Depression affects around 35% of patients with Parkinson's disease. There are some overlapping symptoms between both illnesses, and some evidence seems to suggest that there may exist a common underlying etiological factor, namely changes in cortico-striatal-thalamo-cortical circuits and in the locus coeruleus.

To review the potential role of locus coeruleus alterations in patients with Depression and comorbid Parkinson's disease.

A literature review was performed through MEDLINE and PsycINFO using the terms 'Depression”, 'Parkinson's disease”, 'neurobiology”, 'locus coeruleus”, 'substantia nigra”, 'neuromelanin”, 'neuroimaging”, 'magnetic resonance imaging”, 'Positron emission tomography”. All articles found were selected according to their adequacy to the subject in question.

Noradrenergic pathways are important in the pathophysiology of Depression in Parkinson's disease. Magnetic Resonance Imaging (MRI) studies, with neuromelanin measurements have shown there is neuronal loss not only in the substantia nigra but also in the locus coeruleus. These changes in the locus coeruleus are different when patients with Parkinson's disease are compared with schizophrenic and normal controls. Patients with comorbid Depression and Parkinson's disease have a reduced uptake of [11C]RTI-32 in the locus coeruleus, with an inverse relationship between those changes and symptom severity. There is a higher prevalence of histopathologic changes (neuronal loss 7 times higher, gliosis) in the locus coeruleus of depressed vs. non-depressed patients with Parkinson's disease.

These findings seem to substantiate the potential role of noradrenergic pathways in the aetiology of Depression in Parkinson's disease.