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  • 1
    Electronic Resource
    Electronic Resource
    Spatial reconfiguration of charge transfer effectiveness in active bistable dendritic arborizations (2002)
    Oxford, UK : Blackwell Science, Ltd
    European journal of neuroscience 16 (2002), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The aim of this work was to explore the electrical spatial profile of the dendritic arborization during membrane potential oscillations of a bistable motoneuron. Computational simulations provided the spatial counterparts of the temporal dynamics of bistability and allowed simultaneous depiction the electrical states of any sites in the arborization. We assumed that the dendritic membrane had homogeneously distributed specific electrical properties and was equipped with a cocktail of passive extrasynaptic and NMDA synaptic conductances. The electrical conditions for evoking bistability in a single isopotential compartment and in a whole dendritic arborization were computed and showed differences, revealing a crucial effect of dendritic geometry. Snapshots of the whole arborization during bistability revealed the spatial distribution of the density of the transmembrane current generated at the synapses and the effectiveness of the current transfer from any dendritic site to the soma. These functional maps changed dynamically according to the phase of the oscillatory cycle. In the low depolarization state, the current density was low in the proximal dendrites and higher in the distal parts of the arborization while the transfer effectiveness varied in a narrow range with small differences between proximal and distal dendritic segments. When the neuron switched to high depolarization state, the current density was high in the proximal dendrites and low in the distal branches while a large domain of the dendritic field became electrically disconnected beyond 200 µm from the soma with a null transfer efficiency. These spatial reconfigurations affected dynamically the size and shape of the functional dendritic field and were strongly geometry-dependent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1460-9568.2002.02312.x
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  • 2
    Electronic Resource
    Electronic Resource
    Electrotonic Clusters in the Dendritic Arborization of Abducens Motoneurons of the Rat (1994)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of neuroscience 6 (1994), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Following reconstruction with high spatial resolution of the 3-D geometry of the dendritic arborizations of two abducens motoneurons, we simulated the distribution of electrotonic voltage over the whole dendritic tree. Here, we demonstrate that the complex stochastic electrotonic structure of both motoneurons can be reduced to a statistically significant small set of well discriminated clusters. These clusters are formed by dendritic branches belonging to different dendrites of the neuron but with similar electrotonic properties. A cluster analysis was performed to estimate quantitatively the partition of the branches between the dendritic clusters. The contents of the clusters were analysed in relation to their stability under different values of specific membrane resistivity (Rm), to their remoteness from the soma and their location in 3-D space. The cluster analysis was executed in a 2-D parameter space in which each dendritic branch was described by the mean electrotonic voltage and gradient. The number of clusters was found to be four for each motoneuron when computations were made with Rm= 3 kΩ.cm2. An analysis of the cluster composition under different Rm revealed that each cluster contained invariant and variant branches. Mapping the clusters upon the dendritic geometry of the arborizations allowed us to describe the cluster distribution in terms of the 3-D space domain, the 2-D path distance domain and the total surface area of the tree. As the cluster behaviour reflects both the geometry and the changes in the neuronal electrotonic structure, we conclude that cluster analysis provides a tool to handle the functional complexity of the arborizations without losing relevant information. In terms of synaptic activities, the stable dendritic branches in each cluster may process the synaptic inputs in a similar manner. The high percentage of stable branches indicates that geometry is a major factor of stability for the electrotonic clusters. Conversely, the variant branches introduce the conditions for mechanisms of functional postsynaptic plasticity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.1994.tb00542.x
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  • 3
    Electronic Resource
    Electronic Resource
    Stochastic Geometry and Electrotonic Architecture of Dendritic Arborization of Brain Stem Motoneuron (1993)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of neuroscience 5 (1993), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: We describe how the stochastic geometry of dendritic arborization of a single identified motoneuron of the rat affects the local details of its electrotonic structure. After describing the 3D dendritic geometry at high spatial resolution, we simulate the distribution of voltage gradients along dendritic branches under steady-state and transient conditions. We show that local variations in diameters along branches and asymmetric branchings determine the non-monotonous features of the heterogeneous electrotonic structure. This is defined by the voltage decay expressed as a function of the somatofugal paths in physical distances (voltage gradient). The fan-shaped electrotonic structure demonstrates differences between branches which are preserved when simulations are computed from different values of specific membrane resistivity although the absolute value of their voltages is changed. At given distances from soma and over long paths, some branches display similar voltages resulting in their grouping which is also preserved when specific membrane resistivity is changed. However, the mutual relation between branches inside the group is respecified when different values of specific membrane resistivity are used in the simulations. We find that there are some invariant features of the electrotonic structure which are related to the geometry and not to the electrical parameters, while other features are changed by altering the electrical parameters. Under transient conditions, the somatofugal invasion of the dendritic tree by a somatic action potential shifts membrane potentials (above 10 mV) of dendritic paths for unequal distances from the soma during several milliseconds. Electrotonic reconfigurations and membrane shifts might be a mechanism for postsynaptic plasticity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.1993.tb00216.x
