells are thus isolated from contact or contiguity with the Schwann cells of the PNS generally. They are short, having a mean internodal length of around 60% of that of the most proximal Schwann cells of the PNS proper, which lie immediately distal to the CNS-PNS interface and which are termed transitional Schwann cells. The thickness of the myelin sheaths produced by intercalated Schwann cells is intermediate between that of transitional Schwann cells and that of oligodendrocytes myelinating vagal axons of the same calibre distribution. This is not due to limited blood supply or to insufficient numbers of intercalated Schwann cells, the density of which is greater than that of transitional Schwann cells. These factors are unlikely to restrict expression of their myelinogenic potential. Nevertheless, the regression data show that the setting of the myelin-axon relationship differs significantly between the two categories of Schwann cell. Thus, the myelinogenic response of Schwann cells to stimuli emanating from the same axons may differ between levels along one and the same nerve bundle. Mean myelin periodicity was found to differ between sheaths produced by intercalated and by transitional Schwann cells.

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

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

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

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

Intermingling of central and peripheral nervous tissues in rat dorsolateral vagal rootlet transitional zones

The morphology of the CNS-PNS transitional zone of adult rat dorsolateral vagus nerve rootlets is uniquely complex. A typical rootlet contains a transitional zone over 300 microns long, consisting of a central tissue projection extending distally into each rootlet and a peripheral tissue insertion extending for a longer distance deep into the brainstem. The peripheral tissue insertion is continuous with the peripheral tissue of the free rootlet through channels traversing or running parallel to the central tissue projection. Accordingly, the vagal CNS-PNS interface is topologically much more complex than that found elsewhere. In some rootlets the peripheral tissue in the brainstem constitutes an isolated island deep within the neuraxis. In others, peripheral continuity is established only through a cross connection with the peripheral tissue insertion of a neighbouring rootlet. About one fifth of all vagal myelinated axons alternate between the CNS and PNS tissue compartments. This distinguishes the vagus from all other nerves studied to date. These axons are myelinated by Schwann cells distal to the transitional zone, by oligodendrocytes in the central tissue projection and by one or more short intercalated Schwann internodes further centrally, mostly in the peripheral tissue insertion, where their perikarya commonly form closely apposed aggregates. More than four fifths of all unmyelinated axon bundles alternate between central and peripheral tissue compartments, commonly more than once. In the peripheral tissue insertion axons are enveloped by series of non-myelinating Schwann cells. Schwann processes commonly extend for over 50 microns into the central compartment at each central-peripheral transition. Around one fifth of peripherally unmyelinated axons have an oligodendrocytic sheath in the central compartment. Of these axons possessing more than one intercalated Schwann internode, over one quarter display alternation of myelinated and unmyelinated segments in the peripheral tissue insertion. Astrocytes in the transitional zone segregate PNS tissue, a role played by sheath cells further peripherally in the vagal rootlets. Astrocytes form the surface limiting membranes of the central tissue projection and the barrier between the peripheral tissue insertion and the surrounding brainstem. The barrier consists only of an attenuated layer of processes. This is deficient in places, where oligodendrocytic myelin sheaths are directly exposed to the endoneurial space of the peripheral tissue insertion and in some instances are apposed to myelinating or non-myelinating Schwann cells. Such communication between the central and peripheral compartments is unique to the vagal transitional zone. The findings are consistent with a range of possible events during development.(ABSTRACT TRUNCATED AT 400 WORDS)

The location of extrinsic efferent and afferent nerve cell bodies of the normal canine stomach

The location of the extrinsic efferent and afferent nerve cell bodies to the mucosa, submucosa, and tunica muscularis of the cardiac, gastric, and pyloric gland regions of the ventral stomach and to the mucosa-submucosa alone of these 3 glandular gastric regions was determined using the horseradish peroxidase technique. All animals of the study demonstrated labeling bilaterally in the rostrocaudal extent of the dorsal motor nucleus of the vagus nerve (DMV) although mucosa-submucosa injections resulted in fewer labeled cells in the DMV. There was no evidence of viscerotopic organization within the DMV for the different gastric regions. However, the left nucleus generally contained a greater number of labeled cells than the right nucleus. Injection of the mucosa, submucosa, and tunica muscularis of the cardiac gland region also resulted in labeling in the nucleus ambiguus in 4 of 5 animals. The vast majority of labeled postganglionic sympathetic neurons were found in the celiacomesenteric ganglion. Labeled cells were also located variously in the stellate ganglion, middle cervical ganglion, and sympathetic trunk ganglia for the different groups. There was no discernible pattern of localization of labeled cells within a sympathetic ganglion. For the stomach, afferent labeled cells were located in the range of the first thoracic to fourth lumbar spinal ganglia and the nodose ganglia, bilaterally. As with sympathetic neurons, there was no discernible pattern of localization of labeled cells within a sensory ganglion.

