Endomorphin-2 immunoreactivity in the cervical dorsal horn of the rat spinal cord at the electron microscopic level.
Endomorphin-2 is a newly discovered endogenous opioid peptide with high affinity and selectivity for the micro-opioid receptor, and potent analgesic activity, particularly in the spinal cord. Using immunoelectron microscopy, we examined the ultrastructure of the endomorphin-2-like immunoreactive processes and their synaptic relationships in the spinal cord. Endomorphin-2-like immunopositive dense-cored vesicles were observed in many axon terminals, and, in a few cases, were observed together with immunonegative dense-cored vesicles. Immunopositive axons with or without myelination were also observed. The endomorphin-2-like immunoreactive axon terminals formed synapses with both immunopositive and immunonegative processes. Most synapses were asymmetrical, but symmetrical synapses were also found. Examples of axo-dendritic, axo-somatic and axo-axonic contacts were observed. This first demonstration of the ultrastructure and synaptic relationships of endomorphin-2-like immunoreactive axon terminals in the spinal cord dorsal horn provides morphological evidence that this peptide functions as a transmitter regulating pain processes.
Wang
Q P
QP
Department of Anatomy, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
Zadina
J E
JE
Guan
J-L
JL
Kastin
A J
AJ
Funahashi
H
H
Shioda
S
S
D000818:Animals; D002574:Cervical Vertebrae; D008297:Male; D016253:Microscopy, Immunoelectron; D009842:Oligopeptides / Q000032:analysis* / Q000276:immunology; D020671:Posterior Horn Cells / Q000737:chemistry* / Q000648:ultrastructure*; D017729:Presynaptic Terminals / Q000737:chemistry / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D017450:Receptors, Opioid, mu / Q000819:agonists; D013569:Synapses / Q000737:chemistry / Q000648:ultrastructure
D009842:Oligopeptides; D017450:Receptors, Opioid, mu; C105294:endomorphin 2