Imaging dendritic spine structural plasticity during development in vitro and after acute stroke in vivo

The plasticity of dendritic spine structure is important for neural development and synaptic function and is altered in many pathological conditions. In this study, we investigated the mechanisms underlying spine structural plasticity during development and the pathological changes in spine structure during ischemic stroke by using confocal and two-photon microscopy. We first investigated spine structural dynamics during development and the role of intracellular Ca²⁺ in determining basal spine motility in cultured hippocampal neurons. We found that young cultured neurons displayed significantly more spine motility than older neurons. In addition, we found that global buffering of intracellular Ca²⁺ failed to alter the basal motility of developing spines. Thus basal spine motility may represent an intrinsic feature of developing neurons and is not necessarily choreographed by ongoing changes in intracellular Ca²⁺ levels. We then examined spine structure changes during cerebral ischemia in vivo and investigated the relationships between cortical microcirculation and spine structure and function. We found moderate ischemia did not significantly affect spines within a 5-h time span; however, severe ischemia caused a rapid loss of spines and induced beading of dendrite structure within as little as 10 min following stroke. Surprisingly this damage was found to be reversible if reperfusion occurred within 20-60 min. By monitoring both cortical microcirculation and dendritic spine structure, we found that dendritic integrity deteriorated proportionally with the fraction of blocked vessels and the volume of affected brain during stroke. In ischemic border regions, we demonstrated that intact dendritic structure could be stably maintained for hours by blood flow from vessels that were on average 81 μm away. Functional imaging of intrinsic optical signals indicated that signal changes induced by limb movement were blocked in areas with blebbed dendrites, but were present at ~225 μm and beyond from the border of dendritic damage, suggesting peri-infarct tissues could function under acute ischemia in the core. In summary, our findings indicate that basal spine motility is maintained in a Ca²⁺ independent manner, and changes in spine structure during ischemia can now be directly linked to alterations in synaptic function and reductions in the cortical microcirculation.Medicine, Faculty ofGraduat