Cathepsin B immunoreactive neurons in rat brain. A combined light and electron microscopic study.

The regional distribution and cellular localization of the lysosomal proteinase cathepsin B was studied by use of monospecific antiserum. The application of the peroxidase-antiperoxidase technique at the light microscopic level revealed cathepsin B immunoreactive neurons in many brain areas. A strong immunoreaction was found in pyramidal cells of the cortex, large neurocytes of the septal region, some hippocampal neurons and magnocellular nerve cells of the hypothalamus. Immunogold labeling on ultrathin cryosections of rat neocortex revealed the enzyme protein to be associated with lysosomes.