Figure 2

Figure 2

(a) Example of a mixed synaptic connection from a V2a-B neuron on slower (left) and faster (right) time scales. A brief current pulse (pre, gray traces at top left) evoked a mixed synaptic response in a postsynaptic neuron (post, black traces at bottom left). Mixed synapses are characterized by an earlier electrical component and a later, less reliable chemical component prone to failures (at arrows; fail). Averages of two distinct components of mixed synapses (electrical, blue; chemical, orange) are illustrated top right. Averages in black illustrated bottom right are superimposed on individual sweeps in gray. (b) As in panel (a), but an example of a chemical connection arising from a V2a-D neuron. Note a slow excitatory postsynaptic potential that arises via indirect electrical coupling can be resolved when the chemical connection fails. Here, the chemical connection (orange) is superimposed on the slower postsynaptic potential (gray) observed during failures. (c) Superimposed data illustrate differences in the amplitude and time course of electrical (blue, eEPSP) and chemical (orange, cEPSP) excitatory postsynaptic potentials related to input resistance (Rin). (d) Quantification of electrical EPSP amplitude versus input resistance. **, significant correlation following non-parametric Spearman rank test (ρ₍₈₂₎=–0.24, p<0.05, n=84). Source data are reported in Figure 2—source data 1. (e) Quantification of ‘ohmic current’ calculated from eEPSP amplitude and Rin (ρ₍₈₂₎=–0.67, p<0.001, n=84). Source data are reported in Figure 2—source data 1. (f) Quantification of the failure rate of the chemical component versus the amplitude of the electrical component of mixed eEPSPs (black open circles). **, significant following non-parametric Spearman rank test (ρ₍₃₈₎=–0.69, p<0.001, n=40). Source data are reported in Figure 2—source data 1. (g) As in (f), but for purely chemical synapse amplitude (ns; ρ₍₄₅₎=0.08, p=0.599, n=47). Source data are reported in Figure 2—source data 1. (h) Quantification of chemical EPSP amplitude versus input resistance. **, significant correlation following non-parametric Spearman rank test (ρ₍₄₁₎=0.45, p<0.01, n=43). Source data are reported in Figure 2—source data 1. (i), Quantification of ‘ohmic current’ calculated from cEPSP amplitude and Rin (ρ₍₄₁₎=–0.60, p<0.001, n=43). Source data are reported in Figure 2—source data 1. (j) Quantification of chemical EPSP decay times. **, significant correlation following non-parametric Spearman rank test (ρ₍₄₁₎=0.68, p<0.001, n=43). Source data are reported in Figure 2—source data 1. (k) Quantification of soma size versus Rin before (gray) and after (black) 18βGA application, illustrating the increase in resistance values regardless of size. Dotted lines link the same neurons (n=11 motor neurons, 12 interneurons). Source data are reported in Figure 2—source data 1. (l) Left, quantification of input resistance change expressed as a percent of controls in the presence of the gap junction blocker 18βGA versus glutamatergic blockers NBQX and/or APV. **, significant difference following non-parametric Mann-Whitney U-test (18βGA; U₍₂₂₎=0, p<0.001, n=23). ns, not significant (NBQX; U₍₁₃₎=84, p=0.520, n=14; NBQX+APV; U₍₄₎=10, p=0.602, n=5). Right, quantification of the percentage increase in input resistance in the presence of 18βGA as a function of initial input resistance. **, significant correlation (ρ₍₂₁₎=–0.61, p<0.01, n=23). Source data are reported in Figure 2—source data 1.