bluuebunny/crossref_metadata_2025 huggingface dataset:
OS9: A novel olfactory gene of Drosophila expressed in two olfactory organs
Authors: Raha Debasish , Carlson John
Published: January 2005

A novel olfactory gene, OS9, has been identified in Drosophila by subtractive hybridization. OS9 transcripts have been detected in the third antennal segment, the primary olfactory organ in Drosophila, and in the maxillary palp, which has recently been shown to have olfactory function. The OS9 gene thus represents a molecular link between two distinct olfactory tissues in Drosophila. Little if any OS9 expression has been detected in other segments of the antenna or in other tissues examined. The gene is located in region, 38AB on the cytogenetic map. OS9 encodes a protein of 159 amino acids, which contains a putative leucine zipper. Polyclonal antibodies raised against the C‐terminal half of the encoded protein react with a 24 kD antennal protein. Antisera raised against both C‐terminal and N‐terminal halves of the OS9 protein appear to react with cell nuclei in both the third antennal segment and the maxillary palp; interestingly, both antisera also stain cells in the head, including photoreceptor nuclei, as if OS9 were an olfactory‐specific member of a family of nuclear proteins, possibly transcription factors. 1994 John Wiley & Sons, Inc.
Female marsh wrens do not provide evidence of anatomical specializations of song nuclei for perception of male song
Authors: Brenowitz Eliot A. , Nalls Belinda , Kroodsma Donald E. , Horning Cynthia
Published: January 2005

In songbirds the forebrain nuclei HVC (high vocal center) and RA (robust nucleus of the archistriatum) are larger in individuals or species that produce larger song repertoires, but the extent to which the size of these nuclei reflects a need for either producing or perceiving large repertoires is unknown. We, therefore, tested the hypothesis that species differences in the size of song nuclei reflect a commitment of “brain space” to the perceptual processing of conspecific song. The two species of marsh wren (Cistothorus palustris western and eastern) provide a good test case. Western males produce larger song repertoires, and have larger HVC and RA than do eastern males. Female marsh wrens do not sing, and if they use their song nuclei to assess conspecific male song repertoires, then we predicted that measurable cellular and nuclear parameters of HVC and RA would be greater in western than eastern female wrens. For males we confirmed that the volumes of HVC and RA, and cellular parameters of HVC, are greater in western than in eastern birds. These nuclei were also considerably larger in males than in conspecific females. Western and eastern female wrens, however, did not differ in any measured parameters of HVC or RA. Females of these wren species thus do not provide any direct evidence of anatomical specializations of song nuclei for the perceptual processing of conspecific male song. 1994 John Wiley & Sons, Inc.
Spontaneous Ca2+ transients in developing hippocampal pyramidal cells
Authors: Dailey Michael E. , Smith Stephen J.
Published: January 2005

To determine the spatiotemporal pattern of hippocampal pyramidal cell activity during development, we examined cytosolic Ca2+ dynamics in tissue slices derived from early postnatal rats. After a brief (12–60 h) culture period, slices were stained with a calcium‐sensitive dye, Fluo‐3. Fluorescence imaging of the Fluo‐3‐stained slices with a scanning laser confocal microscope afforded simultaneous observation of many cells at high spatial resolution. Time‐lapse imaging revealed spontaneous Ca2+ transients in the somata and dendrites of many pyramidal cells in areas CA1 and CA3. For the most part, Ca2+ activity in neighboring pyramidal cells appeared to be uncorrelated, although we occasionally observed synchronous Ca2+ transients in adjacent cells. The transients were blocked by both tetrodotoxin (1 μM) and a mixture of the glutamate receptor antagonists, APV (50 μM) + CNQX (10 μM). Thus, spontaneous Ca2+ transients appear to be a consequence of activity‐dependent release of glutamate acting postsynaptically through ionotropic glutamate receptors. Although γ‐aminobutyric acid (GABA) is thought to be an excitatory neurotransmitter during hippocampal development (Cherubini et al., 1991, Trends Neurosci. 14(12):515–519), the spontaneous Ca2+ transients were not blocked by the GABAA receptor antagonist picrotoxin (100 μM). Furthermore, application of GABA (50 μM) abolished the spontaneous Ca2+ events, possibly via GABAB receptor‐mediated inhibition of postsynaptic cells. The present results join other recent observations suggesting that isolated neural tissues support spontaneous activity, although the patterns and mechanisms of the activity reported here appear to differ from those of previous studies. Differences in the patterns of spontaneous activity during development may contribute to variations in the functional organization of different regions of CNS tissue. 1994 John Wiley & Sons, Inc.
Intracellular calcium mobilization and neurite outgrowth in mammalian neurons
Authors: Kocsis Jeffery D. , Rand Mark N. , Lankford Karen L. , Waxman Stephen G.
Published: January 2005

