The Journal of Neuroscience, January 1, 1999, 19(1):391-400
The Modulation of Presynaptic Inhibition in Single Muscle Primary
Afferents during Fictive Locomotion in the Cat
Ariane
Ménard,
Hugues
Leblond, and
Jean-Pierre
Gossard
Centre de Recherche en Sciences Neurologiques,
Département de Physiologie, Faculté de Médecine,
Université de Montréal, Montréal, Québec,
Canada, H3C 3J7
The aim of this study is to understand the functional organization
of presynaptic inhibition in muscle primary afferents during locomotion. Primary afferent depolarization (PAD) associated with presynaptic inhibition was recorded intra-axonally in identified afferents from various hindlimb muscles in L6-L7 spinal segments during fictive locomotion in the decerebrate cat. PADs were evoked by
the stimulation of peripheral muscle nerves and were averaged in the
different epochs of the fictive step cycle. Fifty-three trials recorded
from 39 muscle axons (37 from group I and two from group II) were
retained for analysis. The results showed that there was a significant
phase-dependent modulation of PAD amplitude
(p < 0.05) in a majority of muscle
afferents (30 of 39, 77%). However, not all stimulated nerves led to
significantly modulated PADs in a given axon (36 of 53 trials, 68%).
We also observed that the pattern of modulation (phase for maximum and minimum PAD amplitude and the depth of modulation) varied with each
recorded afferent, as well as with each stimulated nerve. We further
evaluated the effect of PAD modulation on the phasic transmission of
the monosynaptic reflex (MSR) and found that PADs decreased the MSR
amplitude in all phases of the fictive step cycle, independent of the
PAD pattern in individual group I fibers. We conclude that (1) PAD
modulation patterns of all group I fibers contacting motoneurons led to
an overall reduction in monosynaptic transmission, and (2) individual
PAD patterns could participate in the control of transmission in
specific reflex pathways during locomotion.
Key words:
primary afferent depolarization (PAD); presynaptic
inhibition; muscle group I fibers; fictive locomotion; spinal cord; motor control
Copyright © 1999 Society for Neuroscience 0270-6474/99/191391-10$05.00/0