Ultrastructural analysis of the synaptic connectivity of TRPV1-expressing primary afferent terminals in the rat trigeminal caudal nucleus.
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.
Yeo
Eun Jin
EJ
Department of Anatomy and Neurobiology, BK21, School of Dentistry, Kyungpook National University, Daegu, Korea.
Cho
Yi Sul
YS
Paik
Sang Kyoo
SK
Yoshida
Atsushi
A
Park
Mae Ja
MJ
Ahn
Dong Kuk
DK
Moon
Cheil
C
Kim
Yun Sook
YS
Bae
Yong Chul
YC
D000818:Animals; D007150:Immunohistochemistry; D008297:Male; D016253:Microscopy, Immunoelectron; D009475:Neurons, Afferent / Q000737:chemistry / Q000648:ultrastructure*; D017729:Presynaptic Terminals / Q000648:ultrastructure*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000648:ultrastructure*; D050916:TRPV Cation Channels / Q000378:metabolism*; D014275:Trigeminal Caudal Nucleus / Q000648:ultrastructure*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; D005680:gamma-Aminobutyric Acid