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 e xpress NF subunits under culture conditions. However, NF expression in situ is questionable. It has been reported that as chromaffin cell pr ecursors mature and begin to express catecholamine-synthesizing enzyme s, their neuronal traits are extinguished and they become endocrine-li ke ce:Us. This study reports that while NF-L may be lacking in the adr enal. medulla of some species, NF-L immunoreactivity is clearly presen t in the adult bovine adrenal medulla. Immunofluorescence microscopy o f bovine chromaffin cells in culture demonstrated NF immunoreactivity localized to both thin, highly ramified filaments present throughout t he cell and frequently to an intensely immunofluorescent spot located near the nucleus. Double-label immunofluorescence microscopy and immun oblot analysis also demonstrated NF-L immunoreactivity in mature chrom affin cells of the bovine adrenal gland. In vitro and in situ immunofl uorescence results were confirmed by immunogold and immunoperoxidase l abelling, respectively. In both cases, NF-L immunoreactivity was assoc iated 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 chromaff in cells demonstrates that at least one neuronal trait persists in the se catecholamine-producing cells of the mature adrenal gland. In addit ion, this study emphasizes the fact that interspecies comparisons must be interpreted with caution, especially when attempting to formulate a generalized hypothesis. (C) 1996 Wiley-Liss, Inc.