To elucidate the effects and acting sites of methyl scopolamine and atropine methyl bromide which do not cross the blood-brain-barrier (BBB) on the vestibuloocular reflex (VOR), the changes of VOR elicited by rotation of the whole body at frequencies of 0.1, 0.2 and 0.5 Hz were examined after intravenous or intraventricular injection of these anticholinergic drugs in unanesthetized rabbits.
The following results were obtained.
1. In normal VOR, the frequency and velocity of nystagmus were increased by increasing the frequency of stimulus rotation from 0.1 Hz to 0.5 Hz.
2. When methyl scopolamine was injected intravenously, the frequency and velocity of nystagmus were decreased at 3 all stimulus frequencies. And the responses of VOR were also decreased by intraventricular injections.
3. When atropine methyl bromide was injected intravenously, the frequency and velocity of nystagmus were decreased at 3 all stimulus frequencies. In the intraventricular injected group, however, any significant changes _ of the frequency of nystagmus were not observed, and the velocity of nystagmus was increased.
These results suggest that methyl scopolamine may act both on the peripheral and central organ of the VOR system, but atropine methyl bromide may act only on the peripheral organ in the suppression of VOR.
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