- Brain development during the first 10 days or so of rodent infancy is roughly equivalent to the third trimester of the human fetus.
- New research indicates that alcohol's reinforcing properties during rodent infancy can be due to its pharmacological effects, independent of taste or smell.
Animal research has shown that rodent infants are susceptible to the reinforcing effects of alcohol. Scientists also know that exposure to alcohol during rodent infancy can change responsiveness to alcohol later in life. A study in the October issue of Alcoholism: Clinical & Experimental Research has found that alcohol's reinforcing properties during rodent infancy are due to its pharmacological effects.
"In terms of brain development, the first 10 days or so after birth for the rat is, very roughly, equivalent to the third trimester of the human fetus," said Elena I. Varlinskaya, associate research professor at Binghamton University and corresponding author for the study. "The extent to which alcohol is considered "reinforcing" is measured by the extent to which the animal approaches rather than avoids the predictor of alcohol's effects, in this case, a surrogate nipple. Previous research has indicated that infants, but not adults, might find the taste of alcohol reinforcing. Infants readily consume even high concentrations, up to at least 30 percent alcohol, whereas adults are reluctant to consume concentrations higher than six percent alcohol, and will do so only after weeks or months of training; even then they will rarely accept an alcohol concentration higher than 10 percent. Alcohol reinforcement in adult rats has been attributed largely to its pharmacological consequences. This was much less clear for infant rats, which is the reason for the present study."
"Fetuses and infants have an amazing capacity to learn and form associations among events in their environment," added Jennifer D. Thomas, assistant professor of psychology at San Diego State University. "If an infant is exposed to the odor of alcohol in the environment, or the combined taste, odor and pharmacological effects of alcohol during fetal development or breast feeding, it is important to determine how this experience affects preference for alcohol and levels of alcohol consumption later in life. In fact, studies indicate that fetal exposure to alcohol is associated with subsequent alcohol use and abuse. This study demonstrates that the pharmacological effects of alcohol, independent of orosensory cues, contribute to the reinforcing properties of ethanol in the developing fetus/infant."
Researchers examined 196 newborn rats during three experiments. The first experiment paired the infants' experience of suckling on a nipple providing water with alcohol administered through an abdominal injection. This method of alcohol administration minimized its olfactory (smell) and gustatory (taste) attributes. The second experiment paired alcohol with an empty nipple, or alcohol with water delivered apart from a nipple. Experiment three examined blood alcohol concentrations five minutes and 60 minutes after one of four doses of alcohol administered through an abdominal injection.
"Our key finding is that an injection of alcohol, with essentially no accompanying taste or odor, is sufficiently reinforcing to allow a newborn rat to learn with only a single experience what predicted the alcohol," said Varlinskaya. "Since there was negligible odor, taste or calories involved, the rewarding effect of injected alcohol must be derived from its effect on areas of the brain activated by drugs of abuse rather than the taste or smell of ethanol. This implies that the basis of alcohol reinforcement is the same in newborn rats as in adults. This is important theoretically because it suggests that animals and people may find alcohol rewarding for the same reasons throughout their development."
"From a basic science standpoint," added Thomas, "this study will help us to understand the development of brain regions important for the reinforcing effects of alcohol and the types of associations that can be learned. From a practical standpoint, this study has implications for infants exposed to alcohol in utero or via breastfeeding. Exposure to alcohol during development can be teratogenic, damaging the brain and altering behavioral development. In addition, learning takes place both in utero and during neonatal development. Given that the pharmacological effects of ethanol can be reinforcing even during this developmental time, early exposure to alcohol may have implications for later in life."
Alcoholism: Clinical & Experimental Research (ACER) is the official journal of the Research Society on Alcoholism and the International Society for Biomedical Research on Alcoholism. Co-authors of the ACER paper included Evgeniy S. Petrov and Norman E. Spear of the Center for Developmental Psychobiology in the Department of Psychology at Binghamton University - SUNY. The study was funded by the National Institute on Alcohol Abuse and Alcoholism.