bluuebunny/crossref_metadata_2025_split huggingface dataset:
Loss of material from the retrograde axonal transport system in frog sciatic nerve
Authors: Snyder R. E. 
Published: January 2005

AbstractRapid axonal transport was studied in sciatic nerve preparations of the amphibian Xenopus laevis maintained in vitro at 23.0 ± 0.2°C. A pulse of [25S]methionine‐labeled material was allowed to move in the anterograde direction until encountering a lesion, at which a portion of the pulse reversed directions and moved in the retrograde direction. By constricting the nerve during the course of the experiment, it was possible to prevent continuous return of label from the lesion, thus creating a retrogradely moving pulse that contained a defined quantity of radiolabel. Movement of both the anterograde and the retrograde pulse were monitored continuously for up to 24 h using a position‐sensitive detector of ionizing radiation. The front and the back edge of the anterograde pulse were found to move at the rates of (mm/day) 179.9 ± 3.9 (±SEM) and 149.9 ± 5.9, respectively, and the front and the back edge of the retrograde pulse moved at the rates of 155.8 ± 11.3 and 84.6 ± 2.9, respectively. By comparison of the quantity of label lost to the stationary phase to the quantity of label calculated to have been present in the anterrograde pulse, it was determined that 0.068 ± 0.009 of the anterograde pulse is lost to each 3.18‐mm region of nerve. Comparison of the quantity of label calculated to have been present in the retrograde pulse to that in the anterograde pulse revealed that 0.057 ± 0.014 of the retrograde pulse is lost to each 3.18‐mm region of nerve. It is concluded that protein originating in the cell body and which reverses its direction of transport at a lesion can be lost from the retrograde axonal transport system.
The importance of cnidarian synapses for neurobiology
Authors: Anderson Peter A. V. , Spencer Andrew N. 
Published: January 2005

AbstractDespite being the most primitive organisms to possess a nervous system, cnidarians afford rare opportunities for studying various, general aspects of chemical synaptic transmission. This is made possible by the unique organization of their nervous systems and by the fact that in certain species the neurons and synapses are readily accessible for intracellular recordings and voltage clamp. The results obtained from such studies are summarized here, with particular emphasis on work with two species, Cyanea capillata (Scyphozoa) and Polyorchis pennicilatus (Hydrozoa). The potential of these preparations for providing additional data is also discussed.
Metamorphosis and fish vision
Authors: Evans Barbara I. , Fernald Russell D. 
Published: January 2005

AbstractMany species of fish exhibit metamorphosis in which dramatic external transformations occur as a consequence of coordinated changes in gene expression within an organism. Because postembryonic development and change appears to be the rule rather than the exception in teleost fish species, we view metamorphosis as one of many developmental strategies in fish which have continued plasticity as a common theme. Metamorphic changes are manifested in the visual system by modification of photoreceptor peak sensitivity rod photoreceptor cell addition, and retinal reorganization. These changes correspond to significant changes in the natural habitat of the animal and in its visual capabilities as demonstrated behaviorally. Thyroxine is the main metamorphic hormone as has also been found in amphibia. The sequence of metamorphic events occur in all teleosts, but they are compressed in time in direct developing animals suggesting that such animals might prove useful for understanding the evolution of metamorphosis in fish. It seems likely that rod photoreceptors may have evolved in conjunction with the change from larval to juvenile stage through metamorphosis in indirect developing fishes. During evolution, the contraction and/or loss of the larval stage has resulted in earlier appearance of rod photoreceptors during development although they always arise later than cone photoreceptors. This ontogenetic developmental sequence supports Walls's (1942) proposal that cones are phylogenetically older than rods and suggests that rods may have evolved several times.
Slow transport of the cytoskeleton after axonal injury
Authors: McKerracher Lisa , Hirscheimer Andrea 
Published: January 2005

