Figure 2.
Direct (brief and local) application of kainate boosts action-potential-evoked Ca2+ entry in giant MF boutons in area CA3 whereas Ca2+-store blockade abolishes this effect. A, A granule cell axon traced from the soma (Alexa channel; patch pipette seen) with a pressure pipette (lightened area bordered by dotted lines) approaching a giant MF bouton in area CA3. Inset, a schematic illustrating the arrangement of a whole-cell and a pressure pipette in a slice with respect to the dentate gyrus (DG). B–C, A characteristic experiment in which the pressure pipette approaches a giant bouton in CA3 (B). Kainate (100 μm) is ejected, together with Alexa Fluor 594 (2 μm), from the pipette using a 200 or 250 ms pressure pulse (line-scan in C); the fluorescence transient reflects the pulse concentration profile overlapped with the bright bouton profile (a small, <1 μm, deflection corresponds to a mechanical/optical distortion during the pulse onset; dotted line, the apparent diffusion wave front). D, Local pressure application of kainate has no effect on the baseline (resting) Ca2+ but increases action-potential-evoked Ca2+ entry in giant MF boutons in area CA3: a characteristic example of the baseline fluorescence and Ca2+ signals evoked by five action potentials (20 Hz, arrows) in control conditions (Cntrl) and during the kainate puff (KA puff; line-scans and color-coded traces shown; Fluor-4 channel; orange segment, kainate application pulse). E, Statistical summary of experiments shown in D. Bars, average change in the baseline presynaptic Ca2+-dependent fluorescence (Base) and in the action-potential-evoked ΔF/F signals induced by the pulse of kainate (1AP and 5AP, Ca2+ responses to one and five action potentials, respectively); *p < 0.04; ***p < 0.005. F–G, Ca2+ store depletion with ryanodine (Cntrl+Rya) abolishes presynaptic effects of kainate application. A characteristic example and statistical summary are shown. Notation is as in D and E.