bluuebunny/crossref_metadata_2025_split huggingface dataset:
Agrin induces α‐actinin, filamin, and vinculin to co‐localize with AChR clusters on cultured chick myotubes
Authors: Shadiack Annette M. , Nitkin Ralph M. 
Published: May 2005

AbstractAgrin induces discrete high‐density patches of acetylcholine receptors (AChRs) and other synaptic components on cultured myotubes in a manner that resembles synaptic differentiation. Furthermore, agrin‐like molecules are present at developing neuromuscular junctions in vivo. This provides us with a unique opportunity to manipulate AChR patching in order to examine the role of cytoskeletal components. Cultured chick myotubes were fixed and labeled to visualize the distributions of actin, α‐actinin, filamin, tropomyosin, and vinculin. Overnight exposure to agrin caused a small amount of α‐actinin, filamin, and vinculin to reorganize into discrete clusters. Double‐labeling studies revealed that 78% of the AChR clusters were associated with detectable concentrations of filamin, 70% with α‐actinin, and 58% with vinculin. Filamin even showed congruence to AChRs within clustered regions. By contrast, actin (visualized with fluorescein‐phalloidin) and tropomyosin did not show specific associations with agrin‐induced AChR clusters. The accumulation of cytoskeletal components at AChRs clusters raised the possibility that cytoskeletal rearrangements direct AChR clustering. However, a time course of agrin‐induced clustering that focused on filamin revealed that most of the early AChR clusters (3–6 h) were not associated with detectable amounts of cytoskeletal material. The accumulation of cytoskeletal material at later times (12–18 h) may imply a role in maintenance and stabilization, but it appears unlikely that these cytoskeletal elements initiate AChR clustering on myotubes.
Remodeling of retinal ganglion cell dendrites in the absence of action potential activity
Authors: Wong Rachel O. L. , Herrmann Kathrin , Shatz Carla J. 
Published: May 2005

AbstractThe dendrites of ganglion cells in the retina have an excess number of spines and branches that are normally lost during the first postnatal month of development. We investigated whether this dendritic remodeling can be prevented when the action potential activity of ganglion cells is abolished by chronic intraocular injections of tetrodotoxin (TTX) during the first 4 or 5 postnatal weeks in the cat. Dendritic tree morphologies of alpha and beta ganglion cells from TTX‐treated, non‐TTX‐treated (contralateral eye), and normal control retinae were compared after intracellular filling with Lucifer yellow. Qualitative observations and quantitative measurements indicate that TTX treatment does not prevent the normally occurring loss of spines and dendritic branches. Indeed, the dendritic trees of both alpha and beta cells in TTX injected eyes actually have even fewer spines and branches than normal cells at equivalent ages. However, because the total dendritic lengths of these cells are also reduced after TTX blockade, spine density is indistinguishable from untreated animals at the same age. In addition, although dendritic field areas are not altered with treatment, the complexity of the dendritic trees is reduced. These observations suggest that dendritic remodeling can occur in the absence of ganglion cell action potential activity. Thus, the factors that influence the dendritic and axonal development of retinal ganglion cells must differ, because similar TTX treatment during the period of axonal remodeling does have profound effects on the final pattern of terminal arborizations.
Isolation and partial characterization of neuropeptides that mimic prolonged inhibition produced by bag cell neurons in Aplysia
Authors: Eliassen James C. , Rajpara Sanjay M. , Mayeri Earl 
Published: May 2005

