J Neurophysiol (November 1, 2002). 10.1152/jn.01051.2001
Submitted on 27 December 2001
Accepted on 1 July 2002
Positive Proprioceptive Feedback Elicited By Isometric
Contractions of Ankle Flexors on Pretibial Motoneurons in Cats
L.
Brizzi,
L. H.
Ting, and
D.
Zytnicki
Centre National de la Recherche Scientifique 2361, Unité Mixte de Recherche 8119, Université René
Descartes, 75270 Paris, France
Brizzi, L.,
L. H. Ting, and
D. Zytnicki.
Positive Proprioceptive Feedback Elicited By Isometric
Contractions of Ankle Flexors on Pretibial Motoneurons in Cats. J. Neurophysiol. 88: 2207-2214, 2002. Pretibial
flexor motoneurons were recorded intracellularly in anesthetized cats
during unfused isometric contractions of a subpopulation of motor units
from either tibialis anterior (TA) or extensor digitorum longus (EDL)
muscles. The contractions elicited excitatory postsynaptic potentials
in 23 of 28 pretibial flexor motoneurons. No effect was observed in the
remaining motoneurons. In control experiments, the effects of
electrical stimulation of afferents within the TA nerve were
investigated to help identify afferents responsible for the
contraction-induced positive feedback. This feedback was ascribed to
actions of Ia fibers because the pattern of the contraction-induced
excitatory potentials was consistent with the known pattern of Ia
discharge; in control experiments, electrical stimulation of group I
fibers elicited only monosynaptic excitatory potentials; and the
distribution of both the contraction-induced positive feedback among
motor nuclei as well as the electrically evoked Ia excitatory
monosynaptic potentials were restricted to homonymous and synergic
motoneurons. Observation of the Ia contraction-induced positive
feedback was facilitated by the absence of Ib autogenic inhibition.
This contraction-induced Ia excitatory feedback in ankle flexors might
either reinforce Ia-induced reflexes when these muscles are lengthened
or help to lift the leg over an obstacle.
