Background: Infant rats detect the presence of alcohol in milk when the dam
suffers a moderate state of alcohol intoxication. The present study examin
ed when rat pups begin to show behavioral changes indicative of the interac
tion with an intoxicated dam. The study also attempted to determine if infa
ntile experiences involving a moderately intoxicated dam result in alcohol-
derived memories with a particular hedonic content.
Methods: 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 alco
hol-free dams. After the interaction took place, some pups were tested in t
erms of ultrasonic vocalizations (USVs) and motor reactivity when isolated
and placed on each of two distinctive tactile surfaces (sandpaper or soft f
abric) presented in a counterbalanced order, and the second of which was al
ways paired with ambient ethanol odor. At PD 14 pups were evaluated in term
s of the preference for texture (sandpaper versus soft fabric) and odor (al
cohol versus clove) as well as alcohol ingestion.
Results: Very early in life (PD 3) USYs and overall activity were significa
ntly 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 intoxicat
ed dams followed by pairing of ethanol odor and an arousing texture (sandpa
per), later avoided this lexture in the preference test: pups that interact
ed with alcohol-free dams did not show this effect. The former animals also
exhibited less consumption of alcohol than preweanlings never exposed to a
lcohol in the context of nursing.
Conclusions: In conjunction with prior studies these results indicate that
very early in ontogeny the infant processes the presence of ethanol, and pe
rhaps its effect on its mother. within the nursing context. Under the prese
nt experimental circumstances infants appear to acquire alcohol-related inf
ormation that comprises an aversive hedonic component.