Cultured adult rat dorsal root ganglion (DRG) neurons were used to study depolarization‐induced Ca2+ mobilization and the effects of intracellular Ca2+ depletion on neurite outgrowth. Cytoplasmic and nuclear Ca2+ signals were visualized in dissociated DRG neurons using confocal scanning laser microspcopy and the Ca2+ indicator dye fluo‐3. The depolarization‐induced Ca2+ signals were highest in neurons during the first few days in culture, prior to neurite extension; during this time nuclear signals exceeded those of the cytoplasm severalfold. After several days in culture, neurons began to arborize, depolarization‐induced Ca2+ signals became attenuated, and nuclear signals no longer exceeded those of the cytoplasm. Elevated Ca2+ signals were dependent upon both Ca2+ influx and intact intracellular Ca2+ stores, indicating that the signals are generated by calcuim‐induced calcium release (CICR). Thapsigargin, an endoplasmic reticulum Ca2+ ATPase inhibitor, depleted intracellular Ca2+ stores and blocked the induction of the large nuclear Ca2+ signals. Treating DRG neurons briefly with thapsigargin (200 nM for 20 min) shortly after plating reduced subsequent neuritogenesis, impyling that intact Ca2+ stores are necessery for initiating neurite outgrowth. Immunostaining of DRG neurons with antibodies to Ca2+ /calmodulin‐dependent kinase II (CaM kinase II) demonstrated that this enzyme is present in the nucleus at early times in culture. These observations are consistent with the idea that CICR triggered by Ca2+ entry subsequent to depolarization may elicit neurite outgrowth by activating nuclear enzymes appropriate for such outgrowth. © 1994 John Wile & Sons, Inc.
Resonant activation of calcium signal transduction in neurons
Authors: Fields R. Douglas , Nelson Phillip G.
Published: January 2005

The relevant parameters of calcium fluxes mediating activation of immediate‐early genes and the collapse of growth cones in mouse DRG neurons in response to action potentials delivered in different temporal patterns were measured in a multicompartment cell culture preparation using digital flourescence videomicroscopy. Growth cone collapse was produced by trains of action potentials causing a large rise in [Ca2+]i, but after chronic exposure to patterned stimulation growth cones regenerated and became insensitive to the stimulus‐induced increase in [Ca2+]i. Calcium reached similar peak concentrations, but the [Ca2+]i increased more slowly than in naive growth cones (time constant of 6.0 s versus 1.4 s in naive growth cones). Semiquantitative PCR measurements of gene expression showed that pulsed stimulation delivered at 1‐min intervals for 30 min induced expression of c‐fos, but the same total number of action potentials delivered at 2‐min intervals failed to induce c‐fos expression, even though this stimulus induces a larger peak [Ca2+]i than the effective stimulus pattern. The experiments suggest that the kinetics of calcium fluxes produced by different patterns of stimulation, and changes in the kinetics of calcium flux in neurons under different states of activation, are critical in determining the effects of action potentials on growth cone motility or expression of IE genes during development of neuronal circuits. We propose that differences in kinetics of individual reactions in the stimulus–response pathway may lead to resonance of activation in the neuron, such that certain processes will be selectively activated by particular temporal patterns of stimulation. 1994 John Wiley & Sons, Inc.
The plasma membrane calcium pump: Functional domains, regulation of the activity, and tissue specificity of isoform expression
Authors: Carafoli Ernesto , Stauffer Thomas
Published: January 2005

The plasma membrane Ca2+ pump is responsible for the fine regulation of the intracellular Ca2+ level and is thus involved in the control of several cellular processes. The activity of the pump is regulated by a multiplicity of mechanisms, among which are calmodulin, acidic phospholipids, kinase‐mediated phosphorylation, or an oligomerizatin process. The C‐terminal part of the molecule interacts with the region of the pump close to the active site, leading to the decrease of the activity in the resting state. Four genes coding for different isoforms of the plasma membrane Ca2+ ATPase are known in humans. Isoform 1 and 4 represent housekeeping isoforms, whereas isoforms 2 and 3 are only present in specialized tissues. The variability of the protein in further increased by alternative RNA slicing at two sites (A, C). Alternative splicing occurs within (splice site C) or near (splice site A) regions coding for regulatory domains of the protein. In all isoforms a corresponding splice form exists at both splice sites. These common splice forms are present in all tissues, whereas isoform unique splice forms are normally only present in specialized tissues. In neuronal tissues all isoforms and almost the complete set of splice forms are found. The transcripts of the different isoforms are distributed in a region‐specific manner in neuronal tissues. 1994 John Wiley & Sons, Inc.
Acceleration by NMDA treatment of visually induced map reorganization in juvenile Xenopus after larval eye rotation
Authors: Bandarchi Jafar , Scherer Warren J. , Udin Susan B.
Published: January 2005

Each tectal lobe of Xenopus forgs receives two topographic maps, one via the ipsilateral eye and one via the contralateral eye. The alignment of the ipsilateral map with the contralateral map depends upon bincoular visual input during a critical period that extends from late tadpole to early juvenile stages. Rotation of one eye during the critical period leads to reorganization of the ipsilateral map, which eventually comes back into alignment with the contralateral map despite the abnormal eye position. The ipsilateral eye's map initially develops as if there had been no alteration in eye position; there is a delay of 4–6 weeks before reorganization can be detected by electrophysiological mapping. In this paper, the possible role of the NMDA receptor in the delay in reorganization is addressed. The degree of NMDA receptor activation may need to be above some threshold level to trigger reorganization. If NMDA receptor activation normally is below that level until after the first month postmetamorphosis, then exogenous NMDA might boost the process sufficiently to start the reorganization process sooner than usual. In order to test this possibility, the left eye of tadpoles was rotated and NMDA was applied to the right tectal lobe for 3–5 weeks, starting at 1 week postmetamorphosis. Electrophysiological mapping demonstrated that reorganization takes place more rapidly than in untreated forgs or frogs treated with vehicle only. This result is consistent with the interpretation that the activation of the NMDA receptor is a rate‐limiting step in the activity‐dependent matching of binocular maps in Xenopus tectum. 1994 John Wiley & Sons, Inc.
Cell adhesion molecules in the early developing mouse retina: Retinal neurons show preferential outgrowth in vitro on L1 but not N‐CAM
Authors: Hankin Mark H. , Lagenaur Carl F.
Published: January 2005

