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  • 1
    ISSN: 0169-4332
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0169-4332
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 30 (1977), S. 203-218 
    ISSN: 1432-1106
    Keywords: Rubrospinal neurons ; Axon branching ; Spinal cord ; Microstimulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The branching patterns of rubrospinal (RS) axons projecting to the cervical spinal cord between C3 and C8 were studied in the cat. RS neurons were identified by their antidromic responses to microstimulation of local axon branches within the cervical gray matter. Twenty-six of 58 RS neurons projecting to the cervical gray matter also sent axon branches to the thoracic spinal cord. Two out of 40 of these RS neurons also sent axon branches to the lumbar spinal cord. Using a collision technique, it was demonstrated that stem axons of rubrospinal neurons commonly sent multiple collaterals to different cervical segments. Neurons projecting to the cervical spinal cord alone were located in the dorsal quadrants of the red nucleus. Those projecting to cervical, as well as to more caudal segments, were intermingled with the former, and in slightly more ventral portions of the red nucleus. The presence of RS neurons projecting to widely separate levels of the spinal cord suggests that individual RS neurons may be capable of ultimately influencing two or more different motoneuron pools.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 32 (1978), S. 55-68 
    ISSN: 1432-1106
    Keywords: Functional stretch reflex ; Spinal cord ; Cat ; Tracking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A sudden and rapid angular displacement of the limb evokes, in human and monkey subjects, a segmented pattern of electromyographic activity in muscles which are stretched. While the first segment is acknowledged to represent a tendon jerk, it has been proposed that the second segment, occurring with a shorter latency than a reaction time, is mediated by a transcortical loop. The present experiments were conducted in cats to determine the properties of muscle responses to torque perturbations analogous to those used in the monkey, and to determine if the integrity of supraspinal pathways is required for the individual response segments to occur. Torque perturbations which flexed the forearm evoked a segmented response in the electromyogram of the cat triceps muscle. This response typically consisted of three early segments with latencies of 10, 30 and 60 msec which were similar to the M1, M2, and M3 segments described in the monkey. The M3 and occasionally M2 components were depressed when the cat followed rather than resisted the perturbation. A torque pulse of 10 msec duration was sufficient to elicit a near maximal M1 response while torque pulses in excess of 20 msec were required to evoke the M2 response. To determine if any of these components required mediation by the cerebral cortex, experiments were conducted in decerebrate and spinal cats. Similar torque perturbations produced segmented electromyographic responses in the triceps muscles which were indistinguishable in their timing from those observed in intact cats. The torque required to produce the segmented responses was comparable as well. All three segments were dependent upon the activation of receptors in the homonymous muscle and did not require cutaneous input. These observations show that receptor properties and/or spinal mechanisms involved in the stretch reflex are sufficient to produce a segmented response similar to that observed in intact animals.
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  • 5
    ISSN: 1432-1106
    Keywords: Parietal cortex ; Thalamus ; Cerebellar nucleus ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The characteristics of cerebellar input to the parietal cortex through the ventroanterior-ventrolateral (VA-VL) complex of the thalamus were investigated in the adult cat by using combined electrophysiological and anatomical methods. Two distinct parietal regions were activated by stimulation of the cerebellar nuclei (CN). In the first region located in the depth of the bank of the ansate sulcus, stimulation of the CN induced early surface positive-deep negative potentials and late surface negative-deep positive potentials. In this cortical area, potentials of similar shape and time course were evoked at a shorter latency by stimulation of the ventrolateral part of the VA-VL complex where large negative field potentials were evoked by stimulation of the CN. After injection of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) in this part of the VA-VL complex, axon terminals of thalamocortical (TC) fibers were found in layers I, III and IV in the depth of the bank of the ansate sulcus and layers I and III in the motor cortex. In the second region located in the suprasylvian gyrus, late surface negative-deep positive potentials were evoked by stimulation of the CN and similar potentials were evoked at a shorter latency from the dorsomedial part of the VA-VL complex where large cerebellar-evoked potentials could be recorded. PHA-L injection in this thalamic region stained TC fibers and their terminals in layer I of the suprasylvian gyrus, and in layers I and III of the motor cortex. The laminar distribution of TC axon terminals in two different regions of the parietal cortex could account for the depth profiles of the cerebellar- and the thalamic-evoked potentials in each region. These results show that cerebellar information is conveyed to two separate areas in the parietal cortex by two different TC pathways.
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  • 6
    ISSN: 1432-1106
    Keywords: Mossy fibers ; Vestibular afferents ; Vestibular nucleus neurons ; Vestibulo-floccular input ; Semicircular input
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In decerebrate, unanesthetized cats, responses in the flocculus were evoked by electric stimulation of the vestibular nerves and by natural stimulation of horizontal head angular acceleration. Field potentials in the flocculus and intracellular recording from Purkinje cells following vestibular nerve stimulation indicated that the responses were produced by mossy fiber inputs. Field potentials evoked from the contralateral labyrinth were as large as those from the ipsilateral one. There was considerable convergence of bilateral labyrinthine mossy fiber inputs to a Purkinje cell. In view of the effects of incision at the midline of the cerebellum and the brain stem, inputs from the contralateral labyrinth were mainly conveyed through the midline of the brain stem and partly through the midline of the cerebellum. Primary vestibular afferents were involved in the transcerebellar crossed pathway. Fibers of the secondary vestibular neurons projecting to the contralateral flocculus were implicated in the brain stem-mediated pathway and, in part, presumably in the transcerebellar crossed pathway. About one-third of the axon spikes examined in the flocculus responded to horizontal head angular acceleration. Commissural inhibition was observed in more than half of the axon spikes in the flocculus which were presumed to be mono- or polysynaptically activated from the vestibular nerve.
