Journal of Neuroscience, Vol 8, 2827-2835, Copyright © 1988 by Society for Neuroscience
The otolithic origin of the vertical vestibuloocular reflex following bilateral blockage of the vertical semicircular canals in the rabbit
NH Barmack and VE Pettorossi
Department of Ophthalmology, Good Samaritan Hospital and Medical Center, Portland, Oregon 92709.
The influence of bilateral plugs of the anterior and posterior semicircular
canals (ASCs, PSCs) on the vertical vestibuloocular reflex (VVOR-0) of the
rabbit, oscillated about the longitudinal axis maintained in a horizontal
orientation, was studied. Bilateral plugs of either the ASCs or PSCs
reduced the gain of the VVOR-0 evoked by stimulus frequencies above 0.005
Hz, but left a residual gain of the VVOR at higher stimulus frequencies
that could be attributed to the remaining vertical canals and utricular
otoliths. Bilateral plugs of both the ASCs and PSCs totally eliminated the
canal component of the VVOR-0, as determined from measurements made when
the animal was oriented at 90 degrees ("nose up") with respect to the earth
horizontal axis, eliminating changes in the gravitational vector acting on
the utricular maculae (VVOR-90). Bilateral plugs of both the ASCs and PSCs
also eliminated the nonlinear increase in gain observed at intermediate
frequencies in intact rabbits when oscillated about a supine orientation
(VVOR-180). The contribution of the utricular otolith to the VVOR-0 in
rabbits with both the ASCs and PSCs plugged was compared with the predicted
otolith contribution based on the assumption of linear summation of
semicircular canal and utricular signals. The assumption of linear
summation appears to be incorrect. Bilateral plugs of the ASCs and PSCs
increased the latency and the time constant of vertical eye movements
evoked by step-roll stimulation about the longitudinal axis maintained in a
horizontal orientation.