AbstractThe bag cell neurons of the marine mollusk Aplysia are part of a neural system that utilizes four neuropeptides as neurotansmitters. The peptides, derived from the egglaying hormone/bag cell peptide (ELH/BCP) precursor protein, are released during a 20‐min burst discharge of the bag cells and produce several types of responses in various abdominal ganglion neurons. In the identified neurons L3 and L6, bag cell activity produces prolonged inhibition that lasts for more than 2 h. One of the bag cell peptides, alpha‐BCP, mediates an early component of the inhibition in these neurons. To identify the co‐transmitter mediating the prolonged component of inhibition, we purified material from an acid extract of abdominal ganglia using molecular sizing high‐pressure liquid chromatography (HPLC) on TSK 250‐125 followed by two steps of reverse‐phase HPLC on C4 or C18. We isolated three inhibitory factors that mimic the prolonged component of inhibition. Mass spectroscopy and partial amino acid sequence analysis indicate one factor is ELH [2‐36], that is, ELH that lacks the first, N‐terminal amino acid. This inhibitory activity was similar in potency to that of ELH and is the first to be described for an ELH related peptide. The two other factors were approximately 3,300 and 4,700 Da and were effective at 10‐ and 50‐fold lower concentration, respectively, than ELH or its fragment. Amino acid composition analysis suggests that they are not derived from the ELH/BCP precursor protein. The 4,700 Da factor is effective at the lowest concentration and produces an effect that lasts as long as 100 min. Therefore, it is the best candidate for the true inhibitory transmitter. Because the inhibited neurons in nervate the kidney, the function of prolonged inhibition may be to regulate kidney function during egg laying.
Interactions of Schwann cells with neurites and with other Schwann cells involve the calcium‐dependent adhesion molecule, N‐cadherin
Authors: Letourneau Paul C. , Roche Florence K. , Shattuck Terri A. , Lemmon Vance , Takeichi Masatoshi 
Published: May 2005

AbstractDuring embryogenesis, Schwann cells interact with axons and other Schwann cells, as they migrate, ensheath axons, and participate in organizing peripheral nervous tissues. The experiments reported here indicate that the calcium‐dependent molecule, N‐cadherin, mediates adhesion of Schwann cells to neurites and to other Schwann cells. Cell cultures from chick dorsal root ganglia and sciatic nerves were maintained in media containing either 2mM Ca++ or 0.2 mM Ca++, a concentration that inactivates calcium‐dependent cadherins. When the leading lamellae of Schwann cells encountered migrating growth cones in medium with 2 mM Ca++, they usually remained extended, and the growth cones often advanced onto the Schwann cell upper surface. In the low Ca++ medium, the frequency of withdrawal of the Schwann cell lamella after contact with a growth cone was much greater, and withdrawal was the most common reaction to growth cone contact in medium with 2 mM Ca++ and anti‐N‐cadherin. Similarly, when motile leading margins of two Schwann cells touched in normal Ca++ medium, they often formed stable areas of contact. N‐cadherin and vinculin were co‐concentrated at these contact sites between Schwann cells. However, in low Ca++ medium or in the presence of anti‐N‐cadherin, interacting Schwann cells usually pulled away from each other in a behavior reminiscent of contact inhibition between fibroblasts. In cultures of dissociated cells in normal media, Schwann cells frequently were aligned along neurites, and ultrastructural examination showed extensive close apposition between plasma membranes of neurites and Schwann cells. When dorsal root ganglia explants were cultured with normal Ca++, Schwann cells migrated away from the explants in close association with extending neurites. All these interactions were disrupted in media with 0.2 mM Ca++. Alignment of Schwann cells along neurites was infrequent, as were extended close apposition between axonal and Schwann cell plasma membranes. Finally, migration of Schwann cells from ganglionic explants was reduced by disruption of adhesive contact with neurites. The addition of antibodies against N‐cadherin to medium with normal Ca++ levels had similar effects as lowering the Ca++ concentration, but antibodies against the neuronal adhesive molecule, L1, had no effects on interactions between Schwann cells and neurites.
Lack of evidence for cell death among avian spinal cord interneurons during normal development and following removal of targets and afferents
Authors: McKay Sharen E. , Oppenheim Ronald W. 
Published: May 2005

