Document Type

Open Access Thesis

Embargo Period

5-8-2018

Degree Program

Neuroscience & Behavior

Degree Type

Master of Science (M.S.)

Year Degree Awarded

2018

Month Degree Awarded

May

Abstract

Depression and related disorders are characterized by motivational dysfunctions, including deficits in behavioral activation and exertion of effort. Animal models of relevance to depression represent a critical starting point in elucidating the neurobiological mechanisms underlying motivational dysfunctions. The present study explored the use of the Wistar-Kyoto (WKY) animal model of depression to examine effort-related functions as measured by voluntary wheel running and performance on a mixed fixed ratio 5/progressive ratio (FR5/PR) operant task. Given the known link between activational aspects of motivation and the mesocorticolimbic dopamine (DA) system, the behavioral effects of d-amphetamine (0.5 and 1.0 mg/kg, IP), a psychostimulant that increases DA release, were evaluated in WKY and control Sprague-Dawley (SD) male and female rats responding on a mixed FR5/PR task. An additional experiment assessed intracellular content of monoamine neurotransmitters and their metabolites in relevant mesocorticolimbic brain regions, including the medial prefrontal cortex, the nucleus accumbens and the ventrolateral striatum using HPLC-ED. WKY rats demonstrated initial effort-related deficits in FR5/PR responding compared to SD controls, which ameliorated with training. Amphetamine significantly decreased FR5 work output, but increased responding on the PR phase in both SD and WKY rats. This effect was more pronounced in SD rats compare to WKY rats. In addition, sex differences were evident both in FR5/PR performance and in the behavioral response to amphetamine treatment. Moreover, females demonstrated higher levels of voluntary wheel-running than males. Finally, tissue concentrations of dopamine were lower in the NA and VLS of WKY compared to SD rats. Taken together, results suggest dysfunctions in mesolimbic DA neurotransmission in the WKY strain, likely underlying the depressive phenotype. The present study represents an important initial step in validating the WKY strain as a rat model of effort-related dysfunctions relevant to depression and other neuropsychiatric disorders.

First Advisor

Mariana Pereira

Second Advisor

Andrew Farrar

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