SPN and cocaine dependence: Increasing evidence suggests that morphological changes in SPN spines in the NAc are related to addictive behavior in cocaine use,70 which increases synaptic dopamine levels.71 SPN spines in the NAc become enlarged in the withdrawal phase of cocaine exposure.72 Thus, the enlargement of SPN spines in the NAc may account for the psychological dependence of cocaine addiction.72 Taken together, SPN spine enlargement in the NAc of the LID model rat may represent a pathological hallmark associated with behavioral dependence on levodopa in DDS.