bluuebunny/crossref_metadata_2025 huggingface dataset:
Regeneration restores some of the altered electrical properties of axotomized bullfrog B‐cells
Authors: Kelly M. E. M. , Bisby M. A. , Lukowiak Ken
Published: January 2005

In bullfrog B‐type sympathetic neurones axon injury produces substantial changes in somal membrane properties. These include a shortening of action potential afterhyperpolarization (AHP) and an increase in action potential (AP) duration. In the present experiments we compared two injury situations: nerve crush, which was followed by regeneration, and nerve cut, after which regeneration to the original target was prevented, to investigate whether these electrophysiological changes were related to axon regeneration. Both crush and cut injuries produced a similar maximum decrease in AHP duration (to 33 and 30%) by 14 days after axotomy. After nerve crush, AHP duration recovered to within control values by 42 days, while after cut it remained depressed. AHP amplitude decreased to the same extent after nerve crush or cut (to 62 and 58%), but the rate of decrease was slower following crush when compared with cut, and following both types of injury it still remained depressed at 42 and 49 days. Changes in AP duration also took longer to occur following nerve crush, reaching maximal values at 35–42 days, at which time AHP duration had returned to within the normal range. The early reduction in AHP duration and its rapid recovery in regenerating neurones suggests that the current underlying this membrane property is regulated by events associated with axon outgrowth and peripheral reconnection. In contrast, changes in AHP amplitude and AP repolarization appeared to be independent of the occurrence of axon regeneration and remained abnormal at 49 days despite the recovery of AHP duration. These results imply that the electrophysiological changes seen in B‐cells following injury are differentially regulated during subsequent regeneration.
Activation of DUM cell interneurons by ventral giant interneurons in the cockroach, periplaneta americana
Authors: Pollack Alan J. , Ritzmann Roy E. , Westin Joanne
Published: January 2005

Dorsal unpaired median (DUM) cells in orthopteran insects are known to contain the neuromodulatory substance octopamine, and DUM cells with peripheral axons augment synaptic activity at neuromuscular junctions. One of the most studied systems in the cockroach is the giant interneuron (GI) system which controls the initial movements of a wind‐ mediated escape response. Our data demonstrate that DUM cells that are restricted to the central nervous system (DUM interneurons) receive inputs from ventral giant interneurons (vGIs) but not from dorsal giant interneurons (dGIs). In contrast, DUM cells that have peripheral axons consistently fail to be excited by any giant intereurons. The DUM interneurons are excited by vGIs on both sides of the CNS and, when the vGIs are excited in pairs, summation occurs. Wind fields that have been generated for two of the DUM interneurons are omnidirectional. These data, taken along with the known association of DUM cells with the neuromodulatory substance octopamine, suggest that the DUM interneurons may act to modulate central synapses.
Common and specific inhibition in leg muscles of decapods: Sharpened distinctions
Authors: Wiens Theodore J.
Published: January 2005

Crustaceans 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

During 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

Neural 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

We 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

Two 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

Two 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

Systemic 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

The 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

Factors 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

The 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

The 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

The 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

Nerve 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

In 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

Although 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

Sulfated 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.
Castration and antisteroid treatment impari vocal learning in male zebra finches
Authors: Bottjer Sarah W. , Hewer Samantha J.
Published: January 2005

Both song behavior and its neural substrate are hormone sensitive: Castrated adult male zebra finches need replacement of gonadal steroids in order to restore normal levels of song production, and sexsteroids are necessary to establish male‐typical neural song‐controlcircuits during early development. This pattern of results suggests that hormones may be required for normal development of learned songbehavior, but evidence that steroids are necessary for normal neuraland behavioral development during song learning has been lacking. Weaddressed this question by attempting to eliminate the effects of gonadal steroids in juvenile male zebra finches between the time of initial song production and adulthood. Males were castrated at 20 daysof age and received systemic implants of either an antiandrogen (flutamide). an antiestrogen (tamoxifen), or both drugs. The songs of both flutamide‐and tamoxifen‐treated birds were extremely disrupted relative to normal controls in terms of the stereotypy and acoustic quality of individual note production, as well as stereotypy of the temporal structure of the song phrase. We did not discern any differences in the pattern of behavioral disruption between birds that were treated with either flutamide, tamoxifen, or a combination of both drugs. Flutamide treatment resulted in a reduced size of two forebrain nuclei that are known to play some role unique to early phases of song learning [lateral magnocellular nucleus of the anterior neostriatum (IMAN) and area X (X)], but did not affect the size of two song‐control nuclei that are necessary for normal song productionin adult birds [caudal nucleus of the ventral hyperstriatum (HVc) and robust nucleus of the archistriatum (RA)]. In contrast, treatment with tamoxifen did not result in any changes in the size of song‐control nuclei relative to normal controls, and it blocked the effects of flutamide on the neural song‐control system in birds that were treated with both drugs. Castration and antisteroid treatment exerted no deleterious effects on the quality of song behavior in adult birds, indicating that gonadal hormones are necessary for the development of normal song behavior during a sensitive period. © 1992 John Wiley & Sons, Inc.
Consequences of slow wallerian degeneration for regenerating motor and sensory axons
Authors: Brown M. C. , Lunn E. R. , Perry V. H.
Published: January 2005

