NALTREXONE REDUCES ETHANOL-REINFORCED AND SUCROSE-REINFORCED RESPONDING IN RHESUS-MONKEYS

These experiments evaluated the ability of naltrexone (NTX) to reduce selectively oral and IV ethanol-reinforced responding, and examined th e ethanol-NTX interaction in terms of the competitive opioid antagonis t property of NTX. Five rhesus monkeys self-administered ethanol or su crose and concurrently available water. Ethanol concentration was vari ed from 0.25% to 8% (w/v). Naltrexone (0.032-0.32 mg/kg) or saline was given IM 30 min prior to some drinking sessions. NTX (0.32 mg/kg) red uced ethanol-reinforced responding at the concentration that: maintain ed the most responding (1% or 2%). NTX (0.1 mg/kg) reduced ethanol-rei nforced responding, both at a low ethanol concentration (0.25%) that p roduced little ethanol intake (g/kg), and at a higher concentration (4 %) with an appreciable intake. Thus, NTX (0.1 mg/kg) shifted the ethan ol concentration-consumption curve down, in an insurmountable manner. NTX (0.1 and 0.32 mg/kg) also reduced reinforced responding for sucros e 100 g/l. In another experiment, three rhesus monkeys were given oppo rtunities to self-administer ethanol IV. NTX (0.1 mg/kg) reduced the n umber of ethanol injections obtained by the monkeys at all ethanol dos es tested (0.01, 0.032, and 0.1 g/kg per injection). The, dose-effect curve was also shifted down. These results showed that NTX reduced beh avior maintained by either ethanol or sucrose non-selectively. Further more, the ability of NTX to suppress ethanol-reinforced responding did not depend on the route of ethanol administration and was not overcom e by increasing the concentration or dose per injection of ethanol.