Receptor Modulation of Opioid Analgesia in the Mouse

Opioid analgesia is influenced by many factors, including the 1 receptor system. Current studies show the importance of supraspinal mechanisms in these 1 actions. Given supraspinally, the 1 receptor agonist ( )pentazocine diminished systemic , , 1, and 3 opioid analgesia in CD-1 mice. There was a trend for the drugs to be more sensitive to the fixed dose of ( )pentazocine, although the differences did not achieve statistical significance. In contrast to its actions supraspinally, ( )pentazocine was without effect against morphine when both were given spinally. These findings are consistent with a supraspinal site of anti-opioid action of ( )pentazocine. Downregulating supraspinal 1 binding sites using an antisense approach potentiated , , 1, and 3 analgesia in CD-1 mice. Although equally responsive to drugs, BALB-c mice are far less sensitive to analgesics than CD-1 mice. Earlier studies reported that these different responses to drugs between CD-1 and BALB-c were eliminated by the concurrent administration of haloperidol, a 1 antagonist. Antisense treatment of BALB-c mice markedly enhanced the response to drugs, as well as morphine. This enhanced response following antisense treatment was similar to that seen with haloperidol. These observations confirm the importance of 1 receptors as a modulatory system influencing the analgesic activity of opioid drugs. Originally proposed from studies with the benzomorphan ( )-N-allyl-normetazocine [( )SKF-10047] (Martin et al., 1976), receptors are now defined as nonopioid, non-phencyclidine, haloperidol-sensitive, naloxoneinaccessible, ( )benzomorphine-selective binding sites (Quirion et al., 1992). Two subtypes of receptors have been proposed based upon their binding selectivity profiles (Bowen et al., 1993). receptors are conserved across species (Weissman et al., 1988; Su and Wu, 1990; Walker et al., 1992) and are present in almost all tissues, with very high expression in the central nervous system, immune system, and liver (Gundlach et al., 1986; Ryan-Moro et al., 1996). The 1 receptor was first cloned from guinea pig liver (Hanner et al., 1996), followed by human (Kekuda et al., 1996), mouse (Pan et al., 1998), and rat clones (Seth et al., 1997, 1998; Mei and Pasternak, 2001). Structurally, 1 receptors show no homology with any traditional receptor family. Even with the new information available from cloning, many questions regarding the functional significance of 1 receptors remain, although recent work has reported an association with ankyrin (Hayashi and Su, 2001). Functionally, 1 receptors comprise an anti-opioid system and evidence suggests that some of the differences in sensitivity among strains of mice can be attributed to differing tonic levels of 1 receptor activity (Chien and Pasternak, 1993, 1994, 1995a,b; King et al., 1997). Haloperidol, a presumed 1 antagonist, potentiates systemic opioid analgesia, whereas the 1 ligand ( )pentazocine diminishes it. These modulatory functions apply to , , 1, and 3 analgesics. However, haloperidol is not selective for 1 receptors, displaying equally high affinity for D2 dopamine receptors. Uncertainty regarding its actions is further raised by the observation that dopamine D2 receptors also influence opioid actions (King et al., 2001). The present study compares the actions of ( )pentazocine and haloperidol with the effects of down-regulation of 1 receptors by an antisense approach to further define the role of 1 systems in opioid analgesia. Materials and Methods ( )Pentazocine, morphine sulfate, trans-(dl)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide methanesulfonate hydrate, (U50,488H), nalorphine, nalbuphine, and [D-Pen,DPen]enkephalin (DPDPE) were gifts from the National Institute on Drug Abuse Research Technology Branch (Rockville, MD). Halothane was purchased from Halocarcon Laboratories (Hackensack, NJ). Haloperidol, ketamine, and other chemicals were purchased from Sigma-Aldrich (St. Louis, MO). Naloxone benzoylhydrazone This work was supported, in part, by research grant from the National Institute on Drug Abuse (DA06241) and a Senior Scientist Award (DA000220) from NIDA (to G.W.P.), and a core grant to Memorial Sloan-Kettering Cancer Center from the National Cancer Institute (CA008748). ABBREVIATIONS: ( )SKF-10097, ( )-N-allyl-normetazocine, DPDPE, [D-Pen,D-Pen]enkephalin; NalBzoH, naloxone benzoylhydrozone; AS1, antisense treatment; bp, base pair; U50,488H, trans-(dl)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide methanesulfonate hydrate. 0022-3565/02/3004-1070–1074$3.00 THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 300, No. 4 Copyright © 2002 by The American Society for Pharmacology and Experimental Therapeutics 4634/967376 JPET 300:1070–1074, 2002 Printed in U.S.A. 1070 at A PE T Jornals on O cber 5, 2017 jpet.asjournals.org D ow nladed from (NalBzoH) was synthesized, as previously reported (Luke et al., 1988). All the drugs used in the in vivo studies were dissolved in saline, and doses were reported as the free base. Male CD-1 (Crl:CD-1(ICR)BR) and BALB/c (BALB/cAnNCrlBR) mice (25–30 g) were purchased from Charles River Breeding Laboratories (Wilmington, MA) and maintained on a 12-h light/dark cycle with rodent chow and water available ad libitum. All animal studies were approved by the Institutional Animal Care and Use Committee of the Memorial Sloan-Kettering Cancer Center and adhere to National Institutes of Health guidelines. Spinal (i.t.) and supraspinal (i.c.v.) injections were made under halothane anesthesia as previously described (Haley and McCormick, 1957; Hylden and Wilcox, 1980). The anesthetic did not affect analgesia measurements 15 min