Fig. 4: Role of the MRN in generating sound-evoked responses in the MD.

A Schematic of the experimental design showing local optogenetic activation of GABAergic neurons and simultaneous SUA recordings in the MRN of VGAT-ChR2-EYFP mice received AAV-retro-hSyn-cre-mCherry injection into the MD and AAV-DIO-ChrimsonR into the MRN. Created by the authors. B Histological image of EYFP/mCherry/DAPI labeling in the MRN. Green fluorescence indicates axonal fibers from EYFP-expressing local GABAergic neurons; red fluorescence marks MRN neurons projecting to the MD; and blue fluorescence represents nuclear staining (DAPI). Representative AP waveforms, raster plots, and PSTHs of a local FS unit (C) and a RS unit projecting to the MD (D) in the MRN under 589-nm and 473-nm laser stimulation. E Schematic for optogenetic inactivation of MRN (MRN-silencing), and simultaneous SUA and LFP recordings in the MD of VGAT-ChR2-EYFP mice. Created by the authors. F Raster plots and PSTHs of three representative MD neurons with and without MRN-silencing. Quantification of spontaneous firing rates (G) and AUC of sound-evoked Phasic- (H) and Sustained-responses (I) in MD neurons under different conditions. N = 72 units from 8 mice. Representative traces of LFP (J) and corresponding time-frequency spectrograms (K) in response to sound stimuli with or without MRN-silencing. Gray and blue rectangles indicate the presentation of sound and laser stimuli, respectively. Normalized PSD of LFPs in the 0–80 ms (L) and 80–500 ms (M) post-stimulus window. Gray shading indicates the frequency bands of delta, theta, alpha, beta, and gamma. Statistical analysis of normalized PSD across frequency bands in the 0–80 ms (N) and 80–500 ms window (O). N = 16 recording sessions from 8 mice. ^**P < 0.01, as determined by a linear mixed-effects model (LME).