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PreprintDendritic signals from rat hippocampal CA1 pyramidal neurons during coincident pre- and post-synaptic activity : a combined voltage- and calcium-imaging study( 2006-11-16) Canepari, Marco ; Djurisic, Maja ; Zecevic, DejanThe non-linear and spatially inhomogeneous interactions of dendritic membrane potential signals that represent the first step in the induction of activity dependent long-term synaptic plasticity are not fully understood, particularly in dendritic regions which are beyond the reach of electrode measurements. We combined voltage-sensitive-dye recordings and Ca2+-imaging of hippocampal CA1 pyramidal neurons to study large regions of the dendritic arbor, including branches of small diameter (distal apical and oblique dendrites). Dendritic membrane potential transients were monitored at high spatial resolution and correlated with supra-linear [Ca2+]i changes during one cycle of a repetitive patterned stimulation protocol that typically results in the induction of long-term potentiation (LTP). While the increase in the peak membrane depolarization during coincident pre- and post-synaptic activity was required for the induction of supra-linear [Ca2+]i-signals shown to be necessary for LTP, the change in the baseline-to-peak amplitude of the backpropagating dendritic action potential (bAP) was not critical in this process. At different dendritic locations, the baseline-to-peak amplitude of the bAP could be either increased, decreased or unaltered at sites where EPSP-AP pairing evoked supra-linear summation of [Ca2+]i-transients. We suggest that modulations in the bAP baseline-to- peak amplitude by local EPSPs act as a mechanism that brings the membrane potential into the optimal range for Ca2+-influx through NMDA receptors (0 to -15 mV); this may require either boosting or the reduction of the bAP, depending on the initial size of both signals.
ArticleVoltage imaging from dendrites of mitral cells : EPSP attenuation and spike trigger zones(Society for Neuroscience, 2004-07-28) Djurisic, Maja ; Antic, Srdjan ; Chen, Wei R. ; Zecevic, DejanTo obtain a more complete description of individual neurons, it is necessary to complement the electrical patch pipette measurements with technologies that permit a massive parallel recording from many sites on neuronal processes. This can be achieved by using voltage imaging with intracellular dyes. With this approach, we investigated the functional structure of a mitral cell, the principal output neuron in the rat olfactory bulb. The most significant finding concerns the characteristics of EPSPs at the synaptic sites and surprisingly small attenuation along the trunk of the primary dendrite. Also, the experiments were performed to determine the number, location, and stability of spike trigger zones, the excitability of terminal dendritic branches, and the pattern and nature of spike initiation and propagation in the primary and secondary dendrites. The results show that optical data can be used to deduce the amplitude and shape of the EPSPs evoked by olfactory nerve stimulation at the site of origin (glomerular tuft) and to determine its attenuation along the entire length of the primary dendrite. This attenuation corresponds to an unusually large mean apparent "length constant" of the primary dendrite. Furthermore, the images of spike trigger zones showed that an action potential can be initiated in three different compartments of the mitral cell: the soma-axon region, the primary dendrite trunk, and the terminal dendritic tuft, which appears to be fully excitable. Finally, secondary dendrites clearly support the active propagation of action potentials
ArticleFunctional structure of the mitral cell dendritic tuft in the rat olfactory bulb(Society for Neuroscience, 2008-04-09) Djurisic, Maja ; Popovic, Marko ; Carnevale, Nicholas ; Zecevic, DejanThe input–output transform performed by mitral cells, the principal projection neurons of the olfactory bulb, is one of the key factors in understanding olfaction. We used combined calcium and voltage imaging from the same neuron and computer modeling to investigate signal processing in the mitral cells, focusing on the glomerular dendritic tuft. The main finding was that the dendritic tuft functions as a single electrical compartment for subthreshold signals within the range of amplitudes detectable by voltage-sensitive dye recording. These evoked EPSPs had uniform characteristics throughout the glomerular tuft. The Ca2+ transients associated with spatially uniform subthreshold synaptic potentials were comparable but not equal in amplitude in all regions. The average range of normalized amplitudes of the EPSP-driven Ca2+ signals from different locations on dendritic branches in the glomerular tuft was relatively narrow and appeared to be independent of the dendritic surface-to-volume ratio. The computer simulations constrained by the imaging data indicated that a synchronized activation of ~100 synapses randomly distributed on tuft branches was sufficient to generate spatially homogenous EPSPs. This number of activated synapses is consistent with the data from anatomical studies. Furthermore, voltage attenuation of the EPSP along the primary dendrite at physiological temperature was weak compared with other cell types. In the model, weak attenuation of the EPSP along the primary dendrite could be accounted for by passive electrical properties of the mitral cell.