Molecular Imaging of the Noradrenergic System in Idiopathic Parkinson's Disease

Noradrenergic neurons in both the peripheral nervous system and in the central nervous system (CNS) undergo severe degeneration in patients with Parkinson's disease (PD). This loss of noradrenaline may play essential roles in the occurrence of a wide range of prevalent non-motor symptoms and can further complicate the lives of PD patients. In vivo molecular imaging of noradrenaline may provide insights into to the extent of degeneration of noradrenergic neurons and subsequent depletion of noradrenergic projections. Molecular imaging methods exist to quantify the noradrenergic deficiency in peripheral autonomic terminals, such as [¹²³I]-meta-iodobenzylguanidin scintigraphy of the heart. However, the degeneration of noradrenergic nuclei in the brainstem and their projections to the CNS has only been quantified with non-selective positron emission tomography ligands in previous studies. Here, we review recent advances in in vivo molecular imaging techniques that evaluate the role of deficits of noradrenaline in PD patients in the manifestation of motor and non-motor symptoms.