Fig. 2.

TEM observation of vestibular primary synapses following TTK in the utricle. (A,B) Sham vestibular epithelium. Type I hair cells (HCI) are recognised by their amphora-like shape and the calyx afferent (c) encasing the cell body. Type II hair cells (HCII) have a more cylindrical shape and no calyx afferent. (C) Afferents are greatly swollen and the structure of the epithelium is completely distorted 4 h after TTK. Some swollen afferents probably corresponded to calyx terminals (*), whereas others are more likely to correspond to bouton terminals (+). Note the row of supporting cell nuclei (sc) just above the basal membrane of the epithelium. (D) The epithelium has grossly recovered a control-like appearance 1 week after TTK. (E) Higher magnification of the area marked with the left box in D, showing control-like ultrastructure including a presynaptic ribbon (arrow) in a type II hair cell facing a postsynaptic bouton afferent (b). (F) Higher magnification of the area marked with the right box in D, showing a contact between a type I hair cell and the calyx afferent contacting it. The arrowhead points to the calyceal junction, a prominent characteristic of this contact in healthy and mature epithelia. Sample: n=3 in each group. Scale bars: 5 µm (A,B), 10 µm (C,D), 1 µm (E) and 2 µm (F).