Postsynaptic calcium transients evoked by activation of individual hippocampal mossy fiber synapses.
Control of Ca(2+) within dendritic spines is critical for excitatory synaptic function and plasticity, but little is known about Ca(2+) dynamics at thorny excrescences, the complex spines on hippocampal CA3 pyramidal cells contacted by mossy fiber terminals of dentate granule cell axons. We have monitored subthreshold stimulus-dependent postsynaptic Ca(2+) transients in optically and ultrastructurally characterized complex spines and find that such spines can act as discrete units of Ca(2+) response. In contrast to the more common "simple" spines, synaptically evoked Ca(2+) transients at complex spines have only a small NMDA receptor-dependent component and do not involve release of calcium from internal stores. Instead, they result mainly from AMPA receptor-gated Ca(2+) influx through voltage-activated calcium channels on the spine; these channels provide graded amplification of the response of thorny excrescences to individual mossy fiber synaptic events.
Division of Neurophysiology, National Institute for Medical Research, London NW7 1AA, United Kingdom.
C A
CA
Reid
R
R
Fabian-Fine
A
A
Fine
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D015220:Calcium Channels / Q000502:physiology*; D004594:Electrophysiology; D008297:Male; D019599:Mossy Fibers, Hippocampal / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D017470:Receptors, Glutamate / Q000502:physiology; D013569:Synapses / Q000502:physiology*
D015220:Calcium Channels; D017470:Receptors, Glutamate