AbstractThe delivery of cytoskeletal proteins to the axon occurs by slow axonal transport. We examined how the rate of slow transport was altered after axonal injury. When retinal ganglion cell (RGC) axons regenerated through peripheral nerve grafts, an increase in the rate of slow transport occurred during regrowth of the injured axons. We compared these results to axonal injury in the optic nerve where no substantial regrowth occurs and found a completely different response. Slow transport was decreased approximately tenfold in rate in the proximal segment of crushed optic nerves. This decreased rate of slow transport was not induced immediately, but occurred about 1 week after injury. To explore whether a decrease in the rate of slow transport was induced when the regeneration of peripheral nerves was physically blocked, we examined slow transport in motor neurons after the sciatic nerve was transected and ligated. In this case, no change in the rate of the comigrating tubulin and neurofilament (NF) radioactive peaks were observed. We discuss how the changes in the rate of slow transport may reflect different neuronal responses to injury and speculate about the possible molecular changes in the expression of tubulin which may contribute to the observed changes. © 1992 John Wiley & Sons, Inc.
Biogenic amines modulate synaptic transmission between identified giant interneurons and thoracic interneurons in the escape system of the cockroach
Authors: Casagrand Janet L. , Ritzmann Roy E. 
Published: January 2005

AbstractIn the escape system of the cockroach, Periplaneta americana, a population of uniquely identifiable throacic interneurons (type A or TIAs) receive information about wind via chemical synapses from a population of ventral giant interneurons (vGIs). The TIAs are involved in the integration of sensory information necessary for orienting the animal during escape. It is likely that there are times in an animal's life when it is advantageous to modify the effectiveness of synaptic transmission between the vGIs and the TIAs. Given the central position of the TIAs inthe escape system, this would greatly alter associated motor outputs. We tested the ability of octopamine, serotonin, and dopamine to modulate synaptic transmission between vGIs and TIAs. Both octopamine and dopamine significantly increased the amplitude of vGI‐evoked excitatory postsynaptic potentials (EPSPs) in TIAs at 10−4−10−2 M, and 10−3 M, respectively. On the other hand, serotonin significantly decreased the vGI‐evoked EPSPs in TIAs at 10−4−10−3 M. These results indicate that octopamine, serotonin, and dopamine are capable of modulating the efficacy of transmission of important neural connections within this circuit. © 1992 John Wiley & Sons, Inc.
A real‐time analysis of growth cone–target cell interactions during the formation of stable contacts between hippocampal neurons in culture
Authors: Cooper Monica W. , Smith Stephen J. 
Published: January 2005

AbstractMechanisms of cell‐cell recognition and structural changes of growth cones (g.c.) and target membranes during contact formation are poorly understood. To examine these issues, we obtained a high magnification, realtime record of stale contact formation in cultured cells from the hippocampal CA1 area in the newborn rat. We used differential interference contrast (DIC) optics coupled to a video microscope for periods of over 24 h of continuous time‐lapse recording. Our goal was to observe the sequential changes exhibited by afferent and target cells as they form a stable contact. Understanding the process of how stable contacts are made is important because such contacts are the first step in synapse formation. Four principal observations emerged from our study: (1) The target cell was receptive to a contact on a specific patch on its surface defined by the presence of lamellae and filopodia. This specific patch (named target site) was invariably present on the target cell surface before the time the growth cone arrived. (2) Stable adhesion between filopodia on the two cells initiated events leading to cell–cell contact formation. Specifically, the remaining filopodia on the growth cone and target cell were redirected toward the adhering filopodia, and the growth cone size decreased dramatically. (3) The axonal process then grew at a significantly accelerated rate (up to 50 times its baseline growth rate). (4) In addition, a number of observations were obtained on axonal turns towards the target cell, induction of target sites, and architectural remodelling of cells after the formation of a new contact. Our findings indicate that in this neuronal system, filopodia are the means used by cells to interact at stages prior to and during contact formation. We speculate that the molecules involved in cell recognition and the machinery that initiates contact formation are embedded in the fine structure of filopodia. Finally, our results provide possible clues as to some of the stages that may be involved in synapse formation in the mammalian central nervous system. © 1992 John Wiley & Sons, Inc.
Developmental study of the expression of B50/GAP‐43 in rat retina
Authors: Reh T. A. , Tetzlaff W. , Ertlmaier A. , Zwiers H. 
Published: January 2005

