Properties of central vestibular neurons fired by stimulation of the saccular nerve.

In 4 cats all vestibular afferents in one labyrinth except those innervating the saccular macula were transected and allowed to degenerate. 23--53 days after the initial surgery the central connections of the remaining saccular nerve were studied under chloralose anesthesia. Stimulation of the saccular nerve evoked N1 field potentials in the ipsilateral lateral and descending vestibular nuclei; little or no field potential activity was seen in the superior nucleus. The distribution of field potentials overlapped with that of neurons of origin of the vestibulospinal tracts. Forty-two neurons in the ipsilateral vestibular nuclei, many in the lateral nucleus, responded, often monosynaptically, to stimulation of the saccular nerve with single or double shocks; some of the neurons projected to the spinal cord. All saccular-fired neurons were tested for commissural actions by stimulation of the contralateral vestibular nerve. Many were facilitated, almost none were inhibited. In agreement with earlier work, we conclude that commissural inhibition may be a property of the canal system only.