Abstract
Parkinson’s disease (PD) patients often suffer from non-motor symptoms like sleep dysregulation, mood disturbances or circadian rhythms dysfunction. The melanopsin-containing retinal ganglion cells are involved in the control and regulation of these processes and may be affected in PD, as other retinal and visual implications have been described in the disease. Number and morphology of human melanopsin-containing retinal ganglion cells were evaluated by immunohistochemistry in eyes from donors with PD or control. The Sholl number of intersections, the number of branches, and the number of terminals from the Sholl analysis were significantly reduced in PD melanopsin ganglion cells. Also, the density of these cells significantly decreased in PD compared to controls. Degeneration and impairment of the retinal melanopsin system may affect to sleep and circadian dysfunction reported in PD pathology, and its protection or stimulation may lead to better disease prospect and global quality of life of patients.
Highlights
The retina is an accessible and visible tissue, part of the central nervous system (CNS)
Neurodegenerative diseases mainly observed in the brain such as Parkinson’s disease (PD), Alzheimer’s disease, or Multiple Sclerosis present similar signs of degeneration in the retina [14], which is considered as a “window to the brain”
We demonstrate that melanopsin-containing retinal ganglion cells (mRGCs) degenerate in PD, as revealed by its number reduction and their morphological alterations, and this fact may be linked to the circadian and sleep disturbances suffered by PD patients
Summary
The retina is an accessible and visible tissue, part of the central nervous system (CNS). Its main motor clinical features are rigidity, tremor and bradykinesia [19, 21, 46], but people with PD may have several non-motor symptoms including cognitive decline and dementia [11], gastrointestinal and cardiovascular problems [43], mood disturbance [50], visual disruption [2, 55], impairment of the pupillary reflex response [54], and Ortuño-Lizarán et al Acta Neuropathologica Communications (2018) 6:90 sleep disorders [19, 46]. Dysfunction of circadian rhythms in PD is thought to be one of the causes of sleep disturbances and it can lead to cognitive and metabolic deficits, psychiatric and mood symptoms, or cardiovascular problems, negatively impacting quality of life [56]
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