AbstractB50/GAP‐43 has been implicated in neural plasticity, development, and regeneration. Several studies of axonally transported proteins in the optic nerve have shown that this protein is synthesized by developing and regenerating retinal ganglion cells in mammals, amphibians, and fish. However, previous studies using immunohistochemistry to localize B50/GAP‐43 in retina have shown that this protein is found in the inner plexiform layer in adults. Since the inner plexiform layer contains the processes of amacrine cells, ganglion cells, and bipolar cells to determine which cells in the retina express B50/GAP‐43, we have now used in situ hybridization to localize the mRNA that codes for this protein in the developing rat retina. We have found that B50/GAP‐43 is expressed primarily by cells in the retinal ganglion cell layer as early as embryonic day 15, and until 3 weeks postnatal. Some cells in the inner nuclear layer, possibly a subclass of amacrine cells, also express B50/GAP‐43 protein and mRNA; however, the other retinal neurons–bipolar cells, photoreceptors, and horizontal cells express little, if any, B50/GAP‐43 at any stage in their development. Early in development, the protein appears in the somata and axons of ganglion cells, while later in development, B50/GAP‐43 becomes concentrated in the inner plexiform layer, where it continues to be expressed in adult animals. These results are discussed in terms of previous proposals as to the functions of this molecule. © 1993 John Wiley & Sons, Inc.
Mechanisms of early neurogenesis in Drosophila melanogaster
Authors: Campos‐Ortega José A. 
Published: January 2005

AbstractThe neuroectoderm of insects contains an initially indifferent population of cells which during later development will give rise to the progenitor cells of the neural and epidermal lineages. Experimental evidence indicates that cellular interactions determine which cells will adopt each one of these fates. Transplantation experiments suggest that a signal with neuralising character is required to stabilize the primary neural fate in 25% of all the neuroectodermal cells, which will develop as neuroblasts, and that an epidermalising signal contributes to suppress the neural fate in the remaining 75% of the cells, allowing in this way their development as epidermal progenitor cells. The invoked cell interactions are assumed to be mediated by the products of several genes forming a complex, not yet well understood network of interrelationships. Elements of this network are the proteins encoded by Delta and Notch, which appear to convey the regulatory signals between the cells; the proteins encoded by the achaete‐scute gene complex, which regulate neural development; and the proteins encoded by the Enhancer of split gene complex, which give neuroectodermal cells access to epidermal development. © 1993 John Wiley & Sons, Inc.
A putative nicotine pump at the metabolic blood–brain barrier of the tobacco hornworm
Authors: Murray Christine L. , Quaglia Michele , Arnason Jon T. , Morris Catherine E. 
Published: January 2005

AbstractIn mammals, P‐glycoprotein immunostaining at the blood–brain barrier has implicated the multidrug pump in the restricted movement of many cytotoxic agents into the central nervous system (NCS). Since many insects require as sophisticated blood–brain barrier system to protect their CNS from plant‐derived neurotoxins, we have investigated the possibility that a P‐glycoprotein homolog constitutes a component of the insect blood–brain barrier. We have used the nicotine‐resistant tobacco hornworm (Manduca sexta) to address this issue. Manduca has been previously shown, in physiological studies, to have an alkaloid (nicotine/morphine/atropine) pump at its excretory malpighian tubules. We show (1) that the tubules are P‐glycoprotein immunopositive, (2) that Manduca has a metabolic blood–brain barrier for nicotine, (3) that the barrier co‐localizes with P‐glycoprotein immunostaining, and (4) that detoxifying enzymes as well as the nicotine pump are likely to account for the metabolic blood–brain to nicotine. These findings may provide insights on two major fronts, the troublesome problem of multi‐insecticide resistance, a phenomenon that parallels multidrug resistance in tumor cells, and the problem of tolerance to addictive neuroactive drugs like nicotine or morphine. 1994 John Wiley & Sons, Inc.
Confocal laser scanning microscopy reveals voltage‐gated calcium signals within hippocampal dendritic spines
Authors: Jaffe David B. , Fisher Stephen A. , Brown Thomas H. 
Published: January 2005

