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. 2018 Oct 25;7:e38588. doi: 10.7554/eLife.38588

Figure 1. Spiny Projection Neuron model reproduces electrophysiology and calcium imaging data.

(A) Model schematic of morphology (left) and calcium dynamics in spine and dendrite (right). Characteristic morphology with dendritic spines is based on estimated values from morphological reconstructions, including tapered dendrites. The model contains ionic and synaptic channels (not depicted). Right: a single spine and parent dendritic compartment showing axial diffusion layers in the spine head and neck and radial diffusion shells in the dendrite. The model includes sophisticated Ca dynamics (red circles indicate calcium ions): diffusion (green arrows), buffers (blue squares - calmodulin, calbindin, fixed buffer; reversible reaction with calcium indicated by black reaction arrows), pump extrusion (purple arrows), and influx via voltage-gated calcium channels (VGCCs; orange arrows) and synaptic (NMDA/AMPA) channels (blue arrows). (B) Model exhibits similar response to electrophysiological current injection steps, including characteristic sag following hyperpolarizing current, latency to first action potential, firing rate, and AHP shape (Nisenbaum and Wilson, 1995). (C) Model calcium dynamics (red) are consistent with experiments (blue) for dendritic calcium (left) vs. distance from soma in response to a back-propagating action potential (bAP) and for spine calcium (right) in response to a bAP or synaptic stimulation (EPSP). Legend entries refer to published experimental calcium imaging data; D1 or D2 refers to dopamine receptor expression of identified SPNs: (Day et al., 2008; Kerr and Plenz, 2002; Shindou et al., 2011). Figure 1—figure supplement 1 shows peak spine calcium sensitivity to parameter variations; Figure 1—figure supplement 2 shows the fate of calcium entering a spine during an EPSP.

Figure 1.

Figure 1—figure supplement 1. Parameter sensitivity for peak spine calcium concentration in response to a single bAP or EPSP.

Figure 1—figure supplement 1.

Model parameters listed in the left column were varied by ±10% during simulation of one back-propagating action potential (bAP – left) or synaptic stimulation of one spine (one EPSP – right). The amount that each parameter variation changed peak spine calcium concentration is plotted on the x axis with respect to the control (zero change) peak spine calcium. For a bAP, a 20 nM change is 10% of the control, and for an EPSP, a 75 nM change is 30% of control; these values fall within the reported experimental variance (Shindou et al., 2011). Parameters are ordered by type of mechanism: ligand-gated channels; inward currents through voltage-gated calcium or sodium channels; outward currents through potassium channels; calcium dynamics; and spine neck resistance (neckRA).
Figure 1—figure supplement 2. Fate of calcium entering a spine during an EPSP.

Figure 1—figure supplement 2.

The quantity of free calcium, buffer bound calcium, calcium extruded by pumps, and calcium that diffuses out of a dendritic spine head is shown for the first 100 ms following synaptic stimulation, to facilitate comparison with Bartol et al.(2015).