The Journal of Neuroscience, February 1, 2001, 21(3):1007-1021
Presynaptic Inhibition and Antidromic Spikes in Primary Afferents
of the Crayfish: A Computational and Experimental Analysis
Daniel
Cattaert1,
Frédéric
Libersat2, and
Abdeljabbar
El Manira3
1 Laboratoire Neurobiologie et Mouvements, Centre
National de la Recherche Scientifique, 13402 Marseille Cedex 20, France, 2 Department of Life Sciences and Zlotowski Center
for Neuroscience, Ben Gurion University of the Negev, Beer Sheva,
84105, Israel, and 3 The Nobel Institute for
Neurophysiology, Department of Neuroscience, Karolinska Institutet,
S-171 77 Stockholm, Sweden
Primary afferent depolarizations (PADs) are associated with
presynaptic inhibition and antidromic discharges in both vertebrates and invertebrates. In the present study, we have elaborated a realistic
compartment model of a primary afferent from the coxobasipodite chordotonal organ of the crayfish based on anatomical and
electrophysiological data. The model was used to test the validity of
shunting and sodium channel inactivation hypotheses to account for
presynaptic inhibition. Previous studies had demonstrated that GABA
activates chloride channels located on the main branch close to the
first branching point. We therefore focused the analysis on the effect of GABA synapses on the propagation of action potentials in the first
axonal branch. Given the large diameters of the sensory axons in the
region in which PADs were likely to be produced and recorded, the model
indicates that a relatively large increase in chloride conductance (up
to 300 nS) is needed to significantly reduce the amplitude of sensory
spikes. The role of the spatial organization of GABA synapses in the
sensory arborization was analyzed, demonstrating that the most
effective location for GABA synapses is in the area of transition from
active to passive conduction. This transition is likely to occur on the
main branch a few hundred micrometers distal to the first
branching point. As a result of this spatial organization, antidromic
spikes generated by large-amplitude PADs are prevented from propagating distally.
Key words:
presynaptic inhibition; primary afferent
depolarization; antidromic discharge; crayfish; simulation; compartment
model
Copyright © 2001 Society for Neuroscience 0270-6474/01/2131007-15$05.00/0
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