DURATION OF SUCROSE AVAILABILITY DIFFERENTIALLY ALTERS MORPHINE-INDUCED ANALGESIA IN RATS

The effects of duration of sucrose consumption on morphine-induced ana lgesia (MIA) were examined in 20 adult male Long-Evans rats. Ten rats were tested for MIA on a tail-flick apparatus following acute (5 h), c hronic (3 weeks) intake, and subsequent removal of a 32% sucrose solut ion. Ten rats that never received the sucrose solution served as contr ols. Morphine sulfate was administered according to a cumulative dosin g procedure beginning with 2.5 mg/kg morphine. The same dose was admin istered every 30 min until a total dose of 15 mg/kg was achieved. Tail -flick latencies were measured immediately prior to injections, and 30 min following each injection. After acute intake of sucrose, there wa s a trend for animals drinking the sugar solution to show suppressed M IA relative to animals drinking water. In contrast, after drinking the sucrose for 3 weeks, rats showed an enhanced MIA relative to rats dri nking water. Three weeks after sucrose removal, there were no differen ces in MIA as a function of prior dietary conditions. The results supp ort the hypothesis that length of exposure to sucrose influences morph ine-induced analgesia and suggest that any change in physiology result ing from sucrose exposure may be reversible.