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  • 1
    Electronic Resource
    Electronic Resource
    Changes in presynaptic inhibition of Ia fibres to soleus motoneurones during voluntary dorsiflexion of the foot (1989)
    Springer
    Experimental brain research 76 (1989), S. 510-518 
    Details
    ISSN: 1432-1106
    Keywords: Heteronymous Ia facilitation ; Presynaptic inhibition ; Reciprocal inhibition ; Monosynaptic reflex ; Voluntary movement ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Variations of presynaptic inhibition in heteronymous Ia fibres projecting to soleus motoneurones were studied during the first 250 ms of phasic voluntary isometric contractions of the antagonist tibialis anterior muscle in human subjects. During the first 60–80 ms of TA e.m.g activity, presynaptic inhibition was often more marked than at rest, but not in all experimental sessions. After 60–80 ms, presynaptic inhibition was always increased compared to rest and to the onset of TA e.m.g. activity. A “rebound” in femoral nerve induced Ia facilitation was often observed between 90–150 ms. The early increase in presynaptic inhibition was widespread and non specific since it was observed at the onset of extensor carpi radialis contractions of maximal strength. The “rebound” in heteronymous Ia facilitation was interpreted as a relative decrease in presynaptic inhibition to which nonspecific suprasegmental and cutaneous effects contributed. The late increase in presynaptic inhibition in Ia fibers to soleus motoneurones was considered as reciprocally inhibiting the Sol H-reflex, thus counteracting the phasic stretch of the antagonist muscle during TA contraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00248907
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Cortical control of presynaptic inhibition of Ia afferents in humans (1998)
    Springer
    Experimental brain research 119 (1998), S. 415-426 
    Details
    ISSN: 1432-1106
    Keywords: Key words Cortical stimulation ; Ia afferents ; Presynaptic inhibition ; Spinal interneurones ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The effect of transcranial magnetic stimulation was investigated on presynaptic inhibition of Ia terminals in the human upper and lower limb. Presynaptic inhibition of Ia afferents was assessed by three different and independent methods: (1) heteronymous Ia facilitation of the H-reflex (assessing ongoing presynaptic inhibition of Ia afferents in the conditioning volley); (2) long-lasting inhibition of the H-reflex by a group I volley (D1 inhibition, assessing presynaptic inhibition on Ia afferents in the test volley); (3) measurement of the monosynaptic Ia peak evoked in single motor units by a homonymous or heteronymous volley (post stimulus time histogram method). The first two methods were used on the lower limb; the last two on the upper limb. Provided that the corticospinal volley and the explored Ia volley were directed to the same target motoneurones, cortical stimulation evoked significant and congruent changes: (1) In the lower limb, transcranial stimulation provided increased heteronymous Ia facilitation and decreased D1 inhibition, both of which suggest a decrease in presynaptic inhibition of Ia afferents; (2) in the upper limb, transcranial stimulation provided an increase in the radial-induced inhibition of the wrist flexor H-reflex and a decrease in the peak of monosynaptic Ia excitation in single units, both of which suggest an increase in presynaptic inhibition. Selectivity of corticospinal effects was explored by testing presynaptic inhibition of Ia afferents to soleus motoneurones and focusing the transcranial stimulation to excite preferentially different motor nuclei (soleus, quadriceps and tibialis anterior). A cortical-induced decrease in presynaptic inhibition of Ia afferents was seen when, and only when, cortical and peripheral Ia volleys were directed to the same motor nucleus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050357
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Further evidence for non-monoynaptic group I excitation of motoneurones in the human lower limb (1997)
    Springer
    Experimental brain research 115 (1997), S. 35-46 
    Details
    ISSN: 1432-1106
    Keywords: Key words Non-monosynaptic group I excitation ; Group II excitation ; Spinal reflexes ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Non-monosynaptic group I and group II excitation of human lower limb motoneurones was investigated. Changes in the firing probability of individual voluntarily activated motor units belonging to various muscles (soleus, gastrocnemius medialis, tibialis anterior, peroneus brevis, quadriceps and biceps femoris) were investigated after stimulation of various nerves (posterior tibial, common peroneal and femoral nerves) with weak (0.4–0.6×motor threshold) electrical stimuli. In all investigated motor nuclei, stimulation of the ”homonymous” nerve evoked a peak of increased firing probability with a latency that was 3–7 ms longer than the monosynaptic Ia latency. The more caudal the motor nucleus explored, the greater the central delay. This strongly suggests a transmission through neurones located above the lumbar enlargement. If one excepts the sural-induced excitation of peroneus brevis units, which seems to be mediated through a particular pathway, the main peripheral input to neurones mediating non-monosynaptic excitation evoked by these weak stimuli is group I in origin. The pattern of distribution of non-monosynaptic group I excitation was very diffuse, since stimulation of each nerve was able to evoke excitation in all investigated nuclei. In most cases, non-monosynaptic excitation evoked in a given motor unit by stimulation of one nerve was depressed on combined stimulation of two nerves, and evidence is presented that this lateral inhibition is exerted at a premotoneuronal level. By contrast, there was no evidence that increasing the afferent input in a given pathway evokes an ”autogenetic” inhibition in this pathway. The negative correlation found between non-monosynaptic group I-induced and late group II-induced facilitation of the quadriceps H-reflex when using high stimulus intensities applied on the common peroneal nerve suggests that these two effects could be mediated through common interneurones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00005683
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    Paper (German National Licenses)
    Fulltext
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