Leukemia inhibitory factor and ciliary neurotrophic factor cause dendritic retraction in cultured rat sympathetic neurons.
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Dendritic retraction occurs in many regions of the developing brain and also after neural injury. However, the molecules that regulate this important regressive process remain largely unknown. Our data indicate that leukemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF) cause sympathetic neurons to retract their dendrites in vitro, ultimately leading to an approximately 80% reduction in the size of the arbor. The dendritic retraction induced by LIF exhibited substantial specificity because it was not accompanied by changes in cell number, in the rate of axonal growth, or in the expression of axonal cytoskeletal elements. An antibody to gp130 blocked the effects of LIF and CNTF, and both cytokines induced phosphorylation and nuclear translocation of stat3. Moreover, addition of soluble interleukin-6 (IL-6) receptor to the medium endowed IL-6 with the ability to cause dendritic regression. These data indicate that ligands activating the gp130 pathway have the ability to profoundly alter neuronal cell shape and polarity by selectively causing the retraction of dendrites. (+info)
Sympathetic ganglionic blockade masks beneficial effect of isoflurane on histologic outcome from near-complete forebrain ischemia in the rat.
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BACKGROUND: Isoflurane-anesthetized rats have better outcome from global cerebral ischemia than rats anesthetized with fentanyl and nitrous oxide. The authors wanted to determine whether circulating catecholamine concentrations depend on the anesthetic agent and whether sympathetic ganglionic blockade affects anesthetic-mediated differences in outcome from near-complete forebrain ischemia. METHODS: For two different experiments, normothermic Sprague-Dawley rats that had fasted were assigned to one of four groups and subjected to 10 min of 30 mm Hg mean arterial pressure and bilateral carotid occlusion. Rats were anesthetized with 1.4% isoflurane or fentanyl (25 microg x kg(-1) x h(-1)) and 70% nitrous oxide, with or without preischemic trimethaphan (2.5 mg given intravenously). In experiment 1, arterial plasma catecholamine concentrations were measured before, at 2 and 8 min during, and after ischemia (n = 5-8). In experiment 2, animals (n = 15) underwent histologic analysis 5 days after ischemia. RESULTS: In experiment 1, intraischemic increases in plasma norepinephrine and epinephrine levels were 28 and 12 times greater in the fentanyl-nitrous oxide group than in the isoflurane group (P<0.01). Trimethaphan blocked all changes in plasma catecholamine concentrations (P<0.02). In experiment 2, isoflurane reduced the mean +/- SD percentage of dead hippocampal CA1 neurons compared with fentanyl-nitrous oxide (43+/-22% vs. 87+/-10%; P<0.001). Trimethaphan abolished the beneficial effects of isoflurane (91+/-6%; P<0.001). Similar observations were made in the cortex. CONCLUSIONS: Isoflurane attenuated the peripheral sympathetic response to ischemia and improved histologic outcome compared with fentanyl and nitrous oxide. This outcome benefit was reversed by sympathetic ganglionic blockade. The beneficial effects of isoflurane may result from a neuroprotective influence of an intermediate sympathetic response that is abolished by trimethaphan. (+info)
Two populations of sympathetic neurons project selectively to mesenteric artery or vein.
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The objective of this study was to determine whether sympathetic neurons of the inferior mesenteric ganglion (IMG) projecting to mesenteric arteries could be distinguished by their localization, neurochemical phenotype, and electrophysiological properties from neurons projecting to mesenteric veins. In an in vitro intact vasculature-IMG preparation, neurons were labeled following intraluminal injection of Fluoro-Gold or rhodamine beads into the inferior mesenteric artery (IMA) or vein (IMV). The somata of neurons projecting to IMA were localized in the central part of the IMG, whereas those projecting to IMV were localized more peripherally. None of the labeled neurons was doubly labeled. Neuropeptide Y immunoreactivity was found in 18.9% of neurons innervating the IMA, but not in neurons innervating the IMV. Identified neurons were dissociated and characterized using whole cell patch-clamp recording. After direct soma depolarization, all of the labeled arterial and venous neurons were classified as tonic firing, compared with only 40% of unlabeled neurons; the remaining 60% of unlabeled neurons were phasic firing. The results indicate that IMG neurons projecting to mesenteric arteries are distinct from neurons projecting to mesenteric veins. (+info)
Somatic and prejunctional nicotinic receptors in cultured rat sympathetic neurones show different agonist profiles.
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1. The release of [3H]-noradrenaline ([3H]-NA) in response to nicotinic acetylcholine receptor (nAChR) agonists was compared with agonist-induced currents in cultured rat superior cervical ganglion (SCG) neurones. 2. [3H]-NA release in response to high concentrations of nicotinic agonists was reduced, but not fully inhibited, by the presence of either tetrodotoxin (TTX) or Cd2+ to block voltage-gated Na+ or Ca2+ channels, respectively. We used the component of transmitter release that remained in the presence of these substances (named TTX- or Cd2+-insensitive release) to pharmacologically characterize nAChRs in proximity to the sites of vesicular exocytosis (prejunctional receptors). Prejunctional nAChRs were activated by nicotinic agonists with a rank order of potency of dimethylphenylpiperazinium iodide (DMPP) > nicotine > cytisine > ACh, and with EC50 values ranging from 22 microM (DMPP) to 110 microM (ACh). 3. [3H]-NA release in response to low concentrations of nAChR agonists was fully inhibited by the presence of either TTX or Cd2+ (named TTX- or Cd2+-sensitive release). TTX-sensitive release was triggered by nicotinic agonists with a rank order of potency of DMPP > cytisine approximately nicotine approximately ACh, which due to its similarity to TTX-insensitive release indicates that it might also be triggered by prejunctional-type nAChRs. The EC50 values for TTX (Cd2+)-sensitive release were less than 10 microM for all four agonists. 4. By contrast to transmitter release, somatic nAChRs as seen by patch clamp recordings were most potently activated by cytisine, with a rank order of potency of cytisine > nicotine approximately DMPP > ACh. EC50 values for the induction of currents exceeded 20 microM for all four agonists. 5. The nicotinic antagonist mecamylamine potently inhibited all transmitter release in response to nicotine. alpha-Bungarotoxin (alpha-BuTX) was, on the other hand, without significant effect on nicotine-induced TTX-insensitive release. The competitive antagonist dihydro-beta-erythroidine (DHbetaE) caused rightward shifts of the dose-response curves for both TTX-sensitive and TTX-insensitive transmitter release as well as for currents in response to nicotine, with pA2 values ranging from 4.03 to 4.58. 6. Due to clear differences in the pharmacology of agonists we propose that nAChRs of distinct subunit composition are differentially targeted to somatic or axonal domains. (+info)
An essential role for katanin in severing microtubules in the neuron.
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Several lines of evidence suggest that microtubules are nucleated at the neuronal centrosome, and then released for transport into axons and dendrites. Here we sought to determine whether the microtubule-severing protein known as katanin mediates microtubule release from the neuronal centrosome. Immunomicroscopic analyses on cultured sympathetic neurons show that katanin is present at the centrosome, but is also widely distributed throughout the neuron. Microinjection of an antibody that inactivates katanin results in a dramatic accumulation of microtubules at the centrosome, indicating that katanin is indeed required for microtubule release from the centrosome. However, the antibody also causes an inhibition of axon outgrowth that is more immediate than expected on this basis alone. It may be that katanin severs microtubules throughout the cell body to keep them sufficiently short to be efficiently transported into developing processes. Consistent with this idea, there were significantly fewer free ends of microtubules in the cell bodies of neurons that had been injected with the katanin antibody compared with controls. These results indicate that microtubule-severing by katanin is essential for releasing microtubules from the neuronal centrosome, and also for regulating the length of the microtubules after their release. (+info)
Catecholamine synthesis is mediated by tyrosinase in the absence of tyrosine hydroxylase.
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Catecholamine neurotransmitters are synthesized by hydroxylation of tyrosine to L-dihydroxyphenylalanine (L-Dopa) by tyrosine hydroxylase (TH). The elimination of TH in both pigmented and albino mice described here, like pigmented TH-null mice reported previously (Kobayashi et al., 1995; Zhou et al., 1995), demonstrates the unequivocal requirement for catecholamines during embryonic development. Although the lack of TH is fatal, TH-null embryos can be rescued by administration of catecholamine precursors to pregnant dams. Once born, TH-null pups can survive without further treatment until weaning. Given the relatively rapid half-life of catecholamines, we expected to find none in postnatal TH-null pups. Despite the fact that the TH-null pups lack TH and have not been supplemented with catecholamine precursers, catecholamines are readily detected in our pigmented line of TH-null mice by glyoxylic acid-induced histofluorescence at postnatal day 7 (P7) and P15 and quantitatively at P15 in sympathetically innervated peripheral organs, in sympathetic ganglia, in adrenal glands, and in brains. Between 2 and 22% of wild-type catecholamine concentrations are found in these tissues in mutant pigmented mice. To ascertain the source of the catecholamine, we examined postnatal TH-null albino mice that lack tyrosinase, another enzyme that converts tyrosine to L-Dopa but does so during melanin synthesis. In contrast to the pigmented TH-null mice, catecholamine histofluorescence is undetectable in postnatal albino mutants, and the catecholamine content of TH-null pups lacking tyrosinase is 18% or less than that of TH-null mice with tyrosinase. Thus, these extraordinary circumstances reveal that tyrosinase serves as an alternative pathway to supply catecholamines. (+info)
Nr-CAM promotes neurite outgrowth from peripheral ganglia by a mechanism involving axonin-1 as a neuronal receptor.
