Balancing structure and function at hippocampal dendritic spines

Abstract

Dendritic spines are the primary recipients of excitatory input in the central nervous system. They provide biochemical compartments that locally control the signaling mechanisms at individual synapses. Hippocampal spines show structural plasticity as the basis for the physiological changes in synaptic efficacy that underlie learning and memory. Spine structure is regulated by molecular mechanisms that are fine-tuned and adjusted according to developmental age, level and direction of synaptic activity, specific brain region, and exact behavioral or experimental conditions. Reciprocal changes between the structure and function of spines impact both local and global integration of signals within dendrites. Advances in imaging and computing technologies may provide the resources needed to reconstruct entire neural circuits. Key to this endeavor is having sufficient resolution to determine the extrinsic factors (such as perisynaptic astroglia) and the intrinsic factors (such as core subcellular organelles) that are required to build and maintain synapses.

Figure 1

Variability in spine shape and size. A. 3-dimensional reconstruction of a hippocampal dendrite (gray) illustrating different spine shapes including mushroom (blue), thin (red), stubby (green), and branched (yellow). PSDs (red) also vary in size and shape. Scale cube = 0.5 μm³. B. An example of a mushroom spine (blue) with a head diameter exceeding 0.6 microns and a narrow neck. C. An example of a thin spine (red) with a small head and narrow neck. D. An example of a stubby spine (green) with an equal head and neck diameter and an overall length that equals its width. E. An example of a branched spine (yellow) where both branches are thin spines. Scale bar = 0.5 μm and arrows indicate where the head and neck diameters were measured for each spine in B–E. F. A graph plotting the ratio of head diameters to neck diameters for the spines on the dendrite reconstructed in A. Mushroom spines (blue diamonds), stubby spines (green diamonds) and thin spines (red diamonds) segregated into distinct groups. Both branches of the branched spine were of a thin shape and are situated among the thin spine dimensions (yellow diamonds).