Distribution of neurofilament subunits in neurons and neuronal processes: immunohistochemical studies of bovine cerebellum with subunit-specific monoclonal antibodies.

The distribution of individual neurofilament (NF) subunits in bovine cerebellar neurons was examined using monoclonal antibodies (MAs) raised against bovine NF. MAs with immunochemically defined specificities for one or more NF subunits were used. Seven were specific for the Mr 68,000 NF subunit, five were specific for the Mr 150,000 NF subunit, nine were specific for the Mr 200,000 NF subunit, and 30 recognized both high molecular weight subunits. Fresh bovine cerebellum was fixed and processed by five different protocols and subjected to four different immunohistochemical procedures. MAs from each group stained neuronal perikarya and processes. NF immunoreactivity in Purkinje cells was evaluated in detail. Adjacent Purkinje cell bodies and dendrites exhibited variable NF immunoreactivity to the same MA, ranging from intensely positive to completely negative. Similar variability in axonal staining was not observed. Application of the same MA to tissue subjected to different fixation and/or immunohistochemical protocols also resulted in variability in NF subunit immunoreactivity. We conclude that MAs recognize each of the three NF subunits in neuronal perikarya, axons, and dendrites. Variability in NF subunit immunoreactivity appears to reflect both NF microheterogeneity and fixation-dependent modifications of NF subunits.