ORGANIZATION OF RECURRENT INHIBITION AND FACILITATION IN MOTOR NUCLEI
INNERVATING ANKLE MUSCLES OF THE CAT.
Vladimir V. Turkin, Katrina S. Monroe and Thomas M. Hamm.
Division of Neurobiology, Barrow Neurological Institute, St. Joseph's
Hospital and Medical Center, 350 West Thomas Road, Phoenix, AZ 85013.
APStracts 4:296N, 1997.
ABSTRACT
The distribution of recurrent inhibition and facilitation to motor nuclei of
muscles that act at the cat ankle joint was compared to the locomotor activity
and mechanical action of those muscles described in published studies.
Emphasis was placed on motor nuclei whose muscles have a principal action
about the abduction - adduction axis and the pretibial flexors: tibialis
posterior (TP), peroneus longus (PerL), peroneus brevis (PerB), the anterior
part of tibialis anterior (TA) and extensor digitorum longus (EDL). Most
intracellular recordings in spinalized, unanesthetized decerebrate cats showed
only inhibitory or excitatory responses to antidromic stimulation of
peripheral nerves, but mixed effects were also seen. Recurrent effects among
motor nuclei of ankle abductors and adductors were not distributed uniformly.
TP motoneurons received recurrent inhibition from most other nuclei active in
stance, and stimulation of the TP nerve inhibited these motor nuclei. Although
PerB motoneurons are also active during stance, they received primarily
facilitation from most motor nuclei. PerL received mixtures of inhibition and
facilitation from all sources. Stimulation of the nerves to PerL, PerB and
peroneus tertius (PerT) produced weak recurrent inhibition and facilitation,
even in homonymous motoneurons and motoneurons of Ia synergists. The ankle
flexors TA and EDL displayed different patterns of recurrent inhibition and
facilitation. TA motoneurons received prominent homonymous inhibition and
inhibition from semitendinosus (St). EDL, whose activity profile differs from
TA and which also acts at the digits, did not receive strong recurrent
inhibition from either TA or St, nor did stimulation of the EDL nerve produce
much inhibition. The distribution of recurrent inhibition and facilitation is
correlated with the pattern of locomotor activity, but with exceptions that
suggest an influence of mechanical action, particularly in the antagonistic
interactions between TP and PerB. The extended pattern of recurrent
inhibition, the reduction or absence of inhibition produced by motor nuclei
with individualized functions or digit function, and the prevalence of
facilitation suggest that the recurrent Renshaw system is organized into
inhibitory and disinhibitory projections that participate in the control of
sets of motor nuclei engaged in rhythmic and stereotyped movements.
Received 3 March 1997; accepted in final form 21 October 1997.
APS Manuscript Number J184-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 29 October 1997