THE FINE STRUCTURE OF THE LATERAL VESTIBULAR NUCLEUS IN THE RAT : I. Neurons and Neuroglial Cells.

The lateral vestibular nucleus consists of multipolar isodendritic neurons of various sizes The distal segments of some dendrites display broad expansions packed with slender mitochondria and glycogen particles. These distinctive formations are interpreted as being growing tips of dendrites, and the suggestion is advanced that they are manifestations of architectonic plasticity in the mature central nervous system. Unlike large neurons elsewhere, the giant cells (Deiters) contain small Nissl bodies interconnected in a dense mesh-work. The Nissl substance is characterized by randomly arranged cisterns of the endoplasmic reticulum and by a high proportion of free ribosomes. Whether attached or free, ribosomes usually cluster in groups of four to six, and larger polysomal arrays are rare. Free ribosomal clusters also occur in the axon hillock and the initial segment. The neuronal perikarya contain distinctive inclusions consisting of a ball of neurofilaments enveloped by a complex honeycombed membrane. The failure of these fibrillary inclusions to stain with silver suggests that the putative argyrophilia of neurofilaments may reside in an inconstant matrix surrounding them. Giant cells of Deiters are in intimate contact with two kinds of cellular elements-astroglial processes and synaptic terminals. Oligodendroglial cells are only rarely satellites of giant cells; in contrast, they are frequently satellites of small and medium-sized cells.