Aberrant dopamine transmission and cognitive dysfunction in animal models of Parkinson's disease

Due to the relative success of therapeutic interventions aimed at treating the overt motor symptoms evident in Parkinson's disease (PD), a greater appreciation of the non-motor aspects of the disease has emerged in recent time. Indeed, evidence suggests that impairments in emotional processing, behavioural control and cognitive function may emerge early in the onset of the disease. Decades of experimental research have seen the development of diverse animal models, all of which have aimed to mimic the characteristic features of the disease process including the dopaminergic neural cell loss, the molecular neuropathology and the concomitant behavioural impairments. The following review provides an overview of the use of animal, particularly rodent, models in the quest to obtain a greater understanding of the role of corticostriatal dopamine in cognitive and neuropsychiatric functions. Given the limitations of using the available rodent models of PD, including altered motor and motivational function, it has become necessary to employ a range of techniques to eke out the precise function of this neurotransmitter in corticostriatal function. Combinations of lesion and pharmacological studies have allowed the assessment of dopamine depletion and precise receptor populations in the learning or expression of a range of executive functions, which has gained us considerable insight into the relationship between the neuropathology that occurs in PD and the resulting impairments in cognitive and neuropsychiatric function.