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The Role of Primary afferent Depolarisation in Presynaptic Inhibition of Group I Fibres

  • B. Lamotte d’Incamps
  • M.-L. Monnet
  • C. Meunier
  • D. Zytnicki

Abstract

In a previous study, declining inhibitory potentials, ascribed to the action of Ib afferents, were recorded in homonymous and synergic motoneurones during sustained subtotal isometric contractions of gastrocnemius medialis (GM) muscle (Zytnicki, Lafleur, Horcholle-Bossavit, Lamy & Jami, 1990). In a subsequent study, contraction-induced primary afferent depolarisations (PADs) were recorded intra-axonally from the intraspinal portion of homonymous Ib fibres during similar GM contractions (Lafleur, Zytnicki, Horcholle-Bossavit & Jami, 1992). Since PAD is known to be the electrophysiological correlate of presynaptic inhibition (Eccles, Schmidt & Willis, 1962), this observation supported the assumption that presynaptic inhibition of Ib fibres accounted for the decline of contraction-induced inhibition in motoneurones (see Zytnicki & L’Hôte, 1993). The aim of the present computer study was to evaluate the efficacy of the mechanism of presynaptic inhibition received by myelinated afferent fibres. Activation of an axo-axonic synapse may partly shunt the action potentials travelling along the fibre (Segev, 1990), but as recently suggested, the PAD might also contribute by itself to presynaptic inhibition by reducing the spike height (Graham & Redman, 1994). In the present paper, potentiation of the effects of an axo-axonic synapse by the PAD is demonstrated and explained on a simple model of the myelinated axon in terms of the dynamics of ionic currents.

Keywords

Gastrocnemius Medialis Presynaptic Inhibition Action Potential Amplitude Peak Conductance Afferent Action Potential 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. Eccles, J. C., Schmidt, R. F. & Willis, W. D. (1962) Depolarisation of central terminals of group I afferent fibres of muscle. J. Physiol. 160, 62–93.PubMedGoogle Scholar
  2. Graham, B. & Redman, S. (1994) A simulation of action potentials in synaptic boutons during presynaptic inhibition. J. Neurophysiol. 71, 538–549.PubMedGoogle Scholar
  3. Hodgkin, A. L. & Huxley, A. F. (1952) A quantitative description of membrane current and its application to conduction and excitation in nerve. J. Physiol. 117, 500–544.PubMedGoogle Scholar
  4. Lafleur, J., Zytnicki, D., Horcholle-Bossavit, G. & Jami, L. (1992) Depolarisation of Ib afferent axons in the spinal cord during homonymous muscle contraction. J. Physiol. 445, 345–354.PubMedGoogle Scholar
  5. Nicol, M. J. & Walmsley, B. (1991) A serial electron microscope study of an identified Ia afferent collateral in the cat spinal cord. J. Comp. Neurol. 314, 257–277.PubMedCrossRefGoogle Scholar
  6. Segev, I. (1990) Computer study of presynaptic inhibition controlling the spread of action potentials into axonal terminals. J. Neurophysiol. 63, 987–997.PubMedGoogle Scholar
  7. Zytnicki, D., Lafleur, J., Horcholle-Bossavit, G., Lamy, F. & Jami, L. (1990) Reduction of Ib autogenetic inhibition in motoneurons during contractions of an ankle extensor muscle in the cat. J. Neurophysiol. 64, 1380–1389.PubMedGoogle Scholar
  8. Zytnicki, D. & L’Hôte, G. (1993) Neuromimetic model of a neuronal filter. Biol. Cyber. 70, 115–121.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 1995

Authors and Affiliations

  • B. Lamotte d’Incamps
    • 1
  • M.-L. Monnet
    • 2
  • C. Meunier
    • 2
  • D. Zytnicki
    • 1
  1. 1.CNRS URA 1448Université René DescartesParis Cx 06France
  2. 2.CNRS UPR 014Centre de Physique Théorique Ecole PolytechniquePalaiseauFrance

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