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Brain Structure and Function

, Volume 221, Issue 2, pp 1125–1137 | Cite as

Central connectivity of the chorda tympani afferent terminals in the rat rostral nucleus of the solitary tract

  • Sook Kyung Park
  • Dae Seop Lee
  • Jin Young Bae
  • Yong Chul BaeEmail author
Original Article

Abstract

The rostral nucleus of the solitary tract (rNST) receives gustatory input via chorda tympani (CT) afferents from the anterior two-thirds of the tongue and transmits it to higher brain regions. To help understand how the gustatory information is processed at the 1st relay nucleus of the brain stem, we investigated the central connectivity of the CT afferent terminals in the central subdivision of the rat rNST through retrograde labeling with horseradish peroxidase, immunogold staining for GABA, glycine, and glutamate, and quantitative ultrastructural analysis. Most CT afferents were small myelinated fibers (<5 µm2 in cross-sectional area) and made simple synaptic arrangements with 1–2 postsynaptic dendrites. It suggests that the gustatory signal is relayed to a specific group of neurons with a small degree of synaptic divergence. The volume of the identified synaptic boutons was positively correlated with their mitochondrial volume and active zone area, and also with the number of their postsynaptic dendrites. One-fourth of the boutons received synapses from GABA-immunopositive presynaptic profiles, 27 % of which were also glycine-immunopositive. These results suggest that the gustatory information mediated by CT afferents to the rNST is processed in a simple and specific manner. They also suggest that the minority of CT afferents are presynaptically modulated by GABA- and/or glycine-mediated mechanism.

Keywords

Gustatory Synapse GABA Glycine Glutamate Ultrastructure 

Abbreviations

CT

Chorda tympani

EM

Electron microscopy

GG

Geniculate ganglion

Glut

Glutamate

Gly

Glycine

HRP

Horseradish peroxidase

HTM

High threshold mechanoreceptive

LDCV

Large dense core vesicle

LM

Light microscopy

LTM

Low threshold mechanoreceptive

PATs

Primary afferent terminals

rNST

Rostral nucleus of the solitary tract

SDH

Spinal dorsal horn

TSN

Trigeminal sensory nuclei

Notes

Acknowledgments

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP, 2008-0062282). The authors sincerely thank Dr. Juli Valtschanoff for helpful discussion and careful reading of the manuscript.

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© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Sook Kyung Park
    • 1
  • Dae Seop Lee
    • 1
  • Jin Young Bae
    • 1
  • Yong Chul Bae
    • 1
    Email author
  1. 1.Department of Anatomy and Neurobiology, School of DentistryKyungpook National UniversityDaeguKorea

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