[Electrophysiological study of ipsilateral vestibulo-collic reflex by the posterior semicircular canal stimulation]

In 12 anesthetized cats, the posterior semicircular canal nerve (PCN) stimulation evoked disynaptic EPSPs (excitatory postsynaptic potentials) in the ipsilateral neck flexor motoneurons innervating longus capitis muscles in the C1 and C2 segment (i-C1LCmn and i-C2LCmn). The mean latency and maximum amplitude of the EPSPs in the i-C1LCmn and i-C2LCmn were 1.8 and 1.9 ms, and 340 and 350 microV, respectively. Concerning the latency and amplitude of the EPSPs, there were no differences in the i-C1LCmn and i-C2LCmn. The unit activities of 9 PCN-activated vestibulo-collic neurons sending axon to the ipsilateral motoneuron pool of longus capitis muscles in the C2 segment (i-C2LCmnp) were also observed. These neurons were activated orthodromically from the PCN stimulation with latencies of 1.3ms (mean) and with latencies of 1.2ms from the i-C2LCmnp stimulation antidromically. The cell body of these vestibulo-collic neurons located in the ventrolateral part of the lateral nucleus.