Relationship between Collateral Morphology in C1 Spinal Cord and Spatial
Properties of Medial Vestibulospinal Tract Neurons in the Cat.
S.I. Perlmutter, Y. Iwamoto , L.F. Barke, J.F. Baker, B.W. Peterson.
Department of Physiology, Northwestern University School of Medicine, 303
E. Chicago Ave., Chicago, IL 60611.
APStracts 4:0232N, 1997.
ABSTRACT
Twenty-one secondary medial vestibulospinal tract neurons were recorded
intraaxonally in the ventromedial funiculi of the C1 spinal cord in
decerebrate, paralyzed cats. Antidromic stimulation in C6 and the oculomotor
nucleus identified the projection pattern of each neuron. Responses to
sinusoidal, whole-body rotations in many planes in three-dimensional space
were characterized prior to injection of horseradish peroxidase or
Neurobiotin. The spatial response properties of 19 neurons were described by
a maximum activation direction vector (MAD), which defines the axis and
direction of rotation which maximally excites the neuron. The other two
neurons had spatio-temporal convergent behavior and no MAD was calculated.
Collateral morphologies were reconstructed from serial frontal sections to
reveal terminal fields in the C1 gray matter. Axons gave off multiple
collaterals that terminated ipsilaterally to the stem axon. Collaterals of
individual axons rarely overlapped longitudinally, but projected to similar
regions in the ventral horn when viewed in transverse sections. The number of
primary collaterals in C1 was different for vestibulo-collic, vestibulo-
oculo-collic, and C6 projecting neurons: on average one every 1.34, 1.72 and
4.25 mm, respectively. The heaviest arborization and most terminal boutons
were seen in the ventral horn, in laminae VIII and IX. Varicosities on
terminal branches in lamina IX were observed adjacent to large cell bodies -
putative neck muscle motoneurons - in counterstained tissue. Some collaterals
had branches which extended dorsally to lamina VII. Neurons with different
spatial properties had terminal fields in different regions of the ventral
horn. Axons with type I responses and MADs near those of a semicircular canal
pair had widely distributed collateral branches and numerous terminations in
the dorsomedial, ventromedial and spinal accessory nuclei, and in lamina VIII.
Axons with type I responses that suggested convergent canal pair input, with
type II responses, and with spatio-temporal behavior had smaller terminal
fields. Some neurons with these more complex spatial properties projected to
the dorsomedial and spinal accessory, but not to the ventromedial nuclei.
Others had focused projections to dorsolateral regions of the ventral horn
with few branches in the motor nuclei.
Received 1996; accepted in final form 1997.
APS Manuscript Number J.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 7 October 1997