Figure 2.

Larger [Ca²⁺] transients in PV⁺ than in mGluR1α⁺ dendrite-contacting boutons. A, Two-photon (2P) image stack of a CA3 PC basal dendritic tree and axonal arbor filled with 20 μm Alexa Fluor 594 (Alexa594, red), 300 μm Fluo5F, and biocytin. Boxed area is shown at higher magnification in C. Diagram at the upper left corner illustrates the position of the cell in the CA3 area. B, Neurolucida reconstruction of the cell shown in A. Boxed areas correspond to A and C. C, D, High-magnification two-photon (C) and confocal (D) images of the scanned axon collaterals after fixation and visualization of the biocytin. Numbers indicate the boutons that have been line scanned. Inset in C shows bouton #1 at a higher magnification. The line indicates the position of the line scan. E–G, Some of the imaged boutons are in contact with PV (E,F, boutons #6 and #12) or mGluR1α (G, boutons #15 and #16) immunolabeled dendrites (biocytin: white, PV: orange, mGluR1α: cyan). H, Single AP-evoked [Ca²⁺] transients (n = 16 transients from 16 boutons, each trace is the average of two scans) recorded in the axon terminals shown in C. Orange and cyan traces are transients from PV⁺ and mGluR1α⁺ dendrite-contacting boutons, respectively. Inset shows the same traces after Gaussian filtering on an extended time scale. I, Peak [Ca²⁺] transient amplitudes are significantly larger (Kruskal–Wallis test: p = 0.01, MW U post hoc test, p = 0.01 between unidentified and PV and p = 0.01 between PV and mGluR1α) in PV⁺ (orange) than in mGluR1α⁺ dendrite-contacting (cyan) or all other boutons (gray, n = 605 boutons from 30 cells). Black symbols correspond to individual data points obtained from the cell shown in A–G. J, Averaged [Ca²⁺] transients recorded with 100 μm Fluo5F in PV⁺ (orange) or mGluR1α⁺ (cyan) dendrite-targeting boutons. Mono-exponential fits show similar decay kinetics. Inset shows the individual decay time constant values in 18 PV⁺ and 35 mGluR1α⁺ dendrite-innervating boutons. The two populations are not significantly different (p = 0.61, MW U test). Circles indicate individual boutons, boxes indicate IQRs, and horizontal bars indicate medians.