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The distribution of tenascin coincides with pathways of neural crest cell migration.

The distribution of the extracellular matrix (ECM) glycoprotein, tenascin, has been compared with that of fibronectin in neural crest migration pathways of Xenopus laevis, quail and rat embryos. In all species studied, the distribution of tenascin, examined by immunohistochemistry, was more closely correlated with pathways of migration than that of fibronectin, which is known to be important for neural crest migration. In Xenopus laevis embryos, anti-tenascin stained the dorsal fin matrix and ECM along the ventral route of migration, but not the ECM found laterally between the ectoderma and somites where neural crest cells do not migrate. In quail embryos, the appearance of tenascin in neural crest pathways was well correlated with the anterior-to-posterior wave of migration. The distribution of tenascin within somites was compared with that of the neural crest marker, HNK-1, in quail embryos. In the dorsal halves of quail somites which contained migrating neural crest cells, the predominant tenascin staining was in the anterior halves of the somites, codistributed with the migrating cells. In rat embryos, tenascin was detectable in the somites only in the anterior halves. Tenascin was not detectable in the matrix of cultured quail neural crest cells, but was in the matrix surrounding somite and notochord cells in vitro. Neural crest cells cultured on a substratum of tenascin did not spread and were rounded. We propose that tenascin is an important factor controlling neural crest morphogenesis, perhaps by modifying the interaction of neural crest cells with fibronectin.

Animals↗

Avian neural crest-derived neurogenic precursors undergo apoptosis on the lateral migration pathway.

Neural crest cells of vertebrate embryos disperse on distinct pathways and produce different derivatives in specific embryonic locations. In the trunk of avian embryos, crest-derived cells that initially migrate on the lateral pathway, between epidermal ectoderm and somite, produce melanocytes but no neuronal derivatives. Although we found that melanocyte precursors are specified before they disperse on the lateral pathway, we also observed that a few crest-derived neuronal cells are briefly present on the same pathway. Here, we show that neuronal cells are removed by an episode of apoptosis. These observations suggest that localized environmental factor(s) affect the distribution of fate-restricted crest derivatives and function as a 'proof-reading mechanism' to remove 'ectopic' crest-derived cells.

Animals↗

Neural precursor cells possess multiple p53-dependent apoptotic pathways.

Neural precursor cells (NPCs) are markedly sensitive to apoptotic insults. p53-Dependent transcriptional activation of proapoptotic genes has been hypothesized to regulate NPC death in response to DNA damage. Recent studies of non-NPCs have also indicated that p53 may directly interact with Bcl-2 molecules and thereby regulate death independently of transcription. The contribution of transcription-independent p53 activation in NPC death has not been characterized. In this study, we found that apoptosis caused by chemotherapeutic agents in NPCs required p53 expression and new macromolecular synthesis. In contrast, NPC death induced by staurosporine, a broad kinase inhibitor, is regulated by p53 in the absence of macromolecular synthesis. The apoptosis effector molecules Bax and Bak, Apaf-1, and caspase-9 were shown to be downstream of p53 in both pathways. These findings indicate that p53 is in a unique position to regulate at least two distinct signaling portals that activate the intrinsic apoptotic death pathway in NPCs.

Animals↗

Signalling between the hindbrain and paraxial tissues dictates neural crest migration pathways.

Cranial neural crest cells are a pluripotent population of cells derived from the neural tube that migrate into the branchial arches to generate the distinctive bone, connective tissue and peripheral nervous system components characteristic of the vertebrate head. The highly conserved segmental organisation of the vertebrate hindbrain plays an important role in patterning the pathways of neural crest cell migration and in generating the distinct or separate streams of crest cells that form unique structures in each arch. We have used focal injections of DiI into the developing mouse hindbrain in combination with in vitro whole embryo culture to map the patterns of cranial neural crest cell migration into the developing branchial arches. Our results show that mouse hindbrain-derived neural crest cells migrate in three segregated streams adjacent to the even-numbered rhombomeres into the branchial arches, and each stream contains contributions of cells from three rhombomeres in a pattern very similar to that observed in the chick embryo. There are clear neural crest-free zones adjacent to r3 and r5. Furthermore, using grafting and lineage-tracing techniques in cultured mouse embryos to investigate the differential ability of odd and even-numbered segments to generate neural crest cells, we find that odd and even segments have an intrinsic ability to produce equivalent numbers of neural crest cells. This implies that inter-rhombomeric signalling is less important than combinatorial interactions between the hindbrain and the adjacent arch environment in specific regions, in the process of restricting the generation and migration of neural crest cells. This creates crest-free territories and suggests that tissue interactions established during development and patterning of the branchial arches may set up signals that the neural plate is primed to interpret during the progressive events leading to the delamination and migration of neural crest cells. Using interspecies grafting experiments between mouse and chick embryos, we have shown that this process forms part of a conserved mechanism for generating neural crest-free zones and contributing to the separation of migrating crest populations with distinct Hox expression during vertebrate head development.

