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  • Title: Facilitation of quadriceps motoneurones by group I afferents from pretibial flexors in man. 1. Possible interneuronal pathway.
    Author: Forget R, Pantieri R, Pierrot-Deseilligny E, Shindo M, Tanaka R.
    Journal: Exp Brain Res; 1989; 78(1):10-20. PubMed ID: 2591506.
    Abstract:
    The neuronal pathway of the facilitation of quadriceps (Q) motoneurones (MNs) evoked by stimulation of the common peroneal nerve (CPN) has been reinvestigated using both the post-stimulus time histogram (PSTH) method for measurement of the firing probability of individual units and the H reflex technique. It has been found that Ia (and to an unknown extent Ib) afferents from pretibial flexors - but not from peroneal muscles - are responsible for this excitation. The central latency of the CPN-induced excitation of Q MNs was estimated to be 3-3.7 ms longer than that of their monosynaptic Ia excitation. To further investigate the neuronal pathway of the CPN-induced excitation the spatial facilitation technique was used, the effects on the Q H reflex of two conditioning stimuli (applied to the CPN and the femoral nerve - FN) being compared when applied separately and together. When the two conditioning volleys were timed to reach the spinal cord simultaneously the facilitation of the H reflex on combined stimulation was larger than the algebraic sum of the effects by separate stimuli in 40% of the cases. It is argued that this additional facilitation reflects summation at a premotoneuronal level and it is concluded that non-monosynaptic Ia excitation of Q MNs from Q and pretibial flexors is, at least partly, mediated through a common pathway. In those individual units in which stimulation of the FN and/or the CPN evoked a non-monosynaptic Ia excitation, this excitation was reduced on combined stimulation of the two nerves. It is argued that this reflects inhibition of the interneurones mediating the excitation, i.e. consists in a disfacilitation of the MNs. It is suggested that the non-monosynaptic (homonymous and heteronymous) Ia excitation of Q MNs in man (and the inhibition of this excitation) is mediated through a system of neurones similar to the system recently described in the cat by Edgley and Jankowska (1987).
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