1. Overview of injections and proportion of corticocollicular projection from each layer.
Overview of injections and proportion of corticocollicular projection from each layer. A, Latex beads were injected into the IC at least 3 d before brain slicing. B, IC injection site covering portions of the lateral cortex (LC), dorsal cortex (DC), and central nucleus of the IC (CNIC). C, Layer 5 and layer 6 auditory corticocollicular neurons are filled with latex beads after retrograde transport. D, ChR-2 AAV was injected into the MGB at 2–3 weeks before preparation of brain slices. E, Injection site of AAV-CaMKIIa-hChR2(H134R)-mCherry showing the labeled MGB region and radiating labeled axons. F, After 2–3 weeks, ChR-2 is robustly expressed in the MGB with afferents projecting to the AC. G, Low-power imaging showing retrogradely labeled corticocollicular neurons in the AC after Fluoro-Gold injection into the IC. Inset, Injection site. H, Neurolucida image showing the cumulative representation of labeled cells in all sections containing the primary AC of the brain shown in G. The only features marked on each Neurolucida image were the tissue border (green), layer 5 corticocollicular cells (blue), and layer 6 corticocollicular cells (orange). I, Mean percentages of layer 5 corticocollicular cells versus layer 6 corticocollicular cells across n = 10 animals. D, Dorsal; HF, hippocampal formation; L5, layer 5; L6, layer 6; LGN, lateral geniculate nucleus; R, rostral.
Bernard J. Slater et al. J. Neurosci. 2019;39:
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