Immunohistochemical localization of endomorphin-1 and endomorphin-2 in immune cells and spinal cord in a model of inflammatory pain.
Recently, two novel highly selective mu-opioid receptor (MOR) agonists, endomorphin-1 and endomorphin-2, have been isolated from bovine as well as human brains and were proposed to be the endogenous ligand for MOR. Later, endomorphin-1 and endomorphin-2 have been detected in the immune system of rats and humans using radioimmunoassay in combination with reverse-high-phase-liquid chromatography. In the present study, we analyzed the expression of endomorphin-1, endomorphin-2 and MOR by immunohistochemistry in a model of Freund's complete adjuvant (FCA)-induced painful inflammation. While MOR was upregulated on peripheral and central nerve terminals, inflammation did not alter endomorphin-2 expression in nerve fibers either in the dorsal horn of the spinal cord or in subcutaneous tissue. Endomorphin-1 and endomorphin-2 were expressed in immune cells (macrophage/monocytes) in the medullary region of the popliteal lymph nodes. The proportion of immunocytes (macrophage/monocytes, lymphocytes) containing endomorphin-1 and endomorphin-2 was increased in inflamed lymph nodes and subcutaneous paw tissue of animals with local inflammatory pain. Taken together, the upregulation of MOR and of its endogenous ligands endomorphin-1 and endomorphin-2 in immunocytes suggests an involvement of these opioid peptides in the peripheral control of inflammatory pain.
Mousa
Shaaban A
SA
Klinik für Anaesthesiologie und operative Intensivmedizin, Freie Universität Berlin, Universitätsklinikum Benjamin Franklin, Hindenburgdamm 30, D-12200 Berlin, Germany. Shaaban@zop-admin.ukbf.fu-berlin.de
Machelska
Halina
H
Schäfer
Michael
M
Stein
Christoph
C
D000818:Animals; D005620:Freund's Adjuvant; D006614:Hindlimb; D007150:Immunohistochemistry; D008198:Lymph Nodes / Q000166:cytology*; D008214:Lymphocytes / Q000737:chemistry; D008264:Macrophages / Q000737:chemistry; D008297:Male; D009000:Monocytes / Q000737:chemistry; D009842:Oligopeptides / Q000032:analysis*; D010146:Pain / Q000139:chemically induced / Q000276:immunology*; D020671:Posterior Horn Cells / Q000737:chemistry*; D051381:Rats; D017208:Rats, Wistar; D012867:Skin / Q000737:chemistry / Q000276:immunology / Q000294:innervation
D009842:Oligopeptides; C105293:endomorphin 1; C105294:endomorphin 2; D005620:Freund's Adjuvant