A model of dendritic spine Ca2+ concentration exploring possible bases for a sliding synaptic modification threshold.
We used a biophysical model of an isolated dendritic spine to assess quantitatively the impact of changes in spine geometry, Ca2+ buffer concentration, and channel kinetics on Ca2+ dynamics following high-frequency activation of N-methyl-D-aspartate receptors. We found that varying the buffer concentration in the postsynaptic density from 50 to 500 microM can result in an 8-fold difference in the peak Ca2+ concentration following three pulses at 100 Hz. Similarly, varying the spine neck diameter from 0.1 to 0.55 micron can result in a 15-fold difference in the peak Ca2+ concentration. The amplification of peak Ca2+ concentration also depended on temporal summation of N-methyl-D-aspartate-mediated excitatory postsynaptic currents. Variation of the current duration on the order of 100 msec can significantly affect summation at a given stimulation frequency, resulting in a 10-fold difference in the peak Ca2+ concentration at 100 Hz. It is suggested that activity-dependent modifications of these parameters may be important for the regulation of synaptic plasticity in the brain.
Gold
J I
JI
Department of Neuroscience, Brown University, Providence, RI 02912.
Bear
M F
MF
D002118:Calcium / Q000502:physiology*; D003712:Dendrites / Q000502:physiology* / Q000648:ultrastructure; D017774:Long-Term Potentiation; D008962:Models, Theoretical; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology*
D016194:Receptors, N-Methyl-D-Aspartate; D002118:Calcium