Dendritic spines as individual neuronal compartments for synaptic Ca2+ responses

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Abstract
THE possibility that postsynaptic spines on neuronal dendrites are discrete biochemical compartments for Ca2+-activated processes involved in synaptic plasticity1–6 is a widely proposed concept that has eluded experimental demonstration. Using microfluorometry on CA3 neurons in hippocampal slices, we show here that with weak presynaptic stimulation of associative/commissural fibres, Ca2+ accumulates in single postsynaptic spines but not in the parent dendrite. Stronger stimulation also promotes changes in dendrites. The NMDA-receptor antagonist AP-5 blocks changes in Ca2+ in spines. Sustained steep Ca2+gradients between single spines and the parent dendrite, often lasting several minutes, develop with repeated stimulation. The observed compartmentalization allows for the specificity7,8, cooperativity9 and associativity10–14 displayed by memory models such as long-term potentiation.