Developmental changes in distribution of gamma-aminobutyric acid- and glycine-immunoreactive boutons on rat trigeminal motoneurons. I. Jaw-closing motoneurons.
We have previously described the distribution pattern of inhibitory synapses on rat jaw-closing (JC) alpha- and gamma-motoneurons. In the present study, we investigated developmental changes in inhibitory synapses on JC motoneurons. We performed a quantitative ultrastructural analysis of putative inhibitory synaptic boutons on JC motoneuron somata by using postembedding immunogold labeling for GABA and glycine. In total, 206, 350, and 497 boutons contacting JC motoneuron somata were analyzed at postnatal days 2 (P2), 11 (P11) and 31 (P31), respectively. The size of the somata increased significantly during postnatal development. The size distribution was bimodal at P31. Mean length of the boutons and percentage of synaptic covering also increased during postnatal development, whereas bouton density did not differ significantly among the three age groups. Synaptic boutons on the somata of JC alpha-motoneurons could be classified into four types: boutons immunoreactive for 1) GABA only, 2) glycine only, 3) both GABA and glycine, and 4) neither GABA nor glycine. There was no developmental change in the proportion of putative inhibitory boutons to the total number of studied boutons. However, the glycine-only boutons increased significantly (15.1% to 27.3%), and the GABA-only boutons decreased significantly (17.7% to 2.6%) during the period from P11 to P31. Our ultrastructural data indicate that the inhibitory synaptic input to JC motoneurons is developmentally regulated and that there is a postnatal switch from GABA to glycine. The postnatal changes revealed in the present study could play an important role in the maturation of the oral motor system.
Paik
Sang Kyoo
SK
Department of Oral Anatomy and Neurobiology, School of Dentistry, Brain Korea 21, Kyungpook National University, Daegu 700-412, Korea.
Bae
Jin Young
JY
Park
Sang Euk
SE
Moritani
Masayuki
M
Yoshida
Atsushi
A
Yeo
Eun Jin
EJ
Choi
Karp Shik
KS
Ahn
Dong Kuk
DK
Moon
Cheil
C
Shigenaga
Yoshio
Y
Bae
Yong Chul
YC
D000818:Animals; D005998:Glycine / Q000378:metabolism*; D007150:Immunohistochemistry; D007568:Jaw / Q000294:innervation*; D009046:Motor Neurons / Q000166:cytology* / Q000378:metabolism; D017729:Presynaptic Terminals / Q000378:metabolism / Q000648:ultrastructure*; D051381:Rats; D014276:Trigeminal Nerve / Q000254:growth & development* / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D005680:gamma-Aminobutyric Acid; D005998:Glycine