Spontaneous activity of otolith-related vestibular nuclear neurons in the decerebrate rat.
The discharge properties of lateral and descending vestibular neurons responsive to constant velocity off-vertical axis rotations (OVAR) in the clockwise (CW) and counterclockwise (CCW) directions, were studied at the stationary and earth-horizontal position of decerebrate adult rats. From the coefficient of variation (CV), the spontaneous activities of OVAR-responsive neurons were classified into regular and irregular patterns. Of the neurons (n = 36) that showed symmetric and stable bidirectional response sensitivity (delta defined as CW gain over CCW gain) to OVAR (10 degrees tilt), some exhibited progressive phase shift with velocity (1.75-15 degrees/s) while others exhibited stable response phase. Most neurons of the former group (93% or 12/13) showed regular discharge pattern while only 22% (n = 5/23) of the latter group showed such a pattern. Though the phase-stable neurons showed a significantly higher average CV than the phase-shifted neurons, there was no significant difference between the mean spontaneous firing rates of these neurons. The neurons (n = 17) that showed asymmetric and variable delta to OVAR velocity can also be grouped-those that exhibited a greater gain with rotations directed towards the side of recording (I neurons) showed irregular discharge pattern while those that exhibited a greater gain with rotations directed towards the side contralateral to recording (C neurons) showed regular discharge pattern. The I and C neurons also exhibited significant difference in mean firing rates. The relationship between the response characteristics of the OVAR-responsive neurons and their spontaneous activity at the stationary and earth-horizontal position is discussed.
Lai
C H
CH
Department of Physiology, Faculty of Medicine, University of Hong Kong.
Chan
Y S
YS
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D003655:Decerebrate State; D004558:Electric Stimulation; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D010037:Otolithic Membrane / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012399:Rotation; D014726:Vestibular Nuclei / Q000166:cytology / Q000502:physiology*