Cytoarchitecture of the abducens nucleus of man: a Nissl and Golgi study

The abducens nucleus is a pontine nucleus directly involved in oculomotion through its connections with the lateral rectus muscle of the eye. The aim of the present study was to investigate the cytoarchitectural organization of the abducens nucleus in man. The data obtained showed that the nerve cell bodies were small, medium and large in size and polygonal, oval, round or spindle shaped. The cytoplasm of all neurons appeared basophilic due to clearly evident scattered Nissl granules. On the basis of the characteristics of the dendritic arborization, multipolar and fusiform cells were identified. The multipolar neurons showed four to eight primary dendrites which gave off a wide secondary ramification. The fusiform neurons showed two dendrites emerging from the opposite poles of the elongated nerve cell body. The dendrites of all the neurons were largely confined within the boundaries of the nucleus. This finding would suggest that the neuronal relationships of the abducens nucleus supplied by the afferent fibers which pass through or end within it take place almost completely inside the nucleus. The wider dendritic arborization shown by the multipolar cells would indicate the latter as the principal target fields for the afferent inputs.