Vertical Vestibular Input to and Projections from the Caudal Parts of the
Vestibular Nuclei of the Decerebrate Cat.
Endo, K., D. B. Thomson. V. J. Wilson, T. Yamaguchi and B. J. Yates.
The Rockefeller University, 1230 York Avenue, New York, NY 10021.
APStracts 2:0091N, 1995.
SUMMARY AND CONCLUSIONS
1. To investigate the type of vestibular signals that neurons in the caudal
parts of the vestibular nuclei transmit to the cerebellum and spinal cord, we
have studied their responses to natural vestibular stimulation in vertical
planes in decerebrate cats with the caudal cerebellum removed. Most neurons
were in the caudal half of the descending vestibular nucleus, the remainder at
corresponding levels of the medial nucleus or the medial-descending border.
2. Dynamics of the responses of spontaneously firing neurons were studied with
sinusoidal tilts delivered at 0.05-1 Hz near the plane of body rotation that
produced maximal modulation of the neuron's activity (response vector
orientation). For most neurons the predominant vestibular input could be
identified as coming from otolith organs (46%) or vertical semicircular canals
(37%). Some neurons had otolith + canal convergence (9%) and others either had
such converging input or some other form of central processing (8%) 3 . Gain
and phase of the responses of otolith neurons were comparable to values
obtained in earlier studies on Deiters' nucleus and the rostral descending
nucleus. Many canal neurons had a steeper gain slope and more advanced phase
than observed previously for more rostral neurons. This may be due to more
irregular afferent input to many neurons, or to the absence of the
vestibulocerebellum. 4 . Response vector orientations of canal neurons were
closely bunched near the planes of the ipsilateral vertical canals. The small
number of contralaterally projecting vectors showed evidence of convergence
between the two contralateral vertical canals. As is the case elsewhere in the
vestibular nuclei, there was no evidence of convergence from bilateral
vertical canals. Response vector orientations of otolith neurons were
restricted to the roll quadrants; the majority pointed ipsilaterally. 5.
Antidromic stimulation with an electrode in the restiform body or with several
electrodes in the dorsal half of the white matter of the upper cervical cord
was used to identify neurons projecting to the cerebellum and spinal cord,
respectively. A substantial number of spontaneously firing neurons projected
to the cerebellum, but there were few spontaneously active vestibulospinal
neurons. The properties of the vestibular input to cerebellar-projecting
neurons were the same as those of the population as a whole, but the effect of
tilt on vestibulospinal neurons appeared weak or absent. 6. Many neurons were
inhibited by stimulation of the restiform body. We suggest that this is mainly
due to stimulation of the axons of vestibulocerebellar Purkinje cells. 7.
Our results demonstrate a robust vertical vestibular input to the caudal parts
of the vestibular nuclei. Whereas this input is prominent for cerebellar-
projecting neurons it does not appear important for vestibulospinal neurons in
this region. The results are also consistent with the existence of a loop
between the caudal vestibular nuclei and vestibulocerebellum.
Received 27 October 1994; accepted in final form 21 February 1995.
APS Manuscript Number J676-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 April 1995.