AbstractThe induction of long‐term potentiation (LTP) is generally assumed to be triggered by Ca2+ entry into dendritic spines via NMDA receptor‐gated channels. A previous computational model proposed that spines serve several functions in this process. First, they compartmentalize and amplify increases in [Ca2+]i. Second, they augment the nonlinear relationship between synaptic strength and the probability or magnitude of LTP induction. Third, they isolate the metabolic machinery responsible for LTP induction from increases in [Ca2+]i produced by voltage‐gated Ca2+ channels in the dendritic shaft. Here we examine this last prediction of the model using methods that combine confocal microscopy with simultaneous neurophysiological recordings in hippocampal brain slices. Either of two Ca2+‐sensitive dyes were injected into CA1 pyramidal neurons. Direct depolarization of the neurons via the somatic electrode produced clear increases in Ca2+ signals within the dendritic spines, a result that was not predicted by the previous spine model. Our new spine model suggests that some of this signal could theoretically result from Ca2+‐bound dye diffusing from the dendritic shaft into the spine. Dye diffusion alone cannot, however, explain the numerous cases in which the Ca2+ signal in the spine was considerably larger than that in the adjacent dendritic shaft. The latter observations raise the possiblity of voltage‐gated Ca2+ entry directly into the spine or else perhaps via Ca2+‐dependent Ca2+release. The new spine model accommodates these observations as well as several other recent experimental results. 1994 John Wiley & Sons, Inc.
Calcium signaling in dendritic spines of hippocampal neurons
Authors: Connor John A. , Miller Lucas D. Pozzo , Petrozzino Jeffrey , Müller Wolfgang 
Published: January 2005

AbstractIntracellular Ca2+ dynamics have been measured using imaging techniques in dendrites and spines of CA3 hippocampal neurons in brain slice under both acute and tissue culture conditions. In response to presynatic stimulation, micromolar levels of Ca2+ are rapidly reached in spines of distal dendrites. If stimulus parameters are chosen judiciously so as to minimize postsynaptic firing, then the dendrite shaft increases are far less. Spine Ca2+ increases are largely dependent upon activation of NMDA receptors. At the large mossy fiber synapses, presynaptic stimuli also produce large Ca2+ increases but the differences in shaft‐spine Ca2+ levels are much less; often they are insignificant. Also at these locations, postsynaptic firing, without presynaptic stimulation is sufficient to produce large increase in spine Ca2+ levels. 1994 John Wiley & Sons, Inc.
Apoptosis in adult retinal ganglion cells after axotomy
Authors: Garcia‐Valenzulela E. , Gorczyca W. , Darzynkiewicz Z. , Sharma S. C. 
Published: January 2005

AbstractLesions to the mature mammalian central nervous system cause irreversible degeneration, in which neurons have been previously thought to be passive victims. In this study, axon‐lesioned adult rat nerons are shown instead to actively degrade themselves through the process of apoptosis: a programmed type of cell death in which the cellular apparatus is actively involved in the degradation process. To investigate whether retinal ganglion cells of an adult mammal follow an apoptotic type of death when their axons are severed, DNA breaks in nuclei were labeled in situ, using a method that specifically incorporates biotinylated deoxynucleotides by exogenous terminal deoxynucleotidyl transferase on the 3′‐OH ends of DNA. The active nature of the death mechanism was demonstrated by the reduction in biotin‐labeled nuclei after administering the protein synthesis inhibitor cycloheximide. Our results suggest that retinal ganglion cells of the adult rat die through apoptosis when axotomized. This raises new possibilities in the treatment of CNS injuries, by the potential interruptibility of a program for neuronal death. 1994 John Wiley & Sons, Inc.
Secreted forms of β‐amyloid precursor protein modulate dendrite outgrowth and calcium responses to glutamate in cultured embryonic hippocampal neurons
Authors: Mattson Mark P. 
Published: January 2005

