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Motor axon reflex and indirect double discharge: ephaptic transmission? A reappraisal

M R Magistris1, G Roth

  • 1Division of Clinical Neurophysiology, University Hospital, Geneva, Switzerland.

Electroencephalography and Clinical Neurophysiology
|April 1, 1992
PubMed

Insights

This study re-examines motor axon reflex (MAR) and indirect double discharge (IDD) mechanisms. Findings refute the ephaptic transmission hypothesis, supporting axonal branching for MAR and proximal re-excitation for IDD.

Area of Science:

  • Neuroscience
  • Electrophysiology
  • Motor Neuron Physiology

Background:

  • Motor axon reflex (MAR) and indirect double discharge (IDD) are intermediate latency responses observed in electrophysiological studies.
  • Recent hypotheses proposed axono-axonal ephaptic transmission as the underlying mechanism for MAR and IDD.

Purpose of the Study:

  • To re-examine the causal mechanisms of MAR and IDD.
  • To evaluate the validity of the ephaptic transmission hypothesis for these neurophysiological phenomena.

Main Methods:

  • Comparison of theoretical models of axonal cross-talk with experimental observations from limb recordings.
  • Analysis of electrophysiological data to differentiate between proposed and established mechanisms.

Main Results:

  • The ephaptic hypothesis was found to be insufficient in explaining the observed characteristics of MAR and IDD.
  • Model responses based on ephaptic transmission did not align with actual electrophysiological findings.

Conclusions:

  • The study concludes that axono-axonal ephaptic transmission does not cause MAR and IDD.
  • The established understanding that MAR originates from axonal branching and IDD from proximal re-excitation on the axon is reaffirmed.

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