bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanisms of neuronal death in brain aging and alzheimer's disease: Role of endocrine‐mediated calcium dyshomeostasis
Authors: Landfield Philip W. , Thibault Olivier , Mazzanti Mary L. , Porter Nada M. , Kerr D. Steven 
Published: May 2005

AbstractThis paper reviews evidence that brain aging and Alzheimer's disease (AD) are somehow closely related and that the hippocampus (CA1) is highly vulnerable to cell loss under both conditions. In addition, two current lines of evidence on the mechanisms of hippocampal cell loss with aging are considered, including studies of neuronal calcium dysregulation and studies of cumulative glucocorticoid (GC) neurotoxicity. Moreover, recent electro‐physiological studies have shown that excess glucocorticoid activation of hippocampal neurons increases the influx of calcium through voltage‐activated calcium channels. Second messenger systems may mediate the steroid modulation of calcium channels. Therefore, it is hypothesized that excess glucocorticoid activation and neuronal calcium dysregulation may be two phases of a single process that increases the susceptibility of neurons to neurodegeneration during aging and Alzheimer's disease. © 1992 John Wiley & Sons, Inc.
Development of anuran locomotion: Ethological and neurophysiological considerations
Authors: Stehouwer Donald J. 
Published: May 2005

AbstractThere are dramatic quantitative and qualitative differences in the locomotor behavior of larval and juvenile frogs. Larvae (tadpoles) are primarily herbivourous and rely heavily on locomotion via undulations to acquire food and avoid predation. After metamorphosis, juvenile frogs adopt a carnivorous lifestyle and capture prey and avoid predators by remaining motionless in a place of concealment. When they must move, frogs locomote by means of ballistic hops or by more conventional walking. However, locomotion of both tadpoles and frogs can be considered of two fundamental functional types: (a) startle and escape; and (b) sustained locomotion. Neural mechanisms underlying startle responses and sustained locomotion in larvae and juveniles are described and possible ontogenetic relationships those behaviors are proposed. The role of different parts of the nervous system in the ontogeny of locomotion, as well as nonneuronal factors, are described. Results show that the transition from tadpole‐like behavior to frog‐like behavior is not a simple function of maturation of central locomotor controls. Rather, it results from a complex interaction of central nervous system maturation, morphological change, and a change in habitat preference. Examples of similar multidimensional control of behavioral ontogeny in other species are described, and it is argued that to understand the ontogeny of behavior, one must investigate contributions made at all levels, from the neuronal to the environmental. © 1992 John Wiley & Sons, Inc.
Neuroethological approaches to the study of motor development in chicks: Achievements and challenges
Authors: Bekoff Anne 
Published: May 2005

AbstractChicks and chick embryos provide a useful model system for the study of related to the development of motor behaviors. EMG and kinematic analyses of leg movements have been used to provide new data on the organization of embryonic motility. These data suggest that the circuitry needed to produce a basic, coordinated motor pattern is available early in development. This circuitry then appears to be retained throughout life. Evidence from analysis of EMG patterns and leg deafferentation studies suggest that the output of this basic circuit can be modulated by sensory input to produce the motor patterns of later behaviors, such as hatching and walking. If the same circuitry is present throughout life, then mechanisms for initiation and termination of particular behaviors must be available to ensure that specific behaviors are turned on and off at appropriate times. For example, hatching can be turned on by a specific sensory signal: proprioceptive signals from the bent neck. In addition to reviewing current research on the development of chick motor behaviors, methodological considerations and suggestions for future research are presented. © 1992 John Wiley & Sons, Inc.
Developmental plasticity in neural circuits controlling birdsong: Sexual differentiation and the neural basis of learning
Authors: Arnold Arthur P. 
Published: May 2005

AbstractIn many species of passerine songbirds, males learn their song during defined periods of life. Female song in often reduced or absent, as are the brain regions controlling song. Sexual differences in the brain arise because of the action of sex steroids, which trigger the formation of some neural pathways (especially the pathway from the higher vocal center to the robust nucleus) and prevent the atrophy of others in males. These neural changes occur during periods of developmental song learning and can recur during periods of learning in adult birds. The process of learning is correlated with major increases or decreases in the number of neurons in specific neuronal populations, suggesting that the formation or loss of specific neural pathways regulates the ability to learn. Species differences in sexual differentiation and learning allow informative cross‐species comparisons of neural structure and behavior. © 1992 John Wiley & Sons, Inc.
Emergence of pattern in the development of mammalian movement sequences
Authors: Fentress John C. 
Published: May 2005

