0 zyxwvutsrqpo Pharmacology zyxwvutsrqponm & Toxicology zyxwvutsrqpo 1995,71, zyxwvutsrqpo 360-364. Covvriaht 0 Printed in Denmark . All rights reserved zyxwvutsrqpon P I l ~ l i ~ & T O X i C O l ~ ISSN 0901-9928 Effects of CholecystokininReceptor Agonist and Antagonists on Morphine Dependence in Mice zy Mohammad-Reza Zarrindast, Anahita Malekzadeh, Mehdi Rezayat and M. Ghazi-Khansari Department of Pharmacology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran (Received October 13, 1994; Accepted May 10, 1995) Abstract: In the present study, the effect of cholecystokinin agonists and antagonists on dependence to morphine in mice has been investigated. Mice were treated subcutaneously with morphine (50, 50 and 75 mg/kg) three times daily for 2 4 days, and a last dose of morphine (50 mg/kg) was administered on day 3, 4 or 5. Withdrawal syndrome (jumping) was precipitated by naloxone (2.5, 5 and 10 mg/kg) which was administered intraperitoneally 2 hr after the last dose of morphine. To study the effects of cholecystokinin receptor agonists or antagonists, 10 injection of morphine (3 administra- tions each day) for dependence and a dose of 5 mgkg of naloxone for withdrawal induction were employed. Cholecystoki- nin-8 (0.001-0.01 mg/kg), low doses of the cholecystokinin agonists caerulein (0.00001 and 0.0001 mg/kg) and, unsulfated cholecystokinin (but not high doses) as well as the antagonists MK-329 (0.5-1 mg/kg) and L-365,260 (0.5-1 mg/kg) elicit reduction of the nalaxone-induced jumping. The inhibition of jumping induced by caerulein was reduced with the selective cholecystokinin antagonists MK-329 and L-365,260. It is concluded that cholecystokinin mechanism(s) may be involved in morphine dependence, that the agonists may act on a presynaptic receptors and that the antagonists may work on postsynaptic receptors. Cholecystokinin octapeptide (cholecystokinin-8) is found in the peripheral tissue and central nervous system (CNS) (Vanderhaeghen et zyxwvutsrqpo al. 1975; Rehfeld 1978). It is becoming clear that cholecystokinin-8 sulphate may function as a neu- rotransmitter or neuromodulator in the CNS. Thus, chole- cystokinin-8 sulphate is synthesized de noyo, is released from synaptic vesicles in a calcium-dependent manner, binds to specific high affinity cholecystokinin receptors and exerts primarily excitatory effect on CNS neurones (Wang et al. 1984). One potential role that has been proposed for cholecystokinin is the modulation of central opiate nocicep- tive mechanism (Jurna & Zetler 1981; Faris et al. 1983; Hill et al. 1987; Magnuson et al. 1990; Slaninova et al. 1991; Such et al. 1992). Caerulein is a decapeptide isolated from frog skin, which has been shown to possess the same bio- logical and pharmacological activities as cholecystokinin-8 (Jurna & Zetler 1981; Van Ree et al. 1983; Hill et al. 1987). Cholecystokinin receptors are generally divided into two classes, cholecystokinin-A (alimentary) and cholecystokin- in-B (brain) (Moran et al. 1986; Dourish & Hill 1987). Cho- lecystokinin receptor antagonists potentiate morphine anal- gesia (Watkins et al. 1984 & 1985; Katsuura & Itoh 1985; Dourish et al. 1988 & 1990) and reverse or prevent mor- phine tolerance (Dourish et al. 1988 & 1990). Our previous study showed that cholecystokinin receptor activation by cholecystokinin peptides may prevent tolerance to mor- phine antinociception (Rezayat et al. 1994). In the present work the influence of cholecystokinin receptor agonists and Author for correspondence: M. R. Zarrindast, Department of Pharmacology, School of Medicine, PO. Box 13145-784, Tehran, Iran (fax 9821-6461178). antagonists on development of morphine dependence has been studied by use of naloxone precipitated withdrawal. Materials and Methods Animals. Male albino mice (20-25 g) were used through out the experiments. Animals were maintained on standard conditions of food, water, light (12 hr per day) and kept at 2522". Each animal was used only once. Induction of morphine dependence. For dependence induction, groups of animal containing 9 mice, were randomly chosen. Mice were treated subcutaneously with morphine three times a day (1 1 a.m., 2 p.m. and 5 p.m.) for two, three or four days. The doses of morphine was 50, 50 and zyxw 75 mgkg, respectively; the higher dose at the third daily injection was aimed to minimize any overnight withdrawal. On day 3, 4 or 5 they received a last dose of morphine (50 mg/kg). Control animals were injected subcutaneously three times daily with 0.9% saline. Measurement of withdrawal syndrome. Physical dependence was in- ferred if a withdrawal syndrome could be precipitated with the opioid receptor antagonist, naloxone. This syndrome is character- ized by jumping episodes. The method is based on that of Mar- shall & Graham-Smith (1971) with minor modifications. Groups of mice were tested for the occurrence of jumping after 7, 10 and 13 injections of morphine or saline. Two hr after the last administra- tion of morphine, animals were given naloxone and placed individu- ally in a glass cylinder (28 zyxw cm diameter, 30 cm height). The number of jumps was recorded over a 30 min. period beginning 2 min. after the injection of naloxone. The mean*S.E.M. of number of jumps was determined for 9 mice. Drugs. The drugs used were: sulfated cholecystokinin-8 (CCK-8), unsulfated cholecystokinin-8 (CCK-8u) and caerulein; (Sigma Chemical Co, U.S.A.), morphine HCI (MacFarlan Smith Ltd., Eng- land) and naloxone HCl (Sigma Chemical Co.). All the drugs were dissolved in saline. L-365,260 (3R(+)-N-(2,3-dihydro-l-methyl-