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Ultrastructural morphology, synaptic relationships, and CGRP immunoreactivity of physiologically identified c‐fiber terminals in the monkey spinal cord
Author(s) -
Alvarez Francisco J.,
Kavookjian Anahid M.,
Light Alan R.
Publication year - 1993
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.903290405
Subject(s) - postsynaptic potential , synaptic vesicle , biology , synapse , calcitonin gene related peptide , spinal cord , ultrastructure , horseradish peroxidase , anatomy , neuroscience , vesicle , neuropeptide , biochemistry , receptor , membrane , enzyme
The spinal cord terminations of two electrophysiologically identified single C‐fibers (one identified as a C‐nociceptor) were intraaxonally labeled with horseradish peroxidase and analyzed with both light and electron microscopy. Serial section ultrastructural analysis and postembedding immunocytochemical techniques for calcitonin gene‐related peptide (CGRP), substance P (SP), and GABA were used to study the synaptology, and neuropeptide content. All C‐terminal synapses were in laminae I and II. The terminals sampled (n = 73) from these two C‐fibers rarely established glomerular synaptic complexes, but rather, simple terminals, usually measuring 1–4 μm in length and 1–3 μm in diameter. They most often established 1 or 2 (range 1 to 5) quite large asymmetric axodendritic synaptic contacts. Postsynaptic structures included dendritic spines and shafts with and without vesicles. C‐terminals were filled with small round synaptic vesicles (45–60 nm) and also contained variable numbers of large dense‐core vesicles (LDCVs, 80–110 nm). LDCVs inside identified C‐terminals frequently displayed CGRP immunoreactivity. We were unable to detect SP immunoreactivity inside our sample of C‐fiber LDCVs. C‐terminals were never found postsynaptic to other profiles. Thus, the C‐fiber terminals sampled in this study have simple synaptology, do not receive presynaptic control and contain CGRP immunoreactivity. They differ greatly from the terminals of Aδ nociceptors studied previously by our group that had glomerular endings, often received presynaptic input and did not contain CGRP immunoreactivity. This suggests the existence of different processing mechanisms, at the level of the first synapse, for nociceptive inputs arriving to lamina I and II through different types of primary afferents. © 1993 Wiley‐Liss, Inc.