Group mean saccharin preference scores from 2-bottle data averaged over successive 5-day periods.
of extinction testing. However, the 12.5 mg/kg dose produced aversions that extinguished to a greater degree than those of the 25 mg/kg dose over the remaining 40 days of preference testing. These data indicate that resistance to extinction can be a useful indicator of aversion strength. The figure also reveals the remarkable longevity of TAs that were produced by the 25 mg/kg cyclophosphamide dose when aversion strength was measured by two-bottle tests, which afforded the subjects access to plain water and did not force them to endure fluid deprivation or to drink the saccharin solution.
From a practical standpoint, post-conditioning CS availability is unnecessary for the induction of strong CTAs as assessed via two-bottle preference testing. We now routinely provide subjects with ad lib access to water during the interval between the end of conditioning and the beginning of two-bottle testing. Additionally, we now wait at least two days following conditioning before reintroducing the CS flavor as part of the two-bottle testing procedure. The optimal waiting period is dependent on both the UCS dose and variety of UCS agent and must be determined by the use of a pseudo-conditioning (sensitization) control procedure as illustrated elsewhere.13 Pseudoconditioning differs from conditioning only in that plain water is substituted for the CS solution prior to injection of the UCS agent. Pseudoconditioned control subjects encounter the CS solution as a novel substance at the onset of aversion assessment. The pseudoconditioning control procedure is needed to confirm an associative learning interpretation of TA acquisition.
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