Figure 2. Time course of the excitatory and inhibitory components of dGPSPs in E13.5 and E17.5 neurons with physiological E_Cl values.

(A) Patch-clamp recordings of E13.5 MN responses (MN) to a threshold current pulse (i) in the absence (left traces) and presence (right traces) of an isoguvacine-induced response (puff). The red trace is an example of a spike triggering failure during the four-pulse series prior to the isoguvacine puff (see Suppl. Fig. 3). (B) The same disposition as in (A) but for an E17.5 MN; E_Cl: reversal potential for chloride; g_Clp: peak conductance; E_Rest: resting membrane potential. (C) Average time course of the excitatory effect in E13.5 MNs (n = 9). This excitatory effect was quantified every 20 ms by calculating the R_GABA as indicated in Suppl. Fig. 3. (D) Average time course of the inhibitory effect in E17.5 MNs quantified by R_GABA as in (C) (n = 10). The vertical bars represent the standard error of the mean (SEM). The significant differences of the R_GABA values compared to R_GABA at t = 0 ms are indicated by stars (*p < 0.05; **p < 0.01); nS: not significant. (E,F) IETC maps representing the time course (abscissa) of the threshold current (duration: 10 ms) during the simulation of a dGPSP in E13.5 (E) and E17.5 (F) neuron models as measured for a series of E_Rest (ordinate). Horizontal dashed lines represent the average of physiological E_Rest. Vertical black dashed lines represent the simulated dGPSP peak. The magnitude of the excitatory (red colors) and inhibitory (cyan colors) effects is indicated by the color scale (% of change of the threshold current, see bottom bars for values). Contours are disposed at every 1% change. Identical rules hold true in all of the subsequent IETC maps. The time course of the simulated dGPSP is presented below each IETC map (same time scale). Green and red dashed vertical lines indicate the maximum excitatory and inhibitory effects, respectively. As in the following figures, the shape and size of the simulated neurons are presented in the insets on the IETC maps (proximal portion of the axon in blue).