AbstractIn addition to being the major excitatory neurotransmitter in the mammalian brain, glutamate is believed to play a key role in the regulation of neurite outgrowth and snaptogenesis during development. In cultured embryonic hippocampal pyramidal neurons, glutamate inhibits dendrite outgrowth by a mechanism involving elevation of intracellular‐free calcium levels ([Ca2+]i). In the present study, secreted forms of the β‐amyloid precursor protein (APPss) counteracted the inhibitory effect of glutamate on dendrite outgrowth in cultured embryonic hippocampal neurons. The prolonged elevation of [Ca2+]i normally induced by glutamate was significantly attenuated in neurons that had been pretreated with 2–10 nM of APPs695 or APPs751. Immunocytochemistry with β‐amyloid precursor protein antibodies showed that immunoreactivity was concentrated in axons and, particularly, in their growth cones. Because β‐amyloid precursor proteins are axonally transported, and APPss can be released from axon terminals/growth cones in response to electrical activity, the present findings suggest that APPss may play a role in developmental and synaptic plasticity by modulating dentritic responses to glutamate. 1994 John Wiley & Sons, Inc.
Differential effects of dihydrotestosterone and estrogen on the development of motoneuron morphology in a sexually dimorphic rat spinal nucleus
Authors: Goldstein L. A. , Sengelaub D. R. 
Published: January 2005

AbstractThe rat lumbar spinal cord contains a sexually dimorphic motor nucleus, the spinal nucleus of the bulbocavernosus (SNB), whose motoneurons innnervate perineal muscles involved in copulatory reflexes. Dendritic development of SNB motoneurons is biphasic and androgen dependent. During the first 4 postnatal weeks, SNB dendrites grow exuberantly, and subsequently retract to mature lengths by 7 weeks of age. After early postnatal castration, SNB dendrites fail to grow, and testosterone replacement restores this growth. In other systems, testosterone and its metabolites, dihydrotestosterone and estrogen, are important for somatic and neural sexual differentiation. The purpose of the present study was to examine the effects of castration and dihydrotestosterone or estrogen replacement on the growth of SNB motoneuron somata and dendritic arbors.Male rat pups were castrated on postnatal (P) day 7 and treated daily with either dihydrotestosterone propionate (DHTP; 2 mg) or estradiol benzoate (EB; 100 μg) until P28 or P49. By using cholera toxin horseradish peroxidase (BHRP) histochemistry, the soma size, dendritic length, dendritic extent, and arbor area of BHRP‐labeled SNB motoneurons were measured and analyzed. Both DHTP and EB treatment supported the initial exuberant growth of SNB dendrites through P28, but EB treatment was ineffective in maintaining mature, adult lengths at P49. The possible sites of hormone action and functional implications of these hormonal treatments are discussed. 1994 John Wiley & Sons, Inc.
Expression of winged helix genes, BF‐1 and BF‐2, define adjacent domains within the developing forebrain and retina
Authors: Hatini Victor , Tao Wufan , Lai Eseng 
Published: January 2005

AbstractOne of the earliest events in the development of the central nervous system is the establishment of positional identity along the anteroposterior (AP) axis of the neuroepithelium. In recent years, regulatory genes with regionally restricted expression in the neuroepithelium have been idenfitied which are believed to specify its developmental fate. We have previously described Brain Factor‐1 (BF‐1), a winged helix (WH) transcription factor expressed in the telencephalic neuroephithelium (Tao and Lai, 1992) Neuron 8:957–966. Here we report the cloning of the mouse cDNA for a novel WH protein, BF‐2. We show that BF‐2 is a sequence‐specific DNA binding protein with a binding specificity distinct from BF‐1. Its expression in the CNS during embryogenesis is restricted to the rostral diencephalic neuroepithelium. The caudal boundary of BF‐2 expression is at the zona limitans intrathalamica. Rostrally, the BF‐2 expression domain is adjacent to that of BF‐1. The expression domains of these two factors define a boundary within the developing forebrain neuoepithelium. The BF‐1/BF‐2 boundary also extends laterally to divide the optic stalk and the retina into nasal (anterior) and temporal (posterior) domains. These observations suggest that in adition to playing a role in the subdivision of the forebrain, these two WH factors may also function to establish positional information in the retinal neuroepithelium. 1994 John Wiley & Sons, Inc.