Monkeys drink more alcohol when housed alone, and some like to end a long day in the lab with a boozy cocktail, according to a new analysis of alcohol consumption among members of a rhesus macaque social group.
These and other observed behaviors strongly correspond with human patterns of alcohol use. Researchers attribute a predisposition to alcohol abuse in some monkeys and people to a combination of genetic and environmental factors.
In the study subjects, "blood alcohol levels often exceeded the .08 percent level, which is the legal limit for most states in the U.S.," said Scott Chen, one of the study’s authors and a researcher at the National Institutes of Health Animal Center in Maryland.
The study, recently published in the journal Methods, also found that booze affects monkeys much the same way it affects people.
"It was not unusual to see some of the monkeys stumble and fall, sway, and vomit," Chen added. "In a few of our heavy drinkers, they would drink until they fell asleep."
For the initial experiment, 21 females gained access to an aspartame-sweetened ethanol concoction during a group "happy hour." Neck collars registered the amount of fluid consumed, and each monkey received a blood alcohol level test at the end of the period.
In a follow-up experiment, 10 monkeys were housed individually during the "happy hour."
"The singly housed monkeys certainly drank more than the socially housed monkeys- at least two to three-fold more," Chen told Discovery News. "With the socially housed monkeys, there are a number of factors that can potentially compete with access to alcohol, such as social status or dominance ranking."
Lower-ranked monkeys and males tended to drink more overall, but certain individuals consistently drank more than others, regardless of status or housing conditions
"Similar to humans, rhesus macaques have individual differences in taste preference, stress levels, drug tolerance and genetic background that lead to differences in alcohol intake," explained Chen.
In yet another study, the scientists gave a group of male monkeys 24-hour access to the beverage dispensers. According to the researchers, a spike in consumption immediately followed the facility’s working hours.
"Like humans, monkeys are more likely to drink after stressful periods, such as soon after the daily 8-5 testing hours and after a long week of testing," said Chen.
Judy Cameron, a professor and senior scientist at Oregon Health & Science University, told Discovery News, "The fact that different animals consume very different amounts of ethanol suggests that the neural systems in the brain that govern alcohol consumption differ in macaques as they do in humans."
"Monkeys show highly individual responses in their choice to drink alcohol excessively," agreed Kathleen Grant, a senior scientist at the Oregon National Primate Research Center. "There are important parallels to human alcoholism."