Both L1 and N‐CAM are present on optic axons early in the developing mouse retina and optic nerve. In in vitro assays on substrates of purified cell adhesion molecules cells derived from E13 mouse retinae showed vigorous neurite extension on L1 but not on N‐CAM. Although retinal neurons on N‐CAM showed only limited attachment to the substrate, they were able to form lamellipodia immediately around the cell perimeter. In contrast, similarly derived cortical cells showed extensive neurite outgrowth on both substrates. Under these culture conditions, nearly all of the L1 and N‐CAM present in the cell membrane appeared to be sequestered on the lower surface of the growth cones and neurites, indicating that most of these cell adhesion molecules were involved in homophilic interactions. Our results suggest differential roles for L1 and N‐CAM in intitiation and establishment of the optic pathway. © 1994 John Wiley & Sons, Inc.
Influence of interganglionic interactions on steroid‐mediated dendritic reorganization and death of proleg motor neurons during metamorphosis in Manduca sexta
Authors: Weeks Janis C. , Davidson Seana K.
Published: January 2005

In Manduca sexta, the larval abdominal prolegs and their muscles degenerate at pupation. The proleg motor neurons undergo a period of dendritic regression, after which a specific subset of them dies. The surviving motor neurons undergo dendritic outgrowth during pupal‐adult development, and most die after adult emergence. All of these events are regulated hormonally by ecdysteroids and juvenile hormone, but interactions of the motor neurons with other cells may potentially contribute as well. To investigate the possible influence of interganglionic neural interactions, we chronically isolated individual abdominal ganglia by severing the adjacent rostral and caudal connectives in the larval stage. Subsequent metamorphic changes in proleg motor neurons were examined in the isolated ganglia and ganglia adjacent to the isolated ganglia. Two abnormalities were observed: (1) some imprecision in the timing of motor neuron death, both at pupation and after adult emergence, and (2) the growth of ectopic neurites outside the neuropil boundaries during pupal‐adult development (in ganglia with or without neuromas caused by connective transections). Other aspects of proleg motor neuron metamorphosis, including the segment‐specific death of motor neurons at pupation, were the same as that in intact and sham‐operated insects. Thus, interganglionic interactions appear to play a relatively minor role in the steroid‐mediated metamorphic transformation of proleg motor neurons. © 1994 John Wiley & Sons, Inc.
C‐kinase manipulations disrupt activity‐driven retinotopic sharpening in regenerating goldfish retinotectal projection
Authors: Schmidt John T.
Published: January 2005

Regenerating optic axons initially branch over a wide area in tectum to form a crude retinotopic map. The map is sharpened, and retinotopically appropriate synapses are stabilized via NMDA receptors that detect, via summation of EPSPs, the coincident activity of neighboring ganglion cells that make synapses onto common tectal cells. Sharpening shares a number of properties with long‐term potentiation (LTP) in hippocampus. This study tested whether protein kinase C (PKC) activation is necessary for sharpening as it is for LTP. Intracular (IO) or intracranial (IC) injections of kinase inhibitors or activators were made every other day from 19 to 37 days postcrush (sensitive period), and the projections formed were later recorded. Retinotopic sharpening was prevented by IC injection of the following agents: (1) general kinase inhibitors sphingosine and H7 (100‐200 μM in fluid above brain), (2) active but not inactive phorbols (TPA, 1 μM), and (3) calphostin C (1 μM), a specific and irreversible PKC inhibitor. The mature projection on the opposite tectum, however, when examined was not unsharpened. Lack of sharpening was reflected in multiunit fields at each tectal point that averaged 27°–30° versus 11° in Ringers and inactive phorbol control regenerates. Intraocular injections of either TPA (1 μM), or calphostin C (1 μM) also prevented sharpening (26° and 32° multiunit fields), suggesting action on PKC axonally transported to the presynaptic terminals. Calphostin C had no noticeable effect on the firing patterns of retinal ganglion cells. The endogenous activator of PKC, arachidonic acid (AA), disrupted sharpening at 20 μM or higher (IC injection, 32° multiunit fields), while a control fatty acid, elaidic acid, had no effect. Although AA at 5 μM showed no effect, and diacylglycerol at 5 μM exhibited only small effects, together they produced a large synergistic effect (32° multiunit fields). Such synergy mirrors the synergy in the activation of several isoforms of PKC. Actual concentrations in the extradural fluid around the brain were assayed via injections of 3H‐AA. Levels fell about sixfold after a day and by an additional fivefold the second day before the next injection. The results confirm that activity‐driven retinotopic sharpening is very sensitive to manipulations of kinases, especially PKC. © 1994 John Wiley & Sons, Inc.
Origin and clonal relationship of common inhibitory motoneurons CI1 and CI3 in the locust CNS
Authors: Wolf Harald , Lang Dirk M.
Published: January 2005

