bluuebunny/crossref_metadata_2025_split huggingface dataset:
Common and specific inhibition in leg muscles of decapods: Sharpened distinctions
Authors: Wiens Theodore J. 
Published: January 2005

AbstractCrustaceans are characteristically parsimonious in their neuromuscular innervation. In extreme instances, a single efferent axon, excitatory or inhibitory, may innervate two or more muscles that have totally different actions. In particular, the inhibitory axons of the reptantian decapod leg have been reported, in various studies within four different infraorders, to innervate anywhere from one to all seven of the leg's distal muscles and to vary in number from two to four. These axons' often inexplicable combinations of target muscles have in many cases precluded interpretation of their behavioral significance. Recent findings reviewed in this paper suggest that in fact all reptants share the same three inhibitory axons: one is a universal common inhibitor, making synaptic connections within all leg muscles; the other two are specific (single‐target) inhibitors of the opener and stretcher muscles, respectively (muscles which share a single excitatory axon as their sole source of activation even though they act on different joints). The literature suggests two distinct roles in the control of limb movement for these two classes of inhibitors.
Addition of song‐related neurons in swamp sparrows coincides with memorization, not production, of learned songs
Authors: Nordeen K. W. , Marler P. , Nordeen E. J. 
Published: January 2005

AbstractDuring song learning in birds, neurons are added to some song nuclei and lost from others. Previous studies have been unable to distinguish whether these neural changes are uniquely associated with memorizing a song model (sensory acquisition) or vocal practice (sensorimotor learning). In this study we measured changes in neuron number within song nuclei of swamp sparrows, a species in which the two phases of song learning are nonoverlapping. Male swamp sparrows were collected as hatchlings and tape‐tutored from approximately 22 to 62 days of age. Swamp sparrows memorize about 60% of their song material during this period, but do not begin practicing this learned material until approximately 275 days of age. Birds were sacrificed at 23, 41, 61, 71, 274, or 340 days of age. During sensory acquisition, neuron number increased drastically in both the caudal nucleus of the ventral hyperstriatum (HVc) and Area X. The period of sensorimotor learning was not associated with any further changes in neuron number within these regions. We were unable to detect any significant changes in neuron number within the magnocellular nucleus of the neostriatum or the robust nucleus of the archistriatum during either stage of song learning. These results raise the possibility that ongoing addition of HVc and Area X neurons may encourage, and thereby temporally restrict, song acquisition.
Establishment and characterization of multipotent neural cell lines using retrovirus vector‐mediated oncogene transfer
Authors: Ryder Elizabeth F. , Snyder Evan Y. , Cepko Constance L. 
Published: January 2005

AbstractNeural cell lines were produced by retroviral vector‐mediated transduction of the avian myc oncogene. Target cells were mitotic progenitor cells of postnatal mouse olfactory bulb and cerebellum, and postnatal rat cerebral cortex. Infection of the first two areas, where neurogenesis and gliogenesis occur postnatally, produced multipotent clonal lines that exhibited phenotypes of both neuronal and glial cells, and one line with a stable neuronal phenotype. Infection of cerebral cortex, where gliogenesis, but not neurogenesis, occurs postnatally, generated mortal clones that exhibited cells of glial phenotype. These lines should prove valuable for both in vitro and in vivo studies aimed at understanding the control of cell fate and differentiation of neural progenitors.
Examination of paralysis in Drosophila temperature‐sensitive paralytic mutations affecting sodium channels; a proposed mechanism of paralysis
Authors: Nelson James C. , Wyman Robert J. 
Published: January 2005

