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Expression of monoamine oxidase B activity in astrocytes of senile plaques
S Nakamura1, T Kawamata, I Akiguchi
1Department of Neurology, Faculty of Medicine, Kyoto University, Japan.
Abstract:
Monoamine oxidase (MAO) histochemistry has been performed in brains from patients with dementia of Alzheimer type (DAT) and aged controls. Conspicuous MAO-positive cell clusters were frequently observed in the amygdala, hippocampus, and insular cortex in the brains of DAT. Double staining with glial fibrillary acidic protein immunohistochemistry revealed that the cluster-forming MAO-positive cells were astrocytes. Using Bielschowsky's method, Congo red and thioflavin S counterstaining, this astrocytic mass was shown to be associated with senile plaques. By the enzyme inhibition experiment, MAO activity in senile plaques was revealed to be of type B. The present results clearly indicate that MAO-B activity is expressed in fibrillary astrocytes in or around senile plaques, suggesting that these astrocytes metabolize exogenous amines in senile plaques.
Insights
Monoamine oxidase-B (MAO-B) activity is found in astrocytes within senile plaques in Alzheimer
Area of Science:
- Neuroscience
- Biochemistry
- Neuropathology
Background:
- Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by the presence of senile plaques and neurofibrillary tangles.
- Monoamine oxidase (MAO) enzymes play a role in neurotransmitter metabolism and have been implicated in various neurological conditions.
- The specific localization and function of MAO within the neuropathological hallmarks of AD, such as senile plaques, remain incompletely understood.
Purpose of the Study:
- To investigate the presence and type of Monoamine oxidase (MAO) activity in the brains of patients with dementia of the Alzheimer type (DAT).
- To determine the cellular localization of MAO-positive cells associated with neuropathological features in DAT brains.
- To elucidate the specific MAO enzyme type involved in senile plaques and its potential role in metabolizing exogenous amines.
Main Methods:
- Monoamine oxidase (MAO) histochemistry was performed on brain tissue from DAT patients and aged controls.
- Immunohistochemistry using glial fibrillary acidic protein (GFAP) was employed for double staining.
- Bielschowsky's method, Congo red, and thioflavin S staining were used to identify senile plaques.
- Enzyme inhibition experiments were conducted to determine the specific MAO type.
Main Results:
- Conspicuous MAO-positive cell clusters were frequently observed in the amygdala, hippocampus, and insular cortex of DAT brains.
- These MAO-positive cells were identified as astrocytes through double staining with GFAP.
- The astrocytic MAO-positive masses were closely associated with senile plaques.
- Enzyme inhibition experiments revealed that MAO activity within senile plaques is predominantly of type B (MAO-B).
Conclusions:
- Monoamine oxidase-B (MAO-B) activity is expressed in fibrillary astrocytes located in or around senile plaques in Alzheimer's disease brains.
- These plaque-associated astrocytes likely contribute to the metabolism of exogenous amines within the senile plaques.
- This finding provides novel insights into the biochemical environment of senile plaques and the role of glial cells in Alzheimer's pathology.