Mitochondrial accumulation in the distal part of the initial segment of chicken spinal motoneurons.
The axonal initial segment is the initiation site of action potentials and is characterized morphologically by a dense undercoating and fascicles of microtubules connected by cross-bridges. In order to analyze subcellular structures in the initial segment, we made serial transverse sections of initial segments of identified chicken motoneurons by retrograde transport of horseradish peroxidase (HRP) injected into the muscle. The mean (+/-SD) length of the initial segment was 28.1+/-2.3 microm (n=6). Mitochondria accumulated in the distal part of the initial segment, which was 1.4-6.9 microm in length (5-23% of the total length of the initial segment). In the transverse section of the distal part, mitochondrial density was 15.8+/-6.2% (n=5), while in the middle and proximal parts it was 6.1+/-1.6% and 5.6+/-1.4%, respectively. Mitochondrial accumulation was observed in common in phasic and tonic motoneurons in the chicken, and also observed in the distal part of the initial segment of the large ventral horn neurons of the chicken without HRP injection. These findings suggest that accumulated mitochondria play an important role in maintaining the physiological function of the distal part of the motoneuron initial segment.
Department of Anatomy, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Tamaho, Yamanashi 409-3898, Japan.
Yan-Chao
YC
Li
Xiu-Yan
XY
Zhai
Katsunobu
K
Ohsato
Haruo
H
Futamata
Osamu
O
Shimada
Saoko
S
Atsumi
D000818:Animals; D019771:Axotomy / Q000379:methods; D002645:Chickens; D006735:Horseradish Peroxidase / Q000378:metabolism; D046529:Microscopy, Electron, Transmission / Q000379:methods; D008928:Mitochondria / Q000502:physiology*; D009046:Motor Neurons / Q000145:classification / Q000502:physiology* / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000294:innervation; D017729:Presynaptic Terminals / Q000378:metabolism*; D011897:Random Allocation; D013116:Spinal Cord / Q000166:cytology*
D006735:Horseradish Peroxidase