Hair cells of different shapes and their placement along the frog crista ampullaris

The list of distinguishing morphological features of hair cells includes: Type I and Type II afferent innervation, and length, shapes and arrangements of stereo- and kinocilia. We now add to this list the shapes of the hair cells themselves and their placement within the mechanosensory organ, in this case the semicircular canal. Although hair cells of the crista ampullaris of the frog are only of Type II they may now be further classified into three sub-groups according to shape: club-, cigar- and pear-shaped. The cigar- and club-shaped hair cells are each about 40% while the pear-shaped cells are about 20% of the total numbers of hair cells in the crista. The differently-shaped hair cells also distribute differently along the crista. The cigar- and club-shaped are more-or-less uniformly distributed with somewhat higher concentrations at the ends of the crista than in the center. The pear-shaped hair cells, on the other hand, are mostly concentrated toward the center of the crista. This distribution of the pear-shaped hair cells, and their shape is reminiscent of the distribution of calyceal endings (Type I hair cell) in the cristae of amniotes [Goldberg et al., Hear. Res. 49, 89-102 (1990) in Chinchilla; Fernandez et al., Soc. Neurosci. Abstr. 17, 312 (1991) in Monkey]. There are some quantitative differences between hair cells of the same shape but from different portions of the crista. For instance, pear-shaped hair cells of the center are generally of greater cross-sectional area than those of the ends.(ABSTRACT TRUNCATED AT 250 WORDS)