Possible Role of Intracellular Calcium Translocation in the Maturation of Ischemic Damage

The fine structural localization of calcium was studied in 3-month-old female Mongolian gerbils (Meriones unguiculatus) subjected to single 5-min bilateral common carotid artery occlusions. Intracellular calcium deposits were visualized at the electronmicroscopic level with a combined oxalate-pyroantimonate method. Compared with the control, calcium deposits were detected at 24 h in increased number free in the dendritic cytoplasm of pyramidal cells and interneurons in the stratum radiatum of the CA1 subfield of the hippocampus, while the mitochondria were as a rule devoid of electrondense precipitate. At the 3rd day, however, heavy loading of mitochondria with calcium pyroantimonate was apparent in the stratum radiatum within the dendrites of the pyramidal neurons undergoing delayed death. Fragments of dendrites containing mitochondria with abundant calcium deposits were seen even 7 days after the ischemic insult. Considerable free cytoplasmic calcium precipitate was observed in some dendrites of surviving neurons (interneurons) long (several weeks and months) after the primary lesion. The cytoplasmic accumulation of calcium in dendrites can be interpreted as an indication of hyperexcitation going on in these elements, which might eventually participate as a pathogenetic factor in the expression of the maturation phenomenon.