The Journal of Neurophysiology Vol. 84 No. 5 November 2000, pp. 2257-2276
Copyright ©2000 by the American Physiological Society
Vestibulospinal and Reticulospinal Neuronal Activity During
Locomotion in the Intact Cat. II. Walking on an Inclined Plane
Kiyoji
Matsuyama1 and
Trevor
Drew2
1Laboratory of Neurobiology, National
Institute for Physiological Sciences, Okazaki 444, Japan; and
2Department of Physiology, Faculty of Medicine,
University of Montreal, Montreal, Quebec H3C 3J7, Canada
Matsuyama, Kiyoji and
Trevor Drew.
Vestibulospinal and Reticulospinal Neuronal Activity During
Locomotion in the Intact Cat. II. Walking on an Inclined Plane. J. Neurophysiol. 84: 2257-2276, 2000. The
experiments described in this report were designed to determine the
contribution of vestibulospinal neurons (VSNs) in Deiters' nucleus and
of reticulospinal neurons (RSNs) in the medullary reticular formation
to the modifications of the walking pattern that are associated with
locomotion on an inclined plane. Neuronal discharge patterns were
recorded from 44 VSNs and 63 RSNs in cats trained to walk on a
treadmill whose orientation was varied from +20° (uphill) to 
10°
(downhill), referred to as pitch tilt, and from 20° roll tilt left to
20° roll tilt right. During uphill locomotion, a majority of VSNs
(25/44) and rhythmically active RSNs (24/39) showed an increase in peak
discharge frequency, above that observed during locomotion on a level
surface. VSNs, unlike some of the RSNs, exhibited no major deviations
from the overall pattern of the activity recorded during level walking.
The relative increase in discharge frequency of the RSNs (on average,
31.8%) was slightly more than twice that observed in the VSNs (on
average, 14.4%), although the average absolute change in discharge
frequency was similar (18.2 Hz in VSNs and 21.6 Hz in RSNs). Changes in discharge frequency during roll tilt were generally more modest and
were more variable, than those observed during uphill locomotion as
were the relative changes in the different limb muscle electromyograms that we recorded. In general, discharge frequency in VSNs was more
frequently increased when the treadmill was rolled to the right (ear
down contralateral to the recording site) than when it was rolled to
the left. Most VSNs that showed significant linear relationships with
treadmill orientation in the roll plane increased their activity during
right roll and decreased activity during left roll. Discharge activity
in phasically modulated RSNs was also modified by roll tilt of the
treadmill. Modulation of activity in RSNs that discharged twice in each
step cycle was frequently reciprocal in that one burst of activity
would increase during left roll and the other during right roll. The
overall results indicate that each system contributes to the changes in
postural tone that are required to adapt the gait for modification on
an inclined surface. The characteristics of the discharge activity of
the VSNs suggest a role primarily in the overall control of the level
of electromyographic activity, while the characteristics of the RSNs
suggest an additional role in determining the relative level of
different muscles, particularly when the pattern is asymmetric.
