@article {3931, title = {Functional imaging of hippocampal place cells at cellular resolution during virtual navigation.}, journal = {Nature Neuroscience}, volume = {13}, year = {2010}, month = {2010 Nov}, pages = {1433-40}, abstract = {

Spatial navigation is often used as a behavioral task in studies of the neuronal circuits that underlie cognition, learning and memory in rodents. The combination of in vivo microscopy with genetically encoded indicators has provided an important new tool for studying neuronal circuits, but has been technically difficult to apply during navigation. Here we describe methods for imaging the activity of neurons in the CA1 region of the hippocampus with subcellular resolution in behaving mice. Neurons that expressed the genetically encoded calcium indicator GCaMP3 were imaged through a chronic hippocampal window. Head-restrained mice performed spatial behaviors in a setup combining a virtual reality system and a custom-built two-photon microscope. We optically identified populations of place cells and determined the correlation between the location of their place fields in the virtual environment and their anatomical location in the local circuit. The combination of virtual reality and high-resolution functional imaging should allow a new generation of studies to investigate neuronal circuit dynamics during behavior.

}, keywords = {Action Potentials, Animals, Calcium, Cerebral Cortex, Computer-Assisted, Dendrites, Genetic, Hippocampus, Image Processing, Inbred C57BL, Male, Membrane Potentials, Mice, Neurons, Nonlinear Dynamics, Patch-Clamp Techniques, Space Perception, Spatial Behavior, Synapsins, Transduction, User-Computer Interface}, issn = {1546-1726}, doi = {10.1038/nn.2648}, author = {Dombeck, Daniel A and Harvey, Christopher D and Tian, Lin and Looger, Loren L and Tank, David W} } @article {4254, title = {A genetically encoded fluorescent sensor of ERK activity.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {105}, year = {2008}, month = {2008 Dec 9}, pages = {19264-9}, abstract = {

The activity of the ERK has complex spatial and temporal dynamics that are important for the specificity of downstream effects. However, current biochemical techniques do not allow for the measurement of ERK signaling with fine spatiotemporal resolution. We developed a genetically encoded, FRET-based sensor of ERK activity (the extracellular signal-regulated kinase activity reporter, EKAR), optimized for signal-to-noise ratio and fluorescence lifetime imaging. EKAR selectively and reversibly reported ERK activation in HEK293 cells after epidermal growth factor stimulation. EKAR signals were correlated with ERK phosphorylation, required ERK activity, and did not report the activities of JNK or p38. EKAR reported ERK activation in the dendrites and nucleus of hippocampal pyramidal neurons in brain slices after theta-burst stimuli or trains of back-propagating action potentials. EKAR therefore permits the measurement of spatiotemporal ERK signaling dynamics in living cells, including in neuronal compartments in intact tissues.

}, keywords = {Action Potentials, Animals, Artifacts, Bacterial Proteins, Cell Line, Dendrites, Endothelial Cells, Enzyme Activation, Extracellular Signal-Regulated MAP Kinases, Fluorescence Resonance Energy Transfer, Fluorescent Dyes, Genes, Green Fluorescent Proteins, Hippocampus, Humans, Kidney, Luminescent Proteins, MAP Kinase Signaling System, Organ Culture Techniques, Patch-Clamp Techniques, Pyramidal Cells, Rats, Reporter}, issn = {1091-6490}, doi = {10.1073/pnas.0804598105}, author = {Harvey, Christopher D and Ehrhardt, Anka G and Cellurale, Cristina and Zhong, Haining and Yasuda, Ryohei and Davis, Roger J and Svoboda, Karel} } @article {5213, title = {The spread of Ras activity triggered by activation of a single dendritic spine.}, journal = {Science}, volume = {321}, year = {2008}, month = {2008 Jul 4}, pages = {136-40}, abstract = {

In neurons, individual dendritic spines isolate N-methyl-d-aspartate (NMDA) receptor-mediated calcium ion (Ca2+) accumulations from the dendrite and other spines. However, the extent to which spines compartmentalize signaling events downstream of Ca2+ influx is not known. We combined two-photon fluorescence lifetime imaging with two-photon glutamate uncaging to image the activity of the small guanosine triphosphatase Ras after NMDA receptor activation at individual spines. Induction of long-term potentiation (LTP) triggered robust Ca2+-dependent Ras activation in single spines that decayed in approximately 5 minutes. Ras activity spread over approximately 10 micrometers of dendrite and invaded neighboring spines by diffusion. The spread of Ras-dependent signaling was necessary for the local regulation of the threshold for LTP induction. Thus, Ca2+-dependent synaptic signals can spread to couple multiple synapses on short stretches of dendrite.

}, keywords = {Animals, Calcium, Cell Membrane, Dendritic Spines, Diffusion, Fluorescence Resonance Energy Transfer, Glutamic Acid, GTPase-Activating Proteins, Guanine Nucleotide Exchange Factors, Hippocampus, Long-Term Potentiation, N-Methyl-D-Aspartate, Pyramidal Cells, ras Proteins, Rats, Receptors, Recombinant Fusion Proteins, Signal Transduction, Synapses, Transfection}, issn = {1095-9203}, doi = {10.1126/science.1159675}, author = {Harvey, Christopher D and Yasuda, Ryohei and Zhong, Haining and Svoboda, Karel} } @article {4222, title = {Locally dynamic synaptic learning rules in pyramidal neuron dendrites.}, journal = {Nature}, volume = {450}, year = {2007}, month = {2007 Dec 20}, pages = {1195-200}, abstract = {

Long-term potentiation (LTP) of synaptic transmission underlies aspects of learning and memory. LTP is input-specific at the level of individual synapses, but neural network models predict interactions between plasticity at nearby synapses. Here we show in mouse hippocampal pyramidal cells that LTP at individual synapses reduces the threshold for potentiation at neighbouring synapses. After input-specific LTP induction by two-photon glutamate uncaging or by synaptic stimulation, subthreshold stimuli, which by themselves were too weak to trigger LTP, caused robust LTP and spine enlargement at neighbouring spines. Furthermore, LTP induction broadened the presynaptic-postsynaptic spike interval for spike-timing-dependent LTP within a dendritic neighbourhood. The reduction in the threshold for LTP induction lasted approximately 10 min and spread over approximately 10 microm of dendrite. These local interactions between neighbouring synapses support clustered plasticity models of memory storage and could allow for the binding of behaviourally linked information on the same dendritic branch.

}, keywords = {Animals, Dendrites, Excitatory Postsynaptic Potentials, Glutamic Acid, Learning, Long-Term Potentiation, Mice, Models, Neurological, Pyramidal Cells, Synapses}, issn = {1476-4687}, doi = {10.1038/nature06416}, author = {Harvey, Christopher D and Svoboda, Karel} }