AbstractWe have used the identified cells of the Drosophila Giant Fiber System (GFS) to study the defects induced by the temperature‐sensitive paralytic mutations no action potential (nap) and paralytic (para). These mutations paralyze at elevated temperatures, reported as due to a block of action potential propagation. We found, however, that the cells of the GFS still were able to respond to stimuli at 7–10°C above the temperature causing mutant paralysis. Stimulus threshold and conduction time both decrease with increasing temperature in the mutants in a manner indistinguishable from wild‐type. Since action potentials can propagate efficiently in the mutants at elevated temperatures, we looked for other neural defects that might be involved in producing paralysis. We did find reduced neuronal function at sites such as electrical synapses and axonal branch points where current may be limiting. These sites had weakened following frequency, occasional failures, and increased conduction times. We believe the non‐temperature‐dependent defects in nap and para uncover the normally temperature‐sensitive traits latent within all neurons. Increasing temperature increases the rates of channel activation and inactivation. At higher temperatures, Na+ inactivation and K+ activation encroach upon the Na+‐activation time, reducing inward sodium current. In addition to this normal temperature‐dependent effect, the mutations decrease the number of sodium channels in neurons in a non‐temperature‐dependent manner. These two reductions in sodium current combine to prevent spiking threshold from being reached at current limited sites. The temperature at which a sufficient number of these sites block should be the temperature of paralysis.
Embryonic development and evolutionary origin of the orthopteran auditory organs
Authors: Meier Thomas , Reichert Heinrich 
Published: January 2005

AbstractTwo different types of ears characterize the order of Orthopteran insects. The auditory organs of grasshoppers and locusts (Caelifera) are located in the first abdominal segment, those of bushcrickets and crickets (Ensifera) are found in the tibiae of the prothoracic legs. Using neuron‐specific antibody labelling, we describe the ontogenetic origin of these two types of auditory organs, use comparative developmental studies to identify their segmental homologs, and on the basis of homology postulate their evolutionary origin. In grasshoppers the auditory receptors develop by epithelial invagination of the body wall ectoderm in the first abdominal segment. Subsequently, at least a part of the receptor cells undergo active migration and project their outgrowing axons onto the next anterior intersegmental nerve. During this time the receptor cells and their axons express the cell‐cell adhesion molecule, Fasciclin I. Similar cellular and molecular differentiation processes in neighboring segments give rise to serially homologous sensory organs, the pleural chordotonal organs in the pregenital abdominal segments, and the wing‐hinge chordotonal organs in the thoracic segments. In more primitive earless grasshoppers pleural chordotonal organs are found in place of auditory organs in the first abdominal segment. In bushcrickets the auditory receptors develop in association with the prothoracic subgenual organ from a common developmental precursor. The auditory receptor neurons in these insects are homologous to identified mechanoreceptors in the meso‐ and metathoracic legs. The established intra‐ and interspecies homologies provide insight into the evolution of the auditory organs of Orthopterans.
Extraretinal photoreceptors in the brain of the crayfish Cherax destructor
Authors: Sandeman D. C. , Sandeman R. E. , De Couet H. G. 
Published: January 2005

AbstractTwo clusters of red‐brown pigmented cell somata lie among other cell somata along the anterior margin of the cerebral ganglion in the crayfish Cherax destructor. Electron micrographs show these cells to contain round electron dense pigment granules and that the cell membranes of two or more adjacent cells fold together to form rhabdom‐like structures. The pigmented cells specifically bind a monoclonal antibody against the major species of opsin in R1–7 retinula cells of the compound eye of Cherax. When stimulated with light, the pigmented cells respond with a receptor potential‐like depolarization. The axons of the pigmented cells terminate in the neuropil of the protocerebral bridge, together with neuronal elements that label with antibodies against serotonin and substance P. We suggest that the brain photoreceptors of the crayfish are important in the entrainment of circadian rhythms.
The effects of systemic androgen treatment on androgen accumulation in song control regions of the adult female canary brain
Authors: Brenowitz Eliot A. , Arnold Arthur P. 
Published: January 2005