The time course of Wallerian degeneration in the tibial and saphenous nerves was compared in Balb/c mice and mice of the C57BL/Ola strain (Lunn et al., 1989). Axons, particularly myelinated ones, in nerves of C57BL/Ola mice are very slow to degenerate, many still being present 3 weeks after axotomy. Nuclear numbers in the distal stump peak much later and do not reach the levels found in Balb/c mice; debris removal is very slow, and Schwann cell numbers only rise slightly above normal levels in the long term. Regeneration was investigated electrophysiologically and by electron microscopy (EM). Myelinated sensory axons regenerated slowly and incompletely compared with motor ones which were only slightly slowed after nerve crush (although they were significantly hindered after nerve section). Total myelinated axon numbers were still some 20% less than normal even after 200 days in sensory nerves. Even after all axons had degenerated in C57BL/Ola mice, regeneration rates of neither myelinated nor unmyelinated sensory axons reached those achieved in Balb/c mice. It is concluded that while regeneration can eventually proceed slowly when Wallerian degeneration is much delayed, the usual rapid time course of Wallerian degeneration is necessary if axons, particularly sensory ones, are to regenerate at optimal rates and to maximum extent. Whilelocal obstruction to axon growth probably impedes the early phase ofregeneration in C57BL/Ola mice, it seems possible that a lack of adequate early signals affects regeneration permanently by minimizing the cell body reaction to injury. © 1992 John Wiley & Sons, Inc.
Development of gabaergic connections in vitro: Increasing efficacy of synaptic transmission is not accompanied by changes in miniature currents
Authors: Kraszewski K. , Grantyn R.
Published: January 2005

Development of inhibitory synaptic transmission was studied using a dissociated cell culture from the superior colliculus of neonatal rat. Patch‐clamp recordings in the whole‐cell configuration were performed to measure evoked (single‐cell‐activated) inhibitory postsynaptic currents (IPSCs), miniature IPSCs and current responses to maximal concentrations of exogenous γ‐aminobutyric acid (GABA). Over a period of 3 weeks in vitro (DIV3‐24), the fraction of synaptically coupled neurons raised from 0% to 76%. Evoked IPSCs were first observed at DIV5. They had an average amplitude of 33.9 pA during the first week (n = 13) and 129.7 pA during the fourth week (n = 48). This increase by a factor of 3.8 represents a significant rise in the efficacy of GABAergic transmission during in vitro development. However, no developmental change has been observed in the average amplitudes of miniature somatic IPSCs. The latter remained at an average level of about 9 pA (symmetrical chloride concentration and a driving force of 68 mV). No increase was found also in whole‐cell current densities induced by saturating concentrations of exogenous GABA. Our results suggest that under the given conditions, synapse maturation was primarily the result of presynaptic sprouting. This conclusion is further supported by bouton counts in immunostained collicular cultures, where the number of axosomatic and axodendritic GABAergic contacts per neuron increased from 0.54 and 0.37, respectively, at DIV3, to 13.84 and >23.1, at DIV24. The overall density of GABAergic neurons decreased during this period from about 41,000/cm2 to 15,600 cm2, indicating that a growing number of contacts is formed by a declining number of presynaptic neurons. © 1992 John Wiley & Sons, Inc.
Establishment of mouse‐immortalized hybrid clones expressing characteristics of differentiated neurons derived from the cerebellar and brain stem regions
Authors: Satoh Jun‐Ichi , Gallyas Ferenc , Endoh Masumi , Yamamura Takashi , Kunishita Tatsuhide , Kobayashi Takayoshi , Tabira Takeshi
Published: January 2005

