Lack of growth-associated protein-43 reemergence or of growth-associated protein-43 mRNA modulation in deafferented vestibular nuclei during the first 6 weeks after unilateral inner ear lesion.
We investigated whether a unilateral inner ear lesion that destroyed the labyrinthine receptors, the cochlear receptors, and the spiral ganglion induced collateral sprouting in rat vestibular and auditory brainstem nuclei, using growth-associated protein-43 (GAP-43) as an indicator of synaptic remodeling. Both immunocytochemistry and in situ hybridization were performed to detect a potential modulation of GAP-43 and of its messenger RNA (mRNA) at different times after surgery. We failed to observe a reemergence of GAP-43 or a modulation of its mRNA in the deafferented vestibular nuclei at all survival times tested. In contrast, a substantial increase in the expression of GAP-43 was observed in the neuropil of the ipsilateral deafferented cochlear nuclei and in cell bodies of the ipsilateral superior olive. This increase was associated with an up- and downregulation of the mRNA coding for GAP-43 in the ipsilateral ventral cochlear nucleus and in the ipsilateral superior olive, respectively. These data indicate that synaptic remodeling, as assessed by GAP-43 expression, does not seem to occur in the deafferented vestibular complex during the first 6 weeks after labyrinthectomy, whereas it occurs within the first deafferented auditory relays at times as early as 4 days following spiral ganglion and cochlear receptors removal. We conclude that recovery of a normal resting discharge of the deafferented central vestibular neurons and consequently recovery of a normal resting posture and eye position may not depend on collateral sprouting of the remaining vestibular afferents. In contrast, we confirmed that a reactive synaptogenesis occurs in the brainstem auditory nuclei following cochlea and spiral ganglion removal. Its functional significance remains an open question.
Laboratoire de Neurobiologie des Réseaux Sensorimoteurs, ESA 7060, CNRS-Paris 5-Paris 7, Facultè de Mèdecine des Saints Pères, France. cdw@ccr.Jussieu.fr
C
C
de Waele
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G
Loquet
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Campos Torres
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Vidal
D000344:Afferent Pathways; D000818:Animals; D017626:Cochlear Nucleus / Q000378:metabolism; D007758:Ear, Inner / Q000293:injuries / Q000294:innervation*; D019922:GAP-43 Protein / Q000378:metabolism*; D008297:Male; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D020318:Rats, Long-Evans; D014726:Vestibular Nuclei / Q000378:metabolism*
D019922:GAP-43 Protein; D012333:RNA, Messenger