Where does parkinson disease pathology begin in the brain?

Area of Science:

• Neuroscience
• Neuropathology
• Neurodegenerative Diseases

Background:

• Parkinson disease (PD) is a neurodegenerative disorder primarily affecting dopaminergic neurons in the substantia nigra.
• The exact initiation site and early pathological events in PD remain subjects of ongoing research.

Purpose of the Study:

• To investigate the initial anatomical sites of Lewy body and Lewy neurite formation in the human brain.
• To determine if the substantia nigra is the primary induction site for Parkinson disease pathology.

Main Methods:

• Semi-quantitative analysis of brainstem and olfactory structures in 30 autopsy cases with incidental Lewy body pathology.
• Topographical parcellation of nuclear gray matter based on architectonic and pigmentation properties.
• Comparison with 58 age- and gender-matched controls.

Main Results:

• Lewy bodies and Lewy neurites were found to originate in non-catecholaminergic neurons of the dorsal glossopharyngeus-vagus complex, reticular zone, gain setting system (coeruleus-subcoeruleus, raphe nuclei, gigantocellular reticular nucleus), olfactory bulb, olfactory tract, and anterior olfactory nucleus.
• These initial pathological changes occurred in the absence of substantia nigra involvement.
• Known prosencephalic predilection sites for Lewy pathology were devoid of Lewy bodies and neurites in this sample.

Conclusions:

• The substantia nigra is not the induction site for Parkinson disease.
• Early PD pathology initiates in specific brainstem and olfactory neuronal populations.
• These findings necessitate a re-evaluation of the early pathogenesis of Parkinson disease.