AbstractThe manner in which behavior is patterned in space and over time represents a fundamental problem in both ethology and neuroscience. Prior to the analysis of mechanism it is important to be sensitive to issues involved in the provision of descriptive taxonomies. Often alternative modes of description lead to different perspectives and research strategies. In both the development of behavioral patterns and their expression a major question is how underlying organizational systems become self‐organizing through the process of mutual interactions. It is clear that simple static dichotomies in both behavioral and developmental science must be replaced by more sophisticated models that emphasize the dynamics of pattern formation and control. Some of these perspectives are illustrated from our ongoing research on rodent movement patterns. © 1992 John Wiley & Sons, Inc.
A model of selective synapse formation in sympathetic ganglia
Authors: Liestøl Knut , Mæhlen Jan , Njå Arild 
Published: May 2005

AbstractIn the sympathetic system, neurons from several spinal segments are mapped onto targets in the periphery in a topographically ordered way by means of selective synaptic connections in the superior cervical ganglion. Experimental evidence points to a crucial role for chemoaffinity in establishing this topographic map. Furthermore, rearrangements of synapses after surgical manipulations indicate that this chemoaffinity is not based on rigid “key‐and‐lock” markers. Our model is used to study how such nonrigid markers may interact with other regulatory factors, including growth‐regulating signals and the growth potential of individual nerons. In the model, these latter factors are limiting, so that an increasing number of synaptic contacts decreases the likelihood of further synapse formation. These factors are combined with chemoaffinity using a linear threshold model. The model is robust to parameter changes and reproduces experimental observations with reasonable detail. Simulation results are used to discuss characteristic experimental results, such as the substantial plasticity of the connections seen after partial denervation. A surprisingly small effect of transient hyperinnervation in the model may help explain why final connectivities are similar in two real situations with high and low degrees of transient hyperinnervation (development and adult reinnervation). It is shown that spatial restrictions on post‐synaptic neurons (dendrites) may contribute significantly to the segmentally broad innervation of each ganglion cell. Finally, we discuss potential effects of presynaptic neuronal death in systems with a high degree of plasticity. © 1993 John Wiley & Sons, Inc.
Dendritic development in the dorsal lateral geniculate nucleus of ferrets in the postnatal absence of retinal input: A golgi study
Authors: Sutton J. Keith , Brunso‐Bechtold Judy K. 
Published: May 2005

AbstractIn order to determine the ongoing role of retinal fibers in the development of dorsal lateral geniculate nucleus (dLGN) neurons during postnatal development, the development of dLGN neurons in the postnatal absence of retinal input was studied in pigmented ferrets using the Golgi‐Hortega technique. The development of four dLGN cell classes, defined on the basis of somatic and dendritic morphology, was described previously in normal ferrets (Sutton and Brunso‐Bechtold, 1991, J. Comp. Neurol. 309: 71–85). The present results indicate that the morphological development of dLGN neurons is strikingly similar in normal and experimental ferrets. The exuberant dendritic appendages that appear after eye opening in normal ferrets are overproduced and eliminated in the postnatal absence of retinal input; however, the final reduction of these transient appendages is delayed. Because exuberant appendages develop in the absence of retinal input, their production cannot depend upon visual experience. Differences in cell body size between normal and experimental ferrets are apparent only after neurons can be classified at the end of the first postnatal month. Cell body size is markedly reduced for class 1 neurons; class 2 cells also are reduced in size but to a far lesser extent. As there is a general trend for class 1 neurons to have the functional properties of Y‐cells, it is likely that the dLGN neurons most affected by the absence of retinal input also are Y‐cells. © 1993 John Wiley & Sons, Inc.
Sensitivity of neurite outgrowth to microfilament disruption varies with adhesion molecule substrate
Authors: Abosch Aviva , Lagenaur Carl 
Published: May 2005