Two clonal immortalized neurons designated CL8c47 and CL8a5.2 were established by somatic cell fusion between a hypoxanthine phosphoribosyltransferase (HPRT−) deficient neuroblastoma N18TG2 and newborn mouse cerebellar/brain stem neurons. In the serum‐containing medium without extra differentiating agents, both clones exhibited a morphology of differentiated neurons. They contained high levels of glutamate but no gamma‐aminobutyric acid (GABA). The CL8a5.2 clone synthesized choline aceryltransferase and serotonin. In immunocytochemical studies, both clones expressed 200 kD neurofilament protein neuron‐specific enolase, microtubule‐associated protein 2 (MAP2), tau protein, neuronal cell adhesion molecule (N‐CAM), HNK‐1, Thy‐1.2, saxitoxin‐binding sodium channel protein, and glutamate. Synaptophysin immunoreactivity was identified in the neuritic terminals of CL8c4.7 cells. Most of these antigens were barely detectable on N18TG2 cells. Electrophysiologically, both clones generated action potentials in response to electrical stimuli. The hybrid clones that express characteristics of differentiated neurons derived from the cerebellar and brain stem regions might be invaluable for the study of the molecular basis of neuronal differentiation and degeneration in these regions. © 1992 John Wiley & Sons, Inc.
GAP‐43 phosphorylation is dynamically regulated in individual growth cones
Authors: Dent Erik W. , Meiri Karina F.
Published: January 2005

In vivo, kinase C phosphorylation of the growth‐associated protein GAP‐43 is spatially and temproally associated with the proximity of growing axons to their targets. Here we have used dissociated dorsal root ganglia (DRG)s and an antibody specific for the phosphorylated form of GAP‐43 to demonstrate that neurite regeneration in culture also begins in the absence of detectable levels of phosphorylated GAP‐43. Since the β isoform of kinase C was found to be enriched in growth cones before stably phosphorylated GAP‐43 was detected, it may normally be inactive during initial neurite outgrowth; however, premature phosphorylation of GAP‐43 could be stimulated in newly dissociated DRGs by plating them on cultures in which phosphorylation had already been initiated; media conditioned by such cultures caused no response suggesting an effect of either cell‐cell or cell‐substrate contact. Increased GAP‐43 phosphorylation correlated with a reduced extent of neurite outgrowth but not with the rate at which individual growth cones translocated so that motile growth cones contained very low levels of phosphorylated GAP‐43, whereas stationary growth cones showed much more immunoreactivity. Downregulation of kinase C by phorbol ester prevented increased GAP‐43 phosphorylation and led to growth cone collapse. Finally, phosphorylated GAP‐43 was found to be differently distributed within growth cones. Increased immunoreactivity was frequently observed in the neck of the growth cone and was heterogeneously distributed in lamellae and filopodia. These results, which demonstrate the dynamic regulation of GAP‐43 phosphorylation in individual growth cones, are discussed with reference to the association between changes in growth cone shape and the ability to translocate and change direction. © 1992 John Wiley & Sons, Inc.
Mechanism of inhibitory action of capsaicin on particulate axoplasmic transport in sensory neurons in culture
Authors: Kawakami Tadashi , Hikawa Naoshi , Kusakabe Tatsumi , Kano Masato , Bandou Yoko , Gotoh Hideki , Takenaka Toshifumi
Published: January 2005

The inhibitory effect of capsaicin on axoplasmic transport in cultured dorsal root ganglion cells was analyzed by video‐enhanced contrast microscopy. Capsaicin inhibited particle transports in a dose‐dependent manner, irrespective of the diameter of axons. The effect of capsaicin was reversible at low concentrations. Capsaicin affected both the anterograde and retrograde transport. Large organelles were more sensitive to capsaicin than small ones in the retrograde transport. An experiment using calcium‐sensitive dye, Fura 2, indicated that capsaicin raised the intraneuronal free calcium concentration preceding the inhibition of the transport. Electron microscopy revealed that microtubules and neurofilaments are disorganized and disoriented by capsaicin. We reached a conclusion that capsaicin inhibits fast axoplasmic transport of both anterograde and retrograde directions in all types of somatosensory neurons in culture by disorganizing intraaxonal cytoskeletal structures, through the elevated intracellular Ca2+ concentration. © 1993 John Wiley & Sons, Inc.
Approaches to identify genes involved in Drosophila embryonic CNS development
Authors: Noll Elizabeth , Perkins Lizabeth A. , Mahowald Anthony P. , Perrimon Norbert
Published: January 2005

