Date of Thesis

12-16-2015

Thesis Type

Masters Thesis

Degree Type

Master of Science

First Advisor

Kevin Myers

Abstract

Liking" and "wanting" are viewed as two disparate facets of reward. Incentive salience or "wanting" for rewards and reward related stimuli has received a lot of research attention in studies of drug addiction. In experiments using animal subjects, incentive salience attribution is often queried using the sign- tracking (ST) / goal- tracking (GT) paradigm. A large body of literature supports the view that sign- tracking, a behavioral phenotype of enhanced incentive salience attribution, is associated with "wanting" or increased motivation to obtain a drug. However, few studies using this paradigm have explored a possible overlap of how sign-tracking may relate to "liking". This is likely due to the known dissociable nature between "liking" and "wanting". The primary aim of the present study was to examine "wanting" in response to natural reinforcers and extend research to the field of appetite. The study also enabled the exploration of a possible association between sign- tracking and "liking". Another objective of this research was to investigate the role of incentive salience attribution in obesity as it is of interest to explore factors that may perpetuate the condition. Prior evidence in the literature suggests that obese individuals also display enhanced incentive salience attribution to food and food related cues. Thus, the present study sought to observe how the obese state affects incentive attribution using the sign-tracking/ goal-tracking model. In the context of incentive salience and "liking", it was hypothesized that there would be no differences between sign-trackers and goal- trackers in a measure of palatability. However, it was hypothesized that sign- trackers would display more "wanting" than goal ¿ trackers in tests of meal patterns. To test these hypotheses, 26 Sprague-Dawley rats (13 ST, 13 GT) were classified for their Pavlovian approach propensity and then underwent 18 hr meal pattern sessions for 5 days to measure "wanting". The test solution in these sessions was 10% flavored maltodextrin (MD). Following this, rats underwent four total lick-microstructure sessions to measure "liking" in which they received two sessions of 10% flavored MD and two sessions of 10% sucrose. No differences were found between ST and GT in their "wanting" for 10% MD (mean number of meals, t (24) =.137, p = .892; mean number of licks per meal, t (24) =.526, p = .604). Yet, ST showed greater palatability responses, licks per cluster, to 10% sucrose as compared to goal-trackers (t (24) = 2.570, p= .017). However, no difference in palatability responses to MD were seen between the groups (t (24) = 1.402, p= .174). Additionally, it was hypothesized that obese rats put on a high fat- high sugar (HFHS) diet would display more sign-tracking or "approach" behaviors as opposed to goal-tracking behaviors. To test this hypothesis, 58 rats were either placed on a control (n = 28) or a HFHS (n = 30) diet for approximately 18 weeks so that the effects of diet-induced obesity on incentive salience attribution could be observed. Rats were then classified for their Pavlovian approach propensity. Obese rats on a HFHS diet were less likely to display sign-tracking behaviors as compared to rats on a control diet (probability to lever touch, t (51.35) =1.883, p = .065); total lever touches, t (35.48), p = .023); lever touch latency, t (49.92) = 2.243, p = .029). Together these results, reviewed in context with studies from other researchers, suggest that although it is possible that a sign-tracking propensity may precede the obese state, it evident that the obese state is not characterized by sign-tracking. Thus ¿as this research arose from the drug addiction literature¿ it is probable that, like in drug addiction, the factors that precipitate obesity are not the same factors that maintain it.

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