• Effects of Limited and Extended Pavlovian Training on Devaluation Sensitivity of Sign- and Goal-Tracking Rats

      Keefer, S.E.; Bacharach, S.Z.; Kochli, D.E.; Calu, D.J. (Frontiers Media S.A., 2020)
      Individual differences in Pavlovian approach predict differences in devaluation sensitivity. Recent studies indicate goal-tracking (GT) rats are sensitive to outcome devaluation while sign-tracking (ST) rats are not. With extended training in Pavlovian lever autoshaping (PLA), GT rats display more lever-directed behavior, typical of ST rats, suggesting they may become insensitive to devaluation with more Pavlovian training experience. Here, we use a within-subject satiety-induced outcome devaluation procedure to test devaluation sensitivity after limited and extended PLA training in GT and ST rats. We trained rats in PLA to determine GT and ST groups. Then, we sated rats on either the training pellets (devalued condition) or homecage chow (valued condition) prior to brief non-reinforced test sessions after limited (sessions 5/6) and extended (sessions 17/18) PLA training. GT rats decreased conditioned responding under devalued relative to valued conditions after both limited and extended training, demonstrating they are sensitive to satiety devaluation regardless of the amount of PLA training. While ST rats were insensitive to satiety devaluation after limited training, their lever directed behavior became devaluation sensitive after extended training. To determine whether sign-tracking rats also displayed sensitivity to illness-induced outcome devaluation after extended training, we trained a separate cohort of rats in extended PLA and devalued the outcome with lithium chloride injections after pellet consumption in the homecage. ST rats failed to decrease conditioned responding after illness-induced outcome devaluation, while Non-ST rats (GT and intermediates) were sensitive to illness-induced outcome devaluation after extended training. Together, our results confirm devaluation sensitivity is stable in GT rats across training and devaluation approaches. Extended training unmasks devaluation sensitivity in ST rats after satiety, but not illness-induced devaluation, suggesting ST rats respond appropriately by decreasing responding to cues during state-dependent but not inference-based devaluation. The differences in behavioral flexibility across tracking groups and devaluation paradigms have translational relevance for the understanding state- vs. inference-based reward devaluation as it pertains to drug addiction vulnerability. Copyright 2020 The Authors.
    • Stability of individual differences in sucralose taste preference

      Bacharach, S.Z.; Calu, D.J. (Public Library of Science, 2019)
      Outbred rats display variable preferences for bittersweet solutions, expressed as preference or avoidance of high concentrations of artificial sweeteners over water. This may reflect individual differences in appetitive/aversive conflict processing that may have predictive validity for disorders of motivation. Here we use a homecage two-bottle choice procedure to examine the test/retest stability and between-tastant consistency in sucralose preference to determine the reliability of bittersweet taste preference. Sucralose is a non-caloric artificial sweetener that is preferred by some rats and avoided by others. We sought to determine whether sucralose preference is consistent with preference of sucrose/quinine solutions that have known sweet and bitter taste qualities, respectively. We give fluid restricted rats 45-minutes homecage access to water and ascending concentrations of sucralose (SUCRA; 0.0025-10mM) or a compound solution of sucrose (116mM) + quinine (0.002-2mM) (SQ). We use a within-subject counterbalanced design (SUCRA or SQ testing) to determine preference of each bittersweet solution relative to water. We observed individual variability in preference for SUCRA and SQ, such that some rats preferred bittersweet solutions over water (preferring) while other rats preferred water over bittersweet solutions (avoiding). Within tastant, this preference remained stable across repeated testing. Between solutions, SUCRA preference scores correlated with SQ scores, suggesting consistent taste conflict processing for both bittersweet solutions. Population level analyses confirmed that preference generalizes across bittersweet solutions, and that rats' preferences for bittersweet solutions relative to water are stable over time. The test/retest and between-tastant reliability of this taste conflict screening procedure support the potential utility of this model for exploring individual variability in appetitive/aversive conflict processes mediating motivated behavior. Copyright 2019 Bacharach, Calu.