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Distribution Pattern of Inhibitory and Excitatory Nerve Terminals in the Rat Genioglossus Motoneurons

흰쥐의 턱끝혀근 지배 운동신경원에 대한 억제성 및 흥분성 신경종말의 분포 양식

  • Moon, Yong-Suk (Department of Anatomy, College of Medicine, Catholic University of Daegu)
  • 문용석 (대구가톨릭대학교 의과대학 해부학교실)
  • Received : 2010.11.08
  • Accepted : 2010.11.09
  • Published : 2011.01.30

Abstract

The genioglossus muscle plays an important role in maintaining upper airway patency during inspiration; if this muscle does not contract normally, breathing disorders occur due to closing of the upper airway. These occur because of disorders of synaptic input to the genioglossus motoneurons, however, little is known about it. In this study, the distribution of GABA-, glycine-, and glutamate-like immunoreactivity in axon terminals on dendrites of the rat genioglossus motoneurons, stained intracellularly with horseradish peroxidase (HRP), was examined by using postembedding immunogold histochemistry in serial ultrathin sections. The motoneurons were divided into four compartments: the soma, and primary (Pd), intermediate (Id), and distal dendrites (Dd). Quantitative analysis of 157, 188, 181, and 96 boutons synapsing on 3 soma, 14 Pd, 35 Id, and 28 Dd, respectively, was performed. 71.9% of the total number of studied boutons had immunoreactivity for at least one of the three amino acids. 32.8% of the total number of studied boutons were immunopositive for GABA and/or glycine and 39.1% for glutamate. Among the former, 14.2% showed glycine immunoreactivity only and 13.3% were immunoreactive to both glycine and GABA. The remainder (5.3%) showed immunoreactivity for GABA only. Most boutons immunoreactive to inhibitory amino acids contained a mixture of flattened, oval, and round synaptic vesicles. Most boutons immunoreactive to excitatory amino acids contained clear and spherical synaptic vesicles with a few dense-cored vesicles. When comparisons of the inhibitory and excitatory boutons were made between the soma and three dendritic segments, the proportion of the inhibitory to the excitatory boutons was high in the Dd (23.9% vs. 43.8%) but somewhat low in the soma (35.7% vs. 38.2%), Pd (34.6% vs. 37.8%) and Id (33.1% vs. 38.7%). The percentage of synaptic covering of the inhibitory synaptic boutons decreased in the order of soma, Pd, Id, and Dd, but this trend was not applicable to the excitatory boutons. The present study provides possible evidence that the spatial distribution patterns of inhibitory and excitatory synapses are different in the soma and dendritic tree of the rat genioglussus motoneurons.

턱끝혀근은 호흡을 위해 상부기도를 확보하는 중요한 근육이지만 정상적으로 수축하지 못하면 상부기도를 폐쇄함으로써 호흡장애가 생길 수있다. 이것은 턱끝혀근을 지배하는 운동신경원의 연접입력 이상으로 생각하고 있으나 이러한 연접입력에 대해서는 잘 알려져 있지 않다. 본 연구에서는 흰쥐의 턱끝혀근을 지배하는 운동신경원과 연접하는 억제성 및 흥분성 신경종말의 분포 양식에 대해 분석하고자 하였으며, 이를 위해 신경추적자인 HRP를 주입하여 턱끝혀근 지배 운동신경원을 표식하고, 운동신경원을 세포체와 가지돌기의 근위부, 중간부 및 원위부로 구분한 후, 전자현미경용 연속절편을 제작하여 GABA, glycine 및 glutamate 항체를 사용한 postembedding immunogold histochemistry를 시행하였다. 정량적 분석은 3개의 턱끝혀근 운동신경원에 연접한 622개의 신경종말 중 157개는 세포체에서, 188개는 14개의 가지돌기 근위부에서, 181개는 35개의 가지돌기 중간부에서, 96개는 28개의 가지돌기 원위부에서 각각 연접 양상을 분석하였다. 관찰한 신경종말의 71.9%에서 사용된 3종류의 아미노산에 대한 면역양성반응이 나타났는데 이 중 32.8%는 GABA 또는 glycine에 대한 면역양성반응을 보였고, 39.1%는 glutamate에 대한 면역양성반응을 보였다. GABA 또는 glycine에 대한 면역양성 신경종말 중 14.2%는 glycine에만 면역양성반응을 보였고, 13.3%는 glycine과 GABA에 동시에 면역양성반응을 보였으며, 5.3%만이 GABA에만 면역양성반응을 보였다. 억제성 아미노산에 면역양성반응을 보인 신경종말에는 납작하거나, 타원형 또는 둥근 형태의 연접소포가 함유된 반면, 흥분성 아미노산에 면역양성반응을 보인 신경종말에는 구형의 소포와 약간의 큰 치밀연접소포가 함유되어 있었다. 억제성 신경종말과 흥분성 신경종말의 분포 비율은 가지돌기 원위부에서 각각 23.9% 대 43.8%로 가장 높았지만, 세포체(35.7% 대 38.2%), 가지돌기의 근위부(34.6% 대 37.8%), 및 중간부(33.1% 대 38.7%)에서는 큰 차이를 보이지 않았다. 억제성 신경종말의 synaptic covering (%)은 세포체에서 가지돌기 원위부로 갈수록 감소되었지만, 흥분성 신경종말의 synaptic covering (%)은 각 부위에서 큰 차이를 나타내지 않았다. 본 연구를 통하여 턱끝혀근 지배 운동신경원은 세포체와 가지돌기의 부위에 따라 GABA, glycine 및 glutamate를 함유하는 전운동신경원들에 의해 서로 다른 양식의 제어를 받고 있다는 것을 알 수 있었으며, 운동신경원의 부위에 따른 이러한 억제성 및 흥분성 연접입력 양식의 차이는 유연한 혀운동의 제어기전과 밀접한 관련이 있을 것으로 추정된다.

Keywords

References

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