Elsevier

Neuroscience

Volume 77, Issue 3, 3 February 1997, Pages 849-861
Neuroscience

Ischemic damage and subsequent proliferation of oligodendrocytes in focal cerebral ischemia

https://doi.org/10.1016/S0306-4522(96)00517-9Get rights and content

Abstract

In order to achieve a better understanding of the pathophysiology of ischemic white matter lesions, oligodendrocytic degeneration and subsequent proliferation were examined in the mouse model of middle cerebral artery occlusion. In situ hybridization histochemistry for proteolipid protein messenger RNA was employed as a sensitive and specific marker of oligodendrocytes, and immunohistochemistry for myelin basic protein was used as a compact myelin marker. Immunohistochemistry for microtubule-associated protein 2 and albumin was employed to monitor neuronal degeneration and the breakdown of the blood–brain barrier, respectively. In the ischemic core of the caudoputamen, the immunoreactivity for microtubule-associated protein 2 disappeared and massive albumin extravasation occurred several hours after vessel occlusion, while proteolipid protein messenger RNA signals remained relatively strong at this time. The messenger RNA signals began to attenuate 12 h after ischemia and were hardly detectable 24 h after ischemica in the whole ischemic lesion. In situ end-labeling of fragmented DNA showed some cells with proteolipid protein messenger RNAs to have DNA fragmentation at this period. In contrast to proteolipid protein messenger RNA signals, the immunoreactivity for myelin basic protein was detected as long as five days after ischemia. An apparent increase in the cells possessing strong proteolipid protein messenger RNA signals was found five days after ischemia, mainly in the corpus callosum and the cortex bordering the infarcted areas. A double simultaneous procedure with in situ hybridization for proteolipid protein messenger RNA and immunohistochemistry for glial fibrillary acid protein or lectin histochemistry for macrophages/microglia showed proliferating oligodendrocytes to be co-localized with reactive astrocytes and macrophages/microglia.

These findings show that oligodendrocytic damage occurred following ischemic neuronal damage and the breakdown of the blood–brain barrier, but preceded the breakdown of myelin proteins in the ischemic lesion, that an apoptosis-like process was involved in ischemic oligodendrocytic death, and that surviving oligodendrocytes responded and proliferated in the outer border of the infarcted area.

Section snippets

Animal preparation

Adult male C57BL/6 mice (Charles River Laboratories), weighing 21–25 g, were used. The experimental protocols have been approved by the Institutional Animal Care and Use Committee of Osaka University Medical School and were carried out in accordance with the National Institute of Health Guide for the Care and Use of Laboratory Animals. All animals had free access to water and food until the day of surgery. They were maintained in an air-conditioned room at a constant temperature of 25°C and

Results

In the normal mouse cerebellum, the immunoreactivity for MBP was localized in the corpus medullare and the lamina albae, while PLP mRNA signals were localized in the round- to oval-shaped cells, mainly in the white matter. The nuclei of those cells were smaller than those of neurons. With the sense probe, no signal was detected. The results were consistent with the previous findings which showed that PLP mRNA signals were effectively confined to the perinuclear region of oligodendrocytes.1, 45

Discussion

The molecular mechanism causing ischemic white matter lesions still remains obscure, even though it is said to be the central pathophysiology for Binswanger's disease, cerebrovascular dementia [2]and periventricular leukomalacia.[46]In particular, it is not yet clear whether oligodendrocytes are the primary target of ischemic insults or whether they are destroyed together with myelin during active destruction of the white matter. Several investigators, using experimental rodent models of

Conclusions

Although the existence of 0-2A progenitor cells and immature oligodendrocytes in and around infarction must be examined, the present results strongly suggest the involvement of oligodendrocytes in the repair process after brain injury, and raise the possibility for a future therapeutic intervention to modify oligodendrocytic accumulation as well as macrophages/microglia and astrocytes[32]after brain injury.

Acknowledgements

The present work was supported in part by a Grant-in-Aid from the Ministry of Education, Science and Culture and by Health Science Research Grants from the Ministry of Health and Welfare of Japan. We are grateful to Megumi Shimomura, Reiko Manabe and Mizuki Tsunoda for their secretarial assistance.

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