title: Modulation of oral morphine antinociceptive tolerance and naloxone-precipitated withdrawal signs by oral Delta 9-tetrahydrocannabinol.
abstract: Previous studies have demonstrated a functional interaction between cannabinoid and opioid systems in the development and expression of morphine tolerance and dependence. In these experiments, we examined the effect of a low oral dose of Delta 9-tetrahydrocannabinol (Delta 9-THC) on the development of oral morphine tolerance and the expression of naloxone-precipitated morphine withdrawal signs of jumping and diarrhea in ICR mice. Chronic treatment with high-dose oral morphine produced a 3.12-fold antinociceptive tolerance. Tolerance to morphine was prevented in groups receiving a daily cotreatment with a nonanalgetic dose (20 mg/kg p.o.) of Delta 9-THC, except when challenged with a very high dose of morphine. The chronic coadministration of low-dose Delta 9-THC also reduced naloxone-precipitated (1 mg/kg s.c.) platform jumping by 50% but did not reduce diarrhea. In separate experiments, mice treated chronically with high-dose morphine p.o. were not cross-tolerant to Delta 9-THC; in fact, these morphine-tolerant mice were more sensitive to the acute antinociceptive effects of Delta 9-THC. Delta 9-THC (20 mg/kg p.o.) also reduced naloxone-precipitated jumping but not diarrhea when administered acutely to morphine-tolerant mice. These results represent the first evidence that oral morphine tolerance and dependence can be circumvented by coadministration of a nonanalgetic dose of Delta 9-THC p.o. In summary, cotreatment with a combination of morphine and Delta 9-THC may prove clinically beneficial in that long-term morphine efficacy is maintained.
authors.affiliation: Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia, USA.
authors.forename: Diana L
authors.initials: DL
authors.lastname: Cichewicz
authors.forename: Sandra P
authors.initials: SP
authors.lastname: Welch
mesh_terms: D000284:Administration, Oral; D000700:Analgesics / Q000494:pharmacology; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D013759:Dronabinol / Q000494:pharmacology* / Q000627:therapeutic use; D004361:Drug Tolerance; D006213:Hallucinogens / Q000494:pharmacology; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009020:Morphine / Q000494:pharmacology*; D009021:Morphine Dependence / Q000517:prevention & control; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D013375:Substance Withdrawal Syndrome
chemical_list: D000700:Analgesics; D000701:Analgesics, Opioid; D006213:Hallucinogens; D009292:Narcotic Antagonists; D009270:Naloxone; D009020:Morphine; D013759:Dronabinol