“Binge-drinking teenagers could be doing lasting harm to their memories,” The Daily Telegraph has reported.
The story is based on research on the effects of heavy alcohol consumption on the brains of seven rhesus macaque monkeys. It found that heavy alcohol use had a dramatic effect on the normal division of cells in the hippocampus, part of the brain involved in long-term memory. The researchers say this suggests that lasting damage to the brain may happen relatively early, preceding and possibly causing the neurological problems associated with alcoholism in adults.
Only limited conclusions can be drawn from a study in seven monkeys. A key question is whether excessive drinking during adolescence has not only short-term effects on the brain, but also induces permanent damage. As these monkeys were only followed up for another two months after drinking stopped, the permanence of the damage would need to be established in longer-term studies.
However, binge drinking is damaging at all ages and has a variety of health consequences. There is widespread concern about the possible long-term effects of excessive alcohol on adolescent development. This type of study makes a useful contribution.
Where did the story come from?
The study was carried out by researchers from the Scripps Research Institute in La Jolla, California. It was funded by grants from the National Institutes of Health, the National Institute on Alcohol Abuse and Alcoholism, and the National Institute on Drug Abuse. The study was published in the peer-reviewed journal Proceedings of the National Academy of Sciences (PNAS ).
The Daily Telegraph reported that the study was in monkeys and represented the study’s findings about the effect of alcohol on the hippocampus accurately, although it did not mention the small size of the study. However, the Daily Mirror did not mention that this was an animal study at all.
What kind of research was this?
This was a small animal study in seven adolescent rhesus monkeys, looking at the effects of alcohol bingeing on the normal development of nerve cells in the hippocampus. This important part of the brain is associated with long-term memory.
Indirect observations in adolescent alcoholics support the hypothesis that the adolescent brain is more susceptible to the effects of alcoholism than the brains of other age groups. The authors point out that investigating how chronic binge drinking affects the hippocampus in adolescent primates may improve understanding of the mechanisms that contribute to alcohol addiction in adolescent humans.
The authors point out that there is good evidence that the development of nerve cells in the hippocampus is inhibited by alcohol in adult rodent (rat and mice) models, but few studies have been done on adolescent rats. They say they used rhesus monkeys in these experiments because they have the advantage of being genetically more similar to humans than rodents. Rhesus monkeys also readily consume alcohol to the point of intoxication and are similar to humans in many of the physiological and behavioural systems that are potentially affected by alcohol.
What did the research involve?
The seven adolescent monkeys were divided into an alcohol group and a control group. Both groups were initially given the opportunity to consume alcohol, which was made available in a sweet, orange-flavoured drink, with the amount of alcohol in the solution increasing gradually over a series of daily sessions. Alcohol sessions were then stopped in the control group, while the alcohol group continued to be given alcohol for a period of 11 months. The alcohol group was permitted to consume up to 3.0g/kg of alcohol during one-hour daily sessions, which is equivalent to about 21g for each 7kg average monkey. Normal food and water were also supplied to both groups.
At two points during the study the researchers took blood samples to check on alcohol levels. All the monkeys were also given behavioural testing, including memory tasks, during alcohol exposure.
About two months after the final alcohol session, all the monkeys were euthanised. Brain tissue was removed and frozen for examination in the laboratory. The sections of hippocampus from both the alcohol and control groups were examined for cell changes.
The researchers followed standard guidelines for laboratory animal care and their protocols were approved by the Scripps Research Institute.
What were the basic results?
The monkeys in the alcohol group consumed an average of 1.74g/kg of alcohol per session during the 11-month maintenance period. As might be expected, blood alcohol levels reflected their alcohol consumption. The researchers point out that the high blood alcohol levels recorded were equivalent to human blood alcohol levels during intoxication and were above the legal limit for driving a car.
Examinations of the brain tissue revealed that the monkeys who had been exposed to alcohol had significantly less of certain types of nerve cells in the hippocampus, compared to the control group. This indicates that the continued alcohol exposure had significantly reduced the process of cell division and growth that is a normal, healthy part of brain development.
This effect was seen even two months after alcohol consumption had stopped. The researchers say this suggests that the neural damage was long lasting. However, alcohol consumption did not appear actively to cause cell death or degeneration.
How did the researchers interpret the results?
The researchers conclude that alcohol-induced damage to the hippocampus during adolescence may precede and possibly cause the neuro-degeneration and deficits associated with later adult alcoholism.
They suggest that the cellular changes produced by chronic binge alcohol consumption in non-human primates may underlie some of the effects of alcohol drinking in humans, such as deficits in spatial learning, short-term memory and higher-level cognitive function, or “executive function”.
The alcohol-induced reductions in cell turnover suggest that adolescent brains are highly vulnerable to alcohol. These reductions may alter the ongoing process of development.
This is a carefully designed animal study, which looked in detail at the effects of alcohol on the brains of adolescent rhesus monkeys. The fact that it used adolescent primates rather than adult rats or mice makes the results more relevant to humans. It also used a control group for comparison of brain changes. The results suggest that chronic alcohol consumption may alter the process of brain development in adolescents.
The researchers suggest that this early damage may be permanent, and could increase an individual’s vulnerability to alcohol-related disorders. Such early damage may also underlie deficits in spatial learning, short-term memory and higher-level cognitive function (executive function) seen in adult alcoholics.
However, only limited conclusions can be drawn from a study in just seven monkeys. Also, the monkeys drank a substantial amount of alcohol every day for 11 months, and the teenage human equivalent would presumably be heavy, chronic alcohol misuse, rather than episodic binge drinking.
One of the key questions is whether excessive drinking during adolescence has not only short-term effects on the brain, but also induces permanent damage that may itself trigger adult alcoholism. Although the researchers suggest this is the case, the monkeys were only followed up for another two months after drinking stopped and this would need to be established in longer-term studies.
Binge drinking is damaging at all ages, and has a variety of health consequences, such as increasing risk of cancer, heart attack, stroke and liver damage.