Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Psychology

Faculty/School

Faculty of Science

First Advisor

Rudy Eikelboom

Advisor Role

Thesis Supervisor

Abstract

For individuals diagnosed with Binge Eating Disorder (BED) or Bulimia Nervosa (BN) eating is often manifested in intermittent bouts of gorging, a behaviour that is similar to excessive consumption of rewarding drugs in addiction (American Psychiatric Association, 2000; Corwin & Grigson, 2009; Epstein & Shaham, 2010). Our laboratory has found that sucrose solution intake by rats escalates markedly when provided on Discontinuous Access (DisA; 24h once every 3 or 4 days) schedules but is maintained at lower, stable levels with Continuous Access (ConA; ad lib) schedules (Hewitt & Eikelboom, 2008). Once DisA/ConA consumption differences are established, they persist even after both access schedules are equalized to alternate day sucrose exposures. To examine whether taste, rather than the postingestive properties of sucrose, drive these access-induced intake changes, saccharin was substituted for sucrose. In Experiment 1, rats with DisA escalated their intake to consume more than ConA rats over a range of saccharin concentrations (1, 0.5, 0.25, and 0.125%). Taste, even without the postingestive properties of sucrose, drove the access consumption effects. Once DisA/ConA saccharin consumption differences were established in Experiment 2, they were maintained for over 50 days of equal access, even when saccharin was replaced with sucrose.

Whereas intermittent access schedules utilizing repeating 1 to 3 day interexposure intervals result in gradual and sustained intake increases, a single longer, isolated period of abstinence can result in a Deprivation Effect (DE), a transient increase in post-abstinence intake (Gandelman & Trowill, 1969; Neznanova, Zvartau & Bespalov, 2002). To explore the influence of access history on DE expression, intake was examined in rats with DisA and ConA 0.25% saccharin (Experiment 2) and 4% sucrose (Experiment 3) experience. In Experiment 2, a robust saccharin DE was observed in all rats but the intake differences induced by initial DisA/ConA were maintained. In Experiment 3, DisA/ConA differences emerged for sucrose but no DE was observed after either 3 or 9 days of sucrose abstinence. Collectively these findings suggest that 1) taste predominantly drives DisA/ConA induced differences, and 2) that this DisA/ConA difference and the DE may be under control of separate factors. These results highlight the importance of taste and postingestive properties in access consumption effects and suggest that not all experiences with access interruptions are the same. This work underscores the role of access factors in excessive sweets consumption which could be involved in BED or BN etiology and may play a similar role in excessive drug intake in addiction.

Convocation Year

2011

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