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

Animal studies using the self-administration paradigm suggest that duration of drug access (Ahmed, 2005) and individual phenotype (Piazza, Deminiere, Le Moal and Simon, 1989) are important factors in the development of drug addiction. Wheel running in rats has been proposed as a model to study non-drug addictions (Eikelboom & Lattanzio, 2003). When first given ad lib wheel access, young male rats initially run at low levels (about 1000 wheel turns per night) and gradually increase this distance to high levels (about 5000 wheel turns per night) (Afonso and Eikelboom, 2003). Like with self-administration, duration of wheel access has been found to be critical to the development of this excessive running (Eikelboom & Lattanzio, 2003). At this point it is not clear how individual phenotype and duration of access interact to result in the excessive behaviour seen in addiction. Understanding the mechanisms involved in this increase may shed light on the transition from regulated levels of behaviour to high and uncontrollable levels. The three experiments in this thesis manipulated the duration and time of wheel access to determine how these variables affect final running levels. In Experiment 1, 32 male rats had either 30, 45, 60 or 90 minutes of nightly wheel access either starting at 13:00 (one hour after lights went out) or ending at 14:30 for 24 days. Running increased only in the 90 minute group. Rats introduced to the wheel at 13:00 ran more and increased their running more than rats introduced later. This difference was determined to be due to baseline running differences prior to restricted access. In Experiment 2 duration of nightly wheel access was held constant (45 minutes) but time of wheel introduction was manipulated. From lights out to 6 hours after lights off all groups ran equally and did not increase their running significantly. In Experiment 3 time of wheel introduction was held constant and 72 rats were given either 30, 60, 90, or 180 minutes of wheel access 1 hour after lights out. While running increased for all groups the 180 minute group showed the largest increase. Individual correlations suggested that final running levels could be predicted by the mean of the first 4 days of running. A multiple-regression using both duration of access, and the mean of first 4 days suggested that both are important in final running levels. Similar to drug addiction, both duration of access and individual differences may be important in non-drug addictions.

Convocation Year

2008

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