bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanism of agrin‐induced acetylcholine receptor aggregation
Authors: Wallace Bruce G. 
Published: January 2005

AbstractAgrin induces the formation of specializations on chick myotubes in culture at which several components of the postsynaptic apparatus accumulate, including acetylcholine receptors (AChRs). Agrin also induces AChR phosphorylation. Several lines of evidence suggest that agrininduced phosphorylation of tyrosine residues in the β subunit of the AChR is an early step in receptor aggregation: agrin‐induced phosphorylation and aggregation have the same dose dependence; treatments that prevent aggregation block phosphorylation; phosphorylation begins before any detectable change in receptor distribution, reaches a maximum hours before aggregation is complete, and declines slowly together with the disappearance of aggregates after agrin is withdrawn; agrin slows the rate at which receptors are solubilized from intact myotubes by detergent extraction; and the change in receptor extractability parallels the change in phosphorylation. A model for agrin‐induced AChR aggregation is presented in which phosphorylation of AChRs by an agrin‐activated protein tyrosine kinase causes receptors to become attached to the cytoskeleton, which reduces their mobility and detergent extractability, and leads to the accumulation of receptors in the vicinity of the activated kinase, forming an aggregate. © 1992 John Wiley & Sons, Inc.
An antigen present in the Drosophila central nervous system only during embryonic and metamorphic stages
Authors: Go Masahiro J. , Hotta Yoshiki 
Published: January 2005

AbstractWe report here about an antigen that is expressed in the central nervous system (CNS) of Drosophila only during the embryonic and metamorphic stages. In Drosophila, axonogenesis and synaptogenesis occur twice during the development: first in the embryonic and second in the metamorphic stages. We generated monoclonal antibodies (MAbs) in order to obtain molecular probes for analyzing axonogenesis or synaptogenesis in the CNS on the assumption that good candidates for molecules responsible for such phenomena must be present in the neuropil during those stages exclusively. As a result, we found MAb 66B2 whose intense immunoreactivity in the neuropil of the CNS was observed exclusively in the embryo and pupa, and not in the larva and adult. Immunoblot analyses showed that MAb 66B2 binds specifically to a protein with an apparent molecular weight of 350 K and neutral pl in the prepupal CNS. A significant amount of the antigen was isolated in forms that were soluble without detergent. Results of immunohistochemistry with MAb 66B2 in a primary culture of embryos showed that some live cells in the ganglion‐like cluster were stained, and that neuronal cell bodies and neurites emanating from there were negative. These results strongly suggest that the 66B2 antigen observed in the CNS is an extracellular matrix component secreted from nonneuronal cells. These developmental changes in the 66B2 immuno‐reactivity in the CNS presumably reflect dynamic changes of an extracellular matrix in the CNS that are accompanied by axonogenesis or synaptogenesis. © 1992 John Wiley & Sons, Inc.
Environmental influences on neural crest cell migration
Authors: Bronner‐Fraser Marianne 
Published: January 2005

AbstractNeural crest cells migrate extensively and interact with numerous tissues and extracellular matrix components during their movement. Cell marking techniques have shown that neural crest cells in the trunk of the avian embryo migrate through the anterior, but not posterior, half of each sclerotome and avoid the region around the notochord. A possible mechanism to account for this migratory pattern is that neural crest cells may be inhibited from entering the posterior sclerotome and the perinotochordal space. Thus, interactions with other tissue may prescribe the pattern of neural crest cell migration in the trunk. In contrast, interactions between neural crest cells and the extracellular matrix may mediate the primary interactions controlling neural crest cells migration in the head region. © 1993 John Wiley & Sons, Inc.
Symmetrical segregation of potassium channels at cytokinesis
Authors: Lenzi David , Radke Kathryn , Wilson Martin 
Published: January 2005

