The Infant Rat Learns About Alcohol Through Interaction with an Intoxicated Mother

Abstract

Infant rats detect the presence of alcohol in milk when the dam suffers a moderate state of alcohol intoxication. The present study examined when rat pups begin to show behavioral changes indicative of the interaction with an intoxicated dam. The study also attempted to determine if infantile experiences involving a moderately intoxicated dam result in alcohol-derived memories with a particular hedonic content. Infant rats were allowed to interact during postnatal days (PDs) 3, 5, 7, 9, 11 and 13 with alcohol-intoxicated (EtOH dose: 2.5 g/kg) or alcohol-free dams. After the interaction took place, some pups were tested in terms of ultrasonic vocalizations (USVs) and motor reactivity when isolated and placed on each of two distinctive tactile surfaces (sandpaper or soft fabric) presented in a counterbalanced order, and the second of which was always paired with ambient ethanol odor. At PD 14 pups were evaluated in terms of the preference for texture (sandpaper versus soft fabric) and odor (alcohol versus clove) as well as alcohol ingestion. Very early in life (PD 3) USVs and overall activity were significantly higher in pups that had previously interacted with an intoxicated dam than in those exposed to an alcohol-free dam. Although this difference was not apparent during the following days, it was clear that a specific memory of alcohol's chemosensory cues was formed. Pups interacting with intoxicated dams followed by pairing of ethanol odor and an arousing texture (sandpaper), later avoided this texture in the preference test; pups that interacted with alcohol-free dams did not show this effect. The former animals also exhibited less consumption of alcohol than preweanlings never exposed to alcohol in the context of nursing. In conjunction with prior studies these results indicate that very early in ontogeny the infant processes the presence of ethanol, and perhaps its effect on its mother, within the nursing context. Under the present experimental circumstances infants appear to acquire alcohol-related information that comprises an aversive hedonic component.