Effect of early and late postnatal hypoxia on subcellular synaptosomal fractions from cerebral cortex of rats. II. A quantitative ultrastructural study.
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.
D000367:Age Factors; D000818:Animals; D002540:Cerebral Cortex / Q000473:pathology*; D002534:Hypoxia, Brain / Q000473:pathology*; D008854:Microscopy, Electron; D008928:Mitochondria / Q000648:ultrastructure; D008933:Mitochondrial Swelling; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000648:ultrastructure; D013574:Synaptosomes / Q000648:ultrastructure*