AbstractTo determine how voltage‐gated ion channels segregate between sibling cells at cytokinesis, we used a whole‐cell patch clamp to measure the electrophysiological phenotypes of siblings within 45 min of division. Recently born siblings in an immortalized line of embryonic retinal cells were identified as pairs of spherical cells adhering to one another. All siblings were electrically coupled when cells were simultaneously voltage clamped, whereas nonsiblings were not coupled. Twelve paris of siblings were electrically isolated by mechanical separation so that their phenotypes could be measured independently. Cells expressed two principal membrane conductances, delayed rectifier‐like (IK) and inward rectifier (IK(IR)) potassium currents. Despite qualitative and quantitative variability in IK and IK(IR) expression within the population, each cell of a given pair expressed similar steady‐state current densities between –110 and +50 mV. We estimated IK(IR) slope conductance by blocking the current specifically with 5 mM Cs and calculated IK(IR) ratios in siblings and nonsiblings. Three pairs of siblings expressed IK(IR) ratios of approximately 1.2, while ratios in three pairs of adhered nonsiblings varied between 1.6 and 5.4. When currents were sampled continuously through cytokinesis by using the perforated‐patch recording mode, current amplitude showed no net change within 30 min of division. Because channel number did not appear to change in siblings during this interval, parental channels were inherited by each daughter in proportion to the area of membrane received. Heterogeneity therefore arises after siblings reenter interphase and is not due to the asymmetrical segregation of channels at cytokinesis. © 1993 John Wiley & Sons, Inc.
Synaptic repression at crayfish neuromuscular junctions. II. Evidence for calcium involvement
Authors: Gupta Anuj , Smith Edward , Vélez Samuel J. 
Published: January 2005

AbstractThe inability of synaptic junctions to generate normalsized postsynaptic potentials under normal physiological conditions was studied at crayfish neuromuscular synapses. Synaptic repression in the superficial flexor muscle system of the crayfish was induced by surgery: the nerve was cut in the middle of the target field, and the lateral muscle fibers were removed. After this surgery, the remaining medial synapses were unable to generate normal‐sized junction potentials (jp) over the medial muscle population. In an attempt to study the mechanism underlying this response, we varied the extracellular calcium concentration of the Ringers solution bathing the preparation, in both repressed and control animals, while monitoring the size of the same junction potential. The junction potential generated by the spontaneous activity of the nerve increased in size with increasing calcium concentrations in control animals, but failed to do so in repressed animals, that is, changes in external calcium concentrations did not affect repressed synapses. However, in the presence of the calcium ionophore A23187, control and repressed synapses both show an increase in the junction potential sizes they generate. Our data suggest that calcium is involved in the mechanisms that underlie synaptic repression in this crustacean neuromuscular system. © 1993 John Wiley & Sons, Inc.
Cues intrinsic to the retina induce nAchR gene expression during development
Authors: Hankin M. H. , Hoover F. , Goldman D. 
Published: January 2005

AbstractRecent studies of optic nerve regeneration in goldfish have indicated that the optic tectum plays an important role in modulating the induction of nicotinic acetylcholine receptor (nAChR) gene expression in regenerating retinal ganglion cells (Hieber, Agranoff, and Goldman, 1992, J. Neurochem. 58:1009–1015). These observations suggest that induction of these genes is regulated by brain target regions. The appearance of nAChR mRNA in the developing rat retina coincides with a time when ganglion cells are sending axons to their brain targets (Hoover and Goldman, 1992, Exp. Eye Res. 54:561–571). Might a mechanism similar to that seen during goldfish optic nerve regenerationalso mediate induction of nAChR gene expression during development of the mammalian retina? This possibility was tested by either transplanting embryonic rat retina to different brain regions, or explanting it to organ culture and assaying for nAChR gene expression. These studies showed that induction of the nAChR genes in developing rat retina is independent of the environment in which the retina develops. These results indicate that either the retinal microenvironment or a signal intrinsic to the retinal ganglion cell is responsible for this induction. © 1993 John Wiley & Sons, Inc.
Effects of development and altered gravity conditions on cytochrome oxidase activity in a vestibular nucleus of the larval teleost brain: A quantitative electronmicroscopical study
Authors: Paulus Ulrike , Körtje Karl‐Heinz , Rahmann Hinrich 
Published: January 2005

