Rat strain differences in the potentiation of morphine-induced analgesia by stress.
Restraint stress has been shown to increase the magnitude and duration of morphine-induced analgesia; however, this phenomenon has only been investigated using the Sprague-Dawley rat strain. The purpose of this study was to determine if other rat strains would also exhibit a potentiated analgesic response to morphine compared to their unrestrained controls. Dose-response and time course curves for the analgesic effect of morphine (1.0, 3.0, 5.6, 10 mg/kg) were generated in adult, male Wistar, Lewis, Fischer 344, Long-Evans Hooded, and Sprague-Dawley rats either unrestrained or restrained in Plexiglas cylinders, using the tail flick assay. Morphine produced dose-dependent increases in tail flick latencies, and this effect was potentiated by restraint stress in the Sprague-Dawley, Wistar, Lewis, and Fischer 344 strains, but not in the Long-Evans Hooded rats. Because Sprague-Dawley and Wistar rats displayed the most robust stress effect, the use of either of these rat strains is appropriate in studying the mechanisms of stress-induced potentiation of analgesia. The differences among rat strains demonstrated in this study may serve as a basis for correlation with opioid function.
Woolfolk
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DR
Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, USA.
Holtzman
S G
SG
D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D051381:Rats; D011916:Rats, Inbred F344; D011917:Rats, Inbred Lew; D017207:Rats, Sprague-Dawley; D013045:Species Specificity; D013315:Stress, Psychological / Q000523:psychology*
D000700:Analgesics; D009020:Morphine