Characterization of a semi-rapid method for assessing delay discounting in rodents

Delay discounting is a key component of many psychiatric disorders, including drug addiction, compulsive gambling, ADHD, and obesity. However, its underlying mechanisms are not yet fully characterized. One impediment to full characterization of such mechanisms is the fact that rodent models of the task are often complicated and involve extended training of subjects, often requiring more than a month before a stable baseline is obtained. We have therefore characterized a version of the rodent delay discounting task which generates data more quickly than most other published versions. In this version of the task, learning of the operant response is established prior to introduction of the delay component, and delay is tested across subsequent daily sessions with a single delay length per day. We demonstrate here that this version generates a delay discounting curve similar to many published tasks, and is sensitive to changes in reward magnitude and to chronic treatment with cocaine. Furthermore, we present a detailed description of the within-session patterns of behavior in the task, which provides evidence of within-session learning and establishment of stable response patterns. This faster version of the delay discounting task will facilitate future studies involving pharmacological, electrophysiological, and other mechanistic studies of the underlying basis of this important disease process.