Journal of Neurophysiology, Vol 74, Issue 4 1815-1818, Copyright © 1995 by APS
Effect of MLF transection on the vertical vestibulocollic reflex in decerebrate cats
D. B. Thomson, H. Ikegami and V. J. Wilson
Rockefeller University, New York, New York 10021, USA.
1. In the cat, motoneurons supplying biventer cervicis, complexus and
rectus capitis posterior receive disynaptic input from the posterior
semicircular canals and from the contralateral anterior canal via the
medial vestibulospinal tract (MVST). Disynaptic excitation from the
ipsilateral anterior canal reaches these motoneurons via the lateral
vestibulospinal tract. 2. We hypothesized that if the MVST has a unique
role in the production of the vertical vestibulocollic reflex (VCR) in
these muscles then interruption of this tract by transection of the medial
longitudinal fasciculus (MLF) would change the VCR responses. Specifically,
response vector orientations would shift toward the plane of the
ipsilateral anterior canal, and response gains would drop at high
frequencies. 3. We lesioned the MLF bilaterally and observed no substantial
effect on neck-muscle responses. Response vector orientations did not shift
systematically toward a single plane, nor was there a consistent decrease
in response gains at high frequencies. 4. As in the horizontal VCR, there
is no unique contribution from MVST neurons; parallel pathways must play an
important role in the vertical VCR.
