Comparative genomic hybridization (CGH), fluorescence in situ hybridization (FISH), polymerase chain reaction-based microsatellite analysis, and p53 sequencing were performed in paraffin-embedded material from 18 oligodendrogliomas and histologically similar astrocytomas. The study was undertaken because of evidence that concurrent loss of both the 1p and 19q chromosome arms is a specific marker for oligodendrogliomas. Of the six lesions with a review diagnosis of oligodendroglioma, all had the predicted loss of 1p and 19q seen by CGH, FISH, and polymerase chain reaction. Other lesions, including some considered oligodendroglioma or mixed glioma by the submitting institution, did not. There were no p53 mutations in any of the six oligodendrogliomas, whereas 5 of the 10 remaining, successfully studied cases did have p53 mutations. The results suggest that CGH and FISH performed on current or archival tissue can aid in classification of infiltrating gliomas such as oligodendrogliomas and astrocytomas. The results of the p53 studies are consistent with findings of previous investigations that such mutations are less common in oligodendrogliomas than they are in astrocytomas.

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The brain, with the exception of the choroid plexuses and Circumventricular organs, is partially protected from the invasion of blood‐borne chemicals by the specific morphological properties of the cerebral micro‐vessels, namely, the tight junctions of the blood‐brain barrier. Recently, several enzymes that are primarily involved in hepatic drug metabolism have been shown to exist in the brain, albeit at relatively low specific activities. In the present study, the hypothesis that these enzymes are located primarily at blood‐brain interfaces, where they form an “enzymatic barrier,” is tested. By using microdissection techniques or a gradient‐centrifugation isolation procedure, the activities of seven drug‐metabolizing enzymes in isolated microvessels, choroid plexuses, meningeal membranes, and tissue from three Circumventricular organs (the neural lobe of the hypophysis, pineal gland, and median eminence) were assayed. With two exceptions, the activities of these enzymes were higher in the three Circumventricular organs and cerebral microvessel than in the cortex. Very high membrane‐bound epoxide hydrolase and UDP‐glucuronosyltransferase activities (approaching those in liver) and somewhat high 7‐benzoxyre‐sorufin‐O‐dealkylase and NADPH‐cytochrome P‐450 reductase activities were determined in the choroid plexuses. The pia‐arachnoid membranes, but not the dura matter, displayed drug‐metabolizing enzyme activities, notably that of epoxide hydrolase: The drug‐metabolizing enzymes located at these nonparenchymal sites may function to protect brain tissue from harmful compounds.

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