[Effects of ifenprodil on lateral vestibular nucleus neurons in the cat (author's transl)].

Electrophysiological studies were performed to elucidate effects of ifenprodil, an antivertigo drug, on neuron activity in the lateral vestibular nucleus (LVN) of cats anesthetized with alpha-chloralose. LVN neurons were classified into three types, according to the response pattern upon vestibular nerve stimulation: monosynaptic, polysynaptic I and polysynaptic II neurons, which fired spikes with the mean latencies of 1.07 +/- 0.12 (n = 6), 2.20 +/- 0.19 (n = 8) and 16.37 +/- 2.11 msec (n = 7), respectively. Intravenous administration of ifenprodil up to 5 mg/kg did not affect spike generation of monosynaptic neurons. Spike generation of polysynaptic I and II neurons was dose-dependently inhibited by ifenprodil up to 1 mg/kg. However, increasing doses of the drug up to 5 and 10 mg/kg produced complex effects such as an enhancement of the inhibitory effect in some neurons or a facilitation of responses in others. These results indicate that ifenprodil acts on the polysynaptic I and II neurons without affecting the monosynaptic neurons. It is likely that a small dose of ifenprodil may directly inhibit polysynaptic neurons and higher doses may indirectly enhance the responsiveness of the neurons, probably as a result of an increase in blood flow in the vertebral artery.