Electrophysiological and HRP studies on feedback loop between inferior olivary nucleus and lateral vestibular nucleus in the cat.

The role of input from the inferior olivary nucleus (IO) of decerebellate cats were studied on the lateral vestibular nucleus (LVN) neurons which were monosynaptically activated by vestibular nerve stimulation. Out of 168 monosynaptic neurons, test stimuli to the contralateral IO elicited a monosynaptic spike in 43 neurons and an antidromic spike in 9 neurons. Conditioning stimulus applied to the IO preceding vestibular nerve stimulation produced an inhibition of spike generation in 22 other LVN neurons upon the nerve stimulation. When horseradish peroxidase (HRP) was iontophoretically applied into the immediate vicinity of the LVN monosynaptic neurons, HRP-reactive cells were found in the dorsal cap and beta-nucleus of the contralateral IO. These results suggest that the LVN neurons monosynaptically activated by vestibular nerve stimulation receive both excitation and inhibition from the IO.