PT  - JOURNAL ARTICLE
AU  - Carolyn A. Fairbanks
AU  - George L. Wilcox
TI  - Acute Tolerance To Spinally Administered Morphine Compares Mechanistically with Chronically Induced Morphine Tolerance
DP  - 1997 Sep 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 1408--1417
VI  - 282
IP  - 3
4099  - http://jpet.aspetjournals.org/content/282/3/1408.short
4100  - http://jpet.aspetjournals.org/content/282/3/1408.full
SO  - J Pharmacol Exp Ther1997 Sep 01; 282
AB  - The mechanistic similarity between acutely and chronically induced morphine tolerance has been previously proposed but remains largely unexplored. Our experiments examined the modulation of acutely induced tolerance to spinally administered morphine by agonists that affect the N-methyl-d-aspartate receptor and nitric oxide synthase systems. Antinociception was detected via the hot water (52.5°C) tail flick test in mice. Intrathecal pretreatment with morphine (40 nmol) produced a 9.6-fold rightward shift in the morphine dose-response curve. This shift confirmed the induction of acute spinal morphine tolerance. Intrathecal copretreatment with the receptor antagonists (competitive and noncompetitive, respectively) dizolcipine (MK801, 3 nmol) or LY235959 (4 pmol) and morphine [40 nmol, intrathecally (i.t.)] attenuated acute tolerance to morphine measured 8 hr later. A 60-min pretreatment of 7-nitroindazole (6 nmol, i.t.), a selective neuronal NOS inhibitor, followed by administration of morphine (40 nmol, i.t.) blocked the induction of morphine tolerance. Intrathecal copretreatment with morphine (40 nmol, i.t.) and agmatine (4 nmol, i.t.), an imidazoline1 receptor agonist and putative nitric oxide synthase inhibitor, almost completely abolished acute spinal morphine tolerance. The results of these experiments agree with previous reports using models of chronically induced morphine tolerance. This evidence supports the proposal that the mechanisms responsible for acute morphine tolerance parallel those underlying chronic morphine tolerance. This study attests to the powerful predictive value of acute induction as a model for morphine tolerance. The American Society for Pharmacology and Experimental Therapeutics