False-positive artifacts of tracer strategies distort autonomic connectivity maps

The widespread use of new axonal transport tracing techniques in the ANS has resulted in substantially revised and amended descriptions of ANS organization. The present review suggests, however, that at least some of the results on which proposed revisions of ANS anatomy have been based have incorporated artifacts and therefore should be cautiously interpreted. The peripheral nervous system and viscera are composed in part of connective and endothelial tissues that are porous or 'leaky' to solutes with appropriate chemical characteristics, including the major tracer compounds. As a result, several extra-axonal routes for redistribution of label from the application site into other tissues are present. These include (1) diffusion through tissue membranes to enter directly adjacent tissues and (2) leakage into extracellular fluids within the body cavity, vasculature, lymphatics, exocrine ducts, or organ lumens to migrate to more distant tissues. As a consequence of the extreme sensitivity of the methods used, such redistribution of even minute amounts of label can produce false positives. Review of autonomic neuroanatomy suggests additional mechanisms, including tracer uptake by fibers of passage, can produce artifactual staining. Based on these surveys of tissue composition, tracer characteristics and sources of artifact, experimental controls and criteria for identifying and avoiding labeling artifacts are described. Since no single procedure is foolproof for ANS experimentation, the routine application of multiple controls, particularly ones which restrict or prevent tracer diffusion, are needed.

A Golgi analysis of the gustatory zone of the nucleus of the solitary tract in the adult hamster

The somal shapes, dendritic features, and orientations of the neurons within the gustatory zone of the nucleus of the solitary tract were studied with the rapid Golgi method in the adult hamster. These Golgi studies complement previous quantitative morphometric analyses of the distributions of large and small neurons within the gustatory zone. Class 1 neurons are usually fusiform and possess long, relatively unbranched dendrites that often extend beyond the cytoarchitectonic boundaries of the gustatory zone. Class II neurons are multipolar and possess more dendrites that are significantly shorter than those of class I neurons. Both classes of neurons are spine poor. Computer-generated three-dimensional rotational analyses demonstrate that the dendritic arborizations of neurons of the gustatory zone are oriented preferentially in the horizontal plane. Dendrites extend in parallel or perpendicular to the solitary tract, the source of peripheral gustatory inputs, and appear to be positioned spatially to maximize synaptic interactions with these peripheral fibers. These Golgi studies also suggest that individual gustatory neurons may be influenced by incoming gustatory fibers that innervate separate populations of taste buds, a finding that is not predictable from the topographical organization of the gustatory zone.

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

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

Catecholamine and serotonin colocalization in projection neurons of the area postrema

A large population of the rat area postrema (AP) neurons which project to the parabrachial area (PBA) are serotonergic. Many AP neurons contain tyrosine hydroxylase (TH) and are presumed to be noradrenergic. However, it was not previously known whether TH-containing AP neurons also have projections to the PBA. TH-containing and serotonin (5-HT)-containing neurons have wide and overlapping distributions within the AP, and it was therefore possible that TH and 5-HT may be contained within the same AP neurons. In the present study immunohistochemical and retrograde axonal transport techniques were combined to determine whether TH-containing AP neurons project to the PBA and whether TH and 5-HT coexist in AP neurons. Adult male rats were given bilateral injections of the retrograde transport tracer, True blue (TB), into the PBA. After a 4-day survival period, vibratome sections of the caudal brainstem were processed for both TH and 5-HT immunohistochemistry. Examination of the sections revealed that over 25% of the 5-HT and over 30% of the TH-containing AP neurons were retrogradely labelled with TB. More surprising were our findings that many AP neurons displayed both TH and 5-HT immunoreactivity and that almost 40% of these double-labelled cells project to the PBA. Our results indicate that serotonin and noradrenaline coexist in a substantial proportion of the neurons of a major ascending viscerosensory pathway from the AP to the PBA.

