Acute Postischemic Renormalization of the Apparent Diffusion Coefficient of Water is not Associated with Reversal of Astrocytic Swelling and Neuronal Shrinkage in Rats

Bar graph shows changes in ADC values over time in the center of the lesion of the ipsilateral caudoputamen (white bars) and the nonischemic homologous region of the contralateral caudoputamen (striped bars). In all groups, ADC values in the ischemic lesion center decreased significantly (* indicates P < .001) during 30 minutes of ischemia, compared with the contralateral hemisphere. In group B, the reduced ADC values during ischemia recovered to normal 90 minutes (1.5 h) after reperfusion. In group C, the previously renormalized ADC values declined secondarily at 12 hours (12 h) after reperfusion. Occ indicates occlusion.

Photomicrographs of neurons and astrocytes (original magnification ×160). A–D, Neuronal morphology indicated by hematoxylin-eosin staining, and E–H, astrocytic changes indicated by double staining with GFAP plus S-100 protein.

A, Many normal neurons and one dark neuron with perineural vacuoles (arrow) are present in the contralateral nonischemic caudoputamen.

B, At the end of 30 minutes of ischemia when ADC had initially decreased, some neurons show slightly shrunken perikarya and nuclei (arrow).

C, After 90 minutes of reperfusion and recovery of ADC to normal, most neurons are moderately shrunken and surrounded by swollen cellular processes and are scalloped in appearance (arrows). Neuropil shows marked vacuolation (∗), indicative of swollen dendrites and astrocytic processes.

D, After 12 hours of reperfusion and a subsequent or second decrease in ADC, most neurons are severely shrunken (arrows), and the neuropil shows extensive vacuolation, and possibly some vasogenic edema (∗).

E, Dark purple reaction product demarcates S-100 protein in astrocytic nuclei; brown reaction product indicates GFAP in the cytoplasm and processes of astrocytes (arrow) in the contralateral nonischemic caudoputamen.

F, At the end of 30 minutes of ischemia, astrocytes are moderately swollen (arrows).

G, After 90 minutes of reperfusion, astrocytes are severely swollen (arrow) with less intranuclear S-100 reactivity and watery appearance.

H, After 12 hours of reperfusion, astrocytes have begun to disintegrate and lose nearly all S-100 immunoreactivity within their nuclei (arrow). At this time, some GFAP has moved into the extracellular space (arrowhead).

Electron micrographs of neurons (original magnification ×3000) and astrocytes (original magnification ×4500).

A and B, At the end of 30 minutes of ischemia. A, Shrunken neurons (N) with condensed nuclei and cytoplasm are surrounded by a ring of swollen astrocytic processes (a). B, Swollen astrocyte with clumps of heterochromatin around the edge of its nucleus and an abnormally wide rim of watery perikaryal cytoplasm, which contained a few swollen mitochondria (m).

C and D, At the end of 90 minutes of reperfusion. C, Two markedly shrunken neurons with highly condensed nuclei and cytoplasm; these neurons are surrounded by severely swollen astrocytic processes (a). D, Greatly swollen astrocyte with extensive and watery perikaryal cytoplasm and a few contracted mitochondria (m).

E and F, At the end of 12 hours of reperfusion. E, Two necrotic neurons show cytoplasmic and nuclear disintegration with marked chromatin clumping and discontinuous cellular membranes. F, An irreversibly injured astrocyte with breaks in the nuclear membrane (arrows), watery cytoplasm, and severely swollen mitochondria (M).

Bar graph indicates percentage of injured neurons in the ipsilateral ROI in the three groups (mean ± SD). Group A, at end of 30 minutes of MCAO; group B, at 90 minutes of reperfusion after 30 minutes of transient MCAO; and group C, at 12 hours of reperfusion after 30 minutes of transient MCAO.