been shown to exhibit similar physiological responses when compared with the human polymorphism including a 3.5-fold elevated affinity of the G77 allele encoded protein for β-endorphin (Miller et al., 2004) comparable with the 3-fold increased binding reported for the 118G allele in the original in vitro work (Bond et al., 1998). In line with the human observations, rhesus macaques carrying G77 variant showed increased alcohol-preference, consumed higher amounts of alcohol and drank to intoxication (Barr et al., 2004). Studies on rhesus monkeys also support the modulating role of the A118G polymorphisms on the naltrexone response: monkeys carrying the G allele showed greater reductions in alcohol intake after naltrexone administration when compared with the C allele carriers (Barr et al., 2010; Vallender et al., 2010).
