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. 2019 Aug 28;13:55. doi: 10.3389/fncir.2019.00055

FIGURE 1.

FIGURE 1

Calyx labeling, reconstruction in 3D, and analysis. (A) A schematic of the interaural intensity differences (IID) pathway and RDA injection site in the VAS to sparsely label calyces of Held in the MNTB. GBCs in the AVCN receive direct input from the AN. In turn, GBCs synapse on inhibitory neurons in the contralateral MNTB. MNTB neurons then innervate excitatory neurons in the LSO. LSO neurons also receive tonotopically matched excitatory terminals from SBCs in the ipsilateral AVCN. LSO neurons compute the balance of frequency-matched inhibition and excitation arising from both ears to determine the sound source location in the horizontal plane. (B) Timeline of injections. Two age cohorts were included in the study. The P8 mice group received vehicle or BLZ945 injections at P2, P4, and P6, and then were perfused at P8. Animals in the P13 age group were injected every 2 days from P2 until P10, and then perfused at P13. (C) A photograph of an RDA injection site (magenta) in the VAS and sparsely labeled calyces in the mouse brainstem. VGluT1/2 labeling is shown in green. (D) A higher magnification of the left MNTB with sparsely RDA-labeled calyces of Held. (E) Reconstructed calyx area used for size and volume measurements (magenta). MNTB neurons were classified into mono- or polyinnervated based on the presence of PV or VGluT1/2 labeling outside the RDA-labeled calyx. Shown is an example of a monoinnervated neuron. VGluT1/2 labeling is present and is co-localized to the RDA-labeled calyx. Dashed line indicates approximate boundary of the Nissl-stained neuron that is contacted by the RDA-filled calyx of Held. (E’) Schematic illustration of a monoinnervated MNTB neuron contacted by an RDA-labeled calyx. (F) An example of a polyinnervated MNTB neuron. It is contacted by an RDA-filled calyx and an additional VGluT1/2 positive calyceal input (indicated by white asterisks) around the remaining surface of the same neuron (dashed line). (F’) Schematic illustration of a polyinnervated MNTB neuron. Both the RDA-labeled calyx and one or more additional inputs terminate on the same MNTB neuron. Scale bar in panel (C) = 200 μm; scale bar in panel (D) = 100 μm; scale bar in panel (E) = 6 μm; scale bar in panel (F) = 5 μm. Abbreviations: AN – auditory nerve, AVCN – anterior ventral cochlear nucleus, GBC – globular bushy cell, LSO – lateral superior olive, MNTB – medial nucleus of the trapezoid body, SBC – spherical bushy cell, VAS – ventral acoustic stria. Panel (A) has been adapted from Joris and Yin (1998).