Figure 8.

Basolateral processes of type II hair cells form ribbon synapses with vestibular afferents. All images in this panel are derived from CBA/CaJ mice between 6 and 9 weeks of age. A1–A3. Confocal horizontal slices from a Z series showing the same field of a utricle labeled for myosin VIIa (blue), ctbp2 (pink), and dapi (green), focused on type II hair cell nuclei (A1), type I hair cell nuclei and type II hair cell “waists” (A2), or type II hair cell processes (A3). Arrowheads point to the same type II hair cells in all fields. Arrow in A2 indicates ctbp2 labeling in a type I hair cell. B. A horizontal slice through a utricle labeled for myosin VIIa (blue), ctbp2 (pink), and 200 kD neurofilament (nf, yellow-green). Arrowheads point to ctbp2 labeling in a type II hair cell basolateral process that is close association with neurofilament-labeled processes. C,D. Confocal horizontal slices through type II hair cell processes in a utricle labeled for myosin VIIa (blue), ctbp2 (majenta), and glur2 (green). Arrowheads in C point to sites of co-labeling for ctbp2 and glur2. D shows this co-labeling at a higher magnification. EH. Ultrathin sections. E. A transverse section showing segments of basolateral processes (green tint) coursing under a type I HC (HC_I) and over supporting cell (SC) nuclei. The boxed area contains a synaptic ribbon that is shown at higher magnification in G. F. A horizontal section from a second utricle, taken near the supporting cell (SC) nuclei, shows segments of basolateral processes (P, green tint). The boxed area contains a synaptic ribbon that is shown at higher magnification in H. Arrowheads in F indicate positions of additional synaptic ribbons. G,H. Arrowheads point to vesicles around the electron dense region of the ribbon in the basolateral process that is opposed to an afferent (aff) bouton. Arrows point to the post-synaptic density in the afferent. Scale bars: A1 = 5 μm (applies to A1–A3): B = 5 μm (applies to B,C); E = 4 μm; F = 2 μm; G = 200 nm; H = 500 nm.