STRETCH OF QUADRICEPS INHIBITS THE SOLEUS H REFLEX DURING LOCOMOTION IN
DECEREBRATE CATS.
John E. Misiaszek and Keir G. Pearson.
Department of Physiology, University of Alberta, Edmonton, Alberta, T6G
2H1.
APStracts 4:151N, 1997.
ABSTRACT
Previously, it has been demonstrated that afferent signals from the quadriceps
muscles can suppress H reflexes in humans during passive movements of the leg.
To establish whether afferent input from quadriceps contributes to the
modulation of the soleus H reflex during locomotion, the soleus H reflex was
conditioned with stretches of the quadriceps muscle during bouts of
spontaneous treadmill locomotion in decerebrate cats. We hypothesized that 1)
in the absence of locomotion such conditioning would lead to suppression of
the soleus H reflex and 2) this would be retained during periods of locomotor
activity. In the absence of locomotion, slow sinusoidal stretches (0.2 Hz, 8
mm) of quadriceps cyclically modulated the amplitude of the soleus H reflex.
The H reflex amplitude was least during the lengthening of the quadriceps and
greatest as quadriceps shortened. Further, low amplitude vibrations (48 to 78
æm) applied to the patellar tendon suppressed the reflex, indicating that the
muscle spindle primaries were the receptor eliciting the effect. During bouts
of locomotion, ramp stretches of quadriceps were applied during the extensor
phase of the locomotor rhythm. Soleus H reflexes sampled at two points during
the stance phase were reduced compared to phase-matched controls. The
background level of the soleus EMG activity was not influenced by the applied
stretches to quadriceps, either during locomotion or in the absence of
locomotion. This indicates that the excitability of the soleus motoneuron pool
was not influenced by the stretching of quadriceps, and that the inhibition of
the soleus H reflex is due to presynaptic inhibition. We conclude that group
Ia afferent feedback from quadriceps contributes to the regulation of the
soleus H reflex during the stance phase of locomotion in decerebrate cats.
This afferent mediated source of regulation of the H reflex, or monosynaptic
stretch reflex, would allow for rapid alterations in reflex gain according to
the dynamic needs of the animal. During early stance, this source of
regulation might suppress the soleus stretch reflex to allow adequate yielding
at the ankle and facilitate the movement of the body over the foot.
Received 7 May 1997; accepted in final form 14 July 1997.
APS Manuscript Number J375-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 27 August 1997