Ultrastructural analysis of glutamate immunoreactive primary afferent terminals in the trigeminal nucleus principalis and trigeminal nucleus oralis of the rat

Park, Jong Ho; Ihn, Hye Jung; Choi, Moon Hee; Park, Mae Ja; Sohn, Yoon Kyung; Bae, Yong Chul

Abstract

The present study was aimed to investigate the ultrastructure of the primary afferent terminals and whether glutamate may be a transmitter in these terminals within the trigeminal nucleus principalis and oralis of the rat. Labeling of primary afferent terminals was performed by the injection of the CTB-HRP into the trigeminal ganglion. Ultrastructural analysis and assessment of the glutamate like immunoreactivity by the immunogold technique was performed with the 66 peroxidased labeled boutons in the nucleus principalis and 62 in the nucleus oralis. Labeled boutons were presynaptic to dendritic shafts of the secondary neurons and postsynaptic to the pleomorphic vesicles containing endings (p-endings). Most of the labeled boutons made synaptic contact with the dendritic shafts. A little labeled boutons in the nucleus oralis but no in the nucleus principalis was observed to make synaptic contact with the soma or proximal dendrite. Most of the labeled boutons made synaptic contact with one to three neurofiles, but labeled boutons showing complex synaptic connections, such as those with five or more neurofiles, were more in principalis than in oralis. The average diameter of p-endings were smaller than that of labeled boutons (p<0.05). The diameter of the postsynaptic dendritic shafts were smaller in nucleus principalis than in nucleus oralis, thus indicated that the labeled boutons made synaptic contact with more distal portion of the postsynaptic dendrite in the nucleus principalis than in the nucleus oralis. The gold particle density over the labeled boutons were significantly higher than that over the p-endings and average tissue particle density. They were ranged from 110 to 430% of the average tissue particle density. These findings indicate that synaptic connection of the primary afferent terminals is organized in different manner in nucleus principalis and oralis, and suggest that glutamate is involved as neuroactive substance in the primary afferent terminals of the trigeminal system.