Investigation of cytoskeleton proteins in neurons of the cat lateral geniculate nucleus

Abstract

The gross structure of neurons is supported by proteins that compose the cytoskeleton. Neurofilaments are intermediate cytoskeletal proteins that contribute to neuron structure and function, and three neurofilament subunits different in their molecular mass assemble to form heteropolymers that produce a structure-providing intracellular scaffold. The light neurofilament subunit is obligatory and can assemble with either the medium or heavy subunit, indicating some degree of independence between subunits. The presence of the heavy subunit has been shown to be associated with mature cells and is linked to large neurons in the cerebral cortex and thalamus. Spectrin is a membrane-associated actin-binding protein that, like neurofilament, has been linked to neuron shape. In this study of the cat dorsal lateral geniculate nucleus (dLGN) we examined whether labeling for neurofilament subunits and spectrin is linked to neuron size. We found that about one-third of neurons contained a visible amount of labeling for each neurofilament subunit, and the bulk of these labeled cells were large in comparison to the general population of neurons. The distribution of neuron sizes was not different between neurofilament subunits, indicating that neurofilament subunit content is not determined by neuron size. Spectrin labeling was evident in most dLGN neurons, and was not related to the size of neurons. That reactivity for neurofilament was predominant in large cells led us to directly examine the relationship between neurofilament and interneurons. The large majority of neurofilament-positive neurons did not contain GABA, indicating that neurofilament is predominant in projection cells and not in interneurons.