Elsevier

Neuroscience

Volume 15, Issue 1, May 1985, Pages 1-12
Neuroscience

Depolarizing afterpotentials in myelinated axons of mammalian spinal cord

https://doi.org/10.1016/0306-4522(85)90118-6Get rights and content

Abstract

Microelectrode recordings were made from 5–10 μm dia axons of adult rat spinal cord in vitro. Action potentials in response to electrical stimulation were recorded intracellularly and electrical markedly with increase of temperature to physiological levels, in conjunction with the expected decrease in action potential duration. Similar afterpotential components were present in the response of the axon to injected hyperpolarizing current pulses.

The observations are consistent with the suggestion [Barrett and Barrett (1982) J. Physiol., Lond. 323, 117–144] that the afterpotential results from charging of the axolemmal capacitance by current passing through the myelin sheath during the action potential. They are inconsistent with a number of calculations of electrical characteristics of peripheral axons derived from voltage clamp experiments in isolated fibers. It is argued that the electrical resistance of the myelin lamellae is relatively low, though within the range calculated for other glial membranes. This suggestion is found more compatible with the available morphological data than the alternative proposal that a leakage pathway under the myelin sheath might be responsible for the afterpotential [Barrett and Barrett (1982) J. Physiol., Lond. 323, 117–144]. The significance of this organization for the function of myelinated axons and the electrical basis of the afterpotential are examined further in the accompanying paper [Blight (1985) Neuroscience 15, 13–31].

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