The ultrastructural changes of the feline superior vestibular commissural neurons (CNs) were quantitatively assessed 8 weeks following ipsilateral vestibular neurectomy. Results indicated a slight degeneration of synaptic profiles (SPs; 25%) representing the primary vestibular afferent input onto CN soma. The synaptic vesicles of the remaining SPs, which likely originate from the cerebellum and the contralateral CNs, were smaller and rounder, suggesting a transition from an inhibitory to an excitatory mode of response. The SP loss had little impact on the CNs' capacity for protein synthesis and structural maintenance, since there was no change in the volume fraction of intracellular organelles. These data suggest that CNs do not degenerate and are likely functional after vestibular compensation. These findings support the role of the commissural pathway in vestibular compensation as proposed by Galiana et al, which is based on the assumption that the intervestibular commissural connections remain intact following vestibular neurectomy.
GalianaHLFlohrHJonesG Melvill. A re-evaluation of intervestibular nuclear coupling: its role in vestibular compensation. J Neurophysiol1984; 51: 242–59.
4.
BienholdHFlohrH. Role of commissural connexions between vestibular nuclei in compensation following unilateral labyrinthectomy [Abstract]. J Physiol (Lond)1978; 284: 178P.
5.
FlohrHBienholdHAbelnWMacskovicsI. Concepts of vestibular compensation. In: FlohrHPrechtW, eds. Lesion induced neuronal plasticity in sensorimotor systems. Berlin, Germany: Springer-Verlag, 1981: 153–72.
6.
SmithPFDarlingtonCLCurthoysIS. Vestibular compensation without brainstem commissures in the guinea pig. Neurosci Lett1986; 65: 209–13.
7.
DieringerNPrechtW. Mechanisms of compensation for vestibular deficits in the frog. I. Modification of the excitatory commissural system. Exp Brain Res1979; 36: 311–28.
8.
ShimazuHPrechtW. Inhibition of central vestibular neurons from the contralateral labyrinth and its mediating pathway. J Neurophysiol1966; 29: 467–92.
9.
PrechtWShimazuHMarkhamCH. A mechanism of central compensation of vestibular function following hemilabyrinthectomy. J Neurophysiol1966; 29: 996–1010.
10.
GuyotJ-PLyonMJGacekRR. Ultrastructure of cat superior vestibular commissural neurons. Ann Otol Rhinol Laryngol1991; 100: 650–7.
11.
GacekRRLyonMJSchoonmakerJ. Ultrastructural changes in vestibulo-ocular neurons following vestibular neurectomy in the cat. Ann Otol Rhinol Laryngol1988; 97: 42–51.
12.
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.
13.
KorteGEFriedrichVL. The fine structure of the feline superior vestibular nucleus: identification and synaptology of the primary vestibular afferents. Brain Res1979; 176: 3–32.
14.
GacekRRLyonMJSchoonmakerJ. Ultrastructural changes in contralateral vestibulo-ocular neurons following vestibular neurectomy in the cat. Acta Otolaryngol [Suppl] (Stockh) 1991(suppl 477).
15.
GacekRRSchoonmakerJLyonMJ. Ultrastructural changes in contralateral superior vestibulo-ocular neurons one year after vestibular neurectomy in the cat. Acta Otolaryngol [Suppl] (Stockh) 1992(suppl 495).
16.
HighsteinSMGoldbergJMMoschovakisAKFernandezC. Inputs from regularly and irregularly discharging vestibular nerve afferents to secondary neurons in the vestibular nuclei of the squirrel monkey. II. Correlation with output pathways of secondary neurons. J Neurophysiol1987; 58: 719–38.
17.
ShimazuHPrechtW. Tonic and kinetic responses of cat's vestibular neurons to horizontal angular acceleration. J Neurophysiol1965; 28: 991–1013.
18.
PrechtWFrankfurtAM. The physiology of the vestibular nuclei. In: KornhuberHH, ed. Handbook of sensory physiology. Vol 6. Berlin, Germany: Springer-Verlag, 1974: 353–416.
19.
StreitWJGraeberMBKreutzbergGW. Functional plasticity of microglia: a review. Glia1988; 1: 301–7.
CassSPGoshgarianHG. Increased glial fibrillary acidic protein immunoreactivity in astrocytes within the lateral vestibular nucleus of the cat following labyrinthectomy and vestibular neurectomy. Ann Otol Rhinol Laryngol1990; 99: 221–7.
22.
BrodalA. Anatomy of the vestibular nuclei and their connections. In: KornhuberHH, ed. Handbook of sensory physiology. Vol 6. Berlin, Germany: Springer-Verlag, 1974: 239–352.
23.
UchizonoK. Characteristics of excitatory and inhibitory synapses in the central nervous system of the cat. Nature1965; 207: 642–3.
RaymondJEz-ZaherLDememesDLacourM. Quantification of synaptic density changes in the medial vestibular nucleus of the cat following vestibular neurectomy. Rest Neurol Neurosci1991; 3: 197–203.
26.
GacekRRLyonMJSchoonmakerJE. Morphologic correlates of vestibular compensation in the cat. Acta Otolaryngol [Suppl] (Stockh) 1989(suppl 462).
27.
KadotaTMizoteMHoriMFujitaMKadotaK. Synaptic vesicle increase correlated to potentiation of transmission at the synapse of the cat superior cervical ganglion in vivo. J Electron Microsc (Tokyo)1992; 41: 37–45.
28.
PetersAPalaySLWebsterH. The fine structure of the nervous system: the neurons and supporting cells. Philadelphia, Pa: WB Saunders, 1976.
29.
TorvikA. Transneuronal changes in the inferior olive and pontine nuclei in kittens. J Neuropathol1956; 15: 119–45.
30.
SmithPFCurthoysIS. Neuronal activity in the ipsilateral medial vestibular nucleus of the guinea pig following unilateral labyrinthectomy. Brain Res1988; 444: 308–19.
31.
RothmanSMThurstonJHHauhartRE. Delayed neurotoxicity of excitatory amino acids in vitro. Neuroscience1987; 22: 471–80.