AbstractInteractions between the cytoskeleton and cell adhesion molecules are presumed responsible for neurite extension. We have examined the role of microfilaments in neurite outgrowth on the cell adhesion molecules L1, P84, N‐CAM, and on laminin. Cerebellar neurons growing on each substrate exhibited differing growth cone morphologies and rates of neurite extension. Growth of neurites in the presence of cytochalasin B (CB) was not inhibited on substrates of L1 or P84 but was markedly inhibited on N‐CAM. Neurons on laminin were initially unable to extend neurites in the presence of CB but recovered this ability within 9 h. These studies suggest that neurite outgrowth mediated by different cell adhesion molecules proceeds via involvement of distinct cytoskeletal interactions. © 1993 John Wiley & Sons, Inc.
Hormone‐induced changes in identified cell populations of the higher vocal center in male canaries
Authors: Johnson Frank , Bottjer Sarah W. 
Published: May 2005

AbstractMale canaries revise their vocal repertoire every year. Early work indicated that the volume and neuron number of the song‐control nucleus HVC (Higher Vocal Center) declined in late‐summer/fall as birds added and deleted syllables from their repertoire, and increased in spring as the set of song syllables stabilized to a fixed number. Seasonal variation in serum testosterone levels suggested that these changes in brain and behavior were regulated by testosterone (T). However, although initial studies describing growth and regression of HVC used Nissl‐staining to define its borders, recent experiments that have measured the distribution of identified populations of HVC cells (projection neurons, hormone target cells) suggest that there are no seasonal changes in HVC volume or neuron number. In order to clarify the role of T in the regulation of HVC morphology, we castrated male canaries, maintained them on short (fall‐like) days, and treated them with either T, antisteroid drugs, or nothing. After 1 month of treatment, we used a double‐labeling technique to characterize HVC projection neurons and androgen target cells. The results showed that hormonal manipulation influenced HVC volume, the density and size of HVC cells, and the absolute number and percentage of androgen target cells in HVC. Hormonal manipulation did not influence the absolute number of cells in HVC. Moreover, the distribution of projection neurons, androgen target cells, and the Nissl‐defined borders of HVC were closely aligned in all experimental groups, indicating that exposure to T and/or its metabolites (estradiol and dihydrotestosterone) regulates the overall size of HVC by affecting the distributions of both projection neurons and androgen target cells. Analysis of double‐labeling results suggests that T specifically influences both cell size and the ability to accumulate androgen among HVC neurons that project to the robust nucleus of the archistriatum (RA). The results of this study show that steroid hormones exert potent effects on HVC morphology in male canaries, but differences between our results and studies of seasonal males suggest there may be additional factors that can regulate HVC morphology. © 1993 John Wiley & Sons, Inc.
Induction of programmed cell death in a dorsal root ganglia × neuroblastoma cell line
Authors: Linnik Matthew D. , Hatfield Marsa D. , Swope Melissa D. , Ahmed Nahed K. 
Published: May 2005

AbstractGrowth factor‐dependent neurons die when they are deproved of their specific growth factor. This “programmed” cell death (PCD) requires macromolecular synthesis and is distinct from necrotic cell death. To investigate the mechanisms involved in neuronal PCD, we have studied the sequence of events that occur when a neuronal cell line (F‐11: Mouse neuroblastoma X rat dorsal root ganglia) is deprived of serum in a manner analogous to growth factor deprivation from neurons. Protein synthesis was inhibited within the first 8 h of serum deprivation, while DNA cleavage into nucleosome ladders was prominent by 24 h. The DNA cleavage could be inhibited by cycloheximide, consistent with a requirement for protein synthesis. In contrast, mitochondrial function was not compromised by serum deprivation. Rather, the cells appeared to be metabolically activated after serum removal as shown by an increased reduction of MTT by mitochondrial dehydrogenases and an increase in cellular autofluorescence, which is thought to be due to elevated levels of NADH and flavoproteins. Assessment of cell viability by propidium iodide staining showed no indication of cell death within 24 h. After 48 h of serum deprivation, cells decreased in size and increased propidium iodide uptake. Thus, serum deprivation activates PCD in F‐11 cells and may be a useful model to study the intracellular events responsible for PCD. © 1993 John Wiley & Sons, Inc.
Comparison of the physiology of the auditory receptor organs in Gryllus bimaculatus and Ephippiger ephippiger: CSD Recordings within the auditory neuropiles
Authors: Nebeling Bernd , RöUssler Wolfgang , Jatho Martin 
Published: May 2005

