A new model of ethanol self-administration in newborn rats: Gender effectson ethanol ingestion through a surrogate nipple

Background: Ethanol intake in the context of suckling may have distinct and potentially long-lasting consequences for further responsiveness to and ac ceptance of ethanol, compared to other, more indirect and less natural ways of ethanol exposure early in ontogeny. Method: Our findings presented in this paper show that a surrogate nipple t echnique can be used for the study of early ethanol intake in cesarean-deri ved rat pups tested before any suckling experience. Results: Neonatal rats attached to and voluntary ingested ethanol through t he surrogate nipple as early as 4 hr after birth. Moderate concentrations o f ethanol (2% and 5%, v/v) promoted substantial initial suckling behavior, including sustained attachment to the nipple. Higher concentrations (10% an d 15%) were not effective in sustaining suckling. Females responded less po sitively to 10% ethanol than did males. High concentrations of ethanol were less effective in eliciting suckling behavior, probably due to the aversiv eness of ethanol odor. However, when ethanol was presented in solution with milk, newborn pups attached to the nipple and ingested even 15% ethanol. C ontamination of milk with 15% ethanol was more aversive for females than fo r males. Newborn rat pups demonstrated similar patterns of nipple attachmen t and ingestive behavior for 5% ethanol and milk. Initial experience with m ilk in the context of suckling did not prevent further voluntary ethanol in gestion from the same nipple; furthermore, initial exposure to 5% ethanol d id not impair subsequent responsiveness to milk. Conclusions: Gender differences in responsiveness or sensitivity to ethanol can be detected in rat pups as early as a few hours after birth. The resul ts suggest a leftward shift in the dose-response curve for females compared with males, indicating that female neonates are more sensitive or more res ponsive than males to ethanol. The similarity of suckling behaviors produce d by moderate concentrations of ethanol and milk suggests a certain unity i n their reinforcing mechanisms in the context of the first suckling episode .