ANALYSIS OF DENDRITIC SPINES IN RAT CA1 PYRAMIDAL CELLS INTRACELLULARLY FILLED WITH A FLUORESCENT DYE

The dendritic branching pattern and the distribution of dendritic spin es were studied in hippocampal neurones with an improved technique. In slices taken from adult Wistar rats, CA1 pyramidal cells were filled with Lucifer yellow and examined under a laser-scanning confocal micro scope. The basal dendrites were found evenly distributed inside a regu lar cupola-shaped volume. Their total length was about 4,500 mu m. The branches divided between one and three items, with the initial segmen ts comprising less than 2%, and the long terminal segments (mean lengt h, 119 mu m) including more than 80% of the total length of the basal dendrites. The apical dendritic branches emerged obliquely from the ma in shaft, ran for a distance of 50 to 250 mu m, and made up a total le ngth of about 5,100 mu m in stratum radiatum and between 1,100 and 3,2 00 mu m in stratum lacunosum-moleculare. The mean total length of the dendritic tree was 11,900 mu m. All values were corrected for shrinkag e. Shrinkage was measured in three dimensions and was 20.2% in the hor izontal (x/y) plane and 40.9% in the vertical (z) plane. Both the basa l and the apical dendritic branches were covered by regularly spaced s pines. When corrected for dehydration-induced shrinkage and for hidden spines, the density was 1.80 and 2.00 spines/mu m dendritic length fo r the basal and apical dendritic branches, respectively. Apart from th e initial parts of the branches, which had few or no spines, the spine s were remarkably evenly spaced. In particular, the distance between s pine heads was significantly different from a random distribution, sug gesting a regulatory process for the spacing of spines. (C) 1995 Wiley -Liss, Inc.