25th Goettingen Neurobiology Conference
22nd to 25th May 1997, Goettingen, Germany.
Rise of the intracellular Ca2+ concentration in response
to different tetanization paradigms in dendrites of
hippocampas CA1 neurons
T. Jäger, T. Behnisch and K.G. Reymann
Changes in the intracellular calcium concentration ([Ca2+]i) during high frequency stimulation
play an important role in the induction of long-term potentiation (LTP) of Schaffer-collateral-CA1
synapses. However, the kinetics of the [Ca2+]i change necessary for the potentiation of the excitatory
postsynaptic potentials (EPSPs) has still not been systematically investigated. Several tetanization
paradigms, differing in stimulus strength and duration of the applied train can induce plasticity
changes of different durations. This could be explained by the dependence of the involved Ca2+
sources and the dynamics of their transients from the tetanization strength. Thus, LTP induced by a
200 Hz train for 1 s seems to be associated with the coactivation of voltage dependent calcium
channels with N-methyl-D-aspartate receptor channels. In contrast, LTP induced by a single
tetanization (100 Hz for 200 ms) required an additional release of calcium from internal IP3-sensitive
Ca2+ stores.
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
electrical activity. For confocal microscopy imaging of [Ca2+]i, rises single pyramidal neurons were
intracellularly loaded with the Ca2+-sensitive fluorescent indicator Calcium Green-1 (2 mM). Various
tetanizations were applied to one neuron with a 2 min interval, and both the changes in the
fluorescence emission and the induced depolarization was recorded. For analysis of the occurred
fluorescence response, regions of interest on dendrites were chosen. The fluorescent intensities of
these regions were determined over time and after background correction, normalised to the
corrected fluorescence intensity before tetanization (F/Fo).
Different 100 Hz tetanizations with a train-duration in the range of 200 ms to 1 s on single,
double or triple stimulation strengths evoked a calcium response with a respective increase in the
fluorescence. The fluorescence 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 with 400 ms and 1 s trains. 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 & 6 s later respectively.
Our data suggests that the Ca2+ response is dependent both upon the tetanization strength and
the train duration. This variable calcium response might be responsible for the modification of the
activity of various second messenger cascades involved in different phases or forms of LTP.
This work was supported by DFG (SFB 426).
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