Abstract
Naïve humans and rats voluntarily consume little ethanol at concentrations above ~6% due to its aversive flavor. Developing procedures that boost intake of ethanol or ethanol-paired flavors facilitates research on neural mechanisms of ethanol-associated behaviors and helps identify variables that modulate ethanol intake outside of the lab. The present study explored the impact on consumption of ethanol and ethanol-paired flavors of nutritionally significant parametric variations: ethanol vehicle (gelatin or solution, with or without polycose); ethanol concentration (4% or 10%); and feeding status (chow deprived or ad lib.) during flavor conditioning and flavor preference testing. Individual differences were modeled by testing rats of lines selectively bred for high (HiS) or low (LoS) saccharin intake. A previously reported preference for ethanol-paired flavors was replicated when ethanol had been drunk during conditioning. However, indifference or aversion to ethanol-paired flavors generally obtained when ethanol had been eaten in gelatin during conditioning, regardless of ethanol concentration, feeding status, or caloric value of the vehicle. Modest sex and line variations occurred. Engaging different behavioral systems when eating gelatin, rather than drinking solution, may account for these findings. Implications for parameter selection in future neurobiological research and for understanding conditions that influence ethanol intake outside of the lab are discussed.
Highlights
Naïve humans and rats voluntarily consume little ethanol at concentrations above about 6% due to its aversive flavor
We examined compensation for calories consumed as ethanol/polycose gelatin by HiS and LoS
As observed previously [17,21], daily caloric intake was higher among LoS rats (77.9 ± 3.1 kcal) than HiS rats (67.7 ± 2.8 kcal), t(22) = 2.37. This result points to lower metabolic efficiency among LoS rats, the mechanisms of which remain to be determined. Rats readily consumed both kinds of gelatin but consumed more no-ethanol than ethanol gelatin
Summary
Naïve humans and rats voluntarily consume little ethanol at concentrations above about 6% due to its aversive flavor. Ethanol’s aversive flavor is methodologically problematic because it impedes observation of behaviorally and physiologically meaningful voluntary ethanol intake in the lab. One strategy has been selective breeding to produce rats with unusually high ethanol intake, such as UChB, P, AA, and HAD rats [4]. This strategy assures unusually high and/or low ethanol intake, facilitating the study of differential intake mechanisms and sequelae. Another strategy has been the development of parameters and procedures that effectively increase ethanol intake. A third strategy involves pairing an arbitrary flavor with ethanol (flavor conditioning) and examining the expression of preference (or aversion) toward the ethanol-paired flavor [8,9,10,11,12]
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