Date

3-2014

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Behavioral Neuroscience

Institution

Oregon Health & Science University

Abstract

Relative preference for smaller, sooner rewards over larger, later rewards (“delay discounting”) is increased by acute ethanol. However, it is unknown whether this effect is driven by a difference in sensitivity to the reinforcer delay or a difference in sensitivity to the reinforcer magnitude, because typical delay discounting tasks manipulate both parameters simultaneously. Additionally, it is unknown which brain regions may play a role in these different aspects of delay discounting. To investigate this, two studies were conducted in separate groups of male Long Evans rats. The first examined the effects of acute systemic administration of ethanol on performance in two separate tasks that measured sensitivity to delay and sensitivity to magnitude. The second examined the effects of acute temporary inactivation of the nucleus accumbens core (AcbC) and lateral orbitofrontal cortex (lOFC) on two separate tasks that measured sensitivity to delay and sensitivity to magnitude as well as a delay discounting task. None of the acute manipulations had any effect on the measures of sensitivity to delay or sensitivity to magnitude, in contrast to their effects on delay discounting in previous literature. Nonetheless, there were several additional findings of interest. First, rats with high sensitivity to delay were found to be resistant to the behaviorally suppressant effects of a moderate dose of ethanol (0.9 g/kg). Second, inactivation of the AcbC was found to significantly decrease delay discounting. Furthermore, this effect of AcbC inactivation was found to be most prominent in animals with initially low levels of delay discounting. viii In summary, these results suggest a fundamental difference between the tasks used to separately measure sensitivity to delay and magnitude and those traditionally used to measure delay discounting. Additionally, the findings of a possible link between sensitivity to delay and the suppressant effects of ethanol, as well as a novel role for the AcbC in delay discounting, provide a springboard for future research.

Identifier

doi:10.6083/M4TQ5ZV6

School

School of Medicine

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