EXCITATORY CONNECTIONS BETWEEN NEURONS OF THE CENTRAL CERVICAL NUCLEUS AND VESTIBULAR NEURONS IN THE CAT

The central cervical nucleus (CCN) of the cat receives input from uppe r cervical muscle afferents, particularly primary spindle afferents. I ts axons cross in the spinal cord, and while in the contralateral rest iform body give off collaterals to the vestibular nuclei. In order to study the connections between CCN axons and vestibular neurons, we sti mulated the area of the CCN in decerebrate cats while recording intra- or extracellularly from neurons in the contralateral vestibular nucle i. CCN stimulation evoked excitatory postsynaptic potentials (EPSPs) o r extracellularly recorded firing in the lateral, medial and descendin g vestibular nuclei. The latency of EPSPs (mean 1.6 ms) was on average 0.4 ms longer than the latency of antidromic spikes evoked in the CCN by stimulation of the contralateral vestibular nuclei (mean 1.2 ms), demonstrating that the excitation was typically monosynaptic. The resu lts provide further evidence that the CCN is an important excitatory r elay between upper cervical muscle afferents and neurons in the contra lateral vestibular nuclei.