Ultrastructural and MRI study of the substantia nigra evolving exofocal post-ischemic neuronal death in the rat.
To clarify the morphological characteristics of exofocal post-ischemic neuronal death (EPND) in the substantia nigra (SN), we investigated the course of light- and electron-microscopic changes of the SN of rats subjected to occlusion of the left middle cerebral artery (MCA) for 1, 2, 4, 7 and 12 days. To assess cellular edema, sequential magnetic resonance (MR) mapping of the apparent diffusion coefficient (ADC) and the T2 value test was performed. Histological and electron-microscopic examination on day 1 showed dotted chromatin clumps in the nuclei of some neurons and mild swelling of the perivascular endfeet of astrocytes in the ipsilateral SN. On day 2, a few cells of the ipsilateral SN pars reticulata (SNr) revealed key morphological signs of apoptosis--apoptotic body-like condensation and segregation of the chromatin and DNA fragmentation-like nuclear remnants. On day 4, 38% of neurons became swollen (pale neurons) with cytoplasmic microvacuoles, which appeared to originate from rough endoplasmic reticulum (rER), mitochondria and Golgi apparatus. Twenty percent of neurons showed massive proliferation of the cisternae of the rER, some of which were fragmented or had lost their normal parallel arrangement. In addition, MR mapping revealed a transient ADC decrease with a T2 increase (signifying a phase of cellular edema), which coordinated with the phase of ultrastructural cellular swelling. Further, the total number of neurons started to decrease gradually, the perivascular endfeet of astrocytes were markedly swollen, and the neuropil became loose on day 4. On day 7, reactive astrocytes and dark neurons occurred most frequently. These results suggest that the EPND in the SN after occlusion of the MCA in adult rats is due to both apoptosis and necrosis, although necrosis seems to be the dominant mechanism of the EPND. However, the morphologic resemblances of EPND to delayed neuronal death suggest these processes have a common pathomechanism.
Zhao
Fengyu
F
Department of Neurology and Neurological Science, Medical Research Institute, Tokyo Medical and Dental University, Japan.
Kuroiwa
Toshihiko
T
Miyasaka
Naoyuki
N
Nagaoka
Tsukasa
T
Nakane
Makoto
M
Tamura
Akira
A
Mizusawa
Hidehiro
H
D000818:Animals; D017209:Apoptosis; D002545:Brain Ischemia / Q000000981:diagnostic imaging / Q000473:pathology; D004058:Diffusion; D020244:Infarction, Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008854:Microscopy, Electron; D009336:Necrosis; D009410:Nerve Degeneration / Q000209:etiology / Q000473:pathology; D009474:Neurons / Q000648:ultrastructure*; D011859:Radiography; D051381:Rats; D017207:Rats, Sprague-Dawley; D013378:Substantia Nigra / Q000000981:diagnostic imaging* / Q000648:ultrastructure*; D013997:Time Factors