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  • 4
    Electronic Resource
    Electronic Resource
    Anatomical and electrophysiological identification of motoneurones supplying the cat retractor bulbi muscle (1979)
    Springer
    Experimental brain research 34 (1979), S. 541-550 
    Details
    ISSN: 1432-1106
    Keywords: Retractor bulbi motoneurones ; Accessory abducens nucleus ; 6th nerve ; Oculomotricity ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Motoneurones innervating the retractor bulbi muscle in the cat have been identified by retrograde labelling with horseradish peroxidase, by intracellular recording and by intracellular staining with horseradish peroxidase. Their somata are found in an accessory abducens nucleus, analogous to that described in some other species, which consists of a narrow column of cells situated in the lateral tegmental reticular field, above the superior olive and medial to the facial nerve. This column of cells extends over approximately 1.5 mm from P 5.5 to P 7. The retractor bulbi motoneurones number from 80 to 120 and have large, elongated somata which give rise to five or six major dendrites. Their axons cross the reticular formation in a dorso-medial direction to pass through the principal abducens nucleus before turning to leave the brain stem in the 6th nerve. Antidromic latencies ranged from 0.4 to 0.7 ms. Some retractor bulbi motoneurones could also be activated antidromically by stimulation of the lateral rectus muscle nerve.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00239148
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  • 5
    Electronic Resource
    Electronic Resource
    Horizontal vestibular nystagmus. II. Activity patterns of medial vestibular neurones during nystagmus (1976)
    Springer
    Experimental brain research 26 (1976), S. 387-405 
    Details
    ISSN: 1432-1106
    Keywords: Medial vestibular neurones ; Nystagmus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. Identified medial vestibular neurones were studied before, during and after nystagmogenic labyrinthine stimulation in the Encéphale isolé cat. Motor discharges were simultaneously recorded from the contralateral abducens nerve. 2. 87.9% of the recorded neurones showed changes in tonic firing frequency during repetitive labyrinthine stimulation with no nystagmic modulation in behaviour. 3. The secondary vestibular neurones projecting monosynaptically to the contralateral abducens motoneurones were included in this non-rhythmic population. 4. Only 2% of the recorded population fired rhythmically both during nystagmogenic stimulation and poststimulation nystagmus. These neurones showed plasticity in behaviour regarding the phases of nystagmus recorded from the contralateral abducens nerve. 5. The remaining 10.1% of the medial vestibular neurones were excited or inhibited by repetitive stimulation of the labyrinth but showed burst firing patterns correlated with poststimulation nystagmic discharges.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00234221
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  • 6
    Electronic Resource
    Electronic Resource
    Resistance to glycogen depletion of motor units in the cat rectus lateralis muscle (1985)
    Springer
    Experimental brain research 60 (1985), S. 542-550 
    Details
    ISSN: 1432-1106
    Keywords: Extraocular muscle ; Motor units ; Glycogen depletion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In nembutal anesthetized adult cats, intracellular stimulation of single abducens motoneurones was used to elicit glycogen depletion of their muscle units. Stimulation by short trains (13 pulses at 40 Hz) delivered once a second, was applied for 20 to 110 min. The activation of the motor unit was monitored by intracellular recording of motoneurone action potentials and by EMG. After the end of stimulation, the muscle was excised and frozen to be cut in serial sections that were processed for demonstration of either glycogen, ATPases or SDH. In two experiments, a motor unit could be histochemically identified because 10–15 fibres showed zones of complete glycogen depletion measuring about 5 mm in length. All the depleted fibres had the same histochemical profile: ATPases reactions gave dark staining with alkaline preincubation and light staining with acid preincubation whereas SDH activity was low. In other experiments, prolonged stimulation produced either no depletion at all or very limited zones of partial depletion in a few muscle fibres.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00236940
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  • 7
    Electronic Resource
    Electronic Resource
    Horizontal vestibular nystagmus. I. Identification of medial vestibular neurones (1976)
    Springer
    Experimental brain research 26 (1976), S. 367-386 
    Details
    ISSN: 1432-1106
