MRI reveals changes in intracellular calcium in ischaemic areas of rabbit brain

Since calcium overload is thought to be important in ischaemic neuronal death, we have used a focal ischaemic model to determine the relationships between changes in intracellular calcium concentration ([Ca(2+)]( i)), apparent diffusion coefficient (ADC), and relative cerebral blood flow (rCBF). Focal cerebral ischaemia was induced in seven groups of six rabbits, by transorbital permanent occlusion of one middle cerebral artery (MCAo). Diffusion- and perfusion-weighted imaging was performed from 0.5 to 36 h after the occlusion. Brains were removed, and slices were taken. These slices were incubated with fluo-3 solution, and the fluorescent intensity (FI) of [Ca(2+)]( i) was viewed by confocal microscopy. There were significant differences in FI of Ca(2+) between the ischaemic caudoputamen and the contralateral region in the seven groups of animals ( F=24.34, P <0.001), while the difference between the ischaemic frontoparietal cortex and the contralateral region was not significant within 1.5 h of occlusion ( F=1.06, P >0.05). Calcium overload occurred prior to an abrupt reduction in ADC in the peripheral ischaemic area. The relative ADC (rADC) and FI (rFI) were negatively correlated in the frontoparietal cortex ( r=-0.9, P <0.001), but not in the caudoputamen ( r=-0.21, P >0.05). Our findings suggest that ADC of the perifocal ischaemic area might reflect the changes in intracellular calcium which occur in early ischaemia. They may also suggest that, once the calcium level is high enough and infarction ensues, changes in ADC may not induce a further rise in calcium concentration.