Open AccessMultiple Effects of Morphine on Facial Scratching in Monkeys
Author(s) -
David A. Thomas,
Gene M. Williams,
Koichi Iwata,
Dan R. Kenshalo,
Ronald Dubner
Publication year - 1993
Publication title -
anesthesia and analgesia/anesthesia and analgesia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.404
H-Index - 201
eISSN - 1526-7598
pISSN - 0003-2999
DOI - 10.1213/00000539-199311000-00010
Subject(s) - scratching , medicine , morphine , anesthesia , pharmacology , acoustics , physics
The medullary dorsal horn (MDH), the medullary homolog of the spinal dorsal horn, is a site where opioid-receptor agonists can act at opioid receptors to produce pronounced facial scratching, the behavioral correlate of pruritus. In the present study, after a 10-min baseline period, morphine (5.0 micrograms) was micro-injected into the MDH of monkeys. Behavior was videotaped and facial scratches were counted by two independent raters. Morphine greatly increased facial scratching behavior, which is consistent with previous findings where mu-opioid receptor agonists microinjected into the MDH have been to induce dose-dependent, naloxone-reversible facial scratching in monkeys. In the current research, intramuscular (IM) administration of the opioid-receptor antagonist, naloxone (0.5 mg/kg), reversed this MDH morphine-induced scratching. Additionally, IM morphine (1.0 mg/kg) produced a substantial reduction in facial scratching behavior. Scratching behavior continued at a high rate after injection of saline (0.1 mL/kg, IM). These findings support the hypothesis that morphine has both pruragenic and antipruragenic activity, depending on the site of action.