title: Synaptic connections of horizontal canal mediated ascending Deiters tract axons on medial rectus motoneurons in cat.
abstract: This study demonstrates the termination of ascending tract of Deiters' (ATD) axons on ipsilateral medial rectus (MR) motoneurons. Horseradish peroxidase (HRP) was iontophoretically injected into ATD axons which were recorded in the MR motoneuron pool of the oculomotor nucleus. MR motoneuron cell bodies were identified by retrograde transport of HRP injected into MR muscles in the orbit. ATD axons were identified by Type I responses to horizontal rotation, monosynaptic responses on stimulation of the ipsilateral labyrinth, and no response on contralateral labyrinth or contralateral abducens nucleus or on ipsilateral MR nerve stimulation. Light microscopic examination showed the main stem axons to be lateral to the medial longitudinal fasciculus, and terminal boutons were in contact with ipsilateral identified MR motoneurons (Furuya and Markham: Exp. Brain Res. 43: 289-303, 1981). Light microscopy and semi-thin sections showed boutons of ATD in contact with identified MR motoneuron cell bodies and proximal dendrites. The electron micrographs (EM) showed the HRP-injected ATD axons have synapses on MR motoneurons. ATD boutons made axosomatic and axodendritic synapses on MR motoneurons. The boutons contained numerous spheroidal synaptic vesicles. Several examples showed clear asymmetrical post-synaptic membrane specialization. This confirms the synaptic connection between horizontal canal activated elements in the ATD and MR motoneurons.
mesh_terms: D000010:Abducens Nerve / Q000033:anatomy & histology; D000818:Animals; D001369:Axons / Q000648:ultrastructure*; D001931:Brain Mapping; D001933:Brain Stem / Q000033:anatomy & histology*; D002415:Cats; D003712:Dendrites / Q000648:ultrastructure; D008854:Microscopy, Electron; D009046:Motor Neurons / Q000648:ultrastructure*; D009434:Neural Pathways / Q000033:anatomy & histology; D009474:Neurons / Q000648:ultrastructure; D009802:Oculomotor Nerve / Q000033:anatomy & histology; D012027:Reflex, Vestibulo-Ocular; D013569:Synapses / Q000648:ultrastructure*; D014726:Vestibular Nuclei / Q000033:anatomy & histology*; D003689:Vestibular Nucleus, Lateral / Q000033:anatomy & histology*