Acquisition and extinction of gustatory aversion in two lines of rats selectively bred for differential shuttlebox avoidance performance.

Consumption of a palatable saccharin-glucose (SG) solution was compared in Roman High Avoidance (RHA/Verh) and Roman Low Avoidance (RLA/Verh) lines of rats in a taste aversion acquisition and extinction paradigm. Prior to treatment, SG-intake in a 1 -h drinking test by RHA/Verh rats was much greater than that by RLA/Verh rats. Both psychogenetic lines increased SG-intake over a series of exposures when each presentation was followed by saline injection, but decreased SG-intake when each presentation was followed by apomorphine injection. At the end of the acquisition phase, RHA/Verh rats treated with a toxic dose of apomorphine drank 36% less SG than RHA/Verh rats that were injected with saline, whereas RLA/Verh rats treated with apomorphine consumed 54% less SG than RLA/Verh rats injected with saline. Following 16 daily presentations of SG but no injections, extinction of the conditioned gustatory aversion was complete in the RHA/Verh group previously treated with apomorphine, but it remained incomplete in the RLA/Verh rats previously treated with apomorphine. This stronger taste aversion exhibited by RLA/Verh rats is in marked contrast to their extremely inferior performance in a shuttlebox active avoidance task. The basis of the behavioral differences in these two psychogenetically selected lines of rats is discussed.