The TA literature includes numerous variations of CTA induction methodologies. The preponderance of experimental taste aversions (TAs) have been induced by following the subject's ingestion of a distinctive CS flavor with administration of an emetic class UCS agent, usually via intraperitoneal injection. The basic CTA design utilized in our laboratory to produce TA learning in rats will be described for purposes of illustration. The methodologies can be extended to other species and modified as needed to suit the individual researcher's objectives. For present purposes, it is assumed that the CS is a distinctive flavor and the UCS is the postinjection gastrointestinal consequence of an emetic class agent injection.
Two of the most basic decisions prior to CTA induction are whether the study is to involve one or several conditioning trials and if the magnitudes of any resultant aversions will be assessed via single-bottle (forced drinking) or two-bottle (free-choice) drinking tests.
The basic CTA paradigm will be illustrated by describing an early comparison of the effects of single trial conditioning as assessed via one-bottle and two-bottle test methodologies. The objective was to develop parametric data concerning the magnitude and longevity of cyclophosphamide (Cytoxan®, Mead Johnson Laboratories) induced aversions to a saccharin-flavored CS solution.11 Cyclophosphamide is a nitrogen-mustard derivative that produces strong nausea in humans when used during cancer chemotherapy, and presumably has some comparable effect in rats where it can function as a potent CTA inducer. Saccharin solutions are frequently used as CSs during TA experiments with rats. Saccharin is a nonnutritive and therefore does not introduce a caloric source of variability. Additionally, palatable saccharin solutions can be prepared that are usually accepted by fluid-deprived rats without any disruptive neophobia, which is operationally defined as a rejection of unfamiliar flavors.12 The use of highly acceptable (i.e., palatable) CS solutions is important, because initially unacceptable solutions may require a period of preconditioning familiarization, and familiarity with the CS flavor can markedly impede CTA acquisition, as will be elaborated later in this discussion.
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