DENDRITIC SPINES FORM COLLARS IN HIPPOCAMPAL GRANULE CELLS

A QUANTITATIVE study of the distribution of dendritic spines was carri ed out in three orders of dendritic branches of granule cells from the dentate gyrus of the rat hippocampus. Golgi-stained preparations (7-1 9 neurones in each of seven rats) were analysed using computerized mic roscopy. Identification of spines and quantification of stem-spine geo metry was performed using a segmentation algorithm and a line skeleton transformation of dendritic images. Analysis of data using the statis tics of point processes revealed that, in all three branch orders, the distribution of visible spines along dendrites was not evenly random, but included dense clusters of spines surrounding the dendritic stem (spine 'collars'). Three-dimensional reconstructions from serial ultra thin sections have confirmed the presence of such spine groups. We spe culate that spine collars represent a functional element in which asso ciative synaptic plasicity is fostered by the proximity of individual synapses.