The lagