Fig. 1

Overview of the central targets of utricular afferents. (A) Coronal section of 5.5 dpf larval zebrafish showing the total area imaged originally by Hildebrand et al. (18) and the area re-imaged at 4 × 4 × 60 nm3 per voxel (L shaped, dashed outline). This area was re-imaged across 105 μm in the rostrocaudal axis (1,757 coronal sections). Scale bar, 100 μm. Reprinted from (19). (B) Circuit schematic highlighting the central vestibular targets described here (green) in the context of the utricular / motor circuit (gray). We identified both commissurally-projecting central neurons and neurons whose axon could not be traced extensively. (C) Horizontal projection of the utricular circuit. As in (B), greens represent neurons described here and grays represent neurons described in Liu et al. (19). Dashed line represents midline. Utricular afferent somata are in the utricular ganglion. (D) Directional tuning of all 91 hair cells in the utricular macula, horizontal view. Each vector represents the best direction of tilt responsiveness, as inferred from the positions of the kinocilium and stereocilia. To facilitate visualization, the directional tuning is also encoded with a color scheme, lower left. Tuning for ipsilateral and rostral tilt is shown in blue, for ipsilateral and caudal tilt in yellow, and contralateral tilt in red. The directional representation is slightly asymmetric to accommodate the patterns of the hair cells. LPR, line of polarity reversal. Data from Liu et al. (19). (E) Schematic of computed tuning for afferents and central neurons. Afferent tuning was computed as a weighted circular average based on the number of ribbon synaptic inputs from hair cells. Central neuron tuning was in turn computed as a weighted circular average based on the number of afferent synaptic contacts. We note that these directional tuning responses only take into account monosynaptic, utricular inputs, not canal inputs or polysynaptic pathways.