AbstractThe mitochondrial enzyme, cytochrome oxidase, was localized cytochemically in the nucleus magnocellularis, a primary relay nucleus of vestibular information within the area octavolateralis in the fish brain. Larvae of the cichlid fish Oreochromis mossambicus were analyzed at different developmental stages (4, 10, and 35 days posthatching) and after long‐term exposure (8 days) to increased gravity (2–4 g). Quantification of highly reactive, moderately reactive, and nonreactive mitochondria reveals differences in the cytochrome oxidase activity of various cellular structures, for example, perikarya of neurons, presynaptic terminals, and myelinated and nonmyelinated cell profiles. Cytochrome oxidase activity in the mitochondria of neuronal perikarya increases during development which parallels the differentiation of the area octavolateralis. This possibly reflects the increasing energy demand during maturation and innervation of the magnocellular nucleus. Hyper‐g‐exposure of the larvae for 8 days (centrifuge) caused a further augmentation of cytochrome oxidase activity in the perikarya within the nucleus magnocellularis. This may reflect an increased oxidative metabolism resulting from the need for compensation of altered inputs from gravity‐sensitive epithelia in the inner ear. Another possibility is that acceleration within a centrifuge causes physiological stress for the animals and, therefore, influences the cytochrome oxidase activity in neurons. © 1993 John Wiley & Sons, Inc.
Different forms of the neurotrophin receptor TrkB mRNA predominate in rat retina and optic nerve
Authors: Jelsma Tony N. , Friedman Hana Hyman , Berkelaar Michelle , Bray Garth M. , Aguayo Albert J. 
Published: January 2005

AbstractThe expression of TrkB mRNAs was investigated in rat retina and optic nerve. A 11.5 kb transcript that encodes full‐length TRKB was found to predominate in Northern blots of retinal RNA. By in situ hybridization, this trkB expression was concentrated in the ganglion cell and inner nuclear layers. Furthermore, an antibody to the full‐length TRKB immunostained retinal ganglion cells and their axons. In contrast, Northern blots of optic nerve RNA showed a prominent 9.5 kb band that encoded a form of the TRKB receptor lacking the tyrosine kinase domain. This species was also detected in both the sciatic nerve and cultured astrocytes and C6 glioma cells. These results suggest that neurons express the full‐length TRKB containing the tyrosine kinase domain, while non‐neuronal cells express the truncated form of the receptor. These two classes of TRKB may mediate different neurotrophic actions in the retina and optic nerve. © 1993 John Wiley & Sons, Inc.
Position, guidance, and mapping in the developing visual system
Authors: Holt Christine E. , Harris William A. 
Published: January 2005

AbstractPositional identity in the visual system affects the topographic projection of the retina onto its central targets. In this review we discuss gradients and positional information in the retina, when and how they arise, and their functional significance in development. When the axons of retinal ganglion cells leave the eye, they navigate through territory in the central nervous system that is rich in positional information. We review studies that explore the navigational cues that the growth cones of retinal axons use to orient towards their target and organize themselves as they make this journey. Finally, these axons arrive at their central targets and make a precise topographic map of visual space that is crucial for adaptive visual behavior. In the last section of this review, we examine the topographic cues in the tectum, what they are, when, and how they arise, and how retinal axons respond to them. We also touch on the role of neural activity in the refinement of this topography. © 1993 John Wiley & Sons, Inc.
Fiber pathways and positional changes in efferent perikarya of 2.5‐to 7‐day chick embryos as revealed with dil and dextran amiens
Authors: Fritzsch B. , Christensen M. A. , Nichols D. H. 
Published: January 2005

AbstractThe differentiation of facial motoneurons and inner ear (octaval) efferents was examined in chicken embryos by applying Dil or dextran amines to the cut VII/VIII nerve (peripheral label) or to the basal/floor plate of rhombomeres 4/5 (central label). Central labeling found axons of these efferent neurons to leave the brain as early as 2.5 days of incubation. Peripheral labeling identified cell bodies ipsilaterally in rhombomeres 4 and 5 at 2.5 days. Central labeling at 3.5 days showed these fibers to have fully segregated into separate pathways to the facial nerve and the inner ear and that the octaval efferent axons had reached the otocyst wall. By 3.5 days many peripherally labeled octaval efferent somata were found in the floor plate and by 5 days they were found bilaterally. At 6 days, selective peripheral labeling of either the VIIth or VIIIthe nerve showed that the contralateral population consisted of octaval efferents and central label applied to the floor plate of rhombomeres 4/5 identified fibers that entered the octaval nerve via the facial root and entered the vestibular sensory epithelia. To gether these data suggest an initial mingling of two different motoneuron populations (facial and octaval) in rhombomeres 4/5 and a subsequent segregation by differential migration. Our data also find a much earlier arrival of octaval efferent axons at the otic vesicle than previously described and suggest a contralateral migration of many octaval efferents beginning shortly after their axons reach the facial nerve root. © 1993 John Wiley & Sons, Inc.
Distinct mode of microtubule‐associated protein 2 expression in the neuroblastoma/glioma cell line 108CC15/NG108‐15
Authors: Beaman‐Hall C. M. , Vallano M. L. 
Published: January 2005

AbstractThe properties of microtubule‐associated protein‐2 (MAP‐2) expression were examined in a transformed cell line, and compared to neurons from rodent brain where evidence supports both transcriptional and nontranscriptional regulation of MAP‐2 synthesis. A monoclonal antibody that recognizes a common epitope in the adult (HMW MAP‐2) and juvenile (MAP‐2c) forms was used in an immunoblotting assay to assess the protein levels in actively dividing and differentiated neuroblastoma/glioma (108CC15, also designated NG108‐15) cells. Multiply‐phosphorylated MAP‐2c was the predominant form in actively dividing cells, whereas HMW MAP‐2 predominated in differentiated cells, which exhibited several other neuronal‐like properties. A progressive increase in the levels of immunoreactive HMW MAP‐2 was observed with increasing days of cell differentiation using dBcAMP as the inducing agent. However, the absolute levels of both HMW MAP‐2 and MAP‐2c in NG108‐15 cells were significantly lower (at least 10‐fold) than levels measured in rodent brain. To assess whether there are correspondingly lower levels of HMW MAP‐2 and MAP‐2c mRNAs in NG108‐15 cells, relative to rodent brain, a highly sensitive RNA amplification assay (reverse transcription‐polymerase chain reaction; RT‐PCR) was developed. Oligonucleotide primers were designed to specify either HMW MAP‐2 mRNA or MAP‐2c mRNA, and whole tissue RNA extracted from adult and neonatal rodent brain was used to verify the reliability of the RT‐PCR assay. Accordingly, PCR products of the predicted size, specificity, and abundance were obtained, with similar levels of HMW MAP‐2 mRNA and proportionately higher levels of MAP‐2c mRNA in neonatal brain, relative to adult brain. MAP‐2c mRNA was the predominant transcript in actively dividing NG108‐15 cells, and the amount of HMW MAP‐2 mRNA gradually increased and became the predominant transcript in cells exposed to dBcAMP for 6–9 days. Thus, the observed changes in MAP‐2‐specific mRNAs during differentiation paralleled changes in expressed protein, suggesting that MAP‐2 synthesis in NG108y15 cells is transcriptionally controlled. However, the levels of both MAP‐2 mRNAs in NG108‐15 cells were comparable to levels in rodent brain, despite the fact that MAP‐2 protein levels are at least 10‐fold lower in NG108‐15 cells. These data suggest that the low levels of HMW MAP‐2 and MAP‐2c protein expression in NG108‐15 cells are not due to correspondingly lower levels of MAP‐2 mRNAs, and that transformed neuronal cell lines demostrate a unique mode of MAP‐2 regulation. © 1993 John Wiley & Sons, Inc.
Neurotrophin‐3 affects proliferation and differentiation of distinct neural crest cells and is present in the early neural tube of avian embryos
Authors: Pinco Ofrit , Carmeli Chana , Rosenthal Arnon , Kalcheim Chaya 
Published: January 2005

AbstractNeurotrophin‐3 is mitogenic for cultured quail neural crest cells (Kalcheim et al., 1992, Proc. Natl. Acad. Sci. USA 89:1661–1665). We now report that neurotrophin‐3 also influences the survival and/or differentiation of a subset of postmitotic neural crest precursors into neurons, provided these progenitors are grown on a cellular substrate. When cultured for 1 day on monolayers of NT‐3‐producing, chinese hamster ovary cells, 59% of the neural crest clusters growing on the transfected line revealed the presence of intense neuronal outgrowht, compared to 25% of that in controls. Moreover, dissociated neural crest cells grown for 20 h on top of mesodermal cells in the presence of various concentrations of purified recombinant neurotrophin‐3 displayed a dose‐dependent increase in neuronal number. Localization experiments using specific polyclonal antibodies, revealed that neurotrophin‐3 is confined to neuroepithelial cells of quail neural tubes in situ on E2 and E3, and to E2 neural tubes grown in culture for 24 h. At this stage, neural crest cells and somites were negative. At later stages, staining was likewise apparent in peripheral nerves and dorsal root ganglia. We, therefore, propose that NT‐3, a factor that is expressed in the early avian central nervous system, has multiple effects both on the proliferation and differentiation of distinct neural crest cells, which depend on the state of committment of the responsive progenitors. © 1993 John Wiley & Sons, Inc.
Cell recognition during synaptogenesis is revealed after temperature‐shock‐induced perturbations in the developing fly's optic lamina
Authors: Fröuhlich A. , Meinertzhagen I. A. 
Published: January 2005

AbstractHouseflies (Musca domestica) were exposed to pulses of heat (1 h) or cold (several hours) during early pupal life, and the effects were investigated on the development of the first optic neuropile, or lamina, of the visual system. The treatments were designed to perturb the cellular or ganization of the cartridges, the unit synaptic structures of the lamina, so as to provide novel synaptic opportunities amongst the normally fixed composition of these modules, thereby testing the preferences of their component cells during synaptogenesis. Various abnormalities were identified, but these were not always consistent between flies: retinal abnormalities included the loss and fusion of rhabdomeres, especially of the central cells of the ommatidium, whereas in the lamina low frequencies of abnormal cartridges were found. These included seven that were studied with serial sections, which instead of the normal pair of L1 and L2 monopolar interneurons had supernumerary cells of this type. The normal pairing of L1 and L2 at postsynaptic sites of receptor terminal tetrad synapses was preserved in these cases, the cells eschewing pairings of homologous L1/L1 or L2/L2 partners. This meant that more than one L1 could pair with a single L2 and vice versa, even at the same terminal, and appeared to do so opportunistically on the basis of proximity, with cells closer to each other pairing more frequently. Thus the cells behave during synaptogenesis as if they recognize other cells only as cell types (receptor, L1 or L2) and not as individual cells. © 1993 John Wiley & Sons, Inc.
Developmental temperature selectively regulates a voltage‐activated potassium current in Drosophila
Authors: Chopra Maninder , Singh Satpal 
Published: January 2005

AbstractIonic currents are regulated by many conditions including disease states, ageing, learning and memory, and chronic drug treatment. Here we describe a novel phenomenon of regulation of ionic currents by developmental temperature. Raising Drosophila larvae at 28°C instead of 18°C increased one of the two voltage‐activated K+‐ currents, the delayed sustained IK, in their muscles by up to 3.5‐fold, with little effect on the early transient current, IA. Consistent with this increase in IK, the amplitude and the duration of the action potentials were reduced. The major increase in IK occurred between a rather abrupt interval from 25° to 28°C. The activation curve of the increased current was shifted towards hyperpolarizing potentials. There was no change in activation kinetics. This phenomenon has mechanistic implications for activity‐dependent neuronal plasticity, expression of ion channels in cultured cells and heterologus systems, phototransduction, and behavior. The specificity of the regulation suggests a discrete mechanism geared to affect excitability such that it can respond to altered external stimuli such as temperature. 1994 John Wiley & Sons, Inc.
Hu neuronal proteins are expressed in proliferating neurogenic cells
Authors: Marusich Michael F. , Furneaux Henry M. , Henion Paul D. , Weston James A. 
Published: January 2005

AbstractWe have utilized immunochemical techniques to investigate the developmental expression of the Hu proteins, a neuron‐specific family of RNA binding proteins in vertebrates. Previous work suggests that these proteins may play an important role in neuronal development and maintenance. For the present study, we developed a monoclonal antibody (MAb 16A11) that binds specifically to an epitope present in gene products of all known Hu genes, including HuD, HuC, and Hel‐N1. Using brief pulses (1–2 h) of the DNA precursor analog bromodeoxyruridine (BrdU) in conjunction with MAb 16A11, we observed Hu+/BrU+ cells in nascent sensory and sympathetic ganglia in vivo, and in populations of cultured neural crest cells. In addition, a few Hu+ cells were ambiguously BrdU+ in the neural tube. We conclude that Hu+ cells first appear in avian neurogenic populations immediately before neuronal birthdays in the peripheral nervous system, and at the time of withdrawal from the mitotic cycle in the central nervous system. Consistent with these conclusions, we have also observed neural crest‐derived cells that are both Hu+ and in metaphase of the cell cycle. We suggest that Hu proteins function early in neurogenic differentiation. 1994 John Wiley & Sons, Inc.