AbstractSystemic treatment of adult female canaries (Serinus canarius) with testosterone (T) induces song and increases the size of song control regions (SCRs) in the brain. We used autoradiographic techniques to determine whether systemic T treatment also changes the accumulation of tritiated T or its metabolites by SCR cells. T treatment did not change the proportion of T target cells in SCRs, nor did it change the degree of cellular accumulation of T or its metabolites. Neuronal density was not altered by T treatment in any SCR sampled. In HVc (caudal nucleus of the ventral hyperstriatum) and RA (robust nucleus of the archistriatum), cell size did not differ between T‐treated and control females. However, systemic T did increase the mean sizes of labelled cells and of all cells sampled in MAN (magnocellular nucleus of the anterior neostriatum). The results support the hypothesis that the induction of song in female canaries by T relates to increases in the absolute numbers of neurons and of T target neurons in SCRs.
Metamorphosis of the central nervous system of Drosophila
Authors: Truman James W. 
Published: January 2005

AbstractThe study of the metamorphosis of the central nervous system of Drosophila focused on the ventral CNS. Many larval neurons are conserved through metamorphosis but they show pronounced remodeling of both central and peripheral processes. In general, transmitter expression appears to be conserved through metamorphosis but there are some examples of possible changes. Large numbers of new, adult‐specific neurons are added to this basic complement of persisting larval cells. These cells are produced during larval life by embryonic neuroblasts that had persisted into the larval stage. These new neurons arrest their development soon after their birth but then mature into functional neurons during metamorphosis. Programmed cell death is also important for sculpting the adult CNS. One round of cell death occurs shortly after pupariation and a second one after the emergence of the adult fly.
Social control of neuronal soma size
Authors: Davis Mark R. , Fernald Russell D. 
Published: January 2005

AbstractFactors responsible for sexual maturation differ significantly among vertebrate species. In many, age is most important, whereas in others seasonal or social cues play a central role. Here we report that maturation in the African cichlid fish Haplochromis burtoni is socially controlled, and that this control includes regulation of soma growth in a population of preoptic neurons immunoreactive to gonadotropin‐releasing hormone (irGnRH). Males reared in aquaria among fish of the same age mature sexually in about 3 months, whereas males reared in the presence of older, more aggressive conspecifics remain immature even at 5 months of age. Immature males display hypogonadism and have conspicuously undersized preoptic irGnRH neurons in comparison to those of mature siblings of the same age. This variable maturation rate increases the likelihood that individual males will survive to an age when they can successfully reproduce.
Lesions of HVc block the developmental masculinizing effects of estradiol in the female zebra finch song system
Authors: Herrmann Kathrin , Arnold Arthur P. 
Published: January 2005

AbstractThe neural song control system of female zebra finches is permanently masculinized if the females are given estradiol within 1 month after hatching. One hypothesis is that estradiol acts on neurons in the caudal nucleus of the ventral hyperstriatum (HVc) to cause developmental changes that lead to masculinizing influences in other song control regions. To test whether lesions of HVc block the masculinizing effects of estradiol elsewhere in the song system, we gave 20‐day‐old females either a Silastic pellet containing estradiol or no implant, and they received either a unilateral lesion of HVc or no lesion. At 60 days of age, they were sacrificed. The volumes of brain regions and sizes of neurons were measured in four song nuclei: HVc, robust nucleus of the archistriatum (RA), lateral magnocellular nucleus of the neostriatum (lMAN), and Area X. Lesions of HVc blocked the masculinizing effects of estradiol on RA and Area X on the side of the lesion. Thus, HVc must be intact in order for estradiol to masculinize these two nuclei. This observation is compatible with the hypothesis that estradiol acts on or near HVc to masculinize several song nuclei, although other interpretations are also possible.
Formation of the retinal ganglion cell and optic fiber layers
Authors: Watanabe Michiko , Rutischauser Urs , Silver Jerry 
Published: January 2005

