@article {2126, title = {Associative pairing enhances action potential back-propagation in radial oblique branches of CA1 pyramidal neurons.}, journal = {The Journal of Physiology}, volume = {580}, year = {2007}, month = {2007 May 1}, pages = {787-800}, abstract = {

Back-propagating action potentials (bAPs) are involved in associative synaptic plasticity and the modulation of dendritic excitability. We have used high-speed confocal and two-photon imaging to measure calcium and voltage signals associated with action potential propagation into oblique branches of CA1 pyramidal neurons in adult hippocampal slices. The spatial profile of the bAP-associated Ca(2+) influx was biphasic, with an initial increase in the proximity of the branch point followed by a progressive decrease. Voltage imaging in the branches showed that bAP amplitude was initially constant and then steadily declined with distance from the soma. To determine the role of transient K(+) channels in this profile, we used external Ba(2+) (150 microm) as a channel blocker, after characterizing its effect on A-type K(+) channels in the apical trunk. Bath application of Ba(2+) significantly reduced the A-type K(+) current in outside-out patches and nearly eliminated the distance-dependent decrease in bAP amplitude and its associated Ca(2+) signal. Finally, small amplitude bAPs at more distal oblique branch locations could be boosted by simultaneous branch depolarization, such that the paired Ca(2+) signal became nearly the same for proximal and distal oblique dendrites. These data suggest that dendritic K(+) channels regulate the amplitude of bAPs to create a dendritic Ca(2+) signal whose magnitude is inversely related to the electrotonic distance from the soma when bAPs are not associated with a significant amount of localized synaptic input. This distance-dependent Ca(2+) signal from bAPs, however, can be amplified and a strong associative signal is produced once the proper correlation between synaptic activation and AP output is achieved. We hypothesize that these two signals may be involved in the regulation of the expression and activity of dendritic voltage- and ligand-gated ion channels.

}, keywords = {Action Potentials, Animals, Barium, Calcium, Dendrites, Hippocampus, Knockout, Male, Mice, Neuronal Plasticity, Potassium Channel Blockers, Potassium Channels, Pyramidal Cells, Rats, Sprague-Dawley, Synapses}, issn = {0022-3751}, doi = {10.1002/cbic.201000254}, author = {Gasparini, Sonia and Losonczy, Attila and Chen, Xixi and Johnston, Daniel and Magee, Jeffrey C} } @article {2128, title = {State-dependent dendritic computation in hippocampal CA1 pyramidal neurons.}, journal = {The Journal of Neuroscience: The Official Journal of the Society for Neuroscience}, volume = {26}, year = {2006}, month = {2006 Feb 15}, pages = {2088-100}, abstract = {

Depending on the behavioral state, hippocampal CA1 pyramidal neurons receive very distinct patterns of synaptic input and likewise produce very different output patterns. We have used simultaneous dendritic and somatic recordings and multisite glutamate uncaging to investigate the relationship between synaptic input pattern, the form of dendritic integration, and action potential output in CA1 neurons. We found that when synaptic input arrives asynchronously or highly distributed in space, the dendritic arbor performs a linear integration that allows the action potential rate and timing to vary as a function of the quantity of the input. In contrast, when synaptic input arrives synchronously and spatially clustered, the dendritic compartment receiving the clustered input produces a highly nonlinear integration that leads to an action potential output that is extraordinarily precise and invariant. We also present evidence that both of these forms of information processing may be independently engaged during the two distinct behavioral states of the hippocampus such that individual CA1 pyramidal neurons could perform two different state-dependent computations: input strength encoding during theta states and feature detection during sharp waves.

}, keywords = {alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid, Animals, Dendrites, Excitatory Postsynaptic Potentials, Glutamic Acid, Hippocampus, Patch-Clamp Techniques, Pyramidal Cells, Rats, Sprague-Dawley, Synapses, Tetrodotoxin}, issn = {1529-2401}, doi = {10.1002/cbic.201000254}, author = {Gasparini, Sonia and Magee, Jeffrey C} } @article {2133, title = {On the initiation and propagation of dendritic spikes in CA1 pyramidal neurons.}, journal = {The Journal of Neuroscience: The Official Journal of the Society for Neuroscience}, volume = {24}, year = {2004}, month = {2004 Dec 8}, pages = {11046-56}, abstract = {

Under certain conditions, regenerative voltage spikes can be initiated locally in the dendrites of CA1 pyramidal neurons. These are interesting events that could potentially provide neurons with additional computational abilities. Using whole-cell dendritic recordings from the distal apical trunk and proximal tuft regions and realistic computer modeling, we have determined that highly synchronized and moderately clustered inputs are required for dendritic spike initiation: approximately 50 synaptic inputs spread over 100 mum of the apical trunk/tuft need to be activated within 3 msec. Dendritic spikes are characterized by a more depolarized voltage threshold than at the soma [-48 +/- 1 mV (n = 30) vs -56 +/- 1 mV (n = 7), respectively] and are mainly generated and shaped by dendritic Na+ and K+ currents. The relative contribution of AMPA and NMDA currents is also important in determining the actual spatiotemporal requirements for dendritic spike initiation. Once initiated, dendritic spikes can easily reach the soma, but their propagation is only moderately strong, so that it can be modulated by physiologically relevant factors such as changes in the V(m) and the ionic composition of the extracellular solution. With effective spike propagation, an extremely short-latency neuronal output is produced for greatly reduced input levels. Therefore, dendritic spikes function as efficient detectors of specific input patterns, ensuring that the neuronal response to high levels of input synchrony is a precisely timed action potential output.

}, keywords = {Action Potentials, AMPA, Animals, Dendrites, Electrodes, Excitatory Postsynaptic Potentials, Ion Channels, Models, N-Methyl-D-Aspartate, Neurological, Pyramidal Cells, Rats, Receptors, Sprague-Dawley}, issn = {1529-2401}, doi = {10.1002/cbic.201000254}, author = {Gasparini, Sonia and Migliore, Michele and Magee, Jeffrey C} } @article {2142, title = {Phosphorylation-dependent differences in the activation properties of distal and proximal dendritic Na+ channels in rat CA1 hippocampal neurons.}, journal = {The Journal of Physiology}, volume = {541}, year = {2002}, month = {2002 Jun 15}, pages = {665-72}, abstract = {

{At distal dendritic locations, the threshold for action potential generation is higher and the amplitude of back-propagating spikes is decreased. To study whether these characteristics depend upon Na+ channels, their voltage-dependent properties at proximal and distal dendritic locations were compared in CA1 hippocampal neurons. Distal Na+ channels activated at more hyperpolarized voltages than proximal (half-activation voltages were -20.4 +/- 2.4 mV vs. -12.0 +/- 1.7 mV for distal and proximal patches, respectively

}, keywords = {Algorithms, Animals, Axons, Dendrites, Electrophysiology, Enzyme Inhibitors, Hippocampus, Membrane Potentials, Neurons, Patch-Clamp Techniques, Phosphorylation, Protein Kinase Inhibitors, Rats, Sodium Channels, Sprague-Dawley, Staurosporine}, issn = {0022-3751}, doi = {10.1002/cbic.201000254}, author = {Gasparini, Sonia and Magee, Jeffrey C} }