It is commonly accepted that structure and molecular composition of the spine change with the input received but the exact dynamics of those changes at a single spine in a small time frame have not been shown until recent experiments combining two-photon imaging and glutamate uncaging stimulation. These experiments show an absence of changes in postsynaptic density (PSD) protein trafficking and concentration in the early stages after long term potentiation (LTP). However a validation of those observations with a high spatial resolution is absolutely necessary. We have tried to confirm these findings with the combination of a precise (temporal and spatially) paradigm of stimulation and a method to track the structural changes with electron microscopy (EM) resolution at a single spine level. We have imaged CA1 pyramidal neurons in organotypic slices and analyzed stimulated spines 1, 7 and 30 minutes after LTP induction, using two-photon microscopy to visualize, elicit LTP with glutamate-uncaging and photo-generate landmarks to pinpoint the stimulated spines for further study with EM serial reconstruction. We have developed a reliable method to locate a specific spine which enables us to reconstruct and analyze volume and surface areas of the head and neck as well as the PSD and other form factors like the sphericity from stimulated spines. Compared to non-stimulated spines, the overall volume of the LTP-induced spine increased, with the highest increment in the 1 minute potentiated group while the PSD apparently did not show any significant change of its area. The increase in volume seemed to be due to an overall build up and not an abnormal enlargement of a specific part or increase in length of the spine. The surface complexity measured as a ratio between the surface area and volume of a given structure did not change as the surface area increased accordingly with the volume. These results suggest that the structural plasticity in the whole spine and the PSD are independently regulated :

Society for Neuroscience Abstract, 2009.