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. Author manuscript; available in PMC: 2024 Oct 6.
Published in final edited form as: Cell. 2024 Aug 22;187(20):5679–5697.e23. doi: 10.1016/j.cell.2024.07.041

Figure 4. T3 alters synaptic connectivity of cortical glutamatergic neurons.

Figure 4.

(A) Top: AAV encoding Cre-dependent CoChR (FLEX-CoChR) was delivered to the upper layers of M2 in one hemisphere, and a retrograde AAV encoding Cre was delivered to the contralateral hemisphere, resulting in CoChR expression in neurons that send projections to contralateral M2. Bottom: whole-cell recordings from contralateral L2/3 pyramidal neurons within the field of CoChR-expressing axons were used to measure PSCs triggered by whole-field optogenetic stimulation.

(B) Low-magnification (left; scale bar, 100 μm) and enlarged (right; scale bar, 20 μm) images of a streptavidin-labeled L2/3 pyramidal neuron filled with biocytin (pink) via the recording pipette amidst CoChR-expressing axons (green).

(C) Left: example of light-evoked EPSCs. Currents are color coded by the light stimulus intensity. Right: excitatory charge in a post-stimulus 10 ms window normalized by cell capacitance as a function of light stimulus power. Data were fit by a sigmoid (pink) characterized by a saturation amplitude (a), a half-maximum inflection point (b, measure of sensitivity), and the slope (c).

(D) Normalized post-synaptic excitatory charge as a function of laser stimulus power for T3 (orange, n = 21 neurons, 8 mice) and vehicle (blue, n = 29 neurons, 10 mice) treated mice. Dots/shade: mean/bootstrapped SEM.

(E) Boxplot of changes in sigmoid parameter (from single-cell fits of excitatory charge vs. laser power curves) relative to the median control value. T3-treatment significantly increased the saturation amplitude (a, p = 0.001) and decreased the power to half-maximum (b, p = 0.04), without changing the slope (c, p = 0.10). Central line: median, box: IQ, whiskers: data within 1.5× IQR.

(F–H) As in (C)–(E), but for light-evoked IPSCs and normalized inhibitory charge. T3 treatment significantly decreased the power to half-maximum IPSC charge (b, p = 0.005) but did not increase the saturation amplitude (a, p = 0.09) or change the slope (c, p = 0.35).

All statistical comparisons: Wilcoxon rank-sum test. *p < 0.05, **p < 0.01.

See also Figure S5.