2th Meeting of the German Society for Cell Biology,
26. - 28.09.1997, Jena.
Calcium signals during LTP-induction
T. Jäger, T. Behnisch and K.G. Reymann
Long-term potentiation (LTP) is believed to be a cellular experimental model for learning and memory. It is known for several years, that changes in the intracellular calcium concentration ([Ca2+]i) play an important role in the induction of LTP of Schaffer-collateral-CA1 synapses. However, the kinetics of [Ca2+]i changes, necessary for the potentiation of excitatory postsynaptic potentials have still not been systematically investigated. Several tetanization paradigms, differing in their stimulation strength and duration can induce changes in synaptic plasticity with different durations. This could be explained by the involvement of different Ca2+ sources or the different amount of Ca2+ released in response to the employed tetanization.
The aim of our study was to investigate the Ca2+ responses on different tetanization paradigms in CA1 hippocampal pyramidal neurons of rat brain slices, whilst simultaneously recording their electrical activity. For confocal microscopy imaging of [Ca2+]i rises single pyramidal neurons were intracellularly loaded with the Ca2+-sensitive fluorescence indicator Calcium Green-1 (2 mM). The fluorescence intensities were determined over time and, after background correction, normalised to the fluorescence intensity before tetanization (F/Fo). Different 100 Hz tetanizations (interval of tetanisation: 2 min) with a train-duration in the range of 200 ms to 1 s on single, double or triple stimulation strengths (0.1 ms, 0.2 ms and 0.3 ms pulse width, respectively) evoked a Ca2+ response with a respective increase in the fluorescence. The fluorescence intensity reached its maximum at triple stimulation strength independent from the train duration. For example, a triple 200 ms / 100 Hz tetanization evoked in comparison to a single 200 ms / 100 Hz tetanization a 8-fold increase of the fluorescence maximum which was the same as with 400 ms and 1 s tetanizations. The train duration of 200 ms, 400 ms and 1 s using triple stimulation strength caused a prolonged fluorescence signal which after tetanisation reached baseline level 2 s, 4 s and 6 s later, respectively. Our data prove that the Ca2+ response is correlated in a linear manner both to the tetanization strength and the train duration. This variable Ca2+ response might be responsible for the modification of the activity of second messenger cascades necessary in different phases or forms of LTP.
This work was supported by DFG (SFB 426).
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