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Regeneration of axons into the trochlear rootlet after anterior medullary lesions in the rat is specific for ipsilateral IVth nerve motoneurones
Author(s) -
Derouiche Amin,
Berry Martin,
Sievers Jobst
Publication year - 1994
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.903410305
Subject(s) - trochlear nerve , anatomy , axon , biology , midbrain , nucleus , cerebral peduncle , lesion , medulla , medulla oblongata , pyramidal tracts , horseradish peroxidase , central nervous system , pathology , neuroscience , medicine , internal capsule , magnetic resonance imaging , palsy , white matter , enzyme , biochemistry , alternative medicine , radiology
The fibre projection from the IVth nerve nucleus to the superior oblique muscle was determined quantitatively in the normal rat by defining fibre numbers in transverse sections of the IVth nerve, and neurone numbers after retrograde labelling by horseradish peroxidase (HRP) injection into the muscle. There were 183 ± 27 (S.E.) labelled neurones in the nucleus contralateral to the injected muscle and only 2 ± 1 ipsilateral. The ipsilateral fibre number was 234 ± 7 and the cell/axon ratio 0.8 ± 0.1. Extensive analysis of all HRP retrogradely labelled material revealed no central fibre contribution to the IVth nerve other than from neurones resident in the trochlear nucleus. The central portion of the trochlear nerve tract was severed at its point of decussation in the anterior medullary velum. Ninety days after lesion, 10 ± 4 (6% of control) neurones were labelled in the ipsilateral trochlear nucleus; none were labelled in the contralateral nucleus or in any other part of the midbrain, pons, medulla, or cerebellum. The number of myelinated fibres in the IVth nerve had decreased to 21 ± 5 (9% of control) so that the cell/axon ratio was 0.4 ± 0.2, thus suggesting that a single motoneurone has more fibres after lesion. In electron micrographs of the IVth nerve, larger than normal numbers of unmyelinated fibres were seen. Many myelinated fibres displayed signs of abnormal myelination. After regeneration, the projection was exclusively ipsilateral and not crossed as in the normal. These findings establish that there is a high degree of specificity after regeneration since no myelinated central nervous system axons other than trochlear fibres select the IVth nerve root as a trajectory over which to regenerate.

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