Abducens internuclear neurons depend on their target motoneurons for survival during early postnatal development.
The highly specific projection of abducens internuclear neurons onto medial rectus motoneurons in the oculomotor nucleus is a good model to evaluate the dependence on target cells for survival during development and in the adult. Thus, the procedure we chose to selectively deprive abducens internuclear neurons of their natural target was the enucleation of postnatal day 1 rats to induce the death of medial rectus motoneurons. Two months later, we evaluated both the extent of reduction in target size, by immunocytochemistry against choline acetyltransferase (ChAT) and Nissl counting, and the percentage of abducens internuclear neurons surviving target loss, by calretinin immunostaining and horseradish peroxidase (HRP) retrograde tracing. Firstly, axotomized oculomotor motoneurons died in a high percentage ( approximately 80%) as visualized 2 months after lesion. In addition, we showed a transient (1 month) and reversible down-regulation of ChAT expression in extraocular motoneurons induced by injury. Secondly, 2 months after enucleation, 61.6% and 60.5% of the population of abducens internuclear neurons appeared stained by retrograde tracing and calretinin immunoreaction, respectively, indicating a significant extent of cell death after target loss (38.4% or 39.5%). By contrast, in the adult rat, neither extraocular motoneurons died in response to axotomy nor abducens internuclear neurons died due to the loss of their target motoneurons induced by the retrograde transport of toxic ricin injected in the medial rectus muscle. These results indicate that, during development, abducens internuclear neurons depend on their target motoneurons for survival, and that they lose this dependence with maturation.
Morcuende
Sara
S
Departamento de Fisiología y Zoología, Facultad de Biología, Universidad de Sevilla, Avda. Reina Mercedes 6, 41012-Sevilla, Spain.
Benítez-Temiño
Beatriz
B
Pecero
María Luisa
ML
Pastor
Angel M
AM
de la Cruz
Rosa R
RR
D000010:Abducens Nerve / Q000254:growth & development* / Q000473:pathology*; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D064032:Calbindin 2; D002452:Cell Count / Q000379:methods; D002470:Cell Survival; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D015353:Eye Enucleation / Q000379:methods; D005786:Gene Expression Regulation / Q000502:physiology; D006735:Horseradish Peroxidase / Q000378:metabolism; D007150:Immunohistochemistry / Q000379:methods; D009046:Motor Neurons / Q000502:physiology*; D009434:Neural Pathways / Q000254:growth & development* / Q000473:pathology; D009802:Oculomotor Nerve / Q000473:pathology*; D051381:Rats; D017208:Rats, Wistar; D012183:Retrograde Degeneration; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D013194:Staining and Labeling / Q000379:methods; D013997:Time Factors
C576512:Calb2 protein, rat; D064032:Calbindin 2; D064030:S100 Calcium Binding Protein G; D006735:Horseradish Peroxidase; D002795:Choline O-Acetyltransferase