Kl. Williams et al., NALTREXONE REDUCES ETHANOL-REINFORCED AND SUCROSE-REINFORCED RESPONDING IN RHESUS-MONKEYS, Psychopharmacology, 139(1-2), 1998, pp. 53-61
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.