Rat neural tissue cathepsin D: ultrastructural immunocytochemistry

The cellular and subcellular localization of cathepsin D, an aspartyl endopeptidase, was investigated in the central and peripheral nervous systems of the rat by light and electron microscopic immunocytochemistry. The reaction of rabbit anti-rat brain cathepsin D within ventral cervical spinal cord, cerebellum, corpus callosum, caudate nucleus, optic nerve, trigeminal ganglion, fifth cranial nerve and sciatic nerve was localized with an indirect immunoperoxidase technique. A number of tissue processing methods were utilized, but only in tissues fixed in paraformaldehyde-lysine-periodate and sectioned at thicknesses of 25-50 micron could antibody penetration, enzyme protein immunoreactivity and intact morphology be reliably attained. Immunoreactive cathepsin D was present in lysosomes and pleomorphic dense bodies of neurons in the anterior horn of spinal cord, cerebellar Purkinje and granule cell layers, caudate nucleus and trigeminal ganglion. Lysosomal localization of cathepsin D was also documented in oligodendrocytes, astrocytes, endothelial cells and Schwann cells. Reaction product was not observed in microglia although its presence there would be expected. With these methods, reaction product was not detected in the Golgi saccules of any cell type.