Figure 6. POm-evoked synaptic responses in pyramidal neurons of L6a.
(A) (Left) Low-magnification fluorescence image taken of a fixed thalamocortical (TC) section (40 μm) showing EYFP expression 11 days after injecting a virus (AAV2) carrying genes for ChR2-EYFP into the POm of a Ntsr1:tdTomato mouse. The section was counter-stained with DAPI. (Right) High-magnification image showing EYFP-labeled POm axons in L5a, L4 septa, and L1 (inset; scale 100 μm). Arrows in inset point to both POm (green) and L6 CT (red) processes in L1.
(B) Schematic of the recording configuration.
(C) EPSCs and EPSPs for a L6a CT and CC cell pair in response to activation of POm axons (voltage-clamp at −94 mV and current-clamp at −84 mV; 1 ms pulse duration; traces represent the average of 16 voltage-clamp and 9 current-clamp trials). Light intensities were ~3x threshold for evoking an EPSP in CC cells (mean power = 4.9 ± 1.0 mW, n = 14 pairs from 7 mice).
(D–F) Summary data plots. Blue triangles represent means.
(G) POm-evoked EPSCs were much larger in CC than CT cells over a range of light intensities (n = 8 pairs from 5 mice).
(H) Short-term dynamics of POm-evoked responses (EPSCs) across 10 Hz trains for CC cells (n = 11 neurons from 5 mice).
Summary statistics (EPSC peak (D): CT cells = 19.1 ± 3.1 pA; CC cells = 145.0 ± 19.9 pA; n = 13 pairs from 7 mice, p = 2.44 × 10−4, two-tailed paired Wilcoxon signed-rank test; EPSC charge (E): CT cells = 0.02 ± 0.01 pC; CC cells = 0.52 ± 0.08 pC; n = 13 pairs from 7 mice, p = 2.35 × 10−5, two-tailed paired t-test; EPSP peak (F): CT cells = 0.5 ± 0.1 mV; CC cells = 3.9 ± 0.6 mV; n = 14 pairs from 7 mice, p = 1.22 × 10−4, two-tailed paired Wilcoxon signed-rank test). Data are represented as mean ± SEM. See also Figure S7 and S8.