Intake of sweet water attenuates restraint-stress-induced potentiation of morphine analgesia in rats.
The analgesia induced in rats by morphine is potentiated by restraint-stress exposure and is reduced in rats that have been consuming a sweet solution. The purpose of the present study was to determine whether the potentiation of morphine-induced analgesia following restraint immobilization would be attenuated in rats consuming a sweet solution. Groups of rats were maintained on unsweetened water or allowed 2 h of daily access to a solution of saccharin and glucose (SG). Half of the rats in each of these groups were subjected to 1 h of restraint stress (groups RS and RS+SG) and the other half in each group were not stressed (groups NS and NS+SG). Rats then underwent 1 h of RS treatment or were nonstressed (NS). The next day all rats were injected subcutaneously with morphine (0.0, 4.0, 8.0, or 16 mg/kg) and analgesia was assessed using the tail flick assay. ED50S (mg/kg) were calculated for each treatment group; NS = 5.8, RS = 1.6, NS+SG = 6.4, and RS+SG = 4.4. Our results demonstrate that RS potentiated morphine-induced analgesia in rats given access to SG as well as non-SG exposed rats that displayed ED50S 1.5 and 3.9 times lower than their respective controls. RS-treated rats that consumed SG solution had significantly lower tail flick latencies than did non-SG exposed rats. Additionally, tail flick latencies of rats in the nonstressed and NS+SG groups did not significantly differ. We conclude that the brain mechanism(s) responsible for RS-induced potentiation of morphine antinociception are attenuated by intake of a sweet solution.(ABSTRACT TRUNCATED AT 250 WORDS)
Calcagnetti
D J
DJ
Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322.
Holtzman
S G
SG
D000698:Analgesia; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004326:Drinking; D004357:Drug Synergism; D005947:Glucose / Q000494:pharmacology*; D009020:Morphine / Q000494:pharmacology*; D010146:Pain / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012149:Restraint, Physical; D012439:Saccharin / Q000494:pharmacology*; D013315:Stress, Psychological / Q000503:physiopathology*; D013549:Sweetening Agents / Q000494:pharmacology*; D013997:Time Factors
D013549:Sweetening Agents; D009020:Morphine; D012439:Saccharin; D005947:Glucose