Structure and function in the saccule of the goldfish (Carassius auratus):a model of diversity in the non-amniote ear

The vertebrate inner ear is comprised of a remarkable diversity of cell typ es, including several types of sensory hair cells. In amniotes (reptiles, b irds, and mammals), the morphological and physiological characteristics tha t distinguish these cell types have been well documented, while cellular va riation in the ears of non-amniotes (all other vertebrate groups) has remai ned underrecognized. Since non-amniotes have become increasingly popular mo dels for developmental and genetic research, a more comprehensive understan ding of structure and function in the inner ears of these species is warran ted. This paper first reviews the large body of data describing the morphol ogy and physiology of hair cells and afferent neurons in the inner ear of t he goldfish (Carassius auratus). In particular, we examine the structure of the goldfish saccule, an endorgan that has been the subject of numerous in vestigations on audition. New data on the structural variation of synaptic bodies in saccular hair cells are also presented, and the functional implic ations of these data are discussed. Finally, we conclude that hair cell str ucture varies along the length of the goldfish saccule in a manner consiste nt with known physiological characteristics of the endorgan. The saccule pr ovides an excellent model for investigating structure-function relationship s in the vertebrate inner ear, Bs well as the development of auditory and v estibular sensory epithelia. (C) 2000 Elsevier Science B.V. All rights rese rved.