Infant rats eagerly accept high concentrations of alcohol upon first exposure

August 15, 2004

Early exposure to alcohol is believed to enhance the risk of alcohol use and/or abuse later in life. A study in the August issue of Alcoholism: Clinical & Experimental Research examines the acceptance of alcohol by infant rats, finding that they are eager to ingest large amounts of highly concentrated alcohol during a short time period, resulting in extremely high concentrations of alcohol in the blood.

"There are numerous avenues for very early alcohol exposure, some depending upon culture," said Norman E. Spear, Distinguished Professor of psychology at Binghamton University and the study's corresponding author. "One way is through the milk of a breastfeeding mother who has consumed alcohol; this is likely since more than half of the pediatricians in the country tell their patients that breastfeeding may be facilitated by consuming alcohol beforehand. It is also common in some parts of Latin America, for example, to place a cotton ball soaked with alcohol on the stomach of a fussy infant, which brings relief in the presence of alcohol's odor, perhaps making it more attractive, and also results in some alcohol intake through inhalation or the skin. Alcohol is also given medicinally to infants in some cultures, placed in the fussy infant's bottle. In addition, exposure to alcohol's odor is likely when parents drink; it is known that this makes alcohol's odor more or less attractive to these children, depending on the circumstances of the drinking. The danger in all of this is that exposure to alcohol early in life may increase its attractiveness and lead to the onset of drinking at an earlier age than otherwise would occur."

Spear and his co-author, Eric M. Truxell of the department of psychology at Binghamton University, exposed Sprague-Dawley infant rats (n=672) to alcohol at two ages, 12 and 18 days following birth.

"In terms of brain development, rats are much more immature at birth than are humans," said Spear, "but the motor capability of the rat develops more rapidly thereafter in the infant rat than the infant human. In terms of brain development, our rats might correspond to humans between a few days and six months after birth, but in terms of sensorimotor ability, the 18-day-old rat is roughly like a three-year-old human."

The researchers systematically varied alcohol concentrations, duration of exposure, and mode of self-administration in each of the two exposures. Alcohol ingestion was measured in terms of percentage body weight change, grams of absolute alcohol ingested per unit body weight, and blood alcohol concentration.

The infant rats ingested extremely high concentrations of alcohol - as high as 30 percent - without initiation procedures. Acceptance of alcohol by these infant rats upon first exposure contrasts sharply with the standard rejection of alcohol by adult rats upon first exposure.

"The key finding of the study was the discovery that infant rats are vastly different from adults in terms of their affinity for alcohol," said Spear. "It has been known for years that adult rats, like most animals, reject alcohol at least initially. They will ingest concentrations of 10 percent or higher only after weeks or months of tricking them into drinking it by, for instance, adding sweetener and then gradually reducing it, or by always having sweetener associated with the alcohol. This is of course not unlike adult humans."

"In human drinking practice, " noted Elena I. Varlinskaya, research professor at Binghamton University, "comparable blood alcohol concentrations will be reached after about 12 to 15 drinks - such as bottles of beer, glasses of wine, or shots - consumed within a very short time, such as no more than one hour. This brings up an extremely important question: 'why is alcohol so attractive early in life?' The fact that infant rats willingly accept alcohol on first exposure, whereas adult animals require intensive and long-lasting initiation procedures, suggests that mechanisms of alcohol acceptance, especially brain mechanisms, undergo substantial changes from infancy to adulthood."

Spear said that his study also showed that the high blood alcohol levels obtained were largely due to active drinking, not just inhalation or absorption through the skin.

"Establishing unusually high alcohol ingestion at this age is important for understanding the relationships between brain and alcohol intake," he said, "because we know how the infant brain differs from that of older rats, so we can now begin to identify which age-related differences in the brain might account for the age-related differences in alcohol intake. In the long run, this could help us somehow control, pharmacologically, that part of the brain that disposes humans to high alcohol intake."

"These findings can also amplify the warning to parents that alcoholic beverages should be kept away from infants and children, since they might find alcohol extremely attractive," said Varlinskaya. "Developing brain systems are especially susceptible to the damaging effects of alcohol."
Alcoholism: Clinical & Experimental Research (ACER) is the official journal of the Research Society on Alcoholism and the International Society for Biomedical Research on Alcoholism. The ACER study, "Immediate Acceptance of ethanol in infant rats: ontogenetic differences with moderate but not high ethanol concentration," was funded by the National Institute on Alcohol Abuse and Alcoholism.

Alcoholism: Clinical & Experimental Research

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