AbstractThe syllables of the song of the tettigoniid Ephippiger ephippiger consist of a series of short sound impulses with a broad‐banded frequency spectrum. Syllables of the song of the gryllid species Gryllus bimaculatus are nearly pure tones with sharply tuned frequency maxima. A comparison of the physiology of the audiotory receptor organs of both species was carried out by using acoustical stimuli with different carrier frequencies and time‐amplitude patterns. The neuronal ensemble activity of receptor cell groups of the tympanal organ was measured within the prothoracic ganglion using the CSD technique. In E. ephippiger, response maxima were found at carrier frequencies mirroring the broad frequency content of the conspecific song. The receptor cells of E. ephippiger are highly sensitive to transient sound impulses. In G. bimaculatus, the receptor cell population is more sharply tuned to the basic frequencies of the natural songs; pure tones represent more effective stimuli than transient sound signals. The causes for these speciesspecific differences are discussed with regard to probable adaptations of the receptor organs to the parameters of the conspecific songs. © 1993 John Wiley & Sons, Inc.
Calcium regulates neuronal differentiation both directly and via co‐cultured myocytes
Authors: Holliday Janet , Spitzer Nicholas C. 
Published: May 2005

AbstractControl of neuronal development by cellular interactions can be regulated by both extracellular and intracellular calcium. Removal of extracellular calcium affects the differentiation of amphibian spinal neurons in vitro by preventing neuronal calcium influx during the production of calcium‐dependent action potentials (Holliday and Spitzer, Dev. Biol. 141:13‐23, 1990). However, this culture condition affects differentiation through other mechanisms as well. We have investigated the interaction between neurons and myocytes to distinguish direct effects of low extracellular calcium on neuronal differentiation and indirect effects due to interference with neuron‐myocyte interactions. We have examined the initiation of neurite outgrowth and the subsequent extension and orientation of processes. We find that (1) the number of neurons that initiate process outgrowth is reduced by the presence of myocytes in a standard medium containing calcium. Experiments with muscle‐conditioned medium indicate that the production and/or secretion of inhibitory cues is calcium dependent. (2) When neurite initiation occurs, neuronal architecture in the absence of myocytes is similar to that in their presence, either in standard or in calcium‐free medium, although neurite extension is enhanced by the absence of calcium. (3) Conditioned medium (CM) experiments additionally demonstrate that the orientation of neurite outgrowth to myocyte‐derived cues is calcium dependent, although the production of directional cues by myocytes is calcium independent. © 1993 John Wiley & Sons, Inc.
Retrograde signaling and the development of transmitter release properties in the invertebrate nervous system
Authors: Davis Graeme W. , Murphey R. K. 
Published: May 2005

AbstractThe dynamics of presynaptic transmitter release are oftern matched to the functional properties of the prostsynaptic cell. In organisms ranging from cats to crickets, evidence suggests that retrograde signaling is essential for matching these presynaptic release properties to individual postsynaptic partners. Retrograde interactions appear to control the development of presynaptic, short‐term facilitation and depression. 1994 John Wiley & Sons, Inc.
Adrenocorticotropic hormone activation of adenylate cyclase in raphe neurons: Multiple regulatory pathways control serotonergic neuronal differentiation
Authors: Eaton Mary J. , Whittemore Scott R. 
Published: May 2005

