SECONDARY THALAMIC LESIONS AFTER LIGATION OF THE MIDDLE CEREBRAL-ARTERY - AN ULTRASTRUCTURAL-STUDY

Earlier light microscopic, immunocytochemical and morphometric investi gations indicate that noxious substances transported with the vasogeni c edema from hemispheric infarcts influence the character, timing and extent of the secondary thalamic lesions. The object of the present st udy was to analyze the ultrastructure of the secondary damage and the cytolytic nerve cell change which ensues in the thalamus within a week after the infarction. Adult spontaneously hypertensive rats (SHR) wer e stud; led either 7 days after permanent ligation of the right middle cerebral artery (MCA) (n = 4) or 7 days after a 2-h temporary occlusi on of the MCA (n = 4). Light microscopy revealed damage in the ipsilat eral thalamic nuclei and the electron microscopic analysis showed that the cytolytic nerve cell degeneration was somatodendritic. Central ch romatolysis was not observed. Somatodendritic nerve cell degeneration, as found in the secondary thalamic lesions in the present study, has been described in excitotoxic brain damage as well as in chronic, edem atous lesions in stroke-prone spontaneously hypertensive rats. The pos sibility that the cytolytic thalamic nerve cell lesion is influenced b y excitatory, noxious substances spreading with the edema fluid from t he infarct has, thus, to be considered.