Properties of otolith-related vestibular nuclear neurons in response to bidirectional off-vertical axis rotation of the rat.
In decerebrate rats, the responses of tilt-sensitive neurons in the lateral and descending vestibular nuclei were studied during constant velocity 10 degrees off-vertical axis rotations (OVAR) in the clockwise (VW) and counterclockwise (CCW) directions. Seventy three otolith-related units showed a sinusoidal position-dependent discharge modulation to OVAR of both directions; 20 of these showed clipped firing rates in parts of a 360 degree OVAR cycle. With increase in the velocity of rotation (1.75-15 degrees/s), one group of units (n = 36) showed a stable ratio of bidirectional response sensitivity and symmetric response magnitudes to CW and CCW rotations. These units showed gain tuning ratios similar to those of narrowly spatiotemporal-tuned neurons. The other group of OVAR responsive units (n = 13) exhibited velocity-variable and asymmetric bidirectional response sensitivities. Their gain tuning ratios were similar to those of broadly spatiotemporal-tuned neurons. For units with velocity-stable and symmetric bidirectional response sensitivity as well as gain tuning ratio of the narrowly spatiotemporal-tuned neurons, their response gains remained stable with velocity. Some showed stable response phase lead or lag with velocity increase while others showed progressive shifts from response lead of 13 degrees to response lag of -25 degrees. The best response orientations of these units with velocity-stable and symmetric bidirectional response sensitivity were found to point in all directions on the place of rotation. The functional significance of these tilt- and OVAR-sensitive central otolith neurons is discussed.
Lai
C H
CH
Department of Physiology, Faculty of Medicine, University of Hong Kong, Hong Kong.
Chan
Y S
YS
D000818:Animals; D004594:Electrophysiology; D009474:Neurons / Q000502:physiology*; D010037:Otolithic Membrane / Q000166:cytology* / Q000294:innervation / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012399:Rotation; D012680:Sensitivity and Specificity; D014726:Vestibular Nuclei / Q000166:cytology* / Q000502:physiology