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Effect of early and late postnatal hypoxia on subcellular synaptosomal fractions from cerebral cortex of rats. II. A
Insights
Early or late postnatal exposure to intermittent hypoxia alters rat brain synaptosomes and mitochondria. Hypoxia during development impacts mitochondrial swelling and synaptosome condensation, affecting brain cell structure.
Area of Science:
- Neuroscience
- Developmental Biology
- Cell Biology
Background:
- Postnatal development is a critical period for brain maturation.
- Hypoxia, a condition of oxygen deficiency, can significantly impact developing neural tissues.
- Understanding the effects of hypoxia on synaptosomes and mitochondria is crucial for assessing neurodevelopmental outcomes.
Purpose of the Study:
- To investigate the ultrastructural and stereological effects of early and late postnatal intermittent hypobaric hypoxia on rat cerebral cortex synaptosomes and mitochondria.
- To compare the impact of hypoxia exposure during different developmental windows.
Main Methods:
- Isolation of synaptosomal subfractions from rat cerebral cortices using discontinuous sucrose gradient centrifugation.
- Stereological analysis of quantitative parameters (volume density, numerical density, profile size frequency distribution) of synaptosomes and mitochondria.
- Ultrastructural investigation of specific fractions (A and E).
Main Results:
- Early postnatal hypoxia led to irreversible mitochondrial swelling and synaptosome condensation, particularly in larger synaptosomes.
- Late postnatal hypoxia caused significant condensation in both synaptosomes and mitochondria across all size classes.
- Both exposure periods resulted in increased synaptosomal membrane vulnerability and the formation of abnormally large, condensed synaptosomes.
Conclusions:
- Postnatal intermittent hypoxia significantly alters the structural integrity of synaptosomes and mitochondria in the developing rat brain.
- The timing of hypoxia exposure influences the specific ultrastructural changes observed in neural components.
- These findings suggest potential biochemical mechanisms underlying hypoxia-induced neurodevelopmental alterations.
Abstract:
Synaptosomal subfractions were isolated by discontinuous sucrose gradient centrifugation from the P2-fraction of cerebral cortices of juvenile rats exposed to moderate intermittent hypobaric hypoxia from day 2-11 (early postnatal period) or from day 12-21 (late postnatal period) after birth. Ultrastructural investigations were carried out on fractions A and E of the preparation. Quantitative parameters of synaptosomes and mitochondria (volume density, numerical density, profile size frequency distribution) were estimated in a stereological analysis. Early postnatal hypoxia exposition strengthened the irreversible swelling of mitochondria. The effect on synaptosomes was less pronounced, very large synaptosomes showed significant condensation. Late postnatal hypoxia exposition resulted in strong condensation of synaptosomes in all size classes and similar reaction in mitochondria. Both hypoxia experiments produced an enhanced vulnerability of the synaptosomal membranes against the fractionation procedure and the appearance of monstrous large condensed synaptosomes. The results are discussed in view of hypothetical biochemical mechanisms underlying these changes.