Immunomicroscopy of neurofilaments in chromaffin cells of the adult bovine adrenal gland.

Neurofilaments (NFs) represent a class of intermediate filaments which are highly specific for neurons. The most abundant of the native NFs is the 68 kD subunit (NF-L). Chromaffin cells of the adrenal medulla express NF subunits under culture conditions. However, NF expression in situ is questionable. It has been reported that as chromaffin cell precursors mature and begin to express catecholamine-synthesizing enzymes, their neuronal traits are extinguished and they become endocrine-like cells. This study reports that while NF-L may be lacking in the adrenal medulla of some species, NF-L immunoreactivity is clearly present in the adult bovine adrenal medulla. Immunofluorescence microscopy of bovine chromaffin cells in culture demonstrated NF immunoreactivity localized to both thin, highly ramified filaments present throughout the cell and frequently to an intensely immunofluorescent spot located near the nucleus. Double-label immunofluorescence microscopy and immunoblot analysis also demonstrated NF-L immunoreactivity in mature chromaffin cells of the bovine adrenal gland. In vitro and in situ immunofluorescence results were confirmed by immunogold and immunoperoxidase labelling, respectively. In both cases, NF-L immunoreactivity was associated with filaments in close proximity to the nucleus. Additionally, a spheroidal aggregate of immunogold-labelled NFs was seen adjacent to the nucleus in cultured cells. In conclusion, NF-L in bovine chromaffin cells demonstrates that at least one neuronal trait persists in these catecholamine-producing cells of the mature adrenal gland. In addition, this study emphasizes the fact that interspecies comparisons must be interpreted with caution, especially when attempting to formulate a generalized hypothesis.