[Recent findings on the external oculomotor nucleus: the center for horizontal ocular movement]

Various neurobiological methods allowing the analysis of electrophysiological and morphological properties of a cell population within the central nervous system will be illustrated in the study of the abducens nucleus. Intracellular recordings provided the functional identification of the different types of cells within the abducens nucleus. Antidromic excitation, refractoriness, conduction velocity and frequency of discharges indicated the properties of the abducens motoneurones. Various types of afferent stimulations were applied to study the synaptic responses of the neurones. A dye was then electrophoretically injected and the labelled neurone observed with a light microscope. Full reconstruction of dendritic arborization and of axon trajectory was performed. The morphological study has shown the heterogeneity of the population of the motor nucleus, and the ultrastructural features indicated a complex synaptic organisation. The origin of some afferent terminals was determined.