Animals↗

Neural cell adhesion molecule is endocytosed via a clathrin-dependent pathway.

Neural cell adhesion molecule (NCAM) constitutes a group of cell surface glycoproteins that regulate cell-cell interactions in the developing and adult brain. Endocytosis is a mechanism which dynamically controls the amount of cell surface NCAM expression and may involve the rapid changes occurring in NCAM expression under certain physiological or pathological conditions. However, the endocytic pathway of NCAM is presently unknown. Using astrocytes in culture and immunofluorescence we show that NCAM is internalized and that the immunolabelling presents a high degree of colocalization with clathrin, alpha-adaptin and transferrin, suggesting that NCAM is endocytosed by a clathrin-dependent pathway. Potassium depletion which disrupts clathrin-mediated endocytosis, inhibited internalization of NCAM. Electron microscopy and immunogold studies also demonstrate that the surface of clathrin-coated vesicles are also immunolabelled for both alpha-adaptin and PSA-NCAM, the highly sialylated isoform of NCAM. Furthermore, immunoprecipation studies demonstrate that NCAM is associated with both clathrin and alpha-adaptin, a component of adaptor complex AP-2, in brain, neurons and astrocytes. These findings indicate that NCAM is mainly endocytosed via clathrin-coated vesicles, suggesting a possible mechanism that may contribute to the rapid changes in NCAM expression at the cell surface.

Adaptor Protein Complex alpha Subunits↗

Mapping of neural crest pathways in Xenopus laevis using inter- and intra-specific cell markers.

This study examines the pathways of migration followed by neural crest cells in Xenopus embryos using two recently described cell marking techniques. The first is an interspecific chimera created by grafting Xenopus borealis cells into Xenopus laevis hosts. The cells of these closely related species can be distinguished by their nuclear dimorphism. The second type of marker is created by microinjection of lysinated dextrans into fertilized eggs which can then be used for intraspecific grafting. These recently developed fluorescent dyes are fixable and identifiable in both living and fixed embryos. After grafting labeled donor neural tubes into unlabeled host embryos, the distribution of neural crest cells at various stages after grafting was used to define the pathways of neural crest migration. To control for possible grafting artifacts, fluorescent lysinated dextran was injected into a single blastomere which gives rise to a large number of neural crest cells, thereby labeling the neural crest without grafting. By all three techniques, Xenopus neural crest cells were observed along two predominant pathways in the trunk. The majority of neural crest cells were observed along a "ventral" route, between the neural tube and somite, the notochord and somite, and along the dorsal mesentery. A second group of neural crest cells was observed "dorsally" where they populated the dorsal fin. A third minor "lateral" pathway was observed primarily in borealis/laevis chimerae and in blastomere-injected embryos; some neural crest cells were observed underneath the ectoderm lateral to the neural tube. Along the rostrocaudal axis, neural crest cells were not continuously distributed but were primarily located across from the caudal two-thirds of the somite. Fewer than 3% of the neural crest cells were observed across from the rostral third of each somite. When grafted to ventral locations, neural crest cells were not able to migrate dorsally but migrated laterally along the dorsal mesentery. Labeled neural crest cells gave rise to cells of the spinal, sympathetic, and enteric ganglia as well as to adrenal chromaffin cells, Schwann cells, pigment cells, mesenchymal cells of the dorsal fin, and some cells in the integuments and in the region of the pronephros. These results show that the neural crest migratory pathways in Xenopus differ from those in the avian embryo. In avians NC cells migrate as a closely associated sheet of cells while in Xenopus they migrate as individual cells. Both species exhibit a metamerism in the neural crest cell distribution pattern along the rostrocaudal axis.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

Limbic pathways and hypothalamic neurotransmitters mediating adrenocortical responses to neural stimuli.