In the primordial thoracic ganglia of locust embryos, the bromodeoxiuridine (BrdU) technique for labelling proliferating cells and their progeny was combined with intracellular dye injection to investigate the origin and the clonal relationship of common inhibitory motoneurons. Common inhibitors 1 (CI1) and 3 (CI3) were found to be siblings, that is, they are produced by the division of one ganglion mother cell. This ganglion mother cell results from the first division of neuroblast 5–5, at about 30% of embryonic development. A large portion, at least, of the ganglion mother cells produced by subsequent divisions of neuroblast 5–5 give rise to interneurons with contralaterally ascending or descending axons and GABA‐like immunoreactivity. Thus, CI1 and CI3 are more closely related to putative inhibitory interneurons than they are to other, that is, excitatory, motoneurons. Consistent with this, the CI somata are associated with cell bodies of putative inhibitory interneurons rather than with clusters of excitatory motoneuron somata. These results elicit speculations regarding the evolutionary origin of inhibitory motoneurons. 1994 John Wiley & Sons, Inc.
In vitro analysis of neurite outgrowth indicate a potential role for tenascin‐like molecules in the development of insect olfactory glomeruli
Authors: Krull Catherine E. , Oland Lynne A. , Faissner Andreas , Schachner Melitta , Tolbert Leslie P.
Published: January 2005

Tenascin‐like material is associated with glial cells that form borders around developing glomerular units in the olfactory (antennal) lobe of the moth Manduca sexta and is present at critical stages of glomerulus formation (Krull et al., 1994, J. Neurobiol. 25:515–534). Tenascinlike immunoreactivity declines in the mature lobe, coincident with a wave of synapse formation within the glomeruli and glomerulus stabilization. Tenascin‐like molecules associated with neuropilar glia are in the correct position to influence the branching patterns of growing neurites by constraining them to glomeruli. In this study, we examine the growth of cultured moth antennal‐lobe neurons in response to mouse CNS tenascin. Uniform tenascin provides a poor substrate for cell‐body attachment and neurite outgrowth. Neuronal cell bodies provided with a striped substratum consisting of tenascin and concanavalin‐A (con‐A)/laminin attach preferentially to con‐A/laminin lanes. Most neurons restrict their branching to con‐A/laminin lanes both at early and later times in culture but others send processes across multiple tenascin and con‐/laminin lanes in an apparently indiscriminate manner. Tenascin can inhibit the neuritic outgrowth of most antennal‐lobe neurons, and this raises the possibility that the tenascin‐like molecules associated with neuropilar glia in vivo act to constrain growing neurites to glomeruli. Thus, glial cells, acting in concert with olfactory axons, might act to promote glomerular patterns of branching by antennal‐lobe neurons. 1994 John Wiley & Sons, Inc.
Neural organization of the ventilatory activity in the frog, Rana catesbeiana. II
Authors: Kago Naoki , Remmers John E.
Published: January 2005

The paralyzed, decerebrate frog, Rana catesbeiana, displays “fictive” oropharyngeal and pulmonary ventilations. In order to evaluate the neuronal correlates of these two centrally programmed ventilatory bursting patterns, we have performed intra‐and extracellular recordings of bulbar respiratory neurons in this fictively breathing preparation. A total of 123 respiratory neurons were recorded from the caudal medulla. Of 51 antidromically activated neurons, 20 were vagal motoneurons and 31 were hypoglossal motoneurons. Respiratory neurons that depolarized during the lung (L) or non‐lung (N) ventilatory phases were classified as L or N neurons, respectively. Phase spanning neurons (S) were active during both L and N phases. Some neurons showed oscillations of membrane potential synchronous with oropharyngeal ventilation. Those active during the buccal elevation phase were exclusively L neurons whereas those having buccal depressor activity were exclusively N neurons.

Synaptic drive potentials were observed in all neurons recorded intracellularly. In some neurons, hyperpolarization was caused by inhibitory postsynaptic potentials, as demonstrated by reversal of membrane potential trajectory after intracellular chloride iontophoresis. Some individual motoneurons and interneurons exhibited both pulmonary and buccal ventilatory activity, indicating that both pattern generators project to a common motor control system. 1994 John Wiley & Sons, Inc.
Anti‐β1 integrin antibody inhibits schwann cell meylination
Authors: Fernandez‐Valle Cristina , Gwynn Lisa , Wood Patrick M. , Carbonetto Salvatore , Bunge Mary Bartlett
Published: January 2005

Schwann cells (SCs) co‐cultured with sensory neurons require ascorbate supplementation for basal lamina assembly and differentiation into myelinating cells. The ascorbate requirement can be bypased by adding a purifed basal lamina component, laminin, to SC/neuron cocultures. We have examined the role of laminin receptors, Namely, the β1 subfamily of integrins, in the process of myelination. We demonstrate by immunostaining or immunoprecipitation that undifferentiated SCs in contact with axons express large amounts of the β1 subunit in association with the α1 or α6 subunit. In co‐cultures of myelinating SCs, α1β1 is no longer present, α6β1 is still present but at reduced levels, and α6β4 is expressed at much higher levels than in co‐cultures of undifferentiated SCs. Immunogold labelling at the electron microscope level suggested that β1 integrins are randomly distributed on undifferentiated SCs, become localized to the SC surface contacting basal lamina in differentiating SCs before the onset of myelination, and are not detected on myelinating SCs. Fab fragments of β1 function‐blocking antibody block both attachment of isolated SCs to laminin and formation of myelin sheaths by SCs co‐cultured with neurons in ascorbate‐supplemented medium. SCs unable to myelinate in the presence of the anti‐β1 antibody assemble patchy basal lamina that is only loosely attached to the cell surface and in some cases appears to be detaching from the membrane. In contrast, an α1β1 function‐blocking antibody only partially blocks attachment of isolated SCs to laminin but has no inhibitory effect on SC myelination. These results are consistent with the hypothesis that a member of the β1 subfamily of integrins other than α1β1 binds laminin present in basal lamina to the SC surface and transduces signals that are critical for initiation of SC differentiation into a myelinating cell. 1994 John Wiley & Sons, Inc.
Fibrolast growth factors in the nervous system
Authors: Exkenstien Felix P.
Published: January 2005

