Neuronal Intermediate Filaments

Abstract

Neuronal intermediate filaments, or neurofilaments, are among the major fibrous organelles of neurons. Elaborated within the perikaryon, assembled, and extruded to the axon, neurofilaments, together with microtubules, are essential to the neuronal cytoskeletal architecture. Neurofilaments were first recognized by early 19th century light microscopists who used the term neurofibrils to describe the parallel arrays of these elongated structures. Initial investigations in the field of neurofibrillary research have been elegantly discussed by Parker.¹ The pioneering electron microscopic observations of Schmitt and his associates^2–6 in the middle of this century led to the first descriptions of neurofilament fine structure, which studies have served as a basis for a host of later investigations. Although these ubiquitous neuronal organelles have been recognized and measured for over a century, it was not until recently that biochemical and physicochemical methods were applied. Progress was slow in these areas because of obstacles to obtaining undegraded neurofilament protein sufficiently free of other cellular constituents to make studies at the molecular level meaningful. The major portion of the present chapter focuses on this experimentation, with particular attention given to mammalian neurofilaments. Certain aspects of neurofilament research have been evaluated in other recent reviews.^7,8