Recovery of synapses in axotomized adult cat spinal motoneurons after reinnervation into muscle |
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Authors: | T Brännström Jan-Olof Kellerth |
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Institution: | Department of Anatomy, Ume? University, S-901 87 Ume?, Sweden e-mail: thomas.brannstrom.us@vll.se Tel.: +46-90-785-15-23, beeper 6499, Fax: +46-90-785-28-29, SE
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Abstract: | Peripheral axotomy of adult cat spinal motoneurons induces a marked loss of synaptic boutons from the cell bodies and dendritic
trees. The aim of the present study was to analyze the recovery of synaptic contacts in axotomized motoneurons following reinnervation
into muscle. Adult cat spinal motoneurons were first deprived of their muscular contacts for 12 weeks and, then, allowed to
reinnervate their target muscle. Two years later, regenerated motoneurons were labeled with horseradish peroxidase to allow
quantitative ultrastructural analyses of the synaptic covering of the cell bodies and dendrites. Presynaptic boutons were
classified according to their size and the shape of their synaptic vesicles. Results show that a recovery of synaptic covering
occurs in the axotomized neurons after muscle reinnervation, but it affects various bouton types to different degrees. The
number of S-type boutons synapsing with the soma was 70% higher after reinnervation than at 12 weeks after axotomy, while
the number of F-type boutons had increased by only 13%. Compared with the normal situation, the number of S-type boutons synapsing
with the proximal dendrites increased from 82% at 12 weeks after axotomy to 180% in the reinnervated state. In conclusion,
in adult cat spinal motoneurons, the reestablishment of muscular contact is followed by a normalization of some of the synaptological
changes induced by a prolonged state of axotomy. In certain respects restitution is incomplete, but in others it results in
overcompensation.
Received: 10 December 1997 / Accepted: 30 July 1998 |
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Keywords: | Nerve injury Nerve repair Retrograde reaction Regeneration Electron microscopy |
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