AbstractThe early development of retinal ganglion cell and the optic fiber layers has been studied by examining the morphology of differentiating retinal ganglion cells using immunoelectron microscopy and a monoclonal antibody against neuron‐specific beta‐tubulin. This antibody identified retinal ganglion cells during the stages of their most active differentiation and axonogenesis prior to maturation of other retinal neurons. The changing morphology of retinal ganglion cells during these early stages is consistent with a differentiation sequence in which axonogenesis and translocation of the cell body to the vitreal surface occur while the cell is still attached to the vitreal margin through its vitreal endfeet. Thus, the mechanis of retinal ganglion cell axon generation and soma migration to the vitreal surface appears to invove maintenance of this attachment which may act as both a focus for axon differentiation and an anchor for directed nuclear translocation to the vitreal margin.
Regional specificity of developing reticulospinal, vestibulospinal, and vestibulo–ocular projections in the chicken embryo
Authors: Glover Joel C. , Petursdottir Gudrun 
Published: January 2005

AbstractThe regional mapping of reticulospinal, vestibulospinal, and vestibulo–ocular neuron groups onto specific axonal pathways was determined in the chicken embryo by retrograde axonal tracing. Experiments were performed on in vitro preparations of the brain stem to allow for precisely localized tracer injections combined with selective lesions of axon tracts. Brain‐stem neuron groups were labelled from 3 days of embryonic development, when the first reticulospinal axons reached the cervical spinal cord, to 9 days of embryonic development, when each of the three systems studied had acquired a relatively mature organization. A striking feature at all stages was the spatial segregation of many neuron groups that projected along different trajectories. Examples of such segregation were found for neuron groups projecting in the same tract on different sides of the brain stem, in different tracts on the same side of the brain stem, and rostrally versus caudally. The occurrence of this segregation from early stages suggests that the choice of projection pathway by many brain‐stem neurons is in some way linked to cell position. In some regions of the brain stem, neuron groups projecting along different pathways are intermingled. At least some of this intermingling, however, appars to occur subsequent to the initial establishment of axon projection patterns.Comparison of the mapping patterns at progressively older stages, and with previous mapping in the 11‐day‐old embryo (Glover and Petursdottir, 1988; Petursdottir, 1990) suggests that these projections are established with little error. The one obvious example of remodelling involved the pontine reticulospinal projection, in which an early contralateral axon population appeared to retract from spinal to medullary levels over the course of a few days. A similar phenomenon may be involved in the elimination of part of the contralateral reticulospinal projection from the midmedulla.
Nerve growth factor (NGF) induces sprouting of specific neurons of the snail, Lymnaea stagnalis
Authors: Ridgway R. L. , Syed N. I. , Lukowiak K. , Bulloch A. G. M. 
Published: January 2005

AbstractNerve growth factor (NGF) was examined for its ability to elicit sprouting by adult molluscan neurons. Motoneurons and interneurons (but not neurosecretory cells) from Lymnaea exhibited a sprouting response to murine 2.5S NGF in defined medium with a half‐maximal response at about 150 ng/mL. Furthermore, an NGF antiserum blocked sprouting by all normally responsive neurons. We tested whether an NGF‐like molecule is a component of conditioned medium (CM) by attempting to preabsorb its sprout‐inducing activity with NGF antiserum. Treatment of CM with immune (but not nonimmune) serum largely blocked the response of motoneurons, but not that of neurosecretory cells, to CM. We conclude that NGF exerts neurotrophic activity on specific adult Lymnaea neurons, and suggest the possibility that an NGF‐like molecule may exist in the molluscan nervous system.
Cell lines derived from mouse neural crest are representative of cells at various stages of differentiation
Authors: Murphy Mark , Bernard Ora , Reid Kate , Bartlett Perry F. 
Published: January 2005

