Distributed motor pattern underlying whole-body shortening in the medicinal
leech.
Arisi, Ivan, Davide Zoccolan and Vincent Torre.
Scuola Internazionale Superiore di Studi Avanzati, Via Beirut 2, Trieste, Italy and
INFM, Unita' di Trieste, c/o SISSA, Via Beirut 2, Trieste, Italy
APStracts 8:0236J, 2001.
Whole-body shortening was studied in the leech, Hirudo medicinalis, by a combination of
videomicroscopy and multielectrode recordings. Video microscopy was used to monitor
the animal behavior and muscle contraction. Eight suction pipettes were used to obtain
simultaneous electrical recordings from fine roots emerging from ganglia. This vital
escape reaction was rather reproducible. The coefficient of variation of the animal
contraction during whole body shortening was between 0.2 and 0.3. The great majority of
all leech longitudinal motoneurons were activated during this escape reaction, in
particular motoneurons 3, 4, 5, 8, 107, 108 and L. The firing pattern of all these
motoneurons was poorly reproducible from trial to trial and the coefficient of variation of
their firing varied between 0.3 and 1.5 for different motoneurons. The electrical activity
of pairs of co-activated motoneurons did not show any sign of correlation over a time
window of 100 ms. Only the left and right motoneurons L in the same ganglion had a
correlated firing pattern, resulting from their strong electrical coupling. As a consequence
of the low correlation between co-activated motoneurons, the global electrical activity
during whole-body shortening became reproducible with a coefficient of variation below
0.3 during maximal contraction. These results indicate that whole-body shortening is
mediated by the coactivation of a large fraction of all leech motoneurons, i.e. it is a
distributed process, and that co-activated motoneurons exhibit a significant statistical
independence. Probably due to this statistical independence this vital escape reaction is
smooth and reproducible.
Received 20 February 2001; accepted in final form 30 May 2001
APS Manuscript Number J139-1.
Article publication pending Am J Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 31 July 2001