Behavioral Economic Assessment of Price and Cocaine Consumption Following Self-Administration Histories that Produce Escalation of Either Final Ratios or Intake

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Abstract
Various self-administration procedures are being developed to model specific aspects of the addiction process. For example, ‘increased cocaine intake over time’ has been modeled by providing long access (LgA) to cocaine during daily self-administration sessions under a fixed-ratio (FR1) reinforcement schedule. In addition, ‘increased time and energy devoted to acquire cocaine’ has been modeled by providing access to cocaine during daily self-administration sessions under a progressive-ratio (PR) schedule. To investigate the distinctiveness of these models, the behavioral economics variables of consumption and price were applied to cocaine self-administration data. To assess changes in consumption and price, cocaine self-administration was tested across a descending series of doses (0.237–0.001 mg per injection) under an FR1 reinforcement schedule to measure drug intake in the high dose range and thresholds in the low range. Cocaine consumption remained relatively stable across doses until a threshold was reached, at which maximal responding was observed. It was found that a history of LgA training produced an increase in cocaine consumption; whereas a history of PR training produced an increase in the maximal price (Pmax) expended for cocaine. Importantly, the concepts of consumption and price were found to be dissociable. That is, LgA training produced an increase in consumption but a decrease in Pmax, whereas PR training produced an increase in Pmax without increasing consumption. These results suggest that distinct aspects of the addiction process can be parsed using self-administration models, thereby facilitating the investigation of specific neurobiological adaptations that occur through the addiction process.