AbstractThe RN46A cell line was derived from embryonic day 13 rat medullary raphe cells by infection with a retrovirus encoding the temperature‐sensitive mutant of SV 40 large T antigen (tsT‐ag). The RN46A cell line is neuronally restricted and constitutively differentiates following a shift to nonpermissive temperature. Differentiated RN46A cells express low levels of tryptophan hydroxylase (TPH) but no detectable levels of serotonin (5‐HT). Treatment of cultures with the adrenocorticotrophic hormone peptide ACTH4–10 up‐regulates the expression of TPH immunoreactivity in differentiated RN46A cells, but 5‐HT synthesis requires initial treatment with ACTH4–10, followed by partial membrane depolarizing conditions. Up‐regulation of TPH by ACTH4–10 is apparently due to activation of adenylate cyclase, whereas the increased 5‐HT synthesis with membrane depolarization can be blocked with the voltage‐sensitive Ca2+ ‐channel blockers nifedipine and ω‐conotoxin. ACTH4–10 treatment also markedly up‐regulates the expression of the 5‐HT reuptake transporter, as do dibutyryl cyclic AMP and forskolin; chronic membrane depolarization has no effect on 5‐HT reuptake. The expression of the high‐affinity 5‐HT1A receptor is increased threefold by ACTH4–10 treatment during differentiation and fivefold by differentiation under partial membrane depolarizing conditions. Combining ACTH4–10 treatment and membrane depolarization does not increase expression of the 5‐HT1A receptor further. 5‐HT release is constitutive in ACTH‐treated RN46A cells and linked to spontaneous synaptic vesicle fusion in RN46A cells. Considered with previous results, these data indicate that multiple effectors, ACTH, brain‐derived neurotrophic factor, and membrane depolarization, have both distinct and overlapping effects that regulate specific elements of the serotonergic neuronal phenotype during differentiation and maturation. © 1995 John Wiley & Sons, Inc.
An application of the INEPT pulse sequence to the NMR assignment of halogenated marine natural products
Authors: Brownlee R. T. C. , Hall J. G. , Reiss J. A. 
Published: May 2005

AbstractThe routine use of the INEPT pulse sequence is shown to be the method of choice for the assignment of multiplicity from 13C NMR spectra where no prior information about the 1J(CH) coupling constants is available, or where these are expected to vary over a large range. This technique is illustrated using spectra obtained from polyhalogenated monoterpenes isolated from the red alga Plocamium angustum, which have 1J(CH) values varying from 127 to 203 Hz.
Mass spectrometry in structural and stereochemical problems—CLXVI. The electron impact promoted fragmentation of some aliphatic 1,2‐glycols
Authors: Kossanyi Jean , Morizur J. P. , Furth Bernard , Wiemann Joseph , Duffield A. M. , Djerassi Carl 
Published: May 2005

AbstractThe mass spectra of nineteen aliphatic 1,2‐glycols containing a variety of substituents have been recorded and mechanistic rationalizations are presented for the more important degradation processes observed. Fragmentation of the hydroxylated carbon‐carbon bond in these compounds occurred to an appreciable degree often accompanied by the transfer of a hydroxylic hydrogen atom.
Mass spectra of azetidines and 2‐azetidinones
Authors: Jackson M. B. , Spotswood T. M. , Bowie J. H. 
Published: May 2005

AbstractThe mass spectra of twenty three azetidines and seventeen 2‐azetidinones are reported and discussed. The majority of spectra contain molecular ions. Fragmentation modes are largely dependent upon the substitution pattern and involve specific cleavage of the four‐membered ring. Several hydrogen rearrangement reactions occur, and in some cases, cis and trans isomers may be distinguished by large differences in the relative abundances of certain fragment ions.
The oxygen rearrangement of aromatic and unsaturated esters under electron‐impact—I: General regularities of the rearrangement
Authors: Kadentsev V. I. , Zolotarev B. M. , Chizov O. S. , Shachidayatov Ch. , Yanovskaya L. A. , Kucherov V. F. 
Published: May 2005

AbstractSome esters of γ, δ‐unsaturated or β‐arylsubstituted acids undergo a peculiar transformation under electron‐impact including an elimination of the alcohol residue as a radical R. with the following loss of the ketene molecule. One of the oxygen atoms of the carbonyl group enters an ion which is formed from an unsaturated part of the molecule. The possible mechanism of this reaction and the influence of structural modifications on the course of this process are discussed.
The mass spectra of some fluorine‐containing dimethyl esters
Authors: Cotter J. L. 
Published: May 2005

AbstractThe mass spectra of esters of the general formula MeO2C·[CF2]n·CO2Me, n = 6 to 9, are reported and briefly discussed. Common features of the mass spectra are prominent peaks at [M  CO2], [M  CO2  C2F4] and [M  CO2  2C2F4].