Monosynaptic trans-collicular pathways link mouse whisker circuits to integrate somatosensory and motor cortical signals
Fig 4
Whisker-related sensory-motor RNs are organized into overlapping zones within the intermediate layer the LSC.
(A) Trans-synaptic labeling of MC-, BC-, and Bs-RNs in SC (left). Cocktails of AAV1-Cre + AAV-DIO-mCherry were injected into projecting sites (MC, BC, or Bs) and AAV2-DIO-EGFP in SC. Example fluorescent pictures (right) of mCherry expression (red) in the projecting sites. (B) Top left: Schematic of trans-synaptically labeled RNs (green). Top right: Example confocal image of SC showing mCherry-expressing BC axons (red) and Cre-dependent expression of EGFP in BC-RNs (green). Bottom: Fluorescent images of EGFP expression (green) in MC-, BC-, and Bs- RNs. (C) Example reconstructions of the 3 RN populations along the rostro-caudal axis (red: MC-RNs; blue: BC-RNs; green: Bs-RNs), registered to standard anatomical borders within SC. (D) Anterior–posterior distributions of RNs. Data points show mean RN counts per 100 μm bin (red: MC-RNs, 6 mice; blue: BC-RNs, 6 mice; green: Bs-RNs, 7 mice) normalized to their maximum count. Box plots show medians (line in box) and IQRs (first to third quartile) in mm (boxes), ([median, Q1, Q3 in mm] MC-RNs: 3.58, 3.38, 3.88; BC-RNs: 3.68, 3.48, 3.88; Bs-RNs: 3.68, 3.48, 3.88). (E) Comparison of recipient zones in the DV and ML dimensions in SC. Fluorescent thresholded representative slices of each RN population, registered at a similar AP coordinate and to approximate radial SC zones according to [16]. (Centroids: [DV, ML, μm] MC: 1,123, 1,505; BC: 1,035, 1,297; Bs: 1,276, 993). (F) Colabeling experiment of cortical (red, MC-RNs + BC-RNs) and Bs-RNs (green). Top right: Example fluorescent image showing cortical and peripheral RNs. Middle: Fluorescence thresholded RN signals from 15 consecutive images (1 brain). Bottom: Histograms show the thresholded pixel gray value probability for cortical-RNs and Bs-RNs in the DV axis and in the ML axis. ([DV, median and IQR, relative to SC dorsal surface] Cortical-RN [μm]: 1,115, 147; Bs-RN: 1,365, 281; [ML, median and IQR, μm relative to SC midline] Cortical-RN: 1,472, 211; Bs-RN: 1,637, 287, p < 0.001). * represents p < 0.01; D: Kruskal–Wallis, F: Wilcoxon rank-sum; exact p-values in S1 Table, exact N in S2 Table. Data are shown as mean ± SEM. The data for Fig 4D–4F can be found at: https://doi.org/10.11588/data/DNOSZG. BC, barrel cortex; Bs, brainstem; DV, dorsal-ventral; icp, inferior cerebellar peduncle; IQR, interquartile range; LSC, lateral SC; LV, lateral ventricle; MC, motor cortex; ML, medial-lateral; Pia, pia mater; RN, recipient neuron; SC.m, medial superior colliculus; SC.cm, superior colliculus centromedial; SC.cl, centrolateral superior colliculus; SC.l, lateral superior colliculus; sp5, spinal trigeminal tract; Sp5, spinal trigeminal nucleus; WM, white matter; 7N, facial nucleus.