The Journal of Neuroscience, 2001, 21:RC173:1-5
RAPID COMMUNICATION
Ephaptic Interactions in the Mammalian Olfactory System
Hemant
Bokil,
Nora
Laaris,
Karen
Blinder,
Mathew
Ennis, and
Asaf
Keller
Department of Anatomy and Neurobiology, Program in Neuroscience,
University of Maryland, Baltimore, Maryland 21201
Ephaptic coupling refers to interactions between neurons mediated
by current flow through the extracellular space. Ephaptic interactions
between axons are considered negligible, because of the relatively
large extracellular space and the layers of myelin that separate most
axons. By contrast, olfactory nerve axons are unmyelinated and arranged
in tightly packed bundles, features that may enhance ephaptic coupling.
We tested the hypothesis that ephaptic interactions occur in the
mammalian olfactory nerve with the use of a computational approach.
Numerical solutions of models of axon fascicles show that significant
ephaptic interactions occur for a range of physiologically relevant
parameters. An action potential in a single axon can evoke action
potentials in all other axons in the fascicle. Ephaptic interactions
can also lead to synchronized firing of independently stimulated axons.
Our findings suggest that ephaptic interactions may be significant determinants of the olfactory code and that such interactions may occur
in other, similarly organized axonal or dendritic bundles.
Key words:
volume conduction; nonsynaptic interactions; olfactory
bulb; olfactory nerve; unmyelinated axons; olfactory coding
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