One of the major phenomena related to the stress response is the activation of the hypothalamo-pituitary-adrenocortical (HPA) axis. This axis consists of corticotropin releasing factor-41 in the paraventricular nucleus of the hypothalamus (PVN), which in response to a variety of stimuli is released into the portal circulation and stimulates pituitary ACTH secretion and subsequently adrenocortical discharge. The mechanisms involved in the activation are not uniform and the responses to various stimuli are mediated by different neural pathways. Since extrahypothalamic limbic structures play a significant role in the HPA function, it is the purpose of this review to describe the neural pathways between the hippocampus, septum and amygdala and the hypothalamus in relation to adrenocortical activity and the differential role of the medial forebrain bundle as well as the effects of various hypothalamic deafferentation on the transmission of the neural impulses to the hypothalamus. Also, the importance of norepinephrine and serotonin in the activation of the HPA axis will be delineated.

Adrenal Cortex↗

The possible involvement of the nonstrial pathway of the amygdala in neural control of sexual behavior in male rats.

The effect of medial amygdala lesions on male sexual behavior in male rats with stria terminalis cut was examined. First, castrated male rats received bilateral transections of the stria terminals (STC) or sham cut (SC). Most STC males showed no ejaculation, but displayed mount and intromission, although the frequencies were not high compared to those of males with SC. Next, bilateral lesions of the medial amygdala (MAL) or sham lesion (SL) were performed in males with STC or SC. The MAL caused severe loss of all aspects of copulatory behavior in males with STC as well as in males with SC. The suppressive effect of the MAL on copulatory activity was stronger than that of the STC. These results indicate that a neural pathway other than the stria terminalis is involved in the regulation of male sexual behavior by the amydgala in male rats.

Amygdala↗

Adult-onset hypothyroidism impairs paired-pulse facilitation and long-term potentiation of the rat dorsal hippocampo-medial prefrontal cortex pathway in vivo.

Thyroid hormones are critical for the maturation and function of the central nervous system. Insufficiency of thyroid hormones in the adulthood causes a wide range of cognitive dysfunctions, including deficits in learning and memory. The present study investigated whether adult-onset hypothyroidism would alter synaptic functions in the dorsal hippocampo-medial prefrontal cortex (mPFC) pathway, a neural pathway important for learning and memory. Adult hypothyroidism was induced by oral administration of 1% (g/l) antithyroid acting drug 6-n-propyl-2-thiouracil (PTU) to adult male Sprague-Dawley rats for 4 weeks. Postsynaptic potentials (PSP) were recorded in the mPFC by stimulating the dorsal hippocampal CA1 region in vivo. Basal synaptic transmission was evaluated by comparing input-output relationships. Paired-pulse facilitation and long-term potentiation were recorded to examine short- and long-term synaptic plasticity. Adult-onset hypothyroidism did not change the basal synaptic transmission, but significantly reduced paired-pulse facilitation and long-term potentiation of PSP. These inhibitions can be restored by thyroid hormone replacement. The results suggest that such alterations in synaptic plasticity of the dorsal hippocampo-mPFC pathway might contribute to understanding basic mechanisms underlying learning and memory deficits associated with adult-onset hypothyroidism.

Animals↗

Genetic dissection of the signaling pathways that control gastric acid secretion.

