[Occurrence and ultrastructure of mast cells in the hypothalamus of teleost fishes].

From 56 light-, fluorescence- and electronmicroscopically investigated brains of fishes mast cells could be found only in 4 cases. They were concentrated in the meninges of one pike (Esox licius) and in the meninges and at larger blood-vessels of the hypothalamus of 2 trouts (Salmo trutta fario). In the hypothalamus of a carp (Cyprinus carpio) an infiltration of mast cells was detectable in the meninges, at blood-vessels and capillaries, between neuronal and glial fibres and sub- and intraependymaly. Contrary to the pike the granules of the mast cells of the carp show changes, hinting at release of their content. Junctions between mast cells and capillary walls or ependymal cells are characterized by structures indicating an enhanced cytopempsis. The present results are compared with observations on mast cells in the brain and peritoneum of mammals.