title: Investigation of "cross-tolerance" between systemic and intrathecal morphine in rats.
abstract: Animals were implanted subcutaneously with morphine or placebo pellets and assessed daily on the hot plate or the tail flick test. After tolerance developed to morphine-induced analgesia the response to an acute systemic (1-6 mg/kg SC) or intrathecal morphine injection (0-30 micrograms) was determined. "Cross-tolerance" was observed on both the hot plate (6 mg/kg) and the tail flick tests (3 and 6 mg/kg) between the two different routes of subcutaneous administration. "Cross-tolerance" was also observed between systemic and intrathecal morphine on the hot plate test. However, no "cross-tolerance" between systemic and spinal morphine was observed in animals on the tail flick test. Assessment of naloxone-precipitated withdrawal indicated that morphine implanted animals showed more abstinence signs (wet shakes and teeth chattering) than placebo animals. These results suggest that the nociceptive assessment procedure plays a significant role in the expression of "cross-tolerance" between systemic and spinal opiates.
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D007278:Injections, Spinal; D007279:Injections, Subcutaneous; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000187:drug effects; D012018:Reflex / Q000187:drug effects; D013375:Substance Withdrawal Syndrome / Q000209:etiology
chemical_list: D009270:Naloxone; D009020:Morphine