It was revealed that the morphology and projection pattern of terminal arbors from single primary afferent are different among distinct fiber types, functional types and the different subdivision of trigeminal sensory nucleus complex (TSNC). But
it
was
not identified the ultrastructural morphology and synaptic connections of terminal arbors from each primary afferent within TSNC.
So we employed the intra-axonal horseradish peroxidase (HRP) injection technique to define the terminal arbors of primary afferent fiber from slowly adapting mechanoreceptors in the periodontal ligament of the cat, and examined 66 labeled
terminal
arbors within the rostrodorsomedial part (Vo. r) of the trigeminal nuclus oralis, electromicroscopically with 90nm serial sections.
All the boutons labelled with HRP contained clear, spherical and uniform sized synaptic vesicles (diameter : 47.66±3.58nm). Most of the labelled boutons were boutons en passant type and they were connected by unmyelinated axonal strand. In which
neurofilament and microtubule was not developed but occasionally contained synaptic vesicle in contrast to the myelinated axon.
The size of the labelled bouton was relatively small (long diameter : 1.46±0.24㎛) and the shape of which varied from dome to elongated shape, but scalloped glomerulus shape was not developed.
Each primary ending in Vo. r made synapse with one or two neuronal propiles (average : 1.11±0.31), of which, 89.4% of labelle dboutons made synapse with only one neuronal propile, the remainder, 10.6% of labelled boutons, made synapse with two
neuronal
propile. So characteristically they made very simple synapse. Most of labelled boutons (80.03%) made asymmeterical synapse only with dendritic shaft or spine, and 6.1% of labelled boutons received symmeterical synapse from pleomorphic vesicle
containing
axonal ending (p-ending). So presynaptic inhibiton was relatively scarce. Synaptic triad, in which a p-ending is presynaptic both pre-and post-synaptic element of the axo-dendritic contact from the labelled primary ending was not observed.
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