The non-motor complications in Parkinson's disease - what can we learn from animal models?

Sporadic Parkinson's disease is a widespread human disease that has never been reported in non-human vertebrates. The etiopathogenesis of the non-motor symptoms in the disease is not well understood and it is difficult to interpret the roles of affected neurotransmitters in currently available animal models. Most of the non-motor symptoms do not correlate with the stage of motor deficits and precede the development of motor symptoms by many years, before the permanent loss of dopaminergic neurons in the basal ganglia. The aim of this review is to briefly summarize the advantages and limitations of the well-recognized mammalian animal models with special regard to the non-motor complications of the prodromal and early stage Parkinson's disease.