Fibroblast growth factors (FGFs) exhibit widespread mitogenic and neurotrophic activities. Nine members of the family are currently known, and FGF‐1 and FGF‐2 are present in relatively high levels in CNS. FGF‐1 is expressed by a subset of neuronal populations, while FGF‐2 is expressed by astrocytes. FGF‐1 and FGF‐2 lack signal peptides and appear to be present mainly in inracellular compartmens. This suggests that the factors may act as initiators of a repair response after injury. Support for this notion comes from observations that FGF‐1 and FGF‐2 levels are low during critical phases of development, but high in the adult CNS. A family of transmembrane tyrosine kinase receptors (FGFRs) mediates the effects of FGFs. Four different genes coding for FGF receptors are currently known, three of which are expressed in cell type‐specific patterns in the CNS The main receptor variants present in this tissue, however, can by themselves not distinguish between FGF‐1 and FGF‐2. Additional selectivity may be established by interaction of the FGFs and their receptors with select heparan proteoglycans (HSPGs). Therefore, the precise physiological role of FGFs is determined by the combination of cell type‐specific patterns of expression of FGFs, FGFRs and HSPGs together with the mechanisms that regulate the extracellular availability of FGFs. 1994 John Wiley & Sons, Inc.
Neurons in culture maintain acetylcholine receptor levels with far fewer transcripts than in vivo
Authors: Corriveau Roderick A. , Berg Darwin K.
Published: January 2005

Of the 10 neuronal nicotinic acetylcholine receptor (AChR) genes identified in chick, five are expressed by ciliary ganglion neurons in vivo (α3, α5, α7, β2, and β4), and the mRNA levels produced increase during development approximately in parallel with the two major classes of AChRs present. Here we report that when chick ciliary ganglion neurons from 8‐day embryos are transferred to dissociated cell culture, they express the same five genes but at much lower levels. The α3 and α7 transcripts, chosen for detailed analysis because they encode subunits segregated between the two AChR species, decrease rapidly in abundance on transfer to culture and, after 1 week, are at levels less than a 20th of those found in vivo for neurons of the same age. Co‐culturing the neurons with skeletal myotubes did not increase the levels of AChR transcripts in the neurons. Despite low amounts of mRNA from all five genes, neither class of AChRs was much reduced in culture compared to in vivo. The numbers of AChRs on the cell surface actually increased with time in culture. Several culture conditions known to down‐regulate the receptors in culture did not reduce the abundance of the α3 and α7 mRNAs. The results suggest that post‐transcriptional controls can play an important role in determining AChR abundance on the neurons. © 1994 John Wiley & Sons, Inc. 1994 John Wiley & Sons, Inc.
Segmental independence and age dependence of neurite outgrowth from embryonic chick sensory neurons
Authors: Parson Simon H. , Ribchester Richard R.
Published: January 2005

Targets in limb regions of the chick embryo are further removed from the dorsal root ganglia that innervate them compared with thoracic ganglion‐to‐target distances. It has been inferred that axons grow into the limb regions two to three times faster than into nonlimb regions. We tested whether the differences were due to intrinsic properties of the neurons located at different segmental levels. Dorsal root ganglia (DRG) were isolated from the forelimb, trunk, and hind limb regions of stage 25–30 embryos. Neurite outgrowth was measured in dissociated cell culture and in cultures of DRG explants. Although there was considerable variability in the amount of neurite outgrowth, there were no substantive differences in the amount or the rate of outgrowth comparing brachial, thoracic, or lumbosacral neurons. The amount of neurite outgrowth in dissociated cell cultures increased with the stage of development. Overall, our data suggest that DRG neurons express a basal amount of outgrowth, which is initially independent of target‐derived neurotrophic influences; the magnitude of this intrinsic growth potential increases with stage of development; and the neurons of the DRG are not intrinsically specified to grow neurites at rates that are matched to the distance they are required to grow to make contact with their peripheral targets in vivo. We present a speculative model based on Poisson statistics, which attempts to account for the variability in the amount of neurite outgrowth from dissociated neurons. © 1995 John Wiley & Sons, Inc.
Axotomy of developing rat spinal motoneurons: Cell survival, soma size, muscle recovery, and the influence of testosterone
Authors: Lubischer Jane L. , Arnold Arthur P.
Published: January 2005