Gastric acid secretion is regulated by endocrine, paracrine and neurocrine signals via at least three pathways, the gastrin-histamine pathway, the CCK-somatostatin pathway and the neural pathway. Genetically-engineered mice, subjected to targeted gene disruption (i.e., knockout mice), have been used to dissect the signaling pathways that are responsible for the complexity of the regulation of acid secretion in vivo. Both gastrin knockout and gastrin/CCK2 receptor knockout mice displayed greatly impaired acid secretion, presumably because of the loss of the gastrin-histamine pathway. Gastrin/CCK double-knockout mice had a relatively high percentage of active parietal cells with a maintained ability to respond with copious acid secretion to pylorus ligation-evoked vagal stimulation and to a histamine challenge. The low acid secretion in gastrin knockout mice and gastrin/CCK2 receptor knockout mice and the restoration of acid secretion in gastrin/CCK double-knockout mice suggest that CCK plays an important role as inhibitor of the parietal cells via the CCK-somatostatin pathway by stimulating the CCK1 receptor of the D cell. In the absence of both the gastrin-histamine and the CCK-somatostatin pathway (as in gastrin/CCK2 receptor double-knockout mice), the control of acid secretion is probably taken over by neural pathways, explaining the high acid output. The observations illustrate the complexity and plasticity of the acid regulatory mechanisms. It seems that one pathway may be suppressed or allowed to dominate over the others depending on the circumstances.

Animals↗

Soluble and cell-bound forms of steel factor activity play distinct roles in melanocyte precursor dispersal and survival on the lateral neural crest migration pathway.

Trunk neural crest cells segregate from the neuroepithelium and enter a 'migration staging area' lateral to the embryonic neural tube. After some crest cells in the migration staging area have begun to migrate on a medial pathway, a subpopulation of crest-derived cells remaining in the migration staging area expresses mRNAs for the receptor tyrosine kinase, c-kit, and tyrosinase-related protein-2, both of which are characteristic of melanocyte precursors. These putative melanocyte precursors are subsequently observed on the lateral crest migration pathway between the dermatome and overlying epithelium, and then dispersed in nascent dermal mesenchyme. Melanocyte precursors transiently require the c-kit ligand, Steel factor for survival. Although Steel factor mRNA is transiently expressed in the dorsal dermatome before the onset of trunk neural crest cell dispersal on the lateral pathway, it is no longer produced by dermatomal cells when melanocyte precursors have dispersed in the dermal mesenchyme. To assess the role of Steel factor in migration of melanocyte precursors on the lateral pathway, we analyzed melanocyte precursor dispersal and fate on the lateral pathway of two different Sl mutants, Sl, a null allele, and Sld, which lacks cell surface-associated Steel factor but produces a soluble form. No melanocyte precursors were detected in the dermatome of embryos homozygous for the Sl allele or in W mutants that lack functional c-kit. In contrast, in embryos homozygous for the Sld allele, melanocyte precursors appeared on the lateral pathway, but subsequently disappear from the dermis. These results suggest that soluble Steel factor is required for melanocyte precursor dispersal on the lateral pathway, or for their initial survival in the migration staging area. In contrast, membrane-bound Steel factor appears to promote melanocyte precursor survival in the dermis.

Animals↗

CNS innervation of the urinary bladder demonstrated by immunohistochemical study for c-fos and pseudorabies virus.

The aim of the present study is to verify the functional and anatomical neural pathways which innervate the urinary bladder in the central nervous system of the rat. To identify the functional neural pathway, the urinary bladder was stimulated by infusing formalin for 2 h. Then, brain and spinal cord were dissected out and immunohistochemistry was done by using anti-c-fos antibody. Many c-fos immunoreactive (IR) neurons were identified in the telencephalic cortical areas and in several brainstem nuclei, which are known mostly to be related with urinary bladder. In the spinal cord, a number of c-fos IR neurons were found in the lamina I, IIo, dorsal gray commissure, sacral parasympathetic nucleus. To identify the anatomical neural pathway of the urinary bladder, Pseudorabies virus (PRV) was injected into the wall of urinary bladder and was identified with anti-PRV by using immunohistochemistry. Most PRV labeled neurons were found where c-fos IR neurons were identified and few of them were also in the areas where c-fos IR neurons were not found, e.g., prefrontal cortex, agranular insular cortex, and subfornical organ. In the spinal cord, PRV labeled cells were found all over the gray matter. The present study presents morphological evidence demonstrating the supraspinal areas are related with the neural control of the urinary bladder and most functional neural pathway of the urinary bladder is well consistent with the anatomical neural pathway except in some telencephalic cortical areas.

Animals↗

Effect of the concentration of maternal antibodies on the neural invasion of Aujeszky's disease virus in neonatal pigs.

