TOLERANCE TO ETHANOL ANALGESIA IS NOT ACCOMPANIED BY CROSS-TOLERANCE TO MORPHINE ANALGESIA IN RATS

In the present study, we examined the development of environment-indep endent and environment-dependent tolerance to ethanol-induced analgesi a (EIA) and cross-tolerance with morphine-induced analgesia (MIA). To examine the development of environment-independent tolerance, male Lon g-Evans rats were given increasing amounts of ethanol (5 days each of 5% (v/v), 10% (v/v), and 15% (v/v)) added to their drinking water over a 15-day period. A control group was given plain tap water to drink. On day 16, all rats were given plain tap water to drink. On day 17, th e animals were tested for EIA (2.5 g/kg, IP) or MIA (10 mg/kg, IP) in the hot plate test. To examine the development of environment-dependen t tolerance, animals were injected with ethanol (2.5 g/kg, IP) or an e qual volume of saline once a day for 2 days. On day 3, the animals rec eived no treatment. On day 4, the animals were tested for either EIA ( 2.5 g/kg, IP) or MIA (10 mg/kg, IP) in the hot plate test. It was foun d that rats pretreated with ethanol (both self-administration and IP i njections) displayed tolerance to EIA, which was not accompanied by cr oss-tolerance to MIA. (C) 1998 Elsevier Science Inc.