Abstract

The quaternary analogues of the convulsant acridones: 10(2-trimethylaminopropyl)-9-acridone (M-219) and 10(2-triethylaminoethyl)-9-acridone do not penetrate into the central nervous system after intravenous administration, but are effective as convulsants when applied to the cortex or injected into it. Under the latter conditions they appear in the nuclei of nerve cells. After intravenous administration the nuclei of brain capillary endothelium, the tela chorioidia, and the neurohypophysis will fluoresce, and with higher than the minimal doses fluorescence also appears in the nuclei of the pial mesenchyme and glia. This indicates that the chief barrier to the entrance of these dyes lies between the outer wall of the capillary endothelium and the glial plasma membrane, but this barrier is not absolutely impermeable. Above all, this study emphasizes the importance of the concentration gradient between the blood and the brain in the study of the site of the blood-brain barrier.