Expression of neurofilament subunits in neurons of the central and peripheral nervous system: an immunohistochemical study with monoclonal antibodies.

The extent to which all neurofilament (NF) subunits (NF68, NF150, NF200) are expressed by different populations of mature CNS and PNS neurons is controversial. We addressed this issue in immunohistochemical studies of mature bovine tissues using monoclonal antibodies specific for each bovine NF subunit. All three NF subunits were detected in the perikarya and neurites of both CNS and PNS neurons; they were seen in nearly all PNS neuronal perikarya, and in all identifiable CNS and PNS axons. Most, but not all, CNS neuronal perikarya contained each of these NF antigens. CNS neurons devoid of immunodetectable NF antigens were generally small. The presence of low levels of NF antigens in neurons with scant perikaryal cytoplasm may account for the apparent absence of NF immunoreactivity in some classes of neurons, although other explanations, such as microheterogeneity among NF proteins, could account for this finding. NF antigens were also seen in some cells of the diffuse neuroendocrine system (adrenal chromaffin cells and cells of the pars distalis and pars intermedia), but not in other cell types. We suggest that the expression of all three NF subunits is a common feature of CNS and PNS neurons and their processes, and of some cells of the diffuse neuroendocrine system. These findings have implications for hypotheses concerning the structure and function of the intermediate filaments of neurons, and for hypotheses concerning neurodegenerative diseases involving NF proteins.