Dpd. Gilchrist et al., HIGH ACCELERATION IMPULSIVE ROTATIONS REVEAL SEVERE LONG-TERM DEFICITS OF THE HORIZONTAL VESTIBULOOCULAR REFLEX IN THE GUINEA-PIG, Experimental Brain Research, 123(3), 1998, pp. 242-254
While there is agreement that unilateral vestibular deafferentation (U
VD) invariably produces an immediate severe horizontal vestibule-ocula
r reflex (HVOR) deficit, there is disagreement about whether or not th
is deficit recovers and, if so, whether it recovers fully or only part
ly. We suspected that this disagreement might mainly be due to experim
ental factors, such as the species studied, the means chosen to carry
out the UVD, or the nature of the test stimulus used. Our aim was to s
ort out some of these factors. To do this, we studied the HVOR of aler
t guinea pigs in response to low and high acceleration sinusoidal and
high acceleration impulses after UVD by either labyrinthectomy or by v
estibular neurectomy. The HVOR in response to high acceleration impuls
ive yaw rotations was measured before, and at various times after, eit
her unilateral labyrinthectomy or superior vestibular neurectomy Follo
wing UVD, there was a severe impairment of the HVOR for ipsilesional r
otations and a slight impairment for contralesional rotations, after e
ither operation. This asymmetrical HVOR deficit in the guinea pig para
llels the deficit observed in humans. Between the first measurement, w
hich was made 1 week after UVD, and the last, which was made 3 months
after UVD, there was no change in the HVOR. This lack of recovery was
the same after labyrinthectomy as after vestibular neurectomy. The HVO
R to low and high acceleration sinusoidal yaw rotations were measured
after UVD, and the results were compared with those in response to imp
ulsive rotations. For low acceleration sinusoidal rotations (250 degre
es/s(2)), the gain was symmetrical, although reduced bilaterally. As t
he peak head acceleration increased, the HVOR became increasingly asym
metric. The HVOR asymmetry for sinusoidal rotations was significantly
less than for impulsive rotations that had the same high peak head acc
eleration (2500 degrees/s(2)). Our results show that the HVOR deficit
after UVD is the same in guinea pigs as in humans; that it is the same
after vestibular neurectomy as after labyrinthectomy; that it is last
ing and severe in response to high acceleration rotations; and, that i
t is more obvious in response to impulses than to sinusoids.