Many of the steps involved in formation of the Drosophila embryonic central nervous system (CNS) have been identified by both descriptive and experimental studies. In this review we will describe the various approaches that have been used to identify molecules involved in CNS development and the advantages and disadvantages of each of them. Our discussion will by no means be exhaustive; but rather we will discuss our experiences with each approach and provide an overview of what has been learned by using these methodologies. Finally, we will discuss methods that have been recently developed and how they are likely to provide further insight into CNS development. © 1993 John Wiley & Sons, Inc.
Cellular mechanisms governing synaptic development in Drosophila melanogaster
Authors: Keshishian Haig , Chiba Akira , Chang Te Ning , Halfon Marc S. , Harkins Elizabeth W. , Jarecki Jill , Wang Lansheng , Anderson Marydilys , Cash Sydney , Halpern Marnie E. , Johansen Jørgen
Published: January 2005

The neuromuscular connections of Drosophila are ideally suited for studying synaptic function and development. Hypotheses about cell recognition can be tested in a simple array of pre‐and postsynaptic elements. Drosophila muscle fibers are multiply innervated by individually identifiable motoneurons. The neurons express several synaptic cotransmitters, including glutamate, proctolin, and octopamine, and are specialized by their synaptic morphology, neurotransmitters, and connectivity. During larval development the initial motoneuron endings grow extensively over the surface of the muscle fibers, and differentiate synaptic boutons of characteristic morphology. While considerable growth occurs postembryonically, the initial wiring of motoneurons to muscle fibers is accomplished during mid‐to‐late embryogenesis (stages 15–17). Efferent growth cones sample multiple muscle fibers with rapidly moving filopodia. Upon reaching their target muscle fibers, the growth cones rapidly differentiate into synaptic contacts whose morphology prefigures that of the larval junction. Mismatch experiments show that growth cones recognize specific muscle fibers, and can do so when the surrounding musculature is radically altered. However, when denied their normal targets, motoneurons can establish functional synapses on alternate muscle fibers. Blocking synaptic activity with either injected toxins or ion channel mutants does not derange synaptogenesis, but may influence the number of motor ending processes. The molecular mechanisms governing cellular recognition during synaptogenesis remain to be identified. However, several cell surface glycoproteins known to mediate cellular adhesion events in vitro are expressed by the developing synapses. Furthermore, enhancer detector lines have identified genes with expression restricted to small subsets of muscle fibers and /or motoneurons during the period of synaptogenesis. These observations suggest that in Drosophila a mechanism of target chemoaffinity may be involved in the genesis of stereotypic synaptic wiring. © 1993 John Wiley & Sons, Inc.
Temporal patterning of song production: Participation of nucleus uvaeformis of the thalamus
Authors: Williams Heather , Vicario David S.
Published: January 2005

Birdsong is a learned vocal behavior used in intraspecific communication. The motor pathway serving learned vocalizations includes the forebrain nuclei NIf, HVC, and RA; RA projects to midbrain and brain stem areas that control the temporal and acoustic features of song. Nucleus Uvaeformis of the thalamus (Uva) sends input to two of these forebrain nuclei (NIf and HVC) but has not been thought to be important for song production. We used three experimental approaches to reexamine Uva's function in adult male zebra finches. (1) Electrical stimulation applied to Uva activated HVC and the vocal motor pathway, including tracheosyringeal motor neurons that innervate the bird's vocal organ. (2) Bilateral lesions of Uva including the dorso‐medial portion of the nucleus affected the normal temporal organization of song. (3) Chronic multiunit recordings from Uva during normal song and calls show bursts of premotor activity that lead the onset of some song components, and also larger bursts that mark the end of complete song motifs. These results implicate Uva in the production of learned vocalizations, and further suggest that Uva contributes more to the temporal structure than to the acoustic characteristics of song. © 1993 John Wiley & Sons, Inc.
Dendritic reduction in Passover, a Drosophila mutant with a defective giant fiber neuronal pathway
Authors: Baird Douglas H. , Koto Mary , Wyman Robert J.
Published: January 2005

