Beta-amyloid precursor protein localization in the Golgi apparatus in neurons and oligodendrocytes. An immunocytochemical structural and ultrastructural study in normal and axotomized neurons.

We have used a polyclonal antibody raised against a synthetic peptide from the carboxyl terminal of the beta-amyloid precursor protein (APP) to examine the cellular and subcellular localization of this protein in the rat brain. Light and electron microscopic immunocytochemical techniques were used. Immunoreactivity was found throughout the brain in all the neurons examined as well as in oligodendrocytes. At the light microscopic level, a perinuclear filamentous distribution was seen in neurons, suggesting a concentration of the protein to the Golgi apparatus. Axotomy of motor neurons of the facial nucleus produced a decrease in choline acetyltransferase (ChAT) activity and an increase in the perineuronal microglial nucleoside diphosphatase (NDPase)-positive cells in addition to a hypertrophy of the GFAP immunoreactive astrocytes. On the other hand, increased APP-like immunoreactivity all over the neuronal cell bodies accompanied by a dispersion ('rete dispersion') of the Golgi apparatus labeling was demonstrated. In contrast, reactive microglia and hypertrophic astrocytes in axotomized facial nucleus were not immunolabeled. Oligodendrocytes showed a punctate APP immunoreactivity corresponding to the Golgi apparatus in both operated and control facial nucleus. This was further demonstrated by electron microscopic immunolabeling. These results show that the main localization of the C-terminal containing forms of the APP in the rat brain is the Golgi apparatus in both neurons and oligodendroglia and further supporting the secretory nature of these proteins. The increased synthesis of this protein after axotomy is suggestive of a role of the APPs in growth and/or regeneration.