Changes in neural circuitry regulating response-reversal learning and Arc-mediated consolidation of learning in rats with methamphetamine-induced partial monoamine loss

Methamphetamine-induced neurotoxicity results in long-lasting depletions of monoamines and changes in basal ganglia function. We previously reported that rats with methamphetamine-induced neurotoxicity no longer engage dorsomedial striatum during a response reversal-learning task, as their performance is insensitive to acute disruption of dorsomedial striatal function by local infusion of an N-methyl-D-aspartate receptor antagonist or an antisense oligonucleotide against the activity-regulated cytoskeleton-associated (Arc) gene. However, methamphetamine-pretreated rats perform the task as well as controls. Therefore, we hypothesized that the neural circuitry involved in the learning had changed in methamphetamine-pretreated rats. To test this hypothesis, rats were pretreated with a neurotoxic regimen of methamphetamine or with saline. Three to five weeks later, rats were trained on the reversal-learning task and in situ hybridization for Arc was performed. A significant correlation between Arc expression and performance on the task was found in nucleus accumbens shell of methamphetamine-, but not saline-, pretreated rats. Consistent with the idea that the correlation between Arc expression in a brain region and behavioral performance implicates that brain region in the learning, infusion of an antisense oligonucleotide against Arc into the shell impaired consolidation of reversal learning in methamphetamine-, but not saline-, pretreated rats. These findings provide novel evidence suggesting that methamphetamine-induced neurotoxicity leads to a shift from dorsal to ventral striatal involvement in the reversal-learning task. Such reorganization of neural circuitry underlying learning and memory processes may contribute to impaired cognitive function in individuals with methamphetamine-induced neurotoxicity or others with striatal dopamine loss, such as patients with Parkinson's disease.