During the period of synapse elimination, motoneurons are impaired in their ability to generate or regenerate axonal branches: following partial denervation of their target muscle, young motoneurons do not sprout to nearby denervated fibers and after axonal injury, they fail to reinnervate the muscle. In the rat levator ani (LA) muscle, which is innervated by motoneurons in the spinal nucleus of the bulbocavernosus (SNB), synapse elemination ends relatively late in development and can be regulated by testosterone. We took advantage of this system to determine if the end of synapse elimination and the development of regenerative capabilities by motoneurons share a common mechanism, or, alternatively, if these two events can be dissociated in time. Axotomy on or before postnatal day 14 (P14) caused the death of SNB motoneurons. By P21, toward the end of synapse elimination in the LA muscle, SNB motoneurons had developed the ability to survive axonal injury. Altering testosterone levels by castration on P7 followed by 4 weeks of either testosterone propionate or control injections did not change the ability of SNB motoneurons to survive axonal injury during development, although these same treatments alter the time course of synapse elimination in the LA muscle. Thus, we dissociated the inability of SNB motoneurons to recover from axonal injury from their developmental elimination of synaptic terminals. We also measured the effect of early axotomy on motoneuronal soma size and on target muscle weight. Axotomy on P14 caused a long‐lasting decrease in the soma size of surviving SNB motoneurons, whereas motoneurons axotomized on P28 recovered their normal soma size. Axotomy on or before P7 caused severe atrophy of the target muscles, matching the extensive loss of motoneurons. However, target muscle recovery after axotomy on P14 was as good as recovery after axotomy at later ages, despite greater motoneuronal death after axotomy on P14. This result may reflect an increase in motor unit size, a decrease in polyneuronal innervation by SNB motoneurons that survive axotomy on P14, or a combination of the two. © 1995 John Wiley & Sons, Inc.
The role of receptor/channel activity in neuronal cell migration
Authors: Rakic Pasko , Komuro Hitoshi
Published: January 2005

Confocal laser microscopy, in conjunction with carbocyanine dyes and calcium‐sensitive fluorescent indicators, was used in slices and explant cultures of developing cerebellum to study cellular mechanisms underlying a motility of neuronal cell migration. The results indicate that a combination of voltage‐ and ligand‐activated ion channels cooperatively regulates Ca2+ influx into the migrating cells. We suggest that molecules, present in the local cellular milieu, affect cell motility by activating specific ion channels and second messengers that influence polymerization of stiff and contractile cytoskeletal proteins. This early interaction between postmitotic neurons and surrounding cells controls the rate of their movements, sculpts their shapes, establishes their positions, and, therefore, indirectly determines their identities to prior formation of synaptic connections. © 1995 John Wiley Sons, Inc.
Fast and slow excitation of inhibitory cells in the CA3 region of the hippocampus
Authors: Poncer Jean‐Christophe , Miles Richard
Published: January 2005

Pyramidal cells form excitatory synaptic connections with local inhibitory neurons in the hippocampus. This recurrent synapse plays a crucial stabilizing role in the control of hippocampal activity, since it transforms pyramidal cell population. Using a combination of dual recording from presynaptic and postsynaptic cells and anatomical techniques, we show that these synaptic connections often comprise a single site for liberation of excitatory transmitter. The resulting excitatory postsynaptic potentials (EPSCs) have a fast time course and a similar amplitude to miniature EPSCs recorded in tetrodotoxin and cobalt. In contrast, activation of metabotropic glutamate receptors (mGluRs) by transmitter liberated during repetitive activation of these synapses produces an excitation with a much slower time course. In addition to somatodendritic mGluRs, which excite inhibitory cells, a different species of mGluR is present on inhibitory cell terminals. This mGluR is activated by higher concentrations of the agonist t‐1‐amino‐cyclopentyl–1,3‐decarboxylate and acts to reduce γ‐aminobutyric acid release. mGluRs, thus, have a dual action to enhance and to depress synaptic inhibition in the hippocampus. © 1995 John Wiley & Sons, Inc.
Possible strategies for finding the substrate for learning‐induced changes in the hippocampal cortex
Authors: Andersen Per , Trommald Mari
Published: January 2005

For long‐lasting memory traces, structural synaptic changes remain a probable mechanism. However, in higher animals it has proved difficult to provide positive evidence for this notion. The main reason may be that the changes are subtle and are to be found in a relatively small subset of synapses and in a distributed manner in the cellular network in question. Here, we discuss possible strategies for finding structural changes in the hippocampus associated with spatial learning, an activity for which this structure is important. Spatial learning may induce new excitatory synapses in a small subset of hippocampal CA1 neurons because we observe a higher spine density without alteration in dendritic length or branching. The dendritic synapses are regularly spaced, irrespective of spine density, suggesting the operation of an intersynaptic dispersing force. © 1995 John Wiley & Sons, Inc.
Role of the transforming growth factor‐β family in the expression of cranial neural crest‐specific phenotypes
Authors: Leblanc Gabrielle G. , Holbert Timothy E. , Darland Tristan
Published: January 2005

