THREE-DIMENSIONAL ANALYSIS OF VESTIBULAR EFFERENT NEURONS INNERVATING THE
SEMI-CIRCULAR CANALS OF THE GERBIL.
I.M. Purcell and A.A.Perachio.
Department of Otolaryngology, Physiology and Biophysics, Anatomy and
Neurosciences; University of Texas Medical Branch, Galveston, TX. 77550,
USA.
APStracts 4:188N, 1997.
ABSTRACT
1) Anterograde labeling techniques were used to examine peripheral innervation
patterns of vestibular efferent neurons in the crista ampullares of the
gerbil. Vestibular efferent neurons were labeled by extracellular injections
of biocytin or biotinylated dextran amine (BDA) into the contralateral or
ipsilateral dorsal subgroup of efferent cell bodies (group e) located
dorsolateral to the facial nerve genu.
2) Anterogradely labeled efferent terminal field varicosities consist mainly
of boutons en-passant with fewer of the terminal type. The bouton swellings
are located predominately in apposition to the basolateral borders of the
afferent calyces and type II hair cells, but several boutons were identified
close to the hair cell apical border on both types.
3) Three-dimensional reconstruction and morphological analysis of the terminal
fields from these cells located in the sensory neuroepithelium of the
anterior, horizontal, and posterior cristae were performed. We show that
efferent neurons densely innervate each end organ in widespread terminal
fields.
Subepithelial bifurcations of parent axons were minimal, with extensive
collateralization occurring after the axons penetrated the basement membrane
of the neuroepithelium. Axonal branching ranged between the 6th and 27th
orders and terminal field collecting area far exceeds that of the peripheral
terminals of primary afferent neurons.
5) The terminal fields of the efferent neurons display three morphologically
heterogeneous types: a) Central, b) Peripheral, and c) Planum.
6) All cell types possess terminal fields displaying a high degree of
anisotropy with orientations typically parallel to or within + 45o of the
longitudinal axis if the crista. Terminal fields of the central and planum
zones predominately project medially toward the transverse axis from the more
laterally located penetration of the basement membrane by the parent axon.
Peripheral zone terminal fields extend predominately toward the planum
semilunatum. The innervation areas of efferent terminal fields display a trend
from smallest to largest for the central, peripheral, and planum types
respectively.
Received 28 October 1996; accepted in final form 5 August 1997.
APS Manuscript Number J858-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 28 August 1997