Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Neuroscience

Supervisor

Bussey, Timothy J.

2nd Supervisor

Saksida, Lisa M.

Joint Supervisor

Abstract

Increased age and obesity diminish motivation, perseverance, and spatial memory function. Aerobic exercise interventions have successfully rescued some of these processes. However, in older and heavier populations aerobic exercise is not as sustainable due to high risk of injury. Resistance exercise consists of physical activity where maximum oxygen consumption is not increased and has been proposed as a safe and effective intervention for this population. Here, we used touchscreen-based cognitive testing to elucidate the influence of resistance exercise on motivation and spatial memory in aged, diet-induced obese mice, using a water restriction procedure I develop in Chapter 2. Mice underwent a ladder-based resistance exercise intervention. Obese and exercised mice were significantly more motivated in the progressive ratio touchscreen test of motivation than were non-exercised obese mice. Furthermore, exercised mice performed significantly better on a test of spatial memory. These findings suggest that resistance exercise is effective at rescuing cognition in older, overweight mice.

Summary for Lay Audience

Our population is becoming older and heavier. Both increased age and adiposity act as risk factors for many chronic illnesses and present a heavy strain on the healthcare system. In the Western world, structural changes in our physical environment exacerbate the risk of increased adiposity and obesity. Our widespread consumption of what has been coined the “Western diet” – a diet high in processed sugars and fats – has been associated with many negative health outcomes. Aerobic exercise, like running and cycling, has been shown to decrease adiposity and decrease incidence of chronic illnesses. However, high impact exercise such as running and cycling is not always sustainable in this population since they are at a higher risk of falls and heart attacks. Resistance exercise is a lower impact alternative to aerobic exercise. It increases functional strength, bone density, and has led to reduction of some cognitive impairments in recent studies. We wanted to test whether a resistance exercise intervention was able to reduce impairment in motivation, perseverance, and spatial memory and learning in a population of middle-aged mice with diet induced obesity. The cognitive testing was completed in Bussey-Saksida touchscreen chambers that motivate mice to engage in tests of cognition through food restriction and appetitive rewards. Food restriction is not feasible in a model of diet-induced obesity; therefore, we established a water manipulation protocol using 2% citric acid water that reliably motivated completion of a test of learning and memory in groups consuming both standard chow and high-fat, high-sugar chow. The mice that completed an 8-week ladder-based exercise intervention were more motivated, had greater perseverance, and had improved spatial memory function than their non-exercised counterparts.

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