BEYOND SWEET TASTE - SACCHARIN, SUCROSE, AND POLYCOSE DIFFER IN THEIREFFECTS UPON MORPHINE-INDUCED ANALGESIA

The effects of saccharin, sucrose, or Polycose intake on morphine-indu ced analgesia (MIA) were examined in 40 adult male Long-Evans rats. Ra ts were tested for MIA on a tail-flick apparatus following acute (5-h) and chronic (3-wk) intake of a 0.15% saccharin solution, a 32% sucros e solution, a 33.68% Polycose solution, or water. During the chronic p hase, all rats were given a choice between the test solution and water . Morphine sulfate was administered according to a cumulative dosing p rocedure beginning with 2.5 mg/kg morphine. The same dose was administ ered every 30 min. Tail-flick latencies were measured immediately prio r to injections and 30 min following each injection. After acute intak e of flavored solutions or water, there were no differences in MIA as a function of diet. However, after drinking the flavored solutions or water for three weeks rats drinking Polycose or sucrose showed signifi cantly enhanced MIA relative to rats drinking saccharin. Rats drinking Polycose also showed enhanced MIA relative to rats drinking water. Co mparison between the acute and chronic phases of the study demonstrate d that tolerance to morphine's analgesic effects did not develop in ra ts drinking Polycose or sucrose, but did develop in rats drinking sacc harin or water. The results support the hypothesis that, in addition t o palatability, the nutritive value of flavored solutions influences M IA. Copyright (C) 1997 Elsevier Science Inc.