Cytofluorescence localization of ethidium bromide in the nervous system of the mouse. I. Ethidium bromide: its distribution in regions within and without the blood-brain barrier after intravenous injection.

A direct fluorescence-microscopic technique was effected to determine in the central nervous system (CNS) of the mouse the distribution of ethidium bromide after intravenous (i.v.) injection. The compound was visualized in thin cryostat sections of the brain fixed by vascular perfusion through the heart with a 10% buffered formalin solution. Ethidium bromide emitted a bright red fluorescent light in model experiments. The compound could not be detected in the vessel walls or brain parenchyma of the cerebral gray and white matters after i.v. injection indicating the presence of a blood-brain barrier (BBB) phenomenon to this compound. Signs of extravasation of ethidium bromide were present in the choroid plexus, the postremal area, the Gasserian ganglion, and in the circumventricular organs of the brain (neurohypophysis, organum vasculosum lamina terminalis, and median eminence) 3 min after the i.v. injection. Intense fluorescence was present in the nucleus and the cytoplasm of the cells in these areas, located outside of the BBB. Fluorescence had disappeared 24 h after the injection. Unexpectedly, red fluorescent material was seen in the parenchyma of the olfactory lobes of some animals, indicating, possibly, the presence of ethidium bromide. Ethidium bromide is known to suppress RNA, DNA, and protein synthesis in mammalian cells and has been used previously in neuropathology for studies on myelin lesions after injury to oligodendroglial cells. It can now, by a simple fluorescence-microscopic method, be traced directly in fixed tissue. Correlations can therefore be made between localization of the compound and its cytotoxic effects.(ABSTRACT TRUNCATED AT 250 WORDS)