title: Blocking naloxone-precipitated withdrawal in rats and hamsters.
abstract: Three experiments studied the effects of putative antagonists of opiate withdrawal in hamsters and rats. In Experiment 1, the calcium channel antagonists verapamil (20 mg/kg) and nifedipine (20 mg/kg) failed to antagonize naloxone (1 mg/kg)-precipitated withdrawal in hamsters implanted with two 75-mg morphine pellets, whereas clonidine (0.4 mg/kg), the alpha 2-adrenergic agonist, blocked most withdrawal signs. In Experiment 2, clonidine (0.4 mg/kg) and verapamil (20 mg/kg) were tested against naloxone-precipitated withdrawal in hamsters made acutely dependent by a single injection of morphine (15 mg/kg). As in Experiment 1, clonidine but not verapamil was effective. In Experiment 3, the effects of verapamil on naloxone-precipitated withdrawal were studied in morphine-pelleted rats and hamsters. In rats implanted with two morphine pellets, verapamil (20 mg/kg) reversed naloxone-precipitated withdrawal. By contrast, in hamsters implanted with either one or two morphine pellets neither of two doses of verapamil (20 and 30 mg/kg) was effective. These results are discussed in terms of species' differences in sensitivity to calcium channel blockers.
authors: Department of Psychology, University of Southern Colorado, Pueblo 81001-4901.
authors: P
authors: P
authors: Schnur
authors: M
authors: M
authors: Espinoza
authors: R
authors: R
authors: Flores
authors: S
authors: S
authors: Ortiz
authors: S
authors: S
authors: Vallejos
authors: M
authors: M
authors: Wainwright
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003000:Clonidine / Q000494:pharmacology; D006224:Cricetinae; D004343:Drug Implants; D008647:Mesocricetus; D009021:Morphine Dependence / Q000523:psychology; D009270:Naloxone / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013375:Substance Withdrawal Syndrome / Q000517:prevention & control* / Q000523:psychology; D014700:Verapamil / Q000494:pharmacology; D015000:Yawning / Q000187:drug effects
chemical_list: D004343:Drug Implants; D009270:Naloxone; D014700:Verapamil; D009543:Nifedipine; D003000:Clonidine