Fig. 5.

Calyx of Held collaterals can form functional synapses on adjacent principal cells. Paired recordings between a calyx of Held and a nearby principal cell were performed in acute slices at P4. (A) Presynaptic action potentials were triggered in current clamp mode in the calyx (PRE) by injecting 0.3 nA for 2 ms at 0.2 Hz, whereas EPSCs were measured in voltage clamp in the postsynaptic cell (POST). After presynaptic action potentials, a failure, two small responses, and a larger response were observed in the postsynaptic recording. Postsynaptic traces have been vertically offset for display purposes. (B) Amplitude distribution of EPSCs. Note the presence of failures after >50% of the stimulations. Bin size is 10 pA. (Inset) Contact region between the calyx of Held collateral (red) and a spine-like structure on the dendrite of the postsynaptic MNTB cell (green). Note the inverted horizontal axis, with larger EPSCs being more negative. (C) Localized AP-evoked calcium transients in a calyx of Held collateral filled with OGB-1 using a patch pipette. The color code for the spatial distribution of the peak ΔF/F₀ fluorescence is shown on the Bottom. (D) Representative calcium transients recorded during rapid line scanning at locations a–d indicated in C.