AbstractChick embryos and posthatched chicks were examined at several ages for the presence of pyknotic interneurons in the lumbar spinal cord. Because no pyknotic interneurons were found, direct cell counts of healthy interneurons were carried out and a comparison made between early‐and late‐stage embryos and hatchlings. There was no decrease in the number of interneurons in the ventral intermediate gray matter of the spinal cord between embryonic day (E) 8 and 2 weeks posthatching (PH) or in the dorsal horn between E10 and 2 weeks PH. To study whether interneuron survival is regulated by targets or afferents, a situation known to exist in other developing neural populations, early embryos were subjected to (1) removal of one limb, resulting in the loss of lateral motor column motoneurons and dorsal root ganglion sensory afferents; (2) transection of the thoracic spinal cord, thereby removing both descending afferents and rostral targets of spinal interneurons, or (3) a combination of the two operations. No reductions in interneuron numbers were found as a result of these operations. Furthermore, morphometric analysis also revaled no change in neuronal size following these experimental manipulations. By contrast, there was a slight decrease in the total area of spinal gray matter that was most prominent in the dorsal region following limb bud removal. Our results indicate (1) that spinal interneurons fail to exhibit the massive naturally occurring death of postmitotic neurons that has been observed for several other populations of spinal neurons, and (2) spinal interneurons appear to be relatively resistant to induced cell death following the removal of substantial numbers of afferent inputs and targets.
Clonal cells from embryonic retinal cell lines express qualitative electrophysiological differences
Authors: Lenzi David , Radke Kathryn , Wilson Martin 
Published: May 2005

AbstractCells from the embryonic quail retina were immortalized with the v‐mil oncogene and cloned by limiting dilution. Their phenotype was examined using the whole‐cell patch clamp method. Three membrane currents, Ik(IR), INa and IK, were found at different frequencies within a sample of 170 cells drawn from a large clone. Nearly all combinations of these three markers were found and the frequency of combinations showed that the markers assorted independently. Examination of clones of less than 10 cells showed that heterogeneity originates with a high probability within clones, arguing that chromosomal mutation, for example, is unlikely to account for phenotypic diversity. A possible explanation is that phenotypic differences between cells might reflect the local exchange of instructive signals. If so, then the genes for the three phenotypic markers are controlled independently.
Phosphatases modulate transmission and serotonin facilitation at synapses: Studies with the inhibitor okadaic acid
Authors: Swain James E. , Robitaille Richard , Dass Gavin R. , Charlton Milton P. 
Published: May 2005

AbstractWe examined the role of phosphatases in synaptic transmission using the permeant phosphatase inhibitor okadaic acid (OA). In the crayfish neuromuscular junction (NMJ), postsynaptic effects including increases in input resistance occurred at doses greater than 5 μM OA. At lower doses (0.5–5 μM) the effects were solely presynaptic and transmitter release increased over three‐fold despite small reductions in amplitude and duration of presynaptic action potentials. Potentiating effects of serotonin on transmitter release, Which depend on phosphorylation, were increased by OA. Frequency facilitation was reduced but its decay was not affected. In frog NMJs, OA increased spontaneous and evoked release two‐fold through presynaptic mechanisms. An inactive analog of OA, OA tetra‐acetate, had no effect on transmitter release at frog and crayfish NMJ. Therefore, phosphatases have a strong modulating influence on synaptic transmission.
Reinnervation of murine muscle following fetal sciatic nerve transection
Authors: Mallonga Rosa L. , Ontell Marcia 
Published: May 2005

AbstractA technique is reproted that permits transection of the sciatic nerve of mouse fetuses without interfering with fetal viability. Sciaticotomy was performed on Swiss Webster mice at day 17 of gestation; the contralateral side served as a control. Six weeks later the extensor digitorum longus (EDL) muscles on both sides were injected with horseradish peroxidase (HRP). Examination of the lumbar spinal cord revealed that while a substantial number of motor neurons in the region of the spinal cord giving rise to the sciatic nerve died, the EDL muscle did become reinnervated. The size of the EDL motor neuron pool on the denervated‐reinnervated side was ∼43% of that seen on the control side. While the control EDL motor neuron pool was located in lumbar segments L3–L5, the location of the pool to the denervated‐reinnervated EDL was shifted cranially to L2–L4. Denervated‐reinnervated EDL muscles were analyzed immunohistochemically to study the effect of fetal denervation on the neuronal cell adhesion molecule (N‐CAM) expression. At 2 weeks postnatal, N‐CAM immunoreactivity in control muscle was segregated to the motor end plate region, while fetally denervated muscle continued to express N‐CAM along the length of the sarcolemma. Thus fetally denervated muscle does not develop the same pattern of N‐CAM expression as normal, innervated muscle. By 6 weeks of age, the denervated‐reinnervated muscle showed the same level and distribution of N‐CAM immunoreactivity as did age‐matched control muscle, indicating that most, if not all, of its myofibers had been reinnervated.
The timing of initial neuropeptide expression by an identified insect neuron does not depend on interactions with its normal peripheral target
Authors: Wall John B. , Taghert Paul H. 
Published: May 2005