AbstractIn order to study mammalian neural crest differentiation in vitro, a series of clonal neural crest (NC) cell lines have been generated by infection of migrating mouse neural crest cells with two recombinant retroviruses containing either the c‐myc or N‐myc proto‐oncogenes. Many cell lines were generated which could be subdivided into three groups based on their appearance in culture. Eleven of these cell lines representative of each of the morphological groups were characterized for the expression of six antigenic markers expressed by neural cells. In addition, mRNA was prepared from these cell lines and analyzed for the expression of a number of neural specific genes. These analyses show that the cell lines are representative of the following cell types: (1) neural crest‐like cell lines that do not differentiate in 10% serum; (2) progenitor cell lines, some of which can partially differentiate in culture; and (3) mature neuronal cell lines or bipotential cell lines. Southern blot analysis of DNA from these lines indicated that they have multiple integration sites for the provirus and suggest that phenotypically different cell types have arisen from a single cell. None of the cell lines showed any proliferative or morphological response to nerve growth factor (NGF), whereas over two‐thirds of the lines showed both marked proliferative and morphological responses to fibroblast growth factor (FGF). These data indicate that we have generated a range of cell lines representative of a spectrum of mouse neural crest derivatives.
Transfer of molecules from glia to axon in the squid may be mediated by glial vesicles
Authors: Buchheit T. E. , Tytell M. 
Published: January 2005

AbstractAlthough the transfer of glial proteins into the squid giant axon is well documented, the mechanism of the transfer remains unknown. We examined the possibility that the transfer involved membrane‐bound vesicles, by taking advantage of the fact that the fluorescent compound, 3,6‐acridinediamine, N,N,N,',N'‐tetramethylmonohydride [acridine orange (AO)], rapidly and selectively stains vesicular structures in glial cells surrounding the giant axon. We labeled cleaned axons (1–3 cm long) by incubation for 1 min in filtered seawater (FSW) containing AO. Because the AO was concentrated in glial vesicular organelles, these fluoresced bright orange when the axon was examined by epifluorescence microscopy. To look for vesicle transfer, axoplasm was extruded from such AO‐treated axons at various times after labeling. During the initial 15 min, an increasing number of fluorescent vesicles were observed. No further increases were observed between 15 and 60 min post AO. The transfer of the fluorescent vesicles into the axoplasm seemed to be energy dependent, as it was inhibited in axons treated with 2 mM KCN. These results suggest that a special mode of exchange exists between the adaxonal glia and the axon, perhaps involving phagocytosis by the axon of small portions of the glial cells.
Neurite outgrowth on a step gradient of chondroitin sulfate proteoglycan (CS‐PG)
Authors: Snow Diane M. , Letourneau Paul C. 
Published: January 2005

AbstractSulfated proteoglycans (PGs) may play a significant role in the regulation of neurite outgrowth. They are present in axon‐free regions of the developing nervous system and repel elongating neurites in a concentration‐dependent manner in vitro. The addition of growth‐promoting molecules, such as laminin, can modify the inhibitory effect of PGs on neurite outgrowth (Snow, Steindler, and Silver, 1990b). Substrata containing a high‐PG/low‐laminin ratio completely inhibit neurite outgrowth, while normal, unimpeded outgrowth is observed on low‐PG/high‐laminin substrata. Therefore, different patterns of neurite outgrowth may result from regulation of the ratio of growth‐promoting molecules to growth‐inhibiting molecules. Using video microscopy, embryonic chicken dorsal root ganglia neurons (DRG), chicken retinal ganglia neurons (RGC), and rat forebrain neurons (FB) were analyzed as they extended processes from a substratum consisting of laminin alone onto a step gradient of increasing concentrations of chondroitin sulfate proteoglycan (CS‐PG) bound to laminin. In contrast to neurite outgrowth inhibition that occurs at the border of a single stripe of high concentration of CS‐PG (Snow et al., 1990b and this study), growth cones grew onto and up CS‐PG presented in a step‐wise graded distribution. Although the behavior of the different cell types was unique, a common behavior of each cell type was a decrease in the rate of neurite outgrowth with increasing CS‐PG concentration. These data suggest that appropriate concentrations of growth‐promoting molecules combined with growth‐inhibiting molecules may regulate the direction and possibly the timing of neurite outgrowth in vivo. The different responses of different neuronal types suggest that the presence of sulfated PG may have varying effects on different aspects of neuronal development.