    Keywords: Medial vestibular neurones ; Vestibulo-abducens reflex arc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. The properties of inputs from the horizontal semi-circular canal to neurones of the medial vestibular nucleus have been studied intracellularly in the unanaesthetized encéphale isolé cat. 2. Secondary neurones of the vestibulo-abducens reflex arc were identified by their orthodromic response to labyrinthine stimulation and by antidromic excitation from the contralateral abducens nucleus. 3. The responses of medial vestibular cells receiving only labyrinthine inputs are also described. These were seen to be predominantly excitatory though IPSPs were observed in a few cases. 4. Identified vestibular neurones were intracellularly injected with procion yellow and showed different morphological characteristics correlated with function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00234220
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  • 8
    Electronic Resource
    Electronic Resource
    Activités unitaires des neurones vestibulaires et oculomoteurs au cours du nystagmus (1968)
    Springer
    Experimental brain research 5 (1968), S. 16-31 
    Details
    ISSN: 1432-1106
    Keywords: Nystagmus ; Abducens nerve ; Oculomotor neurones ; Interneurones loops ; Rhythm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Extracellular recordings of single cells around the abducens nucleus show that certain cells discharge rythmically during nystagmus. The period of their firing and the period of nystagmus are the same but are slightly out of phase. From this, we assume that interneurones also play a part in producing nystagmic discharges. 1. By antidromic stimulation, it was possible to identify ocular motoneurones (single shock antidromic stimulation) and interneurones of motor reverberating circuits (repetitive antidromic stimulation). 2. Interneurones of the vestibulo-ocular circuit are triggered by stimulation of the ampullar nerve from the horizontal semi-circular canal. The stimulation can produce either a phasic response (single shock) or a nystagmus (repetitive stimulation). 3. Oculomotor nystagmic cells may be discribed by comparing the latencies of their responses and of vestibulo-ocular reflex and also by comparing their firing pattern in relation to the nystagmic discharges. 4. Only one group of interneurones is exclusively concerned with nystagmic activity. They are never activated by antidromic stimulation or by single shock ampullar nerve stimulation. Their rythmic firing during nystagmus is in opposite phase to the motor discharges. They are found in the dorso-medial area of the medial vestibular nucleus. 5. The other groups of interneurones are activated in vestibulo-ocular reflex responses and produces rythmic firing synchronised with the nystagmic discharges. 6. We suggest that those interneurones which are exclusively concerned with nystagmus have an inhibitory function. The other nystagmic interneurones would then have a re-excitatory function. Their opposing functions could explain the periodicity of the nystagmic discharges and also their progressive increase in amplitude by invoking the action of short closed loops of interneurones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00239902
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  • 9
    Electronic Resource
    Electronic Resource
    Morphological and electrophysiological properties of trigeminal neurones projecting to the accessory abducens nucleus of the cat (1983)
    Springer
    Experimental brain research 53 (1983), S. 118-128 
    Details
    ISSN: 1432-1106
    Keywords: Accessory abducens nucleus ; Spinal trigeminal neurones ; Axonal trigeminal trajectory ; Intracellular recordings ; Intracellular HRP ; Retractor bulbi motoneurones control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Horseradish peroxidase was injected into the somata or axons of neurones located in the nucleus oralis of the spinal trigeminal complex and projecting to the accessory abducens nucleus. A group of 43 axons with electrophysiologically identified responses to the stimulation of three different areas of the face were studied. The latencies of their orthodromic responses following trigeminal stimulation and their pattern of discharges were compared to those of secondary trigeminal neurones and retractor bulbi motoneurones. Labelled trigeminal axons were found to generate collaterals for the accessory abducens nucleus. Terminal ramifications are present in the rostro-caudal part of the motor nucleus where the dendritic arborization of the motoneurones has been described. Connections to facial and trigeminal motor nuclei were also present, suggesting that secondary trigeminal axons distributed the information to the three motor targets at the brain stem level. It is suggested that the trigemino-retractor bulbi reflex is part of facial reflexes involved in orienting reactions, and protective responses resulting in coordinated movements of the facial musculature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00239404
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  • 10
    Electronic Resource
    Electronic Resource
    Evidence for a rapid transmission in the cat vestibulo-ocular pathway (1971)
    Springer
    Experimental brain research 13 (1971), S. 327-338 
    Details
    ISSN: 1432-1106
    Keywords: Vestibulo-ocular pathway ; MLF fibers ; Labyrinth stimulation ; Rapid transmission
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Electrical stimulation of the vestibular nerve originating from the ampulla of the horizontal semi-circular canal evoked a “short latency invasion” in certain fibers of the medial longitudinal fasciculus (MLF) in “encéphale isolé” cats. 1. This rapid excitation occurs at a latency of 0.60 msec after the onset of the labyrinth stimulation in 17% of the MLF fibers, recorded intra-axonally. 2. The brevity and the stability of the latency coupled with the ability of the potentials to follow high frequency stimulation suggest a high degree of security in the transmission. 3. Three possible hypotheses are proposed to explain the rapid invasion of the MLF fibers: a monosynaptic connection between labyrinth receptors and ocular motoneurones, or an antidromic excitation of efferent fibers, or an electrotonic coupling phenomenon in the vestibulo-ocular circuit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00234953
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