The jump response to a light‐off startle stimulus in Drosophila melanogaster occurs when the Giant Fiber (GF), a neuron descending from the brain to the thorax, drives the jump (tergotrochanteral) muscle motorneuron (TTMn). Nonjumping mutants have been isolated in which this response is disrupted. Flies bearing the X‐chromosome mutation Passover (Pas) fail to jump in response to a light‐off stimulus, and electrical stimulation of the GF in the brain no longer elicits the normal response in the TTM. We have used retrograde HRP labelling to examine the TTMn motorneuron in wild‐type flies and in a variety of newly identified Pas alleles. In wild type the medial branch (MB) of the TTMn has an extensive region of apposition with the GF. In Pas alleles, there is a general reduction in anterior‐posterior (A‐P) extent of the medial branch but not of the posterior branch. Nevertheless, Pas alleles usually leave the TTMn close enough to the GF so that contact would not be precluded. In flies carrying a particular deficiency of Pas, Df(1) 16–3–22, including Pas/Df(1) 16–3–22 heterozygotes, there can be extensive growth of the medial branch including a contralateral projection; these heterozygotes have more than the normal amount of overlap between the GF and the TTMn. This phenotype, originally ascribed to Pas mutants, is associated with Df(1) 16–3–22, but not with other deletions of the Pas gene. The driving of the TTMn by the GF is defective in mutant genotypes with extensive medial branches as well as in mutants where GF‐TTMn contact is reduced. The fact that the TTMn grows into its normal synaptic region in mutant genotypes, but the GF pathway functions abnormally suggests that pathfinding by the TTMn is not impaired. It is more likely that the Pas mutation disrupts cell recognition, synaptogenesis, or synaptic function in the TTMn or its presynaptic partners. © 1993 John Wiley & Sons, Inc.
Differential ultrastructure of synaptic terminals on ventral longitudinal abdominal muscles in Drosophila larvae
Authors: Atwood H. L. , Govind C. K. , Wu C.‐F.
Published: January 2005

The innervation of ventral longitudinal abdominal muscles (muscles 6, 7, 12, and 13) of third‐instar Drosophila larvae was investigated with Nomarski, confocal, and electron microscopy to define the ultrastructural features of synapse‐bearing terminals. As shown by previous workers, muscles 6 and 7 receive in most abdominal segments “Type I” endings, which are restricted in distribution and possess relatively prominent periodic terminal enlargements (“boutons”); whereas muscles 12 and 13 have in addition “Type II” terminals, which are more widely distributed and have smaller “boutons.” Serial sectioning of the Type I innervation of muscles 6 and 7 showed that two axons with distinctive endings contribute to it. One axon (termed Axon 1) has somewhat larger boutons, containing numerous synapses and presynaptic dense bodies (putative active zones for transmitter release). This axon also has more numerous intraterminal mitochondria, and a profuse subsynaptic reticulum around or under the synaptic boutons. The second axon (Axon 2) provides somewhat smaller boutons, with fewer synapses and dense bodies per bouton, fewer intraterminal mitochondria, and less‐developed subsynaptic reticulum. Both axons contain clear synaptic vesicles, with occasional large dense vesicles. Approximately 800 synapses are provided by Axon 1 to muscles 6 and 7, and approximately 250 synapses are provided by Axon 2. In muscles 12 and 13, endings with predominantly clear synaptic vesicles, generally similar to the Type I endings of muscles 6 and 7, were found, along with another type of ending containing predominantly dense‐cored vesicles, with small clusters of clear synaptic vesicles. This second type of ending was found most frequently in muscle 12, and probably corresponds to a subset of the “Type II” endings seen in the light microscope. Type I endings are thought to generate the ‚fast’︁ and ‚slow’︁ junctional potentials seen in electrophysiological recordings, whereas the physiological actions of Type II endings are presently not known. © 1993 John Wiley & Sons, Inc.
Role of a telencephalic nucleus in the delayed song learning of socially isolated zebra finches
Authors: Morrison Robert G. , Nottebohm Fernando
Published: January 2005

Male zebra finches normally learn their song from adult models during a restricted period of juvenile development. If song models are not available then, juveniles develop an isolate song which can be modified in adulthood. In this report we investigate the features of juvenile experience that underly the timing of song learning. Juvenile males raised in soundproof chambers or in visual isolation from conspecifics developed stable isolate song. However, whereas visual isolate song notes were similar to those of colony‐reared males, soundproof chamber isolates included many phonologically abnormal notes in their songs. Despite having stable isolate songs, both groups copied new notes from tutors presented to them in adulthood (2.7 notes per bird for soundproof chamber isolates, 4.4 notes per bird for visual isolates). Old notes were often modified or eliminated. We infer that social interactions with live tutors are normally important for closing the sensitive period for song learning. Lesions of a forebrain nucleus (IMAN) had previously been shown to disrupt juvenile song learning, but not maintenance of adult song for up to 5 weeks after surgery. In this study, colony‐reared adult males given bilateral lesions of IMAN retained all their song notes for up to 4–7.5 months after lesioning. However, similar lesions blocked all song note acquisition in adulthood by both visual and soundproof chamber isolates. Other work has shown that intact hearing is necessary for the maintenance of adult zebra finch song. We infer that auditory pathways used for song maintenance and acquisition differ: IMAN is necessary for auditorily guided song acquisition—whether by juveniles or adults—but not for adult auditorily guided song maintenance. © 1993 John Wiley & Sons, Inc.