Wg. Gu et al., A photothrombotic ring stroke model in rats with remarkable morphological tissue recovery in the region at risk, EXP BRAIN R, 125(2), 1999, pp. 171-183
The photothrombotic ring stroke model with sustained underperfusion followe
d by late spontaneous reperfusion (Gu et al. 1999) was employed to study it
s morphological consequences. The exposed crania of adult male Wistar rats
were subjected to a ring-shaped laser irradiation beam simultaneously with
intravenous erythrosin B infusion. The ischemic volume was calculated from
serial sections throughout the ischemic lesions at 4, 10, 24, 48, and 72 h
and 7 days and 28 days after irradiation. The ischemic volume, expressed as
a percentage of the ipsilateral hemispheric volume, increased steadily fro
m 4 to 10 to 24 h to reach its maximum value at 48 h after irradiation; at
3 days, 7 days, and 28 days, the ischemic volume was reduced to 75%, 24%, a
nd 22% of the value at 48 h. Evaluation of ischemic volumes at different an
teroposterior levels revealed that the reduced ischemic volume at 72 h and
later was mainly due to morphological restoration in the centrally located,
nonirradiated region at risk. An initial enlargement and development of cy
stic coagulation necrosis was observed in the cortical areas corresponding
to the ring lesion itself. In the region at risk, a gradually deteriorating
neuropil and nerve cell morphology were observed over time, with maximum s
everity at 48 h postirradiation. At this time, most laminae II and III neur
ons in the region at risk exhibited eosinophilia and pyknosis but no incrus
tations, with small islands of less damaged neurons randomly scattered. At
72 h and up to 28 days after irradiation, these cell characteristics were n
o longer observed and the region at risk was well populated with neurons th
at had a chiefly unremarkable cytological appearance. Neuronal counts in th
e central part of the region at risk were performed; no significant differe
nce in neuronal density was observed between sham-operated controls and at
28 days after irradiation. In conclusion, the consistent, late spontaneous
reperfusion coincided with remarkable tissue recovery as assessed morpholog
ically in the region at risk. The data suggest that nerve cell repair may o
ccur even after the detection, by conventional morphological methods, of pr
olonged critical ischemic neuronal damage in the setting of acute ischemic
stroke.