Cobaltic lysine study of the morphology and distribution of the cranial nerve efferent neurons (motoneurons and preganglionic parasympathetic neurons) and rostral spinal motoneurons in the Japanese toad

The morphology and distribution of the cranial nerve motoneurons (except III, IV, and VI) and rostral spinal motoneurons were systematically studied in the Japanese toad (Bufo japonicus) by retrograde labelling with cobaltic lysine complex. The cobaltic lysine clearly labelled whole neurons, i.e., cell bodies, proximal and distal dendrites, and axons. The branchial motoneurons (V, VII, IX, and X) had similar morphological characteristics and formed a more-or-less continuous cell column through the brainstem. The dendrites could be grouped mainly into the dorsomedial and the ventrolateral dendritic arrays. The dorsomedial dendrites formed a dendritic plexus in the subependymal gray matter, which extended as far peripherally as beneath the ependymal layer. The ventrolateral dendrites formed a broom-like dendritic plexus in the lateral to ventrolateral white matter. They usually extended as far peripherally as the pial surface. The rostrocaudal extent of the dendritic field was also wide and usually exceeded the motor nuclear boundaries. The hypoglossal motoneurons were grouped into the dorsomedial and ventrolateral cell groups, and the latter was considered to be part of the rostral spinal motoneuron column, from their morphology and distribution. The former had well-differentiated dendrites and occupied a more medial position than the branchial motoneurons. Besides the equivalent of the dorsomedial and ventrolateral dendritic arrays of the branchial motoneurons, they had dorsal and commissural dendrites. The accessory motoneurons had morphological characteristics and a distribution pattern similar to those of the rostral spinal motoneurons rather than the branchial motoneurons. The rostral spinal motoneurons had morphological characteristics somewhat different from the branchial motoneurons and the hypoglossal motoneurons (dorsomedial group). Functional implications of the motoneuron morphology are discussed, mainly based on the present results and earlier anatomical and physiological studies of the spinal motoneurons. The present study also revealed the anatomical features of the preganglionic parasympathetic neurons supplying some cranial nerves. These neurons had small somata with less elaborate dendrites and formed an almost continuous cell column that occupied a more dorsal position than the motoneurons of the corresponding nerve. They are thought to be homologous to the salivatory nucleus and the dorsal motor nucleus of the vagus. The basic anatomical organization of the general visceral efferent column seems to be similar throughout vertebrates.

Morphology and distribution of the preganglionic parasympathetic neurons of the facial, glossopharyngeal and vagus nerves in the Japanese toad: a cobaltic lysine study

We labelled the preganglionic parasympathetic neurons of the facial, glossopharyngeal and vagus nerves of the Japanese toad by applying the cobaltic lysine to the cut end of the respective nerve, and examined their morphology and distribution. These neurons form an almost continuous cell column consisting of small neurons with less elaborate dendrites, and occupy a more dorsal position than the motoneurons of the corresponding nerves. The results suggest the presence of the amphibian homologues of the salivatory nucleus and the dorsal motor nucleus of the vagus.

Lesions of the area postrema and underlying solitary nucleus fail to attenuate the inhibition of feeding produced by systemic injections of cholecystokinin in Syrian hamsters

A large body of evidence indicates that the intestinal hormone cholecystokinin (CCK) may serve as a signal for satiety. The abdominal vagus has been shown to be important for the satiety response to exogenous, and by inference, endogenous, CCK in rats and hamsters. Thus, it appears that stimulation of CCK receptors on afferent fibers of the abdominal vagus activates a gut-brain pathway to signal satiety. The present study was undertaken to further trace this viscerosensory pathway by examining food intake after administration of one of two doses (2.0 and 8.0 micrograms/kg) of CCK-octapeptide to intact hamsters and to hamsters sustaining lesions of the area postrema (AP) and underlying nucleus of the solitary tract (NST), regions containing neurons postsynaptic to vagal afferent fibers. As lesions of the AP/NST result in many alterations in ingestive behaviour and body weight regulation in rats, various aspects of feeding and drinking behaviour (spontaneous food intake, body weight maintenance, and responsiveness to a palatable drinking solution and osmotic stimulation) were also examined in lesioned hamsters. Aside from producing transient hypophagia and weight loss immediately after surgery, AP/NST lesions had no effects on these various parameters of ingestive behaviour. The lack of lesion effects on these particular parameters may be explained on the basis that hamsters are generally unresponsive to many of the stimuli for feeding and drinking which purportedly act on the vagus and/or AP/NST. Hamsters with AP/NST lesions were as responsive to the two tested doses of CCK as intact animals.(ABSTRACT TRUNCATED AT 250 WORDS)