AbstractTo study the developmental regulation of a neuropeptide phenotype, we have analyzed the biochemical and morphological differentiation of two identifiable neurons in embryos of the moth, Manduca sexta. The central cell, CF, and the peripheral cell, L1, are both neuroendocrine neurons that express neuropeptides related to the molluscan tetrapeptide FMRFamide. Both neurons project axons to the transvers nerve in each thoracic segment. Within the CF and L1 cells, neuropeptide‐like immunoreactivity was localized to secretory granules that had cell specific morphologies and sizes. The onset of neuropeptide expression in the two cell types displayed a similar pattern: immunoreactivity was first detected in distal processes and soon after within cells bodies. However, the onsets occurred at different times: for the CF cell, neuropeptides were first seen at 60%‐63% of embryonic development, after the neuron had extended a long axon into the periphery, while L1 neuropeptide expression began at ∼42%, as it first extended its growth cone. These times were related in that they corresponded to the arrival times of the respective growth cones at a similar position in the developing peripheral nerve. Withinthis region of the nerve, the growth cones of both cell typesexhibited a transient and cell‐specific interaction with an identified mesodermal cell, called the Syncytium. Like the L1 and B neurons (Carr and Taghert, 1988b), the CF growth cones typically grew past this cell, yet remained attached to it by lamellipodial and filopodial processes of the axon. Ultrastructurally, the interaction involved filopodial adhesion to and insertion within the Syncytial cell. Two other nonneuroendocrine cell types grew axons past this same region, but showed no such tendencies. To test the hypothesis that the morphological and biochemical differentiation of these cells was somehow linked, central ganglia were isolated (as individuals or connected as ganglionic chains) in tissue culture, prior to the time when CF growth cones entered the periphery and prior to the development of CF neuropeptide expression. In the majority of cases, CF neurons nevertheless displayed their neuropeptide phenotype at a normal and cell‐specific stage. We conclude that the initiation of neuropeptide expression is highly correlated with schedules of morphological differentiation in these neurons, but that, in the case of the CF neuron, it is not regulated by interactions of the growth cone with peripheral structures.
Tamoxifen's effects on the zebra finch song system are estrogenic, not antiestrogenic
Authors: Mathews Greta A. , Arnold Arthur P. 
Published: May 2005

AbstractAntiestrogens fail to block the masculine ontogeny of the zebra finch song system that is hypothesized to occur as a result of early estrogen action. Moreover, they hypermasculinize the male, and masculinize the female song systems. In experiment 1, we assessed whether these antiestrogenic effects might mimic estrogenic actions. Zebra finch chicks received one of two treatments. They were given estradiol benzoate (EB) or vehicle daily for the first 20 days after hatching and sacrificed at 60 days of age, or they received EB or vehicle for the first 25 days after hatching, at which time they were sacrificed. In the day 60 group, certain attributes of the song system were hypermasculinized in males and masculinized in females by EB, when compared with controls. In the day 25 group, males treated with EB were partially demasculinized, while the females were partially masculinized. In experiment 2, we assessed whether simultaneous treatment with tamoxifen was capable of antagonizing the effects of EB obtained in experiment 1 (day 60 group). Sixty‐day‐old females, previously treated with both EB and tamoxifen for the first 20 days after hatching, had more masculine song regions than females treated with either EB alone or tamoxifen alone. In males, the effects of the combined treatment of EB and tamoxifen over those produced by tamoxifen alone were not as dramatic as in the female. These results are similar to those obtained in systems where tamoxifen is purely estrogenic and suggest that in the song system, tamoxifen acts as an estrogen, not an antiestrogen.
Transient and permanent effects of androgen during synapse elimination in the levator ani muscle of the rat
Authors: Lubischer Jane L. , Jordan Cynthia L. , Arnold Arthur P. 
Published: May 2005