Cranial and trunk neural crest cells produce different derivatives in vitro. Cranial neural crest cultures produce large numbers of cells expressing fibronectin (FN) and procollagen I (PCol I) immunoreactivities, two markers expressed by mesenchymal derivatives in vivo. Trunk neural crest cultures produce relatively few FN or PCol I immunoreactive cells, but they produce greater numbers of melanocytes than do cranial cultures. Treatment of trunk neural crest cultures with transforming growth factor‐β1 (TGF‐β1) stimulates them to express both FN and PCol I immunoreactivities at levels comparable to those normally seen in cranial cultures and simultaneously decreases their expression of melanin. These observations raised the possibility that endogenous TGF‐β is involved in specifying differences in the phenotypes expressed by cranial and trunk neural crest cells in vitro. Consistent with this idea, we found that treatment of cranial cultures with a function‐blocking TGF‐β antiserum inhibits the development of FN immunoreactive cells and stimulates the development of melanocytes. Cranial and trunk neural crest cells express approximately equal levels of TGF‐β mRNA. However, trunk neural crest cells are significantly less sensitive to the FN‐inducing effect of TGF‐β1 than are cranial neural crest cells. These results suggest that: (1) endogenous TGF‐β is required for the expression of mesenchymal phenotypes by cranial neural crest cells, and (2) differences in the phenotypes expressed by cranial and trunk neural crest cells in vitro result in part from differences in the sensitivities of these two cell populations to TGF‐β. © 1995 John Wiley & Sons, Inc.
Purkinje cell dendritic arbors in chick embryos following chronic treatment with an N‐methyl‐D‐aspartate receptor antagonist
Authors: Vogel Michael W. , Prittie Jennifer
Published: January 2005

The normal development of Purkinje cell dendrites is dependent on afferent innervation. To investigate the role of neuronal activity in Purkinje cell dendritic development, chick embryos were chronically treated with a potent, selective, and systemically active competitive N‐methyl‐D‐aspartate (NMDA) receptor antagonist, NPC 12626. The NMDA receptor was chosen as a target for pharmacological blockade because of the importance of the NMDA receptor in synaptic plasticity and stabilization in development. Chick embryos were given daily injections of NPC 12626 (25 to 100 mg/kg) from embryonic day 14 (E14) to E17. The initial injections of NPC 12626 dramatically blocked embryo movements, but activity levels partially recovered following subsequent injections. Embryo movements were reduced by 24% at the end of the experiment. Embryos were killed on E18, and their brains processed for Golgi‐Cox staining. The morphology of Golgi‐stained Purkinje cells in drug‐treated embryos was similar to control embryos. Morphometric analysis showed, however, that chronic treatment with NPC 12626 resulted in a 19% reduction in Purkinje cell dendritic tree area and a 13% reduction in the number of dendritic branch points. The overall width and height of the drug‐treated dendritic trees were not significantly different from controls, suggesting that NPC 12626 reduced Purkinje cell dendritic area by interfering with branch formation. The volume of the granule cell layer and the heights of the molecular and external granule cell layers was not reduced, suggesting that NPC 12626 treatment did not simply delay development. These results suggest that activation of the NMDA receptor may mediate the afferent‐target interactions in the cerebellum that regulate the elaboration of Purkinje cell dendrites. © 1995 John Wiley & Sons, Inc.
Dividing neuron precursors express neuron‐specific tubulin
Authors: Memberg Stacey P. , Hall Alison K.
Published: January 2005

Neuronal differentiation involves specific molecular and morphological changes in precursors and results in mature, postmitotic neurons. The expression of neuron‐specific β tubulin, as detected by the monoclonal antibody TuJ1, begins during the period of neurogenesis. Indeed, TuJ1 expression precedes that of the 160 kD neurofilament protein in both the central and peripheral nervous systems. In the embryonic rat spinal cord, bipolar cells and some mitotic cells in the ventricular zone were TuJ1 immunoreactive (IR). Sensory ganglia also contained cells with TuJ1‐IR mitotic spindles in situ. In embryonic rat sensory and sympathetic ganglion cell cultures pulsed with the thymidine analog bromodeoxyuridine (BrdU), TuJ1 label was detected in the spindle of mitotic cells and in the midbody of cells joined at cytokinesis, indicating that neuron‐specific tubulin expression was initiated during or before the final mitosis of neuronal progenitors. Dorsal root ganglion cultures included TuJ1‐IR cells with several shapes that may reflect morphological transitions, from flattened stellate neural crest‐like cells to differentiated bipolar neurons. Indeed, the presence of flattened TuJ1‐IR cells was correlated with neurogenesis. Some sympathetic neuron precursors possessed long TuJ1‐IR neurites, as well as TuJ1‐IR spindle microtubules and BrdU‐labeled chromosomes, indicating that these precursors can possess long processes during metaphase. These results support the hypothesis that neuron‐specific tubulin expression represents an early molecular event in neuronal differentiation exhibited by a wide range of neuronal precursors. The cessation of proliferation can occur at different points during neuronal differentiation, as TuJ1‐IR was detected in cells undergoing mitosis. Future studies directed toward understanding the molecules that initiate neuron‐specific tubulin expression may lead to the factors that control the initial phases of neuronal differentiation. © 1995 John Wiley & Sons, Inc.
Initial sex differences in neuron growth and survival within an avian song nucleus develop in the absence of afferent input
Authors: Burek Michael. J. , Nordeen K. W. , Nordeen E. J.
Published: January 2005

