Reevaluation of motoneuron morphology: diversity and regularity among motoneurons innervating different arm muscles along a proximal–distal axis

Dendritic fields of spinal motoneurons (MNs) are popularly believed to be stellate; however, variation in dendritic arborization, especially concerning the innervated muscle groups, has not been systematically studied. We addressed this problem by injecting Neurobiotin through patch-pipettes into si...

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Bibliographic Details
Published in:Scientific reports 2020-08, Vol.10 (1), p.13089-13089, Article 13089
Main Authors: Fukuda, Satoshi, Maeda, Hitoshi, Sakurai, Masaki
Format: Article
Language:English
Subjects:
631/378
631/378/1697
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631/378/3920
631/378/87
Animals
Arm
Brain slice preparation
Cell Count
Dendrites
Dendritic branching
Forearm
Forelimb - anatomy & histology
Forelimb - innervation
Humanities and Social Sciences
Morphology
Motor neurons
Motor Neurons - cytology
multidisciplinary
Muscles
Rats
Science
Science (multidisciplinary)
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Summary:Dendritic fields of spinal motoneurons (MNs) are popularly believed to be stellate; however, variation in dendritic arborization, especially concerning the innervated muscle groups, has not been systematically studied. We addressed this problem by injecting Neurobiotin through patch-pipettes into single MNs (rat cervical cord slices) that had been retrogradely labelled from innervated muscle groups situated along a proximal (here named “scapular” including serratus anterior) to distal (forearm) axis. MNs had fairly straight dendrites with small numbers of mainly proximal branches that exhibited acute branch angles, leaving large areas around the cells with no dendrites. MNs in the same group of pools showed similar morphologies, but there were clear differences among groups. Forearm MNs (n = 35) showed hemidirectionally-extended multipolar dendrites, whereas scapular MNs (n = 15) had bipolar dendrites, and pectoralis MNs (n = 20) had an intermediate morphology. MNs thus showed a spectrum of morphologic characteristics along the axis. This may be because more distally-located forearm muscles are involved in finer movements and need a wider variety of inputs for neural control than proximally-located muscles. We also devised a quantitative method for evaluating the degree to which a cell’s dendritic field displays a symmetric spherical shape; only 20% of MNs tested reached this criterion.
ISSN:2045-2322
2045-2322
DOI:10.1038/s41598-020-69662-z