The degree to which maternally derived antibodies may affect neural invasion of Aujeszky's disease virus (ADV) in neonatal pigs was examined. One-week-old pigs with different levels of maternal immunity were inoculated intranasally with 10(7.0) TCID50 of the Ka strain. The invasion of the virus was studied in both the trigeminal neural pathway (nasal mucosa, trigeminal ganglion = 1st level, pons/medulla = 2nd level and cerebellum/thalamus = 3rd level) and the olfactory neural pathway (olfactory mucosa = 1st level, olfactory bulb = 2nd level and lateral olfactory gyrus = 3rd level) by virus titration and immunohistochemistry (IHC). In control pigs without specific antibodies, virus invaded all neuronal levels in both neural pathways. In pigs with a low concentration of maternal antibodies (SN-titer = 2-3), virus infected all neuronal levels in both neural pathways but, compared to the controls, virus titers were significantly lower (approximately 2 log10) in the trigeminal pathway. In pigs with a high concentration of maternal antibodies (SN-titer = 272-384), virus reached the 2nd neuronal level of the olfactory pathway while no neural tissue had been infected in the trigeminal pathway. Virus titers in the affected neuronal levels of the latter pigs were significantly lower than in the controls. IHC revealed, in non-immune pigs, a fibroblast-mediated spread of the virus in the nasal lamina propria, and a local spread of the virus from neurons to their satellite cells in the trigeminal ganglion. Such a spread of the virus was rarely seen in the nasal mucosa and in the trigeminal ganglion of passively immune pigs. These findings suggest that, in the presence of maternal immunity, defence mechanisms operate at these sites. In conclusion, we can state that a correlation exists between the level of maternal immunity and the protection against invasion of ADV in the nervous system of neonatal pigs.

Animals↗

Influence of humoral control peptides on medullary vasomotor control neurons: microstimulation and double-labeling studies using SHR and WKY rats.

To study the influence of humoral control peptides on medullary vasomotor control neurons, angiotensin II (AII), arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) were microinjected into three vasomotor control areas, i.e., the area postrema (AP), the nucleus tractus solitarii (NTS) and the rostral ventrolateral medulla (RVLM), of spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY), and the evoked cardiovascular response was observed. Unlike the injection areas, the threshold dose of one peptide for the cardiovascular response was similar, but the threshold dose differed from peptide to peptide. The threshold dose was lower for AII (0.15-0.29 pmol), in-between for ANP (0.9-1.5 pmol) and higher for AVP (14-30 pmol). No significant difference in the threshold dose was observed between SHR and WKY, suggesting that hypertension in SHR may not be due to the abnormal sensitivity to the three peptides of the vasomotor control neurons in the AP, NTS, and RVLM. The structural basis of the results of the microstimulation experiment was supported by the double-labeling study. The NTS neurons were innervated by (1) the AII-immunoreactive (ir) neurons in both sides of the lateral hypothalamic area (LH), the RVLM and the caudal ventrolateral medulla, and (2) the ANP-ir neurons in both sides of the paraventricular nucleus (Pa) and the LH. The RVLM neurons were innervated by (1) the AII-ir neurons in both sides of the LH and ipsilateral side of the lateral parabrachial nucleus (Pbl) and (2) the ANP-ir neurons in the ipsilateral Pbl. There was no evidence that the AVP-ir neurons in the Pa and the supraoptic nucleus innervate the NTS and the RVLM neurons, or that the AII, ANP or AVP-ir neurons innervate the AP neurons. This study suggests that in common with SHR and WKY rats AII and ANP may influence both the NTS and RVLM not by the humoral pathway but by the neural pathway, and AVP may not influence the three vasomotor control areas by the neural pathway.

Angiotensin II↗

Comparison of SLN-evoked swallows during rest and chewing in the freely behaving rabbit.

