Figure 3: Lack of somatic Ca²⁺ transients and action potential discharge in response to GABAergic afferent stimulation in vivo.

(a) Two-photon fluorescence image of OGB1-stained CP cells in vivo after positioning of an extracellular stimulation electrode (stim). Scale bar, 50 μm. (b) Field of view during recording as indicated by a dashed rectangle in a. Scale bar, 10 μm. (c) Top: for both single trials and averaged traces cells were independently classified as responsive (red) or unresponsive (blue) based on an amplitude-threshold criterion. Each stimulation trial consisted of 25 pulses delivered at 50 Hz. All cells included were tested in standard ACSF (Control, left), in the presence of DNQX (50 μM) plus APV (250 μM, middle) as well as in the presence of DNQX plus APV plus Gabazine (40 μM, right). Bottom: sample traces from five cells indicated in b. Note that DNQX plus APV blocked responses in all cells except one (#49). Scale bars, 0.5 ΔF/F₀, 1 s. (d) Cell-attached voltage-clamp recordings from two different neurons in standard ACSF (Control) and in the presence of DNQX plus APV, respectively. Each repetitive electrical stimulation trial consisted of 25 pulses delivered at 50 Hz. Stimulation artefacts were blanked for clarity (grey bars). Action currents (ACs) are indicated by red vertical lines. Scale bars, 25 pA, 100 ms. (e) Summary plot of excited (red) and non-excited (blue) neurons (n=5 cells in control, n=7 cells in DNQX plus APV). (f) Absolute number of excited and non-excited neurons. (g) The mean number of action currents per neuron and trial. Data presented as mean±s.e.m.