Hair cell morphological patterns and polarity organization in the sea lamprey vestibular cristae

Abstract

The inner ear of the sea lamprey was examined by scanning electron microscopy, antibody labeling with tubulin, Myo7a, Spectrin, and Phalloidin stain to elucidate the canal cristae organization and the morphology and polarity of the hair cells. We characterized the hair cell stereocilia bundles and their morphological polarity with respect to the kinocilia. We identified three types of hair cells. In Type 1 hair cells, the kinocilia were slightly longer than the tallest stereocilia. This type was located along the medial bank of the crista and their polarity, based on kinocilia location, was uniformly pointed ampullipetally. Type 2 hair cells that had kinocilia that were much longer than the stereocilia, were most abundant in the central region of the crista. This type of hair cell displayed variable polarity. Type 3 hair cells had extremely long kinocilia (~40–50 μm long) and with extremely short stereocilia. They were mostly located in the lateral zone crista and displayed ampullipetal polarity. Myo7a and tubulin antibodies revealed that hair cells and vestibular afferents are distributed across the canal cristae in the lamprey, covering the area of cruciate eminence; a feature that is absent in more derived vertebrates. Spectrin shows hair cells of varying polarities in the central zone. In this zone, some cells followed the main polarity vector (lateral) like those in medial and lateral zones, whereas other cells displayed polarities that carried up to 40° from the main polarity vector.

Evolution and Development of Extra-Ocular Nerves and Muscles in Vertebrates

“…By contrast, studies in chondrichthyans (cartilaginous fishes) revealed a different pattern with a combination of ipsilateral and contralateral nerve fibers [11,12]. Many details of vestibular relationships are incomplete in lampreys (which lack a horizontal canal) but can be compared to the pattern of connections in gnathostomes [42,43,[46][47][48]. 1.4.…”

“…Lampreys have a simpler vestibular organization that consists of two canal cristae, the anterior and the posterior cristae (Fig. 6; AC, PC; [46,48]), innervated by three populations of vestibular neurons: the anterior, inferior and posterior nuclei (AN, IN, PN; [42,43,53]). Selectively tracing the anterior crista shows fibers projecting mostly caudally whereas the posterior crista projects rostrally [43].…”

“…Lampreys exhibit robust visuo-vestibular integration, suggesting that visual and vestibular inputs are integrated and respond to saccades and nystagmus. Thus, all basic components of the visuo-vestibular control of gaze have different ocular motor neurons to the eye and lack a horizontal canal [9,42,46,48]. Further investigations are needed that can explain the VOR in lampreys fully.…”