The dynamics of free calcium in dendritic spines in response to repetitive synaptic input.
Increased levels of intracellular calcium at either pre- or postsynaptic sites are thought to precede changes in synaptic strength. Thus, to induce long-term potentiation in the hippocampus, periods of intense synaptic stimulation would have to transiently raise the levels of cytosolic calcium at postsynaptic sites--dendritic spines in the majority of cases. Since direct experimental verification of this hypothesis is not possible at present, calcium levels have been studied by numerically solving the appropriate electro-diffusion equations for two different postsynaptic structures. Under the assumption that voltage-dependent calcium channels are present on dendritic spines, free intracellular calcium in spines can reach micromolar levels after as few as seven spikes in 20 milliseconds. Moreover, a short, but high-frequency, burst of presynaptic activity is more effective in raising levels of calcium and especially of the calcium-calmodulin complex than sustained low-frequency activity. This behavior is different from that seen at the soma of a typical vertebrate neuron.
D000200:Action Potentials; D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002540:Cerebral Cortex / Q000502:physiology; D003712:Dendrites / Q000378:metabolism* / Q000502:physiology; D005728:Ganglia, Sympathetic / Q000502:physiology; D007700:Kinetics; D008564:Membrane Potentials; D008959:Models, Neurological; D009473:Neuronal Plasticity; D011892:Rana catesbeiana; D013569:Synapses / Q000502:physiology*
D002118:Calcium