Ultrastructure of the neurons of the cerebral cortex

Cellular events during partial cerebral ischemia. I. Electron microscopy of feline cerebral cortex after middle-cerebral-artery occlusion

The feline right cerebral hemisphere was subjected to regional (incomplete) ischemia after clipping the middle cerebral artery for 5, 10, 15, 30 or 60 min, respectively. After each ischemic episode, a 10-min recirculation period was allowed, following which the brain was fixed and processed for electron microscopy. The earliest alterations, detected in the cerebral cortex after 15 min, increased in severity with longer ischemic episodes and were distributed multifocally. There was: (a) marked neuronal mitochondrial matrical swelling and progressive condensation of cytoplasm and nucleoplasm; (b) cytoplasmic swelling of astrocytes with preservation of glial mitochondrial volume; (c) capillaries, oligodendrocytes, myelin sheaths and axis cylinders did not change significantly, even after the longest interval studied: 60 min. This type of tissue reaction appears to be common for those forms of cerebral ischemia, in which circulation is either sustained partially (via collateral arteries) or restored after a period of absolute ischemia. Under these conditions, as yet undefined permeability changes in cell membranes lead to pronounced volumetric alterations of cellular compartments. Although no softening is detectable by digital examination, we suggest that such a set of structural abnormalities constitutes encephalomalacia, or the earliest stage of a lesion which is designated infarction, once it reaches irreversibility.

Ultrastructure of intracisternally accumulated dense particles observed in nerve cells of rat cerebellar nuclei

Peculiar dense particles were accumulated within smooth-surfaced cisternae of some neuronal perilarya of cerebellar nuclei in rat. The particles were 200-450 A in size and spheroidal or slightly irregular in outline. They were low in contrast after uranyl acetate treatment, whereas they showed increase in electron density after uranyl and lead staining. Wigh respect to the possible nature of these intracisternal dense particles, the following interpretation was discussed. The particles concerned were probably identified as glycogen which had been synthetized by the agranular endoplasmic reticulum as an unusual cytological event.

Transorbital approach to the middle cerebral artery of the squirrel monkey: a technique for experimental cerebral infarction applicable to ultrastructural studies

An appropriate surgical technique for the production of cerebral infarction must fulfill, among others, the following criteria in order to be suitable for electron microscopy (EM) studies: (1) the method of arterial occlusion should yield a high percentage of infarcts with predictable average size; (2) there must be avoidance of surgical manipulation (i.e., retraction) of the cerebral tissues or exposure of the same to the atmosphere; and (3) the method for occluding the artery must be one that permits fixation by perfusion of the ischemic and nonischemic brain.

Modifications to a previously devised method for induction of cerebral infarct are herein described. This new surgical approach has made it possible to conduct detailed and sequential ultrastructural analysis of experimental cerebral infarctions.