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Nr-CAM is a neuronal cell adhesion molecule (CAM) belonging to the immunoglobulin superfamily that has been implicated as a ligand for another CAM, axonin-1, in guidance of commissural axons across the floor plate in the spinal cord. Nr-CAM also serves as a neuronal receptor for several other cell surface molecules, but its role as a ligand in neurite outgrowth is poorly understood. We studied this problem using a chimeric Fc-fusion protein of the extracellular region of Nr-CAM (Nr-Fc) and investigated potential neuronal receptors in the developing peripheral nervous system. A recombinant Nr-CAM-Fc fusion protein, containing all six Ig domains and the first two fibronectin type III repeats of the extracellular region of Nr-CAM, retains cellular and molecular binding activities of the native protein. Injection of Nr-Fc into the central canal of the developing chick spinal cord in ovo resulted in guidance errors for commissural axons in the vicinity of the floor plate. This effect is similar to that resulting from treatment with antibodies against axonin-1, confirming that axonin-1/Nr-CAM interactions are important for guidance of commissural axons through a spatially and temporally restricted Nr-CAM positive domain in the ventral spinal cord. When tested as a substrate, Nr-Fc induced robust neurite outgrowth from dorsal root ganglion and sympathetic ganglion neurons, but it was not effective for tectal and forebrain neurons. The peripheral but not the central neurons expressed high levels of axonin-1 both in vitro and in vivo. Moreover, antibodies against axonin-1 inhibited Nr-Fc-induced neurite outgrowth, indicating that axonin-1 is a neuronal receptor for Nr-CAM on these peripheral ganglion neurons. The results demonstrate a role for Nr-CAM as a ligand in axon growth by a mechanism involving axonin-1 as a neuronal receptor and suggest that dynamic changes in Nr-CAM expression can modulate axonal growth and guidance during development. (+info)
Contribution of the cervical sympathetic ganglia to the innervation of the pharyngeal arch arteries and the heart in the chick embryo.
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In the chick heart, sympathetic innervation is derived from the sympathetic neural crest (trunk neural crest arising from somite level 10-20). Since the trunk neural crest gives rise to sympathetic ganglia of their corresponding level, it suggests that the sympathetic neural crest develops into cervical ganglia 4-14. We therefore tested the hypothesis that, in addition to the first thoracic ganglia, the cervical ganglia might contribute to cardiac innervation as well. Putative sympathetic nerve connections between the cervical ganglia and the heart were demonstrated using the differentiation markers tyrosine hydroxylase and HNK-1. In addition, heterospecific transplantation (quail to chick) of the cardiac and trunk neural crest was used to study the relation between the sympathetic neural crest and the cervical ganglia. Quail cells were visualized using the quail nuclear antibody QCPN. The results by immunohistochemical study show that the superior and the middle cervical ganglia and possibly the carotid paraganglia contribute to the carotid nerve. This nerve subsequently joins the nodose ganglion of the vagal nerve via which it contributes to nerve fibers in cardiac vagal branches entering the arterial and venous pole of the heart. In addition, the carotid nerve contributes to nerve fibers connected to putative baro- and chemoreceptors in and near the wall of pharyngeal arch arteries suggesting a role of the superior and middle cervical ganglia and the paraganglia of the carotid plexus in sensory afferent innervation. The lower cervical ganglia 13 and 14 contribute predominantly to nerve branches entering the venous pole via the anterior cardinal veins. We did not observe a thoracic contribution. Heterospecific transplantation shows that the cervical ganglia 4-14 as well as the carotid paraganglia are derived from the sympathetic neural crest. The cardiac neural crest does not contribute to the neurons of the cervical ganglia. We conclude that the cervical ganglia contribute to cardiac innervation which explains the contribution of the sympathetic neural crest to the innervation of the chick heart. (+info)