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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    The vibrissal pad as a source of sensory information for the oculomotor system of the cat (1981)
    Springer
    Experimental brain research 44 (1981), S. 409-418 
    Details
    ISSN: 1432-1106
    Keywords: Oculomotricity ; Lateral rectus and retractor bulbi motoneurones ; Infraorbital nerve ; Vibrissal pad ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Responses from lateral rectus, medial rectus and retractor bulbi nerves were obtained following electrical stimulation of the vibrissal pad of the cat. Discharges in afferent fibres dissected from the infraorbital nerve were recorded during movements of the vibrissae and following electrical stimulation of the vibrissal pad. Both stimuli activated the same population of Aα fibers. Intracellular records were obtained from lateral rectus motoneurones identified antidromically in the principal abducens nucleus and from retractor bulbi motoneurones similarly identified in the accessory abducens nucleus. EPSPs (3 mV) were recorded in lateral rectus motoneurones following electrical stimulation of the ipsilateral vibrissal pad at a latency of 3.5 ms. Large-amplitude disynaptic EPSPs (15 mV) were recorded in retractor bulbi motoneurones following the same vibrissal stimulation. The synaptic excitation evoked in both lateral rectus and retractor bulbi motoneurones through stimulation of the ipsilateral vibrissal pad induced an early retraction followed by an abduction of the eye ball. The hypothesis is that the vibrissal message might complement other sensory modalities in the generation of patterned eye movements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00238833
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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Electrotonic coupling between motoneurones in the abducens nucleus of the cat (1974)
    Springer
    Experimental brain research 21 (1974), S. 139-154 
    Details
    ISSN: 1432-1106
    Keywords: Electrotonic coupling ; Antidromic responses ; Abducens motoneurone ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The electrical stimulation of the abducens nerve provokes the classical true antidromic invasion of the abducens motoneurone and a depolarization which is often capable of generating full action potentials in the impaled motoneurone. Experiments studying these depolarizations suggest the existence of electrotonic coupling between the abducens motoneurones of the cat. Intracellular activity of the abducens motoneurones was recorded following intracellular stimulation of the impaled neurone and antidromic stimulation of the abducens nerve. Collision between the outgoing action potential and the antidromic volley differentiated the true antidromic spike from the depolarizations which can induce or not action potentials. The latency of the depolarization ranged between 100 and 1200 μsec. Collision demonstrated that the depolarization and the true antidromic action potential have an independent origin. The depolarizations and action potentials which are not conveyed to the motoneurone by its own axon are interpreted to be generated by electrotonic coupling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00234386
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  • 8
    Electronic Resource
    Electronic Resource
    Phénomènes synaptiques du nystagmus (1969)
    Springer
    Experimental brain research 8 (1969), S. 201-218 
    Details
    ISSN: 1432-1106
    Keywords: Nystagmus ; Presynaptic and postsynaptic inhibition ; Loop circuits
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In a previous work (Horcholle and Tyč-Dumont 1968), sets of nystagmic interneurones have been described in the region of the abducens nucleus of the cat. One set — the inhibitory nystagmic interneurones (INI) —is triggered by nystagmogenic stimulation and its firing during nystagmus is in opposite phase to the motor nystagmic discharges. In this study, intracellular recordings from ocular motoneurones and from INIs have been obtained during nystagmus to analyse the synaptic mechanisms of the periodic activity. Motoneurones are identified by antidromic invasion following single shock stimulation of the abducens nerve. Their intracellular record during nystagmus has shown a periodic depolarization of the membrane which is synchronous with the motor nystagmic discharges. Between the phases of depolarization, the motoneurone is not excitable by orthodromic inputs of vestibular origin although it can be triggered by antidromic invasion. A reduction in amplitude of the evoked EPSPs, which is synchronous with the silent period of the motoneurones, could suggest a presynaptic inhibitory mechanism. INIs are identified by their rhythmic firing during nystagmus which is in opposite phase to the nystagmic discharges recorded simultaneously from the abducens nerve. Intracellular records from INIs have shown a periodic hyperpolarization of their membrane which is synchronous with the nystagmic motor discharges. INIs phase of activity coincides with the silent period of the abducens nerve and is synchronous with the inhibitory phase of the inputs of vestibular origin. A functional relation between the motoneurones and the INIs is highly probable and is considered to play a role in the elaboration of the rhythmic activity of nystagmus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00234249
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  • 9
    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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  • 10
    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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