ANALYSIS OF THE TETANIC AND POSTTETANIC COMPONENTS OF INTRADENDRITIC CA2+ SIGNALS IN HIPPOCAMPAL CA1 NEURONS

The importance of both the activation of second messenger cascades and an increase of the intracellular Ca2+ concentration for the induction of synaptic plasticity in hippocampal CA1 neurons is well established . Using the dye Calcium Green-1, we analysed the Ca2+ increases evoked by different 100-Hz tetanization paradigms commonly used tu induce lo ng-term potentiation. We found that the normalized total area of fluor escence intensity changes (F/F-0) was correlated with both the strengt h and the duration of tetanization. Furthermore, the normalized area o f fluorescence intensity changes during the time of tetanization (teta nic component) correlated strongly in a linear manner with the tetaniz ation duration. Moreover, the tetanic component strongly determined th e area of the post tetanic Ca2+ signal. Interestingly, the normalized relationship of the post-tetanic Ca2+ signal to the total Ca2+ change decreased with prolonged tetanizations. In contrast, with an increased stimulation strength, a positive correlation of the relationship of t he post-tetanic component to the total amount Ca2+ could be obtained. The time constants of the Ca2+ extrusion depend linearly on both the t etanization duration and the amount of the tetanic Ca2+ signal. Our da ta demonstrate that augmenting the stimulation strength leads to a res pective increase of the post-tetanic Ca2+ portion within the total Ca2 + signal, whereas a prolongation of the tetanization duration does not . Thus, no further significant prolongation of the Ca2+ signal occurs during increased durations of tetanization. (C) 1998 IBRO. Published b y Elsevier Science Ltd.