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Can calcium ion contribute to morphological plasticity of a spine?
BMC Neuroscience volume 9, Article number: P101 (2008)
Structural plasticity of a spine, which is a change in the spine morphology with synaptic stimulation, has been reported from several labs. Structural plasticity is thought to be a consequence of the induction of long-term potentiation. Some reports suggested the role of actin molecules in the structural plasticity, and the change in F-actin structure will play a pivotal role in the morphological change of a spine [1–4]. The structure of F-actin is controlled by complex mechanisms, and the molecular mechanisms which contribute to morphological plasticity of a spine are not understood yet. Here, we performed several simulations to see whether the intracellular calcium ion can trigger the structural plasticity of a spine. Simulation results have shown calcium could be a molecule triggering the morphological change of a spine. From these simulation results, we propose a hypothetical mechanism involved in the structural plasticity.
Morphological models including mushroom spines and filopodium with different size in head and neck diameter were constructed using A-Cell software [5, 6]. The 3D morphology was compartmentalized, and Ca2+ entry through NMDA receptors and medium- and low-affinity Ca2+ buffers were embedded to corresponding compartments. Ca2+ diffusion within a spine or filopodum was calculated using Fick's equation. Figure 1 shows the overall reaction schemes and the model morphology.
First we simulated the change in the concentration of intracellular calcium ion ([Ca2+]i) in filopodia. The peak [Ca2+]i was increased as the length of filopodium was increased as was expected (Fig. 2 left). However, it was saturated at the filopodium length longer than 1 μm and kept almost the same level. Next, the diameter of a spine head was changed with fixed length of spine neck. With the increase in the spine head diameter, the peak [Ca2+]i was decreased as was expected (Fig. 2 right). However, [Ca2+]i reached a minimum and it kept almost the same level even if the diameter was increased further.
The present simulation results have shown the change in [Ca2+]i with a change in the size of a filopodium and a spine. This suggests that [Ca2+]i can be a triggering molecule for the structural plasticity. The hypothetical mechanism is shown in Figure 3. First, calcium concentration in a localized region of a dendrite is increased forming a 'hot spot'. Second, actin polymerization begins at the 'hot spot' and the protrusion develops increasing the peak [Ca2+]i at its tip. Third, this increase in [Ca2+]i results in further actin polymerization and its bundling. Fourth, protrusion develops further and the peak [Ca2+]i increased. At some level of [Ca2+]i (threshold level), the actin structure at the tip of filopodium is changed from bundling to a meshwork forming a spine head.
Maletic-Savatic M, Malinow R, Svoboda K: Rapid dendritic morphogenesis in CA1 hippocampal dendrites induced by synaptic activity. Science. 1999, 283: 1923-1927. 10.1126/science.283.5409.1923.
Matsuzaki M, Honkura N, Ellis-Davies GC, Kasai H: Structural basis of long-term potentiation in single dendritic spines. Nature. 2004, 429: 761-766. 10.1038/nature02617.
Fukazawa Y, Fukazawa Y, Saitoh Y, Ozawa F, Ohta Y, Mizuno K, Inokuchi K: Hippocampal LTP is accompanied by enhanced F-actin content within the dendritic spine that is essential for late LTP maintenance in vivo. Neuron. 2003, 38: 447-460. 10.1016/S0896-6273(03)00206-X.
Okamoto K, Nagai T, Miyawaki A, Hayashi Y: Rapid and persistent modulation of actin dynamics regulates postsynaptic reorganization underlying bidirectional plasticity. Nat Neurosci. 2004, 7: 1104-1112. 10.1038/nn1311.
Ichikawa K: A Modeling Environment with Three-Dimensional Morphology, A-Cell-3D, and Ca2+ Dynamics in a Spine. Neuroinformatics. 2005, 3: 49-64. 10.1385/NI:3:1:049.
Ichikawa K: A-Cell: graphical user interface for the construction of biochemical reaction models. Bioinformatics. 2001, 17: 483-484. 10.1093/bioinformatics/17.5.483.
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Nozawa, K., Ichikawa, K. Can calcium ion contribute to morphological plasticity of a spine?. BMC Neurosci 9, P101 (2008) doi:10.1186/1471-2202-9-S1-P101
- Actin Polymerization
- Structural Plasticity
- Head Diameter
- Morphological Plasticity
- Present Simulation Result