Choice in C57BL/6n Mice: Behavioral and Pharmacological Mechanisms of Concurrent Schedule Performance

Abstract

Evidence from clinical and laboratory studies converge on the same neurochemical and neuroanatomical substrates underlying choice behavior. The findings suggest that behavioral adjustments in choice procedures are the product of specific neurochemical pathways, and DA, NE, and 5-HT neurotransmitter systems in the frontal cortex might be especially important (Robbins & Roberts, 2007). However, the findings are either mixed (e.g., dopaminergic agonist and RL) or poorly explored in mice (e.g., noradrenergic agonist and RL). To examine the impact of three monoamine transporter blockers, the behavior of mice was established under concurrent schedules of reinforcement. Characteristic features of concurrent responding were seen, including equal allocation of responding when the probability of reinforcement for one alternative was 0.5 and preference (i.e., bias) for the richer alternative when the reinforcer probabilities were unequal. Undermatching was seen, a finding typically observed with concurrent schedules and the changeover rate was highest when the two alternatives produced the same reinforcement probabilities. To examine rate-dependent effects, mice producing high- and low response rates were examined separately. For the high rate group, one of the doses tested for both d-amphetamine and atomoxetine increased total responses in the equal reinforcement probability condition. Escitalopram increased response rates in the equal reinforcement condition but not the number of reinforcers or response-reinforcer ratio. In the unequal reinforcement ratio condition none of the doses tested produced a significant increase in responding or reinforcement or change the proportion of responses made on the rich.