Properties of horizontal semicircular canal nerve-activated vestibulospinal neurons in cats.
Axonal pathways, projection levels, and locations of horizontal semicircular canal (HC) nerve-activated vestibulospinal neurons were studied. The HC nerve was selectively stimulated. Vestibulospinal neurons were activated antidromically with four stimulating electrodes, inserted bilaterally into the lateral vestibulospinal tracts (LVST) and medial vestibulospinal tracts (MVST) at the C1/C2 junction. Stimulating electrodes were also positioned in the C3, T1, and L3 segments and in the oculomotor nuclei. Most HC nerve-activated vestibulospinal neurons were located in the ventral portion of the medial, lateral, and the descending nuclei. Among the 157 HC nerve-activated vestibular neurons, 83 were antidromically activated by stimulation at the C1/C2 junction. Of these 83 neurons, axonal pathways of 56 HC nerve-activated vestibulospinal neurons were determined. Most (48/56) of these had axons that descended through the MVST, with the remainder (8 neurons) having axons that descended through the ipsilateral (i-) LVST. Laterality of the axons' trajectories through the MVST was investigated. The majority of vestibulospinal neurons (24/28) with axons descending through the contralateral MVST were also antidromically activated from the oculomotor nucleus, whereas almost all vestibulospinal neurons (19/20) with axons descending through the i-MVST were not. Most HC nerve-activated vestibulospinal neurons were activated antidromically only from the C1/C2 or C3 segments. Only one neuron that was antidromically activated from the T1 segment had an axon that descended through the i-LVST. None of the HC nerve-activated vestibulospinal neurons were antidromically activated from the L3 segment. It is likely that the majority of HC nerve-activated vestibulospinal neurons terminate in the cervical cord and have strong connections with neck motoneurons.
Department of Otolaryngology, St. Marianna University School of Medicine, 2-16-1 Sugao, Miyamae-ku, Kawasaki, 216-8511 Kanagawa, Japan. akemiffy@swan.syscom.ne.jp
Akemi
A
Sugita
Rishu
R
Bai
Midori
M
Imagawa
Hitoshi
H
Sato
Mitsuyoshi
M
Sasaki
Naoharu
N
Kitajima
Izumi
I
Koizuka
Yoshio
Y
Uchino
D000818:Animals; D001369:Axons / Q000502:physiology; D002415:Cats; D004525:Efferent Pathways / Q000502:physiology*; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000502:physiology; D007839:Functional Laterality / Q000502:physiology; D009334:Neck Muscles / Q000502:physiology; D009431:Neural Conduction / Q000502:physiology; D004856:Postural Balance / Q000502:physiology*; D012018:Reflex / Q000502:physiology; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology; D012665:Semicircular Canals / Q000294:innervation / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology*; D014725:Vestibular Nerve / Q000502:physiology*; D014726:Vestibular Nuclei / Q000502:physiology*