Endomorphins suppress nociception-induced c-Fos and Zif/268 expression in the rat spinal dorsal horn.
We evaluated the potency of endomorphin-1 and -2 as endogenous ligands on c-Fos and Zif/268 expression in the spinal dorsal horn by formalin injection to the rat hind paw. Endomorphin-1, -2, or morphine was administered intrathecally or intracerebroventricularly 5 min before formalin injection (5%, 100 microl). All drugs produced marked reductions of formalin-induced c-Fos and Zif/268 immunoreactivity in laminae I and II, and laminae V and VI in the rat lumbar spinal cord. The reductions of Zif/268 expression by endomorphins were greater than those by morphine, while the reductions of c-Fos expression by endomorphins were smaller than those by morphine. These effects of endomorphins were attenuated by pretreatment with naloxone. These results indicate that endomorphin-1 and -2 act as endogenous ligands of mu-opioid receptor in neurons of the spinal dorsal horn and suppress the processing of nociceptive information in the central nervous system.
Tateyama
Shingo
S
Department of Anesthesiology, Miyazaki Medical College, 5200 Kihara, Kiyotake, Miyazaki 889-1692, Japan. shingot@post1.miyazaki-med.ac.jp
Ikeda
Tetsuya
T
Kosai
Kazuko
K
Nakamura
Tadashi
T
Kasaba
Toshiharu
T
Takasaki
Mayumi
M
Nishimori
Toshikazu
T
D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D004268:DNA-Binding Proteins / Q000187:drug effects*; D051766:Early Growth Response Protein 1; D017874:Immediate-Early Proteins; D007278:Injections, Spinal; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology*; D020671:Posterior Horn Cells / Q000187:drug effects*; D016760:Proto-Oncogene Proteins c-fos / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014157:Transcription Factors / Q000187:drug effects*
D000701:Analgesics, Opioid; D004268:DNA-Binding Proteins; D051766:Early Growth Response Protein 1; C486110:Egr1 protein, rat; D017874:Immediate-Early Proteins; D009842:Oligopeptides; D016760:Proto-Oncogene Proteins c-fos; D014157:Transcription Factors; C105293:endomorphin 1; C105294:endomorphin 2; D009020:Morphine