On the mechanism of tolerance to morphine-induced Straub tail reaction in mice.
The effect of 5-HT and opioid receptor antagonists on morphine-induced Straub tail was studied in mice. Straub tail behavior was induced by subcutaneous administration of different doses (20, 30, and 40 mg/kg) of morphine hydrochloride to mice. The effect of morphine was dose-dependent. Maximum response was obtained with 40 mg/kg of the drug. The response induced by morphine (20 and 40 mg/kg) was decreased by different doses of intraperitoneal injection of naloxone (1 and 2 mg/kg) or methysergide, mianserin, and ritanserin (1 and 2 mg/kg). The effect of morphine (40 mg/kg) was also reduced by intracerebroventricular injection of naloxone (0.4-0.8 microg/animal) or mianserin (2 and 4 microg/animal). Different groups of mice received one daily dose (50 mg/kg sc) of morphine sulfate for 3 days to develop tolerance to morphine. The Straub tail reaction induced by morphine hydrochloride (40 mg/kg) was tested on the fourth day. Naloxone injection (1 and 2 mg/kg ip) on Day 3 (1 h after morphine sulfate injection) or on Day 4 (1 h before test dose of morphine hydrochloride), decreased tolerance induced to morphine. Methysergide, mianserin, or ritanserin (intraperitoneal) on Days 2 and 3 (1 h after morphine sulfate injection) or on Day 4 (1 h before test dose of morphine hydrochloride), also decreased tolerance induced to morphine. Intracerebroventricular injection of either naloxone or mianserin also reduced tolerance to morphine. It is concluded that 5-HT(2) and opioid receptor mechanisms are involved in morphine-induced Straub tail reaction and tolerance induced to morphine also may be mediated through these receptors.
Zarrindast
M R
MR
Department of Pharmacology, School of Medicine, Tehran University of Medical Sciences, PO Box 13145-784, Tehran, Iran.
Alaei-Nia
K
K
Shafizadeh
M
M
D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance / Q000502:physiology*; D008297:Male; D051379:Mice; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D011957:Receptors, Opioid / Q000502:physiology; D011985:Receptors, Serotonin / Q000502:physiology; D012702:Serotonin Antagonists / Q000494:pharmacology
D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D011957:Receptors, Opioid; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D009270:Naloxone; D009020:Morphine