The Flinders sensitive line of rats is a widely accepted and validated model of depression. These rats demonstrate abnormalities in limbic dopamine neurotransmission, suggesting disturbed neuronal activity in the ventral tegmental area. Interspike interval time-series were recorded from the ventral tegmental area of control Sprague-Dawley and Flinder sensitive line rats. These data were analyzed using standard measures (mean firing rate, bursting activity and spectral analysis) as well as the pointwise correlation dimension, a nonlinear measurement characterizing the complexity degree of dynamic systems. Pointwise correlation dimension, but not standard analysis revealed a significant difference between the animal lines. Our results suggest that nonlinear analyses can detect dysregulation of the mesolimbic dopaminergic system and shed light on the pathophysiology of depression.