METHYLENE-BLUE SUPRAVITAL STAINING - AN EVALUATION OF ITS APPLICABILITY TO THE MAMMALIAN BRAIN AND PINEAL-GLAND

Methylene blue supravital staining of mammalian brain reveals typical staining patterns in different brain regions. Within the cerebellum of the mouse, the dye showed a peculiar affinity for the somata and the axons of Purkinje cells. Additionally, large polymorphic neurons chara cterized by long descending axons were detected within the granular la yer and the white matter. These cells might represent another type of projection neuron. In the stratum pyramidale and stratum oriens of the murine hippocampus, a subpopulation of non-pyramidal cells, i.e. intr insic interneurons, were selectively stained. Additionally, a labellin g of perineuronal nets of extracellular matrix covering single cells c ould be achieved; this phenomenon might be due to the occurrence of st rong anionic residues which attract the cationic dye. Therefore, perin euronal nets might also trap other cations and play an important role in the control of cell excitability. The electron microscopic investig ation revealed drop-like dye accumulations within the cytoplasm and a staining of material at the site of the plasma membrane. Throughout th e pineal gland, a network of a subpopulation of polymorphic cells with manifold long processes could be visualized. Syncytial connections of cells seemed to occur. The oxygen-dependent selective staining is pro bably functionally connected with the generation of oxygen radicals an d subsequent oxidative stress for the cells. This reaction indicates a certain vulnerability to hypoxia; therefore, the intracellular dye-up take might be interpreted as an early sign of metabolic disturbance.