SPATIAL TRAINING IN A COMPLEX ENVIRONMENT AND ISOLATION ALTER THE SPINE DISTRIBUTION DIFFERENTLY IN RAT CA1 PYRAMIDAL CELLS

The hippocampus is critically involved in spatial learning. Spatial tr aining in adult rats, which improved their spatial learning ability, i ncreased the number of excitatory hippocampal CA1 spine synapses on ba sal dendrites as compared with either isolated or standardly housed an imals (Moser et al. [1994] Proc. Natl. Acad. Sci. USA 91:12673-12675). In this article, we report that spine synapses on oblique apical dend ritic branches do not increase in density or number after the same typ e of training. When examining the variability of the spine density on basal CA1 dendrites by using variance component analysis, the variance associated with the cells was twice as large in all three groups as t hat coupled to the rats. Analysis of the spine density plots shows tha t the enhanced spine density after spatial training is found in most c ells recorded from the trained group but that a small subset of CA1 ne urones are particularly well. supplied with spines. The trained group had a significant right-skewed tail of the spine distribution, i.e., t raining caused high spine density to occur in a small subset of dendri tic segments. Conversely, the isolated group had a significant left-sk ewed spine distribution, indicating that some of the dendritic segment s were undersupplied with spines, whereas the paired group displayed n o asymmetry. (C) 1997 Wiley-Liss, Inc.