Operant conditioning with a stimulus discrimination: An alternative method for evaluating alcohol reinforcement in preweaning rats.

BACKGROUND: Ethanol exposure at early ontogeny promotes further predisposition to consume the drug. Operant conditioning allows motivational alcohol properties to be assessed. To date, the operant conditioning approach used during infancy consisted in paired subjects being trained to learn an operant response, using simultaneously a yoked partner, which received reinforcer solution as a result of a paired animal instrumental response (OYS). NEW METHOD: In our study, we attempted to evaluate ethanol reinforcing effects during PDs 15-18 in an operant conditioning schedule with a stimulus discrimination procedure (OSD), as an alternative control learning. This new proposal includes a single subject, who has to choose between an S+ nose-poke hole, which delivers the reinforcer into the mouth, or an S- nose-poke hole with no reinforcement effect. RESULTS: The OSD results seemed to be more reliable than those obtained using the OYS procedure, since some data appeared to be more robust when using a yoked nose-poke hole than when employing a yoked subject, such as in control learning. Consequently, OSD has the following advantages compared to the OYS procedure: a) the operant response learned is controlled by the overall behavior of the same subject, resulting in a relatively clearer data; b) a yoked animal is not necessary, thereby reducing the number of rats used in the operant conditioning procedure. COMPARISON WITH EXISTING METHODS AND CONCLUSIONS: A novel technique of operant conditioning adapted to infancy was developed by training animals to emit a particular response to gain access to alcohol solution as a reinforcer.

Maternal manipulation during late gestation (GDs 17-20) enhances ethanol consumption and promotes changes and opioid mRNA expression in infant rats.

Fetal ethanol experience generates learning and memories capable to increase ethanol consummatory behaviors during infancy. Opioid system seems to be involved in mediating those alcohol-related behaviors. In this work, we proposed to study the impact of prenatal exposure to a moderate ethanol dose, upon ingestion of the drug and possible ethanol-induced molecular changes on opioid precursor peptides (POMC, Pro-enk and Pro-DYN) and receptors (MOR, DOR and KOR) mRNA expression, in hypothalamus. Pregnant rats received during gestational days (GDs) 17-20, a daily intragastric (i.g.) administration with 2g/kg ethanol or water. A third group of dams was left undisturbed during pregnancy (Unmanipulated group). Intake test was conducted at postnatal days (PDs) 14-15. Three groups of pups were performed: control (no intake test), water (vehicle) and 5% ethanol. At the end of intake test blood samples were taken to quantify blood ethanol concentrations (BECs) and hypothalamus sections were obtained to perform qRT-PRC assessment of opioid precursor peptides and receptors. The analysis of the consummatory responses (% of consumption) and pharmacokinetic profiles (BECs) suggested that maternal manipulation induced by i.g. intubations, during the last four days of gestation (whenever ethanol or water), are sufficient to induce infantile ethanol intake during infancy. Gene expression from the hypothalamus of unmanipulated group revealed that infantile ingestive experiences with ethanol can down-regulate expression of mRNA Pro-Dyn and up-regulate mRNA expression of MOR and KOR. Finally, MOR mRNA expression was attenuated by prenatal i.g. manipulation in pups exposed to 5% ethanol.