Objective: To delineate the age-related changes in the neuronal size and neuromelanin (NM) intensity in autopsied tissues of human locus coeruleus (LC).

Background: Many studies have shown the active involvement of LC in Parkinson’s disease (PD) and Alzheimer’s disease (AD) pathology. However, the role of normal aging in LC pathology is still unclear. Besides, the extent of pathology may differ in individuals/populations prone to the disease, yet such studies are unavailable. Interestingly, our previous studies reported preserved melanized nigral neurons, and a sub-threshold pathology in aging Asian Indians compared to the Caucasian population. Hence, it might be valuable to study other neuronal clusters on the gut-brain axis, involved in PD. Therefore, this study focuses on the age-associated neuronal attributes in the LC.

Method: We collected autopsied human LC tissues (n=12) from deceased road traffic accident cases of age-range 18 to 74 years. The portion of the LC included extended from the level of cerebral aqueduct to the full extent of the fourth ventricle. On an average 150-200 Nissl-stained neurons per specimen were subjected to morphometric analysis for neuronal area and NM intensity using a ‘Windows’ based image analysis system on high magnification images of the entire LC; roughly divided into medial (MED) and lateral (LAT) subregions based on its proximity to the ventricles.

Results: Pearson’s correlation coefficient was used to assess the relationship between age and neuronal size/NM intensity. There was no correlation with neuronal size indicating no significant age-related changes (r²<0.001; p=.98) in total, or its MED (r²=.01; p=.77) and LAT (r²=.04; p=.55) parts. Likewise, no correlation was noted between age and NM intensity in the entire LC (r²=.02; p=.61) and its subregions: MED (r²=.05; p=.50) and LAT (r²=.07; P value=.44).

Conclusion: Our study shows preserved neuronal size and NM intensity in the LC of aging adult Asian Indians, which is in line with our previous studies with no change in neuronal size in the nigra of Asian Indians. Since reports suggest prior and more pathological involvement of LC i.e., Braak’s Stage-2 than substantia nigra i.e., Braak’s Stage-3, its preservation in aging adds to crucial data on the less susceptibility of Asian Indians to PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/morphometric-assessment-of-age-associated-neuronal-changes-in-the-human-locus-coeruleus/