SELECTIVE FASCICULATION AND DIVERGENT PATHFINDING DECISIONS OF EMBRYONIC CHICK MOTOR AXONS PROJECTING TO FAST AND SLOW MUSCLE REGIONS

Citation
Ld. Milner et al., SELECTIVE FASCICULATION AND DIVERGENT PATHFINDING DECISIONS OF EMBRYONIC CHICK MOTOR AXONS PROJECTING TO FAST AND SLOW MUSCLE REGIONS, The Journal of neuroscience, 18(9), 1998, pp. 3297-3313
Citations number
83
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Neurosciences
Journal title
ISSN journal
0270-6474
Volume
18
Issue
9
Year of publication
1998
Pages
3297 - 3313
Database
ISI
SICI code
0270-6474(1998)18:9<3297:SFADPD>2.0.ZU;2-6
Abstract
Proper motor function requires the precise matching of motoneuron and muscle fiber properties. The-lack of distinguishing markers for early motoneurons has made it difficult to determine whether this matching i s established by selective innervation during development or later via motorneuron-muscle fiber interactions. To examine whether chick moton eurons selectively innervate regions of their target containing either fast or slow muscle fibers, we backlabeled neurons from each of these regions with lipophilic dyes. We found that motor a)tons projecting t o fast and slow muscle regions sorted into separate but adjacent fasci cles proximally in the limb; long before they reached the muscle. More distally, these fascicles made divergent pathfinding decisions to cou rse directly to the appropriate muscle fiber region. In contrast, axon s projecting to different areas of an all-fast muscle did not fascicul ate separately and became more intermingled as they coursed through th e limb. Selective fasciculation of fast-and slow-projecting motoneuron s was similar both before and after motoneuron cell death, suggesting that motoneurons specifically recognized and fasciculated with axons g rowing to muscle regions containing the appropriate muscle fiber type. Taken together, these results strongly support the hypothesis that '' fast'' and ''slow'' motoneurons are molecularly distinct before target innervation and that they use these differences to selectively fascic ulate, path-find to, and branch within the correct muscle fiber region from the outset of neuromuscular development.