High resolution imaging of calcium dynamics in single spines of CA1 pyramidal neurons in the hippocampus

Whole-cell recordings and confocal fluorescence imaging were used to investigate the properties of intracellular Ca2+ dynamics in CA1 hippocampal pyramidal cells in acute slices.; We first measured the properties of Ca2+ entry during AP firing of a cell and synaptic stimulation. The back-propagation of a single AP into the dendrites caused [Ca2+]; to rise in dendrites and spines simultaneously and it invaded the whole dendritic tree. The measured synaptically evoked Ca2+ signals in individual spines were different depending on the intracellular solution. In K +-based solution, synaptic stimulation evoked a Ca2+ signal that was restricted to single spines (dendritic spread <2 microns). In Cs+-based solution, that blocks K+ conductances, there was always a much larger spread (>4 microns). This suggests an important role for K+ channels in regulating dendritic Ca2+ signals.; I also describe a result which gave us the first view of synaptic function at a single connection. In one experiment the recorded electrical responses was demonstrated to arise from a single optically identified synapse. The surprisingly high coefficient of variation of the recorded signals suggests that either vesicles have different neurotransmitter concentration or the synapse generates responses to multiple released vesicles.; We then investigated the role of Ca2+ entry during the pairing protocol for UP induction. We found that the post-synaptic depolarization required for LTP induction leads to a large maintained elevation of [Ca 2+]; in all spines due to VDCC activation; the [Ca2+]; elevation was greatly reduced by intracellular application of D890, a VDCC blocker. D890 almost completely blocked LTP, suggesting that Ca2+ entry through VDCC could be essential for LTP induction. The effect of D890 is not due to L-type Ca2+ channels, since a specific blocker of these channels did not affect LTP. When tested by Tom Soderling, high concentrations of D890 (IC-50 = 1mM) inhibited CaMKII, an enzyme whose activity is required for LTP induction. These results leave the role of VDCC in LTP induction uncertain and suggest caution using D890 as a tool in the study of LTP.