FUNCTIONAL ANALYSIS OF THE SENSORY MOTOR PATHWAY OF RESISTANCE REFLEX IN
CRAYFISH. II- INTEGRATION OF SENSORY INPUTS IN MOTOR NEURONS.
Didier LE RAY, François CLARAC, and Daniel CATTAERT.
Laboratoire de Neurobiologie et Mouvements, CNRS, 31 chemin Joseph Aiguier,
Marseille, France.
APStracts 4:162N, 1997.
ABSTRACT
The in vitro preparation of the fifth thoracic ganglion of the crayfish was
used to analyze the connections supporting the monosynaptic reflex responses
recorded from the depressor motor neurons (Dep MNs). Dep MNs are directly
connected by the release-sensitive afferents from a proprioceptor, the coxo-
basipodite chordotonal organ (CBCO) which is released by upward movements of
the leg. Sine wave movements, applied to the CBCO strand from the most
released position, allowed us to stimulate the greatest part of release-
sensitive CBCO fibers. Systematic intracellular recordings from all Dep MNs
performed in high divalent cation saline allowed us to determine the
connections between CBCO afferents and their postsynaptic Dep MNs: it
highlighted the sequential activation of the different Dep MNs involved in the
monosynaptic reflex. The convergence of different sensory afferents onto a
given Dep MN, and the divergence of a given sensory afferent onto several Dep
MNs illustrates the complexity of the sensory-motor reflex loops involved in
the control of locomotion and posture. Electrophysiological experiments and
simulations were performed to analyze the mechanisms by which Dep MNs
integrate the large amount of sensory input that they receive. Paired
intracellular recording experiments demonstrated that postsynaptic
response shapes characteristic of both phasic and phaso-tonic afferents could
be induced by varying the presynaptic firing frequency, whatever the
postsynaptic Dep MN. Compartment model simulations were used to analyze the
role of the sensory-motor synapse characteristics in the summation properties
of postsynaptic MN. They demonstrated the importance of the postsynaptic
compartment geometry, since large postsynaptic compartments allowed to
generate greater EPSP summations than small ones. The results presented show
that velocity information is the most effective to elicit large compound EPSPs
in MNs. We therefore suggest that the negative feedback reflex is mainly based
upon the detection of leg movements.
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Received 14 April 1997; accepted in final form 22 July 1997;.
APS Manuscript Number J301-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 28 August 1997