Only male zebra finches (Poephila guttata) sing, and nuclei implicated in song behavior exhibit marked sex differences in neuron number. In the robust nucleus of the anterior neostriatum (RA), these sex differences develop because more neurons die in young females than in males. However, it is not known whether the sexually dimorphic survival of RA neurons is a primary event in sexual differentiation or a secondary response to sex differences in the number of cells interacting trophically with RA neurons. In particular, since sexual differentiation of the RA parallels the development of dimorphisms in the numbers of neurons providing afferent input from the lateral magnocellular nucleus of the anterior neostriatum (lMAN) and the high vocal center (HVC), it has been hypothesized that sex differences in the size of these afferent populations trigger differential RA neuron survival and growth. To test this hypothesis, we lesioned either the lMAN or both the lMAN and HVC unilaterally in 12‐day‐old male and female zebra finches. Subsequently, RA cell death and RA neuron number and size were measured. Unilateral lMAN lesions increased cell death and decreased neuron number and size within the ipsilateral RA of both sexes. However, even in the lMAN‐lesioned hemisphere, these effects were less pronounced in males than in females, so that by day 25 the volume, number, and size of neurons were sexually dimorphic in both the contralateral and ipsilateral RA. Similarly, the absence of both lMAN and HVC afferents did not prevent the emergence of sex differences in the number and size of RA neurons by 25 day posthatching. We conclude that these sex differences within the RA are not a secondary response to dimorphisms in the numbers of lMAN or HVC neurons providing afferent input. © 1995 John Wiley & Sons, Inc.
Astroglia demonstrate regional differences in their ability to maintain primary dendritic outgrowth from mouse cortical neurons in vitro
Authors: Le Roux Peter D. , Reh Thomas A.
Published: January 2005

To determine whether glia from different regions of the central nervous system (CNS) initiate or maintain primary dendritic growth, embryonic day 18 mouse cortical neurons were co‐cultured with rat (postnatal day 4) astroglial cells derived from retina, spinal cord, mesencephalon, striatum, olfactory bulb, retina, and cortex. Axon and dendrite outgrowth from isolated neurons was quantified using morphological and immunohistochemical techniques at 18 h and 1, 3, and 5 days in vitro. Neurons initially extend the same number of neurites, regardless of the source of glial monolayer; however, glial cells differ in their ability to maintain primary dendrites. Homotypic cortical astrocytes maintain the greatest number of primary dendrites. Glia derived from the olfactory bulb and retina maintained intermediate numbers of dendrites, whereas only a small number of primary dendrites were maintained by glia derived from striatum, spinal cord, or mesencephalon. Longer axons were initially observed from neurons grown on glia that did not maintain dendrite number. Axonal length, however, was similar on the various monolayers after 5 days in vitro. Neurons that were grown in media conditioned by either mesencephalic or cortical glia for the first 24 h followed by culture media from glia of the alternate source for 4 days in vitro confirmed that glia maintained, rather than initiated, the outgrowth of the primary dendritic arbor. These results indicate that glial cells derived from various CNS regions differ in their ability to maintain the primary dendritic arbor from mouse cortical neurons in vitro. © 1995 John Wiley & Sons, Inc.
Formation and specification of neurons during the development of the leech central nervous system
Authors: Shankland Marty
Published: January 2005

In the leech embryo, neurogenesis takes place within the context of a stereotyped cell lineage. The prospective germ layers are formed during the early cleavage divisions by the reorganization and segregation of circumscribed domains within the cytoplasm of the fertilized egg. The majority of central neurons arise from the ectoderm, and central neuroblasts are distributed throughout both the length and width of each ectodermal hemisegment. Much of the segmental ganglion arises from medial neuroblasts, but there are also lateral ectodermal neuroblasts and mesodermal neuroblasts that migrate into the nascent ganglion from peripheral sites of origin. Some of these migratory cells are committed to neurogenesis prior to reaching their central destination. In addition, the leech embryo exhibits a secondary phase of neurogenesis that is restricted to the two sex segment ganglia. Secondary neurogenesis requires that a mitogenic or trophic signal be conveyed from the peripherally located male sex organ to a particular set of centrally located neuroblasts, apparently via already differentiated central neurons that innervate the sex organ. The differential specification of neuronal phenotypes within the leech central nervous system occurs in multiple steps. Some aspects of a neuron's identity are already specified at the time of its terminal cell division and would seem to involve the lineal inheritance of developmental commitments made by one of the neuron's progenitors. This lineage‐based identity can then be modified by interactions between the postmitotic neuron and other neurons or non‐neuronal target cells encountered during its terminal differentiation. © 1995 John Wiley & Sons, Inc.
Neuronal control of leech swimming
Authors: Brodfuehrer Peter D. , Debski Elizabeth A. , O'Gara Bruce A. , Friesen W. Otto
Published: January 2005

Leech swimming is produced by the antiphasic contractions of dorsal and ventral longitudinal muscles that travel rearward along the animal and propel it forward. Research over the past three decades has focused on identifying the underlying neuronal circuit and mechanisms that produce and control this coordinated movement pattern. Investigations have also tested whether leech swimming is modifiable, both by experience and by neuromodulators. One outcome has been the identification of several functional classes of neurons associated with swimming. Systematic analysis of the interactions between these neurons had led to the elucidation of a neuronal circuit that adequately accounts for the generation of the swim motor program cord. The swim motor program appears to be produced by a chain of coupled segmental oscillators whose intrinsic properties and intersegmental connections ensure the coordinated expression of swimming along the nerve cord. In addition, neurons identified in the head ganglion comprise two parallel, but opposite‐acting, systems that control the initiation of swimming in response to sensory input. Also, the pathway by which body wall stimulation initiates swimming show a simple form of learning, that is habituation. Repeatedly stroking the leech body wall decreases both the probability of initiating swimming and the length of elicited swim episodes. Finally, the biogenic amine serotonin, which is found in the nerve cord, affects leech swimming in a number of ways. Serotonin's modulation of swimming is due, in part, to its effect on the membrane properties of swim‐initiating interneurons and several swim motor neurons. © 1995 John Wiley & Sons, Inc.