Objective: To determine the age-effects on galanin (Gal)-enriched synaptic boutons and neuropil of human locus coeruleus (LC) using autopsied human tissues.

Background: The LC has been reported to be involved in Parkinson’s (PD) pathogenesis. We have previously reported preserved nigral neurons and sub-threshold pathology in aging Asian Indians; hence it is worthy to study the same in the LC, which as per Braak staging is affected at stage 2 in PD. Neuronal soma and phenotype loss are reported in PD pathogenesis, but there are few studies on alterations in the perineuronal segment of neuropil of LC, which harbor the (co)transmitter laden processes and synapses and any damage to them would have equally degenerative consequences.

Method: Here, we examined the age effects on the neuropil as well as the “co-transmitter enriched non-cellular profiles” there-in; henceforth termed as “boutons”.  The tissues used extended from the cerebral aqueduct to IV ventricle. Immunohistochemistry for Gal (n=11) was performed on every 1 in 40 serial sections of LC, loosely divided into medial (MED) and lateral (LAT) groups based on their distance from the ventricles. High magnification images were used for densitometric analysis to assess co-transmitter levels in the neuropil and the boutons using a ‘Windows’ based image analysis system. Morphometric evaluation of the boutons was performed for their size. Pearson’s Correlation Coefficient was the test of choice.

Results: Gal was present in long processes in the neuropil and was also associated with the boutons. The enrichment in boutons was noticeable due to much higher expression compared to the neuropil (p=.09; neuropil vs. boutons) in both MED and LAT clusters. Age did not affect Gal expression in neuropil and boutons in both MED and LAT aspects as well as the bouton size. Although the LAT aspect showed a mild reduction, it did not reach statistical significance (p=.09).

Conclusion: More samples need to be studied to confirm the observations. However, Gal-enriched boutons and the neuropil associated staining appears to be preserved with age, suggesting structural preservation of perineuronal features in the aging LC of Asian Indians.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-study-of-age-related-changes-in-galanin-expression-in-the-neuropil-and-associated-boutons-in-the-human-locus-coeruleus/