Functional roles played by lateral vestibular neurons during locomotor movements and postural changes in the acute mesencephalic cat.

Abstract

Stimulation delivered to the mesencephalic locomotor region (MLR) in the acute decerebrate cat elicits “controlled” locomotion on a moving treadmill.
Stimulation to the dorsolateral part of the MLR elicits alternating rhythmic shifting of the weight between hindlimbs (stepping) on a still surface. Stimulation to the MLR increases postural muscle tone of the hindlimbs augenting reflex standing of a decerebrate cat.
The changes in the discharge characteristics of 84 neurons in the lateral vestibular nucleus (VLD-neurons) were studied during these locomotor movements and postural changes. VLD-neurons were antidromically identified and extracellularly recorded by means of microelectrodes. EMGs of representative hindlimb muscles were recorded. During hindlimb stepping and postural changes, the forces exerted at the foot contacts of the hindlimbs were measured by means of force transducers.
The results obtained from 84 VLD-neurons (conduction velocity : 93.1±17.8m/s, firing rate : 12.1±11.5spikes/s) are summarized as follows : 1) With shortening of the cycle time during locomotion, the majority of VLD-neurons (43/54) tended to discharge rhythmically in phase with bursting discharges of the triceps surae muscle.
The rest of the VLD-neurons (11/54) maintained tonic discharges irrespective of the changes in cycle time. 2) During hindlimb stepping, some VLD-neurons (8/16) exhibited rhythmic bursting discharges slightly preceding the onset of force increase in the ipsilateral hindlimb. 3) Most VLD-neurons (17/18) increased their tonic firing rates during augmented reflex standing.
All these results demonstrate that VLD-neurons play roles not only in the phase contral system but also in the power or postural tone control system both during locomotor movements and postural adjustments.