Integration in descending motor pathways controlling the forelimb in the cat |
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| Authors: | Illert M Lundberg A Tanaka R |
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| Institution: | (1) Department of Physiology, University of Göteborg, Fack, S - 40033 Göteborg, Sweden;(2) Present address: Department of Physiology, University of München, Pettenkoferstrasse 12, D - 8000 München 2, Federal Republic of Germany;(3) Present address: Department of Neurobiology, Tokyo Metropolitan Institute of Neurosciences, Musashi-Dai 2-6, Fuchu, 183 Tokyo, Japan |
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| Abstract: | Summary With intracellular recording from forelimb motoneurones the spatial facilitation technique has been used to investigate interaction between descending pathways and forelimb afferents.As previously shown for the hindlimb, pyramidal volleys effectively facilitate interneuronal transmission in reflex pathways from different primary afferents. Evidence is presented suggesting disynaptic excitation from corticospinal fibres of interneurones in the reciprocal Ia inhibitory pathway. Interneurones of other reflex pathways from group I muscle afferents receive monosynaptic pyramidal excitation. During pyramidal facilitation volleys in cutaneous afferents may evoke PSPs in motoneurones after a central delay of 1.3 ms suggesting that the minimal linkage is disynaptic.Information regarding convergence on the neurones intercalated in the disynaptic cortico-motoneuronal pathway was obtained by investigating the effect from primary afferents and from other descending pathways on the disynaptic pyramidal EPSPs. Volleys in cutaneous and group I muscle afferents facilitate transmission in the disynaptic cortico-motoneuronal pathway with a time course showing oligosynaptic (probably monosynaptic) action on the intercalated neurone. Rubrospinal volleys likewise effectively facilitate disynaptic cortico-motoneuronal transmission with a time course showing monosynaptic action on the intercalated neurone. Spatial facilitation experiments involving three tests revealed that those intercalated neurones which receive convergent monosynaptic excitation from corticospinal and rubrospinal fibres are excited also from cutaneous forelimb afferents.Disynaptic cortico-motoneuronal transmission was also monosynaptically facilitated by stimuli in the dorsal mesencephalic tegmentum probably activating tectospinal fibres. Disynaptic, presumed tectospinal EPSPs were facilitated from cutaneous forelimb afferents.The convergence onto the neurones intercalated in the disynaptic excitatory cortico-motoneuronal pathway suggests that these neurones integrate the activity in different descending pathways and primary forelimb afferents.Supported by the Deutsche ForschungsgemeinschaftIBRO/UNESCO Fellow |
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| Keywords: | Forelimb motoneurones Disynaptic pyramidal EPSPs Intercalated neurones Convergence Rubrospinal fibres Primary forelimb afferents |
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