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KMID : 0848120160410030133
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International Journal of Oral Biology
2016 Volume.41 No. 3 p.133 ~ p.139
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Quantitative Ultrastructural Analysis of Endings Presynaptic to the Tooth Pulp Afferent Terminals in the Trigeminal Oral Nucleus
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Lee Suk-Ki
Kim Tae-Heon
Lee Cheon-Hee
Park Sook-Kyung
Bae Yong-Chul
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Abstract
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The ultrastructural parameters related to synaptic release of endings which are presynaptic to tooth pulp afferent terminals (p-endings) were analyzed to understand the underlying mechanism for presynaptic modulation of tooth pulp afferents.
Tooth pulp afferents were labelled by applying wheat-germ agglutinin conjugated horseradish peroxidase to the rat right lower incisor, whereafter electron microscopic morphometric analysis with serial section and reconstruction of p-endings in the trigeminal oral nucleus was performed. The results obtained from 15 p-endings presynaptic to 11 labeled tooth pulp afferent terminals were as follows.
P-endings contained pleomorphic vesicles and made symmetrical synaptic contacts with labeled terminals. The p-endings showed small synaptic release-related ultrastructural parameters: volume, 0.82 ± 0.45 μm3 (mean ± SD); surface area, 4.50 ± 1.76 μm2; mitochondrial volume, 0.15 ± 0.07 μm3; total apposed surface area, 0.69 ± 0.24 μm2; active zone area, 0.10 ± 0.04 μm2; total vesicle number, 1045 ± 668.86; and vesicle density, 1677 ± 684/μm2. The volume of the p-endings showed strong positive correlation with the following parameters: surface area (r=0.97, P<0.01), mitochondrial volume (r=0.56, P<0.05), and total vesicle number (r=0.73, P<0.05). However, the volume of p-endings did not positively correlate or was very weakly correlated with the apposed surface area (r=-0.12, P=0.675) and active zone area (r=0.46, P=0.084).
These results show that some synaptic release-related ultrastructural parameters of p-endings on the tooth pulp afferent terminals follow the “size principle” of Pierce and Mendell (1993) in the trigeminal nucleus oralis, but other parameters do not. Our findings may demonstrate a characteristic feature of synaptic release associated with p-endings.
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KEYWORD
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tooth pulp , afferent , presynatptic ending , ultrastructure , morphometry
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