A MODIFIED RAT MODEL OF MIDDLE CEREBRAL-ARTERY THREAD OCCLUSION UNDERELECTROPHYSIOLOGICAL CONTROL FOR MAGNETIC-RESONANCE INVESTIGATIONS

Previous magnetic resonance (MR) investigations of middle cerebral art ery (MCA) occlusion in rats were limited by the lack of early post-occ lusion MR measurements and/or electrophysiological monitoring. Therefo re, we have developed a technique which allows to perform MCA occlusio n inside the magnet under simultaneous recording of EEG and direct cur rent (DC) potentials for monitoring the ischemic insult. Rats underwen t intraluminal thread occlusion of the right MCA inside the MR tomogra ph via a catheter extension device, while EEG and DC potentials were r ecorded by non-magnetic graphite electrodes. The thread was slowly adv anced until electrophysiological changes appeared. Diffusion-weighted MR images (DWI) were obtained before and repeatedly after MCA occlusio n for up to 7 h. Thereafter, rat brains were frozen in situ or fixed b y transcardiac perfusion and investigated by biochemical and histologi cal techniques. In 15 of 18 animals (83%), MCA thread insertion caused immediate EEG changes and a negative DC potential shift sat 4.4 +/- 1 .8 min (mean +/- SD) after occlusion. In all animals with electrophysi ological changes, signal intensity of DWI began to increase within the MCA territory at 12-14 min post-occlusion (the end of the first measu rement), and continued to rise throughout the observation period. Isch emia was confirmed by demonstrating focal areas of energy depletion on ATP images. In the animals without electrophysiological changes, DWI or biochemical alterations were absent or confined to the central part of caudate-putamen. The histological lesion area of successfully occl uded animals amounted to 70.1 +/- 5.8% of the ipsilateral hemisphere a t the level of caudate-putamen. Our observations demonstrate that intr aluminal thread occlusion of the rat MCA can be performed inside the m agnet but has to be supplemented by electrophysiological recording to ascertain correct positioning of the occluding device.