Differential dendritic Ca2+ signalling in young and mature hippocampal granule cells.
Neuronal activity is critically important for development and plasticity of dendrites, axons and synaptic connections. Although Ca(2+) is an important signal molecule for these processes, not much is known about the regulation of the dendritic Ca(2+) concentration in developing neurons. Here we used confocal Ca(2+) imaging to investigate dendritic Ca(2+) signalling in young and mature hippocampal granule cells, identified by the expression of the immature neuronal marker polysialated neural cell adhesion molecule (PSA-NCAM). Using the Ca(2+)-sensitive fluorescent dye OGB-5N, we found that both young and mature granule cells showed large action-potential evoked dendritic Ca(2+) transients with similar amplitude of approximately 200 nm, indicating active backpropagation of action potentials. However, the decay of the dendritic Ca(2+) concentration back to baseline values was substantially different with a decay time constant of 550 ms in young versus 130 ms in mature cells, leading to a more efficient temporal summation of Ca(2+) signals during theta-frequency stimulation in the young neurons. Comparison of the peak Ca(2+) concentration and the decay measured with different Ca(2+) indicators (OGB-5N, OGB-1) in the two populations of neurons revealed that the young cells had an approximately 3 times smaller endogenous Ca(2+)-binding ratio ( approximately 75 versus approximately 220) and an approximately 10 times slower Ca(2+) extrusion rate ( approximately 170 s(-1) versus approximately 1800 s(-1)). These data suggest that the large dendritic Ca(2+) signals due to low buffer capacity and slow extrusion rates in young granule cells may contribute to the activity-dependent growth and plasticity of dendrites and new synaptic connections. This will finally support differentiation and integration of young neurons into the hippocampal network.
Stocca
Gabriella
G
Physiologisches Institut, Universitat Freiburg, Hermann-Herder-Str. 7, D-79104 Freiburg, Germany.
Schmidt-Hieber
Christoph
C
Bischofberger
Josef
J
D000200:Action Potentials / Q000502:physiology*; D000375:Aging / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D003712:Dendrites / Q000502:physiology*; D006624:Hippocampus / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009473:Neuronal Plasticity / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology
D002118:Calcium