Imaging synaptic protein dynamics using photoactivatable green fluorescent protein

Considerable evidence has accumulated that structural changes in dendritic spines and their synapses are associated with adaptive functional changes in cortical circuits, such as during circuit refinement in young animals and in learning and memory in adults. Understanding the mechanisms of circuit plasticity requires detailed investigation of the structural dynamics of dendritic spines and how they are regulated by neural activity and sensory experience. Studying the dynamic localization of synaptic proteins in dendritic spines and how their stabilization and exchange rates influence spine structural plasticity is also important. This protocol describes imaging approaches to study synaptic protein dynamics in dendritic spines of the rodent cerebral cortex. It gives a strategy for generating photoactivatable green fluorescent protein (PA-GFP)-tagged synaptic proteins and in vitro and in vivo transfection methods for coexpression of these proteins with a spectrally separable cell-filling marker (DsRed-Express). Methods for tracking synaptic protein localization using photoactivation and time-lapse imaging of PA-GFP in spiny pyramidal neuron dendrites are given. A discussion of imaging hardware and software preferences is also included. The methods described here can be used to study the dynamic processes underlying spine synapse development during the formation and plasticity of neural circuits in the mammalian brain.