Doctor of Philosophy (PhD)
Faculty of Science
Dr. Rudy Eikelboom
Availability can have profound influence on the consumption of foods and drinks. The 2-phase intermittent-continuous protocol (ICP) examines sucrose solution intake in two groups of rats and finds intermittent access significantly increases intake. In Phase I, rats receive intermittent or continuous access to a 4% sucrose solution, and with adults this results in a long-term elevation (a doubling) in the intermittent group. In Phase II, when rats are shifted to common sucrose schedule, this difference is maintained. Adult rats given 16% sucrose in Phase I do not differ in consumption, but in Phase II with 4% sucrose, an unexpressed elevation in the intermittent rats becomes evident. From my MSc work, it appeared pups were protected from the ICP associated intake elevation. I tested rats with sucrose solutions to explore how availability changes intake over age. First, intake of 4% sucrose was examined in a cross-sectional experiment that compared two or three intermittent exposures to sucrose (with continuous access) across three developmental periods (pups, adolescent, and adult) using weight corrected consumption. All rats increased intake over 2 intermittent exposures and decreased it with continuous access. Adolescent rats consumed more sucrose than pups and adults. I then tested pup and adult rats (in the ICP) with 4% or 16% in Phase I, with all receiving 4% in Phase II. In parallel ICP experiments with adult and pup rats, adults demonstrated the difference in Phase II with both sucrose concentrations while pups only developed the difference with the 16% solution, and when differences developed to 4% in Phase II, they remained latent until mid to late adolescence. I then tested pups with the ICP and 16% in Phase I, and included additional 10-day gap without sucrose for some groups (+Gap groups) between Phase I-II to examine the robustness of developing sucrose intake differences in younger rats. A very robust sucrose intake difference slowly emerged in Phase II, with the gap itself inducing an additional elevation in consumption (often called the elation effect) that was independent of the intermittent vs. continuous difference. The sucrose intake difference emerged slowly in both the non-gap and the +Gap groups when given access. Lastly, I examined how these access-induced sucrose differences relate to the brain’s response by exploring sucrose intake-related Fos-expression and complimentary complex network analysis of the Fos-data. The ICP-Fos study identified the ventral pallidum, posterior part of the paraventricular thalamus, parts of the paraventricular hypothalamus, and the ventral part of the lateral septum as areas that are possibly involved with the sucrose intake differences that develop with the ICP, while the network analysis revealed some differences in functional connectivity that might be related to the behavioural differences with a complex developmental profile. The primary finding of this work was that sucrose availability can have a profound delayed influence on pups, and importantly, the potentially maladaptive behaviour of prolonged elevated sucrose intake can develop in pups but remains latent until later in life.
Senthinathan, Gehan, "Age, Access, and Sweets-Motivation" (2020). Theses and Dissertations (Comprehensive). 2327.