Comparison of the structural organisation of reeler hippocampal CA1 region with wild type CA1.

Abstract

The dendritic pattern defines the input capacity of a neuron. Existing methods such as Golgi impregnation or intracellular staining only label a small number of neurons. By using high-resolution imaging and 3D reconstruction of green fluorescent protein-expressing neurons, the present study provides an approach to investigate the anatomical organization of dendritic structures in defined brain regions. We characterized the structural organization of dendrites in the CA1 region of the mouse hippocampus by analyzing Sholl intersections, dendritic branches, branching and orientation angles of dendrites, and the different types of spine on the dendritic branches. Utilizing this quantitative imaging approach, we show that there are differences in the number of Sholl intersections and in the orientation of apical and basal dendrites of CA1 pyramidal neurons. Performing 3D reconstructions of the CA1 region of the reeler hippocampus, we show that neurons of this mutant display an arbitrary orientation of apical dendrites at angles ranging from -180 to +180 degrees in contrast to wild-type mice that show a preferred orientation angle. This methodology provides a way of analyzing network organization in wild type and mutant brains using quantitative imaging techniques. Here, we have provided evidence that in reeler a sparse, weakly connected network results from the altered lamination of CA1 pyramidal neurons and the variable orientation of their dendrites. Highlights-High-resolution imaging and 3D reconstruction of CA1 pyramidal neurons -Analysis of Sholl intersections -Analysis of the orientation of apical and basal dendrites of CA1 pyramidal neurons -Altered dendrite orientation angle of apical dendrites in reeler mutant mice -More stubby spines compared to thin and mushroom spines in wild-type CA1