Correlation between N-acetylaspartate levels and histopathologic changes in cortical infarcts of mice after middle cerebral artery occlusion

The aim of the present study was to evaluate the use of the endogenous neur onal compound N-acetylaspartate (NAA) as a marker of neuronal damage after focal cerebral ischemia in mice. After occlusion of the middle cerebral art ery (MCAO) the ischemic cortex was sampled, guided by 2,3,5-triphenyltetraz olium chloride (TTC) staining, and the NAA concentration was measured by hi gh-pressure liquid chromatography (HPLC). Conventional histology and immuno histological methods using antibodies against neuron-specific enolase (NSE) , neurofilaments (NF), synaptophysin, glial fibrillary acidic protein (GFAP ), and carbodiamide-linked NAA and N-acetylaspartylglutamate (NAAG). The le vel of NAA rapidly declined to 50% and 20% of control levels in infarcted t issue after 6 hours and 24 hours. respectively. No further decrease was obs erved during the observation period of 1 week. Within the first 6 hours the number of normal-appearing neurons in the infarcted cortical tissue decrea sed to 70% of control, of which the majority were eosinophilic. After 24 ho urs almost no nor-mal-appearing neurons were seen. The number of eosinophil ic neurons decreased steadily to virtually zero after 7 days. The number of immunopositive cells in the NSE, NF, and synaptophysin staining within the infaret was progessively reduced, and after 3 to 7 days the immunoreaction s were confined to discrete granulomatous structures in the center of the i nfarct, which otherwise was infested with macrophages. This granulomatous m aterial also stained positive for NAA. The number of cells with positive GF AP immunoreactions progressively increased in the circumference of the infa rct. They also showed increased immunoreaction against NAA and NSE. The stu dy shows that the level of NAA 7 days after ischemia does not decline to ze ro but remains at 10% to 20% of control values. The fact NAA is trapped in cell debris and NAA immunoreactivity is observed in the peri-infarct areas restricts its use as a marker of neuronal density.