Morphology of neurons in the lateral geniculate nucleus of the monkey

Summary Rapid Golgi preparations of the lateral geniculate nucleus of old- and new-world monkeys were analysed in an attempt to classify the neuronal types. Four main types are described. The commonest, the multipolar neurons, are found in all laminae. Their somata can be large, medium or small and bear dendrites with sparse spines. Some have a radiate dendritic arbor and others have dendrites grouped in tufts. The next most frequent class is of bipolar neurons with two thick dendrites arising from opposite poles of the soma, which is usually large. Otherwise the dendrites are similar to those of multipolar neurons. Relatively rare is a class of medium-sized neurons with beaded dendrites, found here only in magnocellular laminae. There is a fourth class of small neurons distinguished by fine axonlike dendritic processes. They are in all laminae and form two subgroups, one with very long, cylindrical dendrites and few axon-like processes, the other with shorter dendritic arbors and many axon-like processes. In addition, a class of capsular neurons is found in the circumgeniculate capsule between layer 6 and the pregeniculate nucleus. They are large neurons with umbrella-like dendritic arbors sending ramifications into layer 6. The interlaminar zones contain scattered somata of all types except beaded and capsular neurons.The work described in this paper forms part of a study for a doctoral dissertation in the University of Lausanne by K.D. Saini