Interactions between the swallowing central neural pathway and the chewing central neural pathway were examined in freely behaving, unanesthetized rabbits. Pharyngeal swallows were elicited by electrical stimulation of the superior laryngeal nerve (SLN) and defined by thyrohyoid muscle (TH) activity in the electromyogram (EMG). Recordings were obtained from rabbits at rest and during chewing. The number of swallows elicited by the SLN stimulation was significantly increased (P<0.001) during quiet oral function (at rest) and during chewing. The increased number of swallows from each baseline was similar, signifying that the effect of the SLN stimulation was similar in generating swallowing in both groups. The swallows induced with SLN stimulation were very similar to natural swallows as defined by the temporal pattern of the EMG duration and the timing of EMG activities. Our results suggest that: (1). the peripheral inputs to the swallowing pathway may rarely be modulated by the chewing pathway in the generation of swallows; (2). the swallowing pathway and the chewing pathway may interact at the level of the rhythm generators; (3). each animal has its own threshold for eliciting pharyngeal swallowing, and the threshold may be independent of the number of chews.

Animals↗

Physiopharmacology of the peristaltic reflex: an update.

The peristaltic reflex is one of the simplest models which can be used to study the function of enteric neurons by recording intestinal motor activity. Peristalsis consists of a coordinated, aborally propagating motor activity which requires the functional integrity of receptor pathways, excitatory and inhibitory neural pathways and neuromuscular junctions. Luminal distension elicits polarized responses: an ascending excitatory response (ascending contraction) and a descending inhibitory response (descending relaxation). The present paper reviews the most recent acquisitions on the neural pathways and neurotransmitters involved in the regulation of the peristaltic reflex.

Humans↗

Potential use of drugs that target neural-immune pathways in the treatment of rheumatoid arthritis and other autoimmune diseases.

Many autoimmune disorders share two common features, dysregulation of the immune system and stress pathways. Two stress pathways, the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS), regulate immune system responses, through release of corticosteroids and norepinephrine (NE), respectively. These neuromediators act on immune cells via specific receptors on their surface to modulate the production of key regulatory cytokines. Glucocorticoids modulate immune responses by glucocorticoid binding to cytoplasmic glucocorticoid receptors within target cells. NE regulates immune responses through interaction with plasma membrane beta- or alpha-adrenergic receptors (AR). Both NE and glucocorticoids promote humoral immunity by altering macrophages and T cell cytokine production after an antigen challenge. Glucocorticoids and NE do this by inhibiting interleukin (IL)-12, and interferon (IFN)-gamma, which drives cell-mediated immunity. Additionally, catecholamines drive humoral immunity by stimulating macrophage IL-10 production. These catecholamine effects are mediated largely via beta(2)-AR activation. Both glucocorticoids and NE inhibit inflammation. However, under some circumstances NE promotes inflammation through interaction with macrophage alpha1-AR and subsequent increases in tumor necrosis factor alpha (TNFalpha production. Although macrophages do not normally express alpha(1)-AR, expression of this receptor on macrophages and monocytes occurs in some disease states, including rheumatoid arthritis (RA). Through these mechanisms the HPA axis and the SNS influence the course and progression of RA. Thus, the HPA axis and the SNS are likely to play key roles in the pathology of RA. Furthermore, therapeutic agents targeting the neural pathways that normally regulate immune system homeostasis may prove beneficial for treating RA and other autoimmune diseases.

Adjuvants, Immunologic↗

Can we learn from the clinically significant face processing deficits, prosopagnosia and Capgras delusion?

This review describes two clinically significant face processing deficits, prosopagnosia and Capgras delusion, and provides new knowledge about the face recognition process by a convergence of empirical findings. These empirical findings are structured around two questions that are reviewed from the perspectives of the two deficits. First is the question of hemispheric specificity, which inquires into the degree of each hemisphere's contribution to the face recognition process. Second is the question of dual neural pathways, which addresses the possibility that the face recognition process proceeds along two parallel pathways in the brain. Findings from the hemispheric specificity studies reinforce the current view that right hemispheric involvement is necessary for face recognition while left hemispheric involvement is minimal. Findings from the dual neural pathways studies reinforce the plausible but yet unproven hypothesis that two neural pathways pass information from the visual association cortex in the occipital lobe toward the temporal lobes and limbic system when faces are seen and recognized. These findings, which also indicate that each of the dual neural pathways carries different, nonredundant information, could be instrumental in showing that the pathways play different roles in the manifestations of the clinically significant face processing deficits, prosopagnosia and Capgras delusion.

Agnosia↗