Document Type


Degree Name

Doctor of Philosophy (PhD)



Program Name/Specialization

Behavioural Neuroscience


Faculty of Science

First Advisor

Roelof Eikelboom

Advisor Role



Previous work has shown that non-deprived rats’ intake of a 4% sucrose solution increases over 24 h access periods if it is provided every 3 or 4 days (E3D or E4D) relative to every day (ED; (Eikelboom & Hewitt, 2016)⁠. Once these access-intake differences are established, they can be enduring, even if all rats are shifted to a common access schedule. Do changes in value accompany these access-induced solution intake changes? Three approaches were applied to test for access-induced value changes. First, following extended 24 h E3D (12 exposures) or ED (36 days) access to a flavoured 4% (Experiment 1) or 12% (Experiment 2) standard sucrose solution, the standard solution was compared in a series of 24 h choice tests against ascending concentrations of a differently flavoured alternate solution on a common E2D access schedule. Experiment 1 revealed access-induced preference increases for the standard solution after E3D relative to ED access while Experiment 2 did not, possibly due to the higher concentration of sucrose used. Second, a progressive ratio procedure was used to evaluate changes in the reinforcing efficacy of a 4% sucrose solution after an extended period of E3D or ED access. This traditional operant procedure failed to reveal access-induced changes in the breakpoint for the sucrose. The failure to reveal breakpoint differences is suggested to be due to context effects; E3D/ED sucrose solutions were provided in the home-cage while sucrose solution breakpoints were evaluated in operant chambers. Third, in Experiments 4 and 5, palatability changes of the 4% solution were evaluated with lick microstructure analysis. Water and sucrose microstructures were compared (positive control), before comparing the microstructure of sucrose solutions during ED or E4D access periods. Both microstructure comparisons revealed a similar pattern of changes, suggesting that palatability increases after E4D relative to ED access. Collectively, these results suggest that sucrose solution increases in value with E3D or E4D relative to ED access. The results highlight that tests conducted over longer durations (24 h) may yield different results than similar tests conducted over shorter (~1 h), restricted access sessions. Experiments 1 and 2 also suggested that rats treated the two, distinctly flavoured solutions as different food sources in the preference tests, something that is not readily revealed with shorter preference tests. Similarly, the lick microstructure appeared to be different withthe longer, 24 h sucrose solution access duration relative to previous shorter (~1 h), access microstructure palatability studies. Finally, Experiment 5, which also measured food intake, revealed that changes in foods provided could also profoundly affect sucrose consumption, highlighting the importance of considering the complete nutritional environment of the rat. This work underscores the need for further study of the impact of access on value. Moreover, it encourages a holistic approach that includes monitoring the rat’s 24 intake of food and fluids as a consideration in appetitive behaviour studies.

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