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Ultrastructural analysis of the synaptic connectivity of TRPV1‐expressing primary afferent terminals in the rat trigeminal caudal nucleus
Author(s) -
Yeo Eun Jin,
Cho Yi Sul,
Paik Sang Kyoo,
Yoshida Atsushi,
Park Mae Ja,
Ahn Dong Kuk,
Moon Cheil,
Kim Yun Sook,
Bae Yong Chul
Publication year - 2010
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.22369
Subject(s) - trpv1 , postsynaptic potential , trigeminal ganglion , synaptic vesicle , neuroscience , biology , neurotransmission , inhibitory postsynaptic potential , nociception , nucleus , anatomy , microbiology and biotechnology , sensory system , transient receptor potential channel , receptor , vesicle , biochemistry , membrane
Trigeminal primary afferents that express the transient receptor potential vanilloid 1 (TRPV1) are important for the transmission of orofacial nociception. However, little is known about how the TRPV1‐mediated nociceptive information is processed at the first relay nucleus in the central nervous system (CNS). To address this issue, we studied the synaptic connectivity of TRPV1‐positive (+) terminals in the rat trigeminal caudal nucleus (Vc) by using electron microscopic immunohistochemistry and analysis of serial thin sections. Whereas the large majority of TRPV1+ terminals made synaptic contacts of an asymmetric type with one or two postsynaptic dendrites, a considerable fraction also participated in complex glomerular synaptic arrangements. A few TRPV1+ terminals received axoaxonic contacts from synaptic endings that contained pleomorphic synaptic vesicles and were immunolabeled for glutamic acid decarboxylase, the synthesizing enzyme for the inhibitory neurotransmitter γ‐aminobutyric acid (GABA). We classified the TRPV1+ terminals into an S‐type, containing less than five dense‐core vesicles (DCVs), and a DCV‐type, containing five or more DCVs. The number of postsynaptic dendrites was similar between the two types of terminals; however, whereas axoaxonic contacts were frequent on the S‐type, the DCV‐type did not receive axoaxonic contacts. In the sensory root of the trigeminal ganglion, TRPV1+ axons were mostly unmyelinated, and a small fraction was small myelinated. These results suggest that the TRPV1‐mediated nociceptive information from the orofacial region is processed in a specific manner by two distinct types of synaptic arrangements in the Vc, and that the central input of a few TRPV1+ afferents is presynaptically modulated via a GABA‐mediated mechanism. J. Comp. Neurol. 518:4134–4146, 2010. © 2010 Wiley‐Liss, Inc.