The ultrastructure of the feline superior vestibular commissural neurons (CNs) was studied after labeling by contralateral injection of horseradish peroxidase. These small spindle-shaped cells are found in clusters oriented in a rostrocaudal, dorsoventral, or lateromedial direction. The CNs have a cleft nucleus, with the majority of nerve terminals contacting the CN near the emergence of polar dendrites. Polarization of the afferent synaptic profiles suggests a bidirectional nature of inputs to CNs by the vestibular nerve, contralateral CNs, and/or cerebellar systems. One type of labeled cell does not conform to this pattern, instead resembling a vestibulo-ocular neuron. Hence, it may function as a commissural and a vestibulo-ocular neuron. Characterization of different types of synapses, based on the size and eccentricity of their synaptic vesicles, indicates a continuum rather than separate populations. Volume fraction of intracellular organelles showed a larger volume fraction percent of polyribosomes in larger cells. Since this organelle is involved with protein synthesis, this finding may indicate that larger CNs have a more extensive dendritic tree.
GrayLP. Some experimental evidence on the connections of the vestibular mechanism in the cat. J Comp Neurol1926; 41: 319–56.
2.
LadpliRBrodalA. Experimental studies of commissural and reticular formation projections from the vestibular nuclei in the cat. Brain Res1968; 8: 65–96.
3.
RasmussenAT. Secondary vestibular tracts in the cat. J Comp Neurol1932; 54: 143–59.
4.
GacekRR. Location of commissural neurons in the vestibular nuclei of the cat. Exp Neurol1978; 59: 479–91.
5.
PompeianoOMergnerTCorvajaN. Commissural, peri-hypoglossal and reticular afferent projections to the vestibular nuclei in the cat. Arch Ital Biol1978; 116: 130–72.
PrechtWShimazuHMarkhamCH. A mechanism of central compensation of vestibular function following hemilabyrinthectomy. J Neurophysiol1966; 29: 996–1010.
13.
BienholdHFlohrH. Role of commissural connexions between vestibular nuclei in compensation following unilateral labyrinthectomy [Abstract]. J Physiol (Lond)1978; 284: 178P.
14.
FlohrHBienholdHAbelnWMacskovicsI. Concepts of vestibular compensation. In: FlohrHPrechtW, eds. Lesion-induced plasticity in sensorimotor systems. Berlin, Germany: Springer-Verlag, 1981: 153–72.
15.
BermanAL. The brain stem of the cat. A cytoarchitectonic atlas with stereotaxic coordinates. Madison, Wis: University of Wisconsin Press, 1968.
16.
GacekRRLyonMJSchoonmakerJ. Ultrastructural changes in vestibulo-ocular neurons following vestibular neurectomy in the cat. Ann Otol Rhinol Laryngol1988; 97: 42–51.
17.
MalmgrenLOlssonY. A sensitive histochemical method for light- and electron-microscopic demonstration of horseradish peroxidase. J Histochem Cytochem1977; 25: 1280–3.
18.
PeacheyLD. Thin sections. I. A study of section thickness and physical distortion produced during microtomy. J Biophys Biochem Cytol1958; 4: 233–42.
19.
SchockACWarshawBS. Analytic geometry and an introduction to calculus. Englewood Cliffs, NJ: Prentice-Hall, 1960: 42–5.
20.
DixonWJ. Description of groups (strata) with histograms and analysis of variance. In: DixonWJ, ed. BMDP statistical software. Berkeley, Calif: Berkeley University Press, 1983: 105–15.
21.
LeveneH. Robust test for equality of variance. In: OlikenI, ed. Contributions to probability and statistics. Palo Alto, Calif: Stanford University Press, 1960: 278–92.
22.
BrownMBForsytheAB. The small sample behavior of some statistics which test the equality of several means. Technometrics1974; 16: 129–32.
23.
HamoriJMezeyE. Serial and triadic synapses in the cerebellar nuclei of the cat. Exp Brain Res1977; 30: 259–73.
24.
KorteGEFriedrichVL. The fine structure of the feline superior vestibular nucleus: Identification and synaptology of the primary vestibular afferente. Brain Res1979; 176: 3–32.
25.
PetersAPalaySLWebsterH. The fine structure of the nervous system: The neurons and supporting cells. Philadelphia, Pa: WB Saunders, 1976.
26.
MitsacosAReisineHHighsteinSM. The superior vestibular nucleus: An intracellular HRP study in the cat. II. Non-vestibulo-ocular neurons. J Comp Neurol1983; 215: 92–107.
27.
KochCPoggioTTorreV. Nonlinear interactions in a dendritic tree: Localization, timing, and role in information processing. Proc Natl Acad Sci USA1983; 80: 2799–802.
28.
Hauglie-HanssenE. Intrinsic neuronal organization of the vestibular nuclear complex in the cat. A Golgi study. Ergeb Anat Entwicklungs Gesch1968; 40: 1–105.
29.
SoteloCPalaySL. The fine structure of the lateral vestibular nucleus in the rat. II. Synaptic organization. Brain Res1970; 18: 93–115.
30.
HopsuVKArstilaAU. An apparent somato-somatic synaptic structure in the pineal gland of the rat. Exp Cell Res1965; 37: 484–7.
31.
GacekRR. The course and central termination of first order neurons supplying vestibular endorgans in the cat. Acta Otolaryngol [Suppl] (Stockh)1969(suppl 254).
32.
BrodalA. Anatomy of the vestibular nuclei and their connections. In: KornhuberHH, ed. Handbook of sensory physiology. Vol 6. Berlin, Germany: Springer-Verlag, 1974: 266–327.
33.
CullheimSKellerthJO. A morphological study of the axons and recurrent axon collaterals of cat sciatic α-motoneurons after intracellular staining with horseradish peroxidase. J Comp Neurol1978; 178: 537–58.
34.
ValdiviaO. Methods of fixation and the morphology of synaptic vesicles. J Comp Neurol1971; 142: 257–74.
35.
RastadJ. Morphology of synaptic vesicles in axo-dendritic and axo-somatic collateral terminals of two feline spinocervical tract cells stained intracellularly with horseradish peroxidase. Exp Brain Res1981; 41: 390–8.
