title: Tolerance to the antinociceptive effect of intrathecal morphine in intact and chronic spinal rats.
abstract: The antinociceptive effect of daily acute intrathecal morphine injections on the tail-flick withdrawal response was compared in Intact rats and rats that were spinally transected 3 to 4 weeks prior to morphine administration (Spinal rats). Spinal rats became tolerant to repeated intrathecal injections of 5, 15, or 30 micrograms of morphine within 3 days. Intact rats were not tolerant to these doses after 4 daily injections. Spinal rats, made tolerant to repeated intrathecal morphine injections, were not tolerant to a subcutaneous injection of 6.0 mg/kg of morphine. These data suggest that, in intact animals, tolerance to the antinociceptive effect of spinal morphine is modulated by descending, supraspinal input.
authors.affiliation: Department of Pharmacology, University of Illinois College of Medicine, Chicago 60612.
authors.forename: C
authors.initials: C
authors.lastname: Advokat
authors.forename: D
authors.initials: D
authors.lastname: Flershem
authors.forename: J
authors.initials: J
authors.lastname: Siuciak
mesh_terms: D000818:Animals; D004334:Drug Administration Schedule; D004361:Drug Tolerance; D007278:Injections, Spinal; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009619:Nociceptors / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000187:drug effects; D012684:Sensory Thresholds / Q000187:drug effects; D013116:Spinal Cord / Q000187:drug effects*
chemical_list: D009020:Morphine