Orientation of dendrites in the lateral geniculate nucleus of the monkey

Quantitative analysis of dendritic orientation in rapid Golgi sections of the lateral geniculate nucleus of Old World monkeys was performed with the help of a computer-microscope and a tree-analysing program. The orientation of intermediate and terminal dendritic segments of parvocellular and magnocellular multipolar neurons was measured at different ages in relationship to a reference line defined by the major direction of afferent fibres visualized in Golgi preparations and by silver staining. The direction of fibre bundles crossing the nucleus is approximately perpendicular to the layers near their apex, but more oblique laterally and medially. There is a clear tendency for terminal dendritic segments of both parvocellular and magnocellular neurons to be oriented preferentially along these fibres and fewer are perpendicular to them. The orientation of intermediate segments is much less clear, showing a more random orientation with regard to the fibres. There is no obvious influence of the order of branching or of the age of the animal (between late gestation and maturity) on the orientation of terminal and intermediate dendritic segments. A parallel study (Leuba and Garey 1984) suggests that there is greater plasticity in the terminal part of the dendritic tree, and it is possible that the maturation of afferent fibres causes these terminal segments to orient along them very early during normal development.