Calcitonin gene‐related peptide (CGRP) is a neuropeptide that is associated with a subset of primary afferent fibers and appears to have a role in nociception. The purpose of the present study was to perform a qualitative light, and especially electron microscopic (LM and EM), examination of CGRP‐immunoreactivity (IR) within lamina II (substantia gelatinosa) of the feline pars caudalis/medullary dorsal horn (PC/MDH) of the spinal trigeminal nucleus. The LM investigation revealed massive CGRP‐IR within lamina II outer, with fewer fibers that traversed lamina II inner. The EM preparations showed CGRP‐IR in small, thinly myelinated and unmyelinated axons, preterminal axons, and in axon terminals that formed asymmetric synaptic contacts onto small dendritic profiles. The terminals with CGRP‐IR were often the central element within glomeruli, where the terminal usually formed 2 or more asymmetric synaptic specializations onto 1 or more dendrites. Many of these postsynaptic dendrites contained synaptic vesicles. Other profiles were seen forming presynaptic contacts onto the terminal with CGRP‐IR, and these profiles most likely represent presynaptic dendrites and/or other axon terminals of intrinsic origin. The synaptic association of terminals showing CGRP‐IR with vesicle‐containing dendrites, presynaptic dendrites, and/or other axon terminals suggests that terminals with CGRP‐IR are especially susceptible to modulation. © 1993 Wiley‐Liss, Inc.
- Primary afferents
- Substantia gelatinosa
- Synaptic glomeruli
ASJC Scopus subject areas
- Cellular and Molecular Neuroscience