Light and electron microscopic evaluation of hydrogen ion-induced brain necrosis

Abstract

Excessive accumulation of hydrogen ions in the brain may play a pivotal role in initiating the necrosis seen in infarction and following hyperglycemic augmentation of ischemic brain damage. To examine possible mechanisms involved in hydrogen ion-induced necrosis, sequential structural changes in rat brain were examined following intracortical injection of sodium lactate solution (pH 4.5), as compared with injections at pH 7.3. Following pH 7.3 injection, neuronal swelling developed between 1 and 6 h, but only a needle track wound surrounded by a thin rim of necrotic neurons and vacuolated neuropil was present 24 h after injection. In contrast, pH 4.5 injection produced neuronal necrosis as soon as 1 h after injection, followed by necrosis of astrocytes and intravascular thrombi at 3 and 6 h. Alterations common to both groups included vascular permeability to horseradish peroxidase, dilation of extracellular spaces, astrocyte swelling, capillary compression, and vascular stasis. These data suggest that neurons, astrocytes, and endothelia can be directly damaged by increased acid in the interstitial space. Lethal injury initially appeared to affect neurons, while subsequent astrocyte necrosis and vascular occlusion may damage tissue by secondary ischemia.

FIG. 1

A: Forty micron section, 6 h after pH 7.3 injection, shows area of extravasated horseradish peroxidase measuring 0.7 cm in diameter. Neurons are surrounded by but do not stain with horseradish peroxidase. B: Forty micron section, 24 h after pH 7.3 injection, shows needle track containing horseradish peroxidase. Adjacent parenchyma is slightly vacuolated. C: Forty micron section, 3 h after pH 4.5 injection, shows area of extravasated horseradish peroxidase that surrounds the central needle track and that measures 0.66 mm in diameter. D: Paraffin section, 24 h after pH injection (see Kraig et al., 1987), shows a well-circumscribed area of necrosis that surrounds central needle track (arrow). Hematoxylin-eosin; × 160.

FIG. 2

A: A cortical neuron, 1 h after pH 7.3 injection, shows perinuclear clustering of organelles and clearing of peripheral cytoplasm. Adjacent extracellular space on the left is filled with horseradish peroxidase and cell processes in this region are swollen. × 4,800. B: Capillary lumen 3 h after pH 7.3 injection, is markedly narrowed to a slit-like lumen and is surrounded by markedly swollen astrocyte processes. × 7,000.

FIG. 3

A: Neuron from the central zone (Region 2), 1 h after pH 4.5 injection, has a relatively electron dense cytoplasm that contains ribosomes and dilated vesicles of the Golgi apparatus (G). Polyribosomes are absent. A perineuronal astrocyte process (A) is swollen. × 30,000. B: Neuron from Region 2, 6 h after pH 4.5 injection, has focal loss of organelles and fragmented plasma membrane (arrow). Remaining cytoplasm contains usual complement of polyribosomes and endoplasmic reticulum. × 5,600.

FIG. 4

A: Lumens of two capillaries, 3 h after pH 4.5 injection, are markedly narrowed and contain circulating horseradish peroxidase (arrows). Perivascular astrocyte processes are markedly swollen. × 4,000. B: Peripheral region, 3 h after pH 4.5 injection, containing two astrocytes (upper right) that have enlarged nuclei containing small chromatin clumps and mildly dilated cytoplasm. Capillary is slightly compressed and is surrounded by markedly swollen astrocyte foot processes. Two neurons on the bottom are normal. × 3,000.