Itch-associated response and antinociception induced by intracisternal endomorphins in mice.
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.
Yamaguchi
T
T
Department of Applied Pharmacology, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Japan.
Kitagawa
K
K
Kuraishi
Y
Y
D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D002946:Cisterna Magna; D004305:Dose-Response Relationship, Drug; D007276:Injections, Intraventricular; D008297:Male; D051379:Mice; D009020:Morphine / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects*; D009842:Oligopeptides / Q000494:pharmacology*; D010147:Pain Measurement / Q000187:drug effects; D017288:Pain Threshold / Q000187:drug effects; D011537:Pruritus / Q000139:chemically induced*; D017450:Receptors, Opioid, mu / Q000819:agonists; D013997:Time Factors
D000701:Analgesics, Opioid; D009842:Oligopeptides; D017450:Receptors, Opioid, mu; C105293:endomorphin 1; C105294:endomorphin 2; D009020:Morphine