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  • 7
    ISSN: 1432-1106
    Keywords: Area 3a ; Motor cortex ; Muscle afferents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Two receiving areas in the pericruciate cortex are known for inputs from group I muscle afferents of forelimb nerves. One focus is near the postcruciate dimple of area 3a, and the other in the lateral sigmoid gyrus of the motor cortex (area 4γ). The cortico-cortical projection of area 3a to 4γ, and the relay by this projection of group I muscle afferent input to the motor cortex were investigated in cats. The following results were obtained. 1. Seventy-four neurons within area 3a were antidromically activated by intracortical microstimulation of the motor cortex. 2. Although excitation evoked by stimulation of group I muscle afferents could be demonstrated for only a few (8 of 48) cortico-cortical neurons in extracellular recordings, due to the methodological limitations discussed, this input evoked EPSPs in 8 of 9 cortico-cortical neurons recorded intracellularly. Therefore, it is likely that the majority of neurons projecting from area 3a to the motor cortex have an excitatory synaptic input from group I afferents. 3. Neurons projecting from area 3a to the motor cortex were most commonly found in cortical layer III, although some were found in layer V. 4. Five of nine pyramidal tract neurons of area 3a had a strong excitatory synaptic input from group I muscle afferents. 5. A new type of pyramidal tract neuron was found which has cortico-cortical axon collaterals connecting the two cytoarchitectonic regions. These various neurons may be part of a feedback system from muscle afferents to the motor cortex.
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  • 8
    ISSN: 1432-1106
    Keywords: Pyramidal tract neurons ; Axon branching ; Spinal cord ; Monkey
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The branching pattern of individual pyramidal tract (PT) neurons of the monkey motor cortex was studied by activating these neurons antidromically from within the cervical motor nuclei and also from other regions of the spinal cord. 1. Fifty-four neurons were activated from motor nuclei in the cervical cord. Twenty-eight of these were activated from one segment and six (11%) were activated from motor nuclei of different segments. The remaining 20 neurons were activated from motor nuclei and also from unspecified region(s) of the gray matter. 2. Another 156 neurons were activated from unspecified region(s) of cervical gray matter which could have been motor nuclei or outside the nuclei, and 64 of these were activated from more than one segment. 3. The branching patterns of PT neurons sending axons directly to motor nuclei innervating distal forelimb muscles suggested that they branch less than the rest of PT neurons.
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  • 9
    ISSN: 1432-1106
    Keywords: Intraaxonal HRP ; Mossy fibers ; Cerebellar cortex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Several unidentified units recorded in the intermediate zone of lobules IV and V of the cerebellar cortex responded to superficial radial nerve stimulation with a distinctive short train of 5 to 11 low amplitude spikes (less than 5 mV) at a frequency of 800 to 1200 Hz. Responses of this type have in the past been attributed to mossy fiber afferents. Following the electrophysiological characterization horseradish peroxidase was successfully injected by iontophoresis into four axon terminals. The labelled axons presented the typical structure of mossy fibers with terminal rosettes and corresponded to the morphology of these axons described in Golgi material.
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  • 10
    ISSN: 1432-1106
    Keywords: Vestibular nystagmus ; Abducens motoneuron ; Presynaptic impulse ; Vestibular neuron ; Burst neuron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. Unit spikes of axons projecting to the abducens nucleus and responding to horizontal rotation of the head were recorded within the cat abducens nucleus. Their discharge pattern related to vestibular nystagmus was investigated with reference to PSP changes of abducens motoneurons as monitored by the field potentials in the nucleus. There were four groups of presynaptic axons whose activity was tightly related to motoneuronal PSPs. 2. The first and second groups of axons were activated mono- and disynaptically from the contralateral labyrinth, respectively, and fired in phase with abducens nerve discharges. Their tonic activity during the slow excitatory phase of motoneurons was abruptly suppressed at the onset of positive field potential (motoneuronal hyperpolarization). The disynaptically activated axons exhibited burst-tonic discharges at the quick excitatory phase and steep increases in their discharge frequency were synchronous with the onset of negative field potential (motoneuronal depolarization). 3. The third group was activated monosynaptically from the ipsilateral labyrinth and fired in phase with the silent period of the abducens nerve. Their tonic activity during the slow inhibitory phase of motoneurons was abruptly silenced at the onset of negative field potential. At the quick inhibitory phase they tended to begin firing slightly later than the onset of positive field potential. 4. The fourth group exhibited high frequency burst discharges at the quick inhibitory phase of motoneurons. Steep increases in discharge frequency occurred synchronously with the onset of the positive field potential. These axons were silent during the slow inhibitory phase of motoneurons. 5. The characteristic time course of PSPs in abducens motoneurons during vestibular nystagmus was well explained by synaptic actions of these four groups of presynaptic axon on motoneurons. The origin of each group of axon was discussed in view of their responses to electric stimulation of the vestibular nerve.
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