Distribution of excitatory and inhibitory axon terminals on the rat hypoglossal motoneurons

Sang Kyoo Paik, Hong Il Yoo, Seung Ki Choi, Jin Young Bae, Sook Kyung Park, Yong Chul Bae

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

Abstract

Detailed information about the excitatory and inhibitory synapses on the hypoglossal motoneurons may help understand the neural mechanism for control of the hypoglossal motoneuron excitability and hence the precise and coordinated movements of the tongue during chewing, swallowing and licking. For this, we investigated the distribution of GABA-, glycine (Gly)- and glutamate (Glut)-immunopositive (+) axon terminals on the genioglossal (GG) motoneurons by retrograde tracing, electron microscopic immunohistochemistry, and quantitative analysis. Small GG motoneurons (< 400 μm2 in cross-sectional area) had fewer primary dendrites, significantly higher nuclear/cytoplasmic ratio, and smaller membrane area covered by synaptic boutons than large GG motoneurons (> 400 μm2). The fraction of inhibitory boutons (GABA + only, Gly + only, and mixed GABA +/Gly + boutons) of all boutons was significantly higher for small GG motoneurons than for large ones, whereas the fraction of Glut + boutons was significantly higher for large GG motoneurons than for small ones. Almost all boutons (> 95%) on both small and large GG motoneurons were GABA + , Gly + or Glut +. The frequency of mixed GABA +/Gly + boutons was the highest among inhibitory boutons types for both small and large GG motoneurons. These findings may elucidate the anatomical substrate for precise regulation of the motoneuron firing required for the fine movements of the tongue, and also suggest that the excitability of small and large GG motoneurons may be regulated differently.

Original languageEnglish
Pages (from-to)1767-1779
Number of pages13
JournalBrain Structure and Function
Volume224
Issue number5
DOIs
StatePublished - 1 Jun 2019

Keywords

  • Electron microscopy
  • Excitatory
  • Hypoglossal motoneuron
  • Immunohistochemistry
  • Inhibitory
  • Presynaptic axon terminal

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