Open AccessItch-Associated Response and Antinociception Induced by Intracisternal Endomorphins in Mice
Author(s) -
Tomomi Yamaguchi,
Kouki Kitagawa,
Yasushi Kuraishi
Publication year - 1998
Publication title -
japanese journal of pharmacology/japanese journal of pharmacology
Language(s) - English
Resource type - Journals
eISSN - 1347-3506
pISSN - 0021-5198
DOI - 10.1254/jjp.78.337
Subject(s) - scratching , morphine , (+) naloxone , pharmacology , potency , chemistry , opioid , endogeny , nociception , subcutaneous injection , receptor , medicine , in vitro , biochemistry , physics , acoustics
Endomorphin-1 and endomorphin-2 are newly identified endogenous peptides and have high affinity and selectivity for mu-opioid receptors. The present experiments were conducted to determine whether intracisternal injection of these peptides would produce an itch-associated response and antinociception and to compare their effects to that of morphine. Endomorphin-1 and endomorphin-2 (0.3-3 nmol/mouse) elicited facial scratching characterized by bell-shaped dose-response curves with a peak effect at endomorphin-1 at 0.3 nmol/mouse and endomorphin-2 at 1 nmol/mouse. Their peak effects were inhibited by subcutaneous pretreatment with naloxone (1 mg/kg). Morphine (0.3-30 nmol/mouse) produced facial scratching, and its dose-response curve was also bell-shaped. Scratching of the body trunk, head and ears were not elicited by these doses of endomorphins and morphine. Endomorphin-1 and -2 at doses of 0.3-3 nmol/mouse produced dose-dependent antinociception, as measured with the tail-pressure test. The potency and duration of actions of these peptides were comparable to those of morphine. The results suggest that endomorphin-1 and endomorphin-2 are involved in itch-signaling and pain-inhibiting functions of the brain.