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Published on: June 5, 2017
Coincidence Detection within the Excitable Rat Olfactory Bulb Granule Cell Spines
S Sara Aghvami1,2, Max Müller2, Babak N Araabi1
1School of Electrical and Computer Engineering, University of Tehran, 14395-515 Tehran, Iran, and.
In olfactory bulb granule cells, coincident local synaptic input and global action potentials cause sublinear calcium (Ca2+) summation due to voltage-gated sodium channels in the spine head.
Area of Science:
- Neuroscience
- Cellular Neuroscience
- Computational Neuroscience
Background:
- Mammalian olfactory bulb granule cells (GCs) possess reciprocal synapses with mitral and tufted cells.
- GCs exhibit excitable spines capable of generating local action potentials (APs) or 'spine spikes'.
- GCs can also fire global APs that propagate dendritically, influencing synaptic integration.
Purpose of the Study:
- To investigate the summation rules of local spine Ca2+ entry and global APs in GC dendrites.
- To elucidate the role of voltage-gated channels and temporal dynamics in synaptic integration.
- To validate computational models with experimental data in rat olfactory bulb slices.
Main Methods:
- Developed a compartmental GC model to simulate Ca2+ summation under varying temporal separations (Δt) of local and global signals.
- Experimentally validated simulations using two-photon glutamate uncaging at spines and somatic current injection to evoke APs.
- Imaged spine Ca2+ signals in acute slices of juvenile rat brain (both sexes).
Main Results:
- Simulations revealed strongly sublinear Ca2+ summation for coincident (Δt = 0 ms) local and global signals, with efficiency rising for non-coincident inputs.
- Sublinear summation at coincidence depends on voltage-gated Na+ channels in the spine head, not NMDARs.
- Experimental data confirmed simulated summation efficiency and showed that synaptically evoked global APs and EPSPs occur at Δt ≈ 10 ms, explaining observed linear summation.
Conclusions:
- GC spine Ca2+ signaling exhibits sublinear summation for coincident local and global inputs due to spine head voltage-gated Na+ channels.
- The temporal dynamics of GC activation explain the integration of synaptic inputs and global APs.
- Findings support the existence and functional significance of the GC spine spike mechanism in olfactory processing.
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