Paik Sang Kyoo, Bae Jin Young, Park Sang Euk, Moritani Masayuki, Yoshida Atsushi, Yeo Eun Jin, Choi Karp Shik, Ahn Dong Kuk, Moon Cheil, Shigenaga Yoshio, Bae Yong Chul
Department of Oral Anatomy and Neurobiology, School of Dentistry, Brain Korea 21, Kyungpook National University, Daegu 700-412, Korea.
J Comp Neurol. 2007 Aug 20;503(6):779-89. doi: 10.1002/cne.21423.
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.
我们之前描述过大鼠闭口（JC）α运动神经元和γ运动神经元上抑制性突触的分布模式。在本研究中，我们调查了JC运动神经元上抑制性突触的发育变化。我们通过对GABA和甘氨酸进行包埋后免疫金标记，对JC运动神经元胞体上假定的抑制性突触终扣进行了定量超微结构分析。分别在出生后第2天（P2）、第11天（P11）和第31天（P31）分析了与JC运动神经元胞体接触的206个、350个和497个终扣。在出生后发育过程中，胞体大小显著增加。在P31时，大小分布呈双峰型。在出生后发育过程中，终扣的平均长度和突触覆盖百分比也增加了，而在三个年龄组中终扣密度没有显著差异。JCα运动神经元胞体上的突触终扣可分为四种类型：1）仅对GABA免疫反应的终扣，2）仅对甘氨酸免疫反应的终扣，3）对GABA和甘氨酸都免疫反应的终扣，4）对GABA和甘氨酸都不免疫反应的终扣。在假定的抑制性终扣占所研究终扣总数的比例方面，没有发育变化。然而，在从P11到P31的期间，仅对甘氨酸反应的终扣显著增加（从15.1%增至27.3%），而仅对GABA反应的终扣显著减少（从17.7%降至2.6%）。我们的超微结构数据表明，对JC运动神经元的抑制性突触输入在发育过程中受到调节，并且在出生后存在从GABA到甘氨酸的转换。本研究中揭示的出生后变化可能在口腔运动系统的成熟中起重要作用。
