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Published on: July 13, 2015
Mitochondrial accumulation in the distal part of the initial segment of chicken spinal motoneurons
Yan-Chao Li1, Xiu-Yan Zhai, Katsunobu Ohsato
1Department of Anatomy, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Tamaho, Yamanashi 409-3898, Japan.
Abstract:
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.
Insights
Mitochondria accumulate in the distal axonal initial segment, crucial for action potential initiation. This finding in chicken motoneurons suggests a key role for these organelles in neuronal function.
Area of Science:
- Neuroscience
- Cell Biology
- Neuroanatomy
Background:
- The axonal initial segment (AIS) is the primary site for action potential generation in neurons.
- The AIS is morphologically defined by a dense undercoating and microtubule fascicles.
Purpose of the Study:
- To investigate the subcellular structures within the AIS, specifically focusing on mitochondrial distribution.
- To determine the functional significance of mitochondrial localization in the AIS.
Main Methods:
- Serial transverse sectioning of chicken motoneuron AIS.
- Retrograde transport of horseradish peroxidase (HRP) for neuron identification.
- Quantitative analysis of mitochondrial density in different AIS regions.
Main Results:
- The mean length of the chicken motoneuron AIS was 28.1 ± 2.3 µm.
- Mitochondria were significantly accumulated in the distal AIS (5-23% of total length).
- Mitochondrial density was highest in the distal AIS (15.8%) compared to middle (6.1%) and proximal (5.6%) regions.
Conclusions:
- Mitochondrial accumulation is a common feature in the distal AIS of both phasic and tonic chicken motoneurons.
- This pattern was also observed in non-injected ventral horn neurons, indicating it's not an artifact of HRP injection.
- Accumulated mitochondria likely play a vital role in supporting the physiological functions of the distal AIS.
