Responses to Vertical Vestibular Stimulation of Neurons in the Nucleus
Reticularis Gigantocellularis in Rabbits.
Fagerson, M. H., and H. Barmack.
Deptartment of Cell Biology, Oregon Health Sciences University, R. S. Dow
Neurological Sciences, Portland, Oregon 97209.
APStracts 2:0017N, 1995.
SUMMARY AND CONCLUSIONS
1.Because the nucleus reticularis gigantocellularis (NRGc) receives a
substantial descending projection from the caudal vestibular nuclei, we used
extracellular single-unit recording combined with natural vestibular
stimulation to examine the possible peripheral origins of the vestibularly
modulated activity of caudal NRGc neurons located within 500 [mu]m of the
midline. Chloralose-urethan anesthetized rabbits were stimulated with an
exponential "step" and/or static head-tilt stimulus, as well as sinusoidal
rotation about the longitudinal or interaural axes providing various
combinations of roll or pitch, respectively. Recording sites were
reconstructed from electrolytic lesions confirmed histologically. 2. More
than 85% of the 151 neurons, in the medial aspect of the caudal NRGc,
responded to vertical vestibular stimulation. Ninety-six percent of these
responded to rotation onto the contralateral side ([beta] responses). Only a
few also responded to horizontal stimulation. Seventy-eight percent of the
neurons that responded to vestibular stimulation were sensitive to static
roll-tilt and responded during static tilt. One-half of these neurons also
responded transiently to the change in head position during exponential
"step" stimulation, suggesting input mediated by otolith and semicircular
canal receptors or tonic-phasic otolith neurons. 3. Seventy-five percent of
the responsive neurons had a "null plane." The planes of stimulation
resulting in maximal responses, for cells that responded to static
stimulation, were distributed throughout 150 degrees in both roll and pitch
quadrants. Five of these cells responded only transiently during exponential
"step" stimulation and responded maximally when stimulated in the plane of
one of the vertical semicircular canals. 4. The phase of the response of the
25% of medial NRGc neurons that lacked "null planes" gradually shifted 180
degrees during sinusoidal vestibular stimulation as the plane of stimulation
was shifted about the vertical axis. These neurons likely received convergent
input with differing spatial and temporal properties. 5. The activity of
neurons in the medial aspect of the caudal NRGc of rabbits was modulated by
both otolithic macular and vertical semicircular canal receptor stimulation.
This vestibular information may be important for controlling the intensity of
the muscle activity in muscles such as neck muscles where the load on the
muscle is affected by the position of the head with respect to gravity. Some
of these neurons may also shift muscle function from an agonist to an
antagonist as the direction of head tilt changes.
Received 16 March 1994; accepted in final form 19 January 1995.
APS Manuscript Number J138-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 3 April 1995.