AbstractYoung male rats were castrated at 7 days of age, and treated with testosterone propionate daily from 7 to 34 days of age. At 13 months of age, motor axons and terminals innervating the levator ani (LA) muscle were stained with tetranitroblue tetrazolium (TNBT). The number of separate axons innervating individual muscle fibers was counted, and muscle fiber diameter was measured. Previous studies have shown that this androgen treatment increases muscle fiber diameter and delays synapse elimination, measured as (1) a greater percentage of muscle fibers innervated by multiple axons and (2) larger motor units. The present results indicate that the androgenic effect on synapse elimination is permanent, in that high levels of multiple innervation persisted for 12 months after the end of androgen treatment. In contrast, the effect on muscle fiber diameter was not maintained for this period. This dissociation of androgenic effects on the pattern of innervation from androgenic effects on muscle fiber diameter offers further evidence that the androgenic maintenance of multiple innervation is not dependent on muscle fiber size. In addition, circulating testosterone levels were measured at 50 and 60 days of age in animals similarly treated with androgen or oil from 7 to 34 days of age. By 60 days of age, testosterone levels in hormone‐treated animals had dropped below detectability, comparable to levels in oil‐treated controls. This provides additional evidence that androgen treatment during juvenile development can have permanent effects on the adult pattern of innervation in the LA muscle.
The relationship of intramuscular nerve branching and synaptogenesis to motoneuron survival
Authors: Landmesser Lynn 
Published: May 2005

AbstractThe target has been considered for some time to play a major role in allowing neurons to survive the period of naturally occurring cell death. For the motoneurons that innervate the chick limb, evidence is presented that suggests access to target‐derived trophic factor via intramuscular nerve branches and synapses may be important in regulating neuronal survival. Alterations in branching and synapse formation produced by activity blockade as well as by alteration of adhesion molecule function are shown to result in changes in motoneuron survival consistent with the proposed hypothesis. The relevance of these observations to the numerical‐matching hypothesis of vertebrate neuronal cell death is also considered. © 1992 John Wiley & Sons, Inc.
Cell death and the creation of regional differences in neuronal numbers
Authors: Finlay Barbara L. 
Published: May 2005

AbstractRegional variations in cell death are ubiquitous in the nervous system. In the retina, cell death in retinal ganglion cells is elevated in the retinal periphery and may be important in setting up the initial conditions that produce central retinal specializations such as an area centralis or visual streak. In central visual system structures, pronounced spatial and spatiotemporal inhomogeneities in cell death are seen both in layers and regions of the lateral geniculate nucleus and superior colliculus; similar indications of inhomogeneities are seen in those nonvisual structures that have been examined. Cell death in the cortex is highly nonuniform, by layer and by cortical area. A variety of possible functions for these regional losses are proposed, in the context of a uniform mechanism for cell death that allows it to assume multiple functions. © 1992 John Wiley & Sons, Inc.
Matters of life and death in the songbird forebrain
Authors: Bottjer Sarah W. , Johnson Frank 
Published: May 2005

AbstractMale zebra finches learn a specific vocal pattern during a restricted period of development. They produce that song in stereotyped form throughout adulthood, and are unable to learn new song patterns. Development of the neural substrate for song learning and behavior is delayed relative to other brain regions, and neural song‐control circuits undergo dramatic changes during the period of vocal learning due to both loss of neurons as well as incorporation of newly generated neurons. In contrast, canaries do learn new song patterns in adulthood and modify their vocal repertoires each breeding season. Adult canaries also maintain a large population of dividing cells in the ependymal zone of the telencephalon, and vast numbers of newly generated neurons migrate out to become incorporated into functional circuits and replace older neurons. We review the relationships between cellular and behavioral aspects of song learning in both zebra finches and canaries, as well as the role of gonadal hormones in regulating diverse aspects of the song‐control system. © 1992 John Wiley & Sons, Inc.