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Monoamine oxidase-B-positive granular structures in the hippocampus of aged senescence-accelerated mouse (SAMP8)
S Nakamura1, I Akiguchi, N Seriu
1Department of Neurology, Faculty of Medicine, Kyoto University, Japan.
Abstract:
We examined the histochemical localization of monoamine oxidase in the hippocampus of young and old senescence-accelerated mouse (SAM). We found a monoamine oxidase-B-positive granular structure (MGS) in the hippocampus of old SAMP8, an accelerated senescence-prone line of SAM. The MGS was a round-shaped granular structure of 0.5 to 5 microns diameter and usually formed a cluster, the largest diameter of which ranged from 50 to 150 microns. No MGS were found in the hippocampus of young SAMP8 or of young SAMR1, an accelerated senescence resistant line of SAM, and only few, if any, were seen in old SAMR1. A monoamine oxidase-positive astrocyte was usually observed in the central area of each cluster of MGS. Furthermore, the MGS was in close anatomical relationship with monoamine oxidase-positive astrocytic processes. The enzyme inhibition experiments showed that monoamine oxidase activities localized in the MGS and astrocytes were both predominantly of type B. These findings suggest MGS occurs at least partly in monoamine oxidase-B-positive astrocytes. Furthermore, the MGS was similar to a periodic acid-Schiff-positive granular structure, a polyglucosan body previously documented in the brains of old SAMP8 and some other aged mice strains including C57BL/6 and nude mice, in terms of their size, morphological appearances and topographical distribution in the hippocampus. Thus, the present results suggest that monoamine oxidase type B is a proteinaceous component of the periodic acid-Schiff-positive granular structure in aged mice brains, and might provide some clues for clarifying the mechanisms of age-related occurrence of periodic acid-Schiff-positive granular structures in mice brains.
Insights
Monoamine oxidase-B forms granular structures in aged mouse brains, specifically in astrocytes. These structures resemble polyglucosan bodies, suggesting a role for MAO-B in age-related brain changes.
Area of Science:
- Neuroscience
- Biochemistry
- Aging Research
Background:
- Senescence-accelerated mouse (SAM) models exhibit accelerated aging phenotypes.
- Monoamine oxidase (MAO) plays a role in neurotransmitter metabolism and is implicated in aging processes.
- Polyglucosan bodies are observed in the brains of aged individuals and animal models.
Purpose of the Study:
- To investigate the histochemical localization of monoamine oxidase (MAO) in the hippocampus of young and old senescence-accelerated mice (SAM).
- To characterize the nature and cellular association of MAO-positive granular structures (MGS) found in aged mouse brains.
- To explore the potential link between MGS and polyglucosan bodies in the context of brain aging.
Main Methods:
- Histochemical staining for MAO in the hippocampus of young and old SAMP8 (senescence-prone) and SAMR1 (senescence-resistant) mice.
- Enzyme inhibition experiments to determine MAO type (A or B) activity.
- Morphological and topographical analysis of MAO-positive granular structures (MGS).
- Comparison of MGS with periodic acid-Schiff (PAS)-positive granular structures (polyglucosan bodies).
Main Results:
- Monoamine oxidase-B-positive granular structures (MGS) were identified in the hippocampus of old SAMP8 mice, but not in young SAMP8 or young/old SAMR1 mice.
- MGS were round, granular structures (0.5-5 microns) often clustered within the hippocampus.
- MAO-positive astrocytes and astrocytic processes were closely associated with MGS clusters.
- Enzyme inhibition confirmed predominantly MAO-B activity in both MGS and associated astrocytes.
- MGS shared morphological and topographical similarities with previously documented PAS-positive polyglucosan bodies in aged mouse brains.
Conclusions:
- Monoamine oxidase-B is a component of MGS, which appear to be located within MAO-B-positive astrocytes.
- MGS are likely related to polyglucosan bodies found in aged mouse brains.
- MAO-B may play a role in the formation or presence of polyglucosan bodies, contributing to age-related brain changes.