Cupula-receptor cell relationships with evidence provided by SEM microdissection

Ampullae from the inner ear of the skate, Raja ocellata, were examined by SEM to further elucidate the relationships of the sensory hairs of the receptor cells to the overlying cupula. Specimens were prepared by a variety of methods and were fractured to visualize these relationships. Critical point drying resulted in good cellular and sensory hair preservation, but the cupulae were grossly shrunken. Freeze-dried cupulae, in contrast, more closely approximated the in vivo condition. Although tissues suffered freezing damage, sensory hair bundles were readily discerned. In both critical point dried and freeze-dried ampullae, the peripheral hair cell bundles and the kinocilia of most of the central hair cells, extended across the subcupular space and contacted the cupular material. Some of the specimens were further investigated by dissection in the SEM, the process being viewed in real time stereo. Microdissection confirmed that most kinocilia were attached to the cupula. When the cupula was displaced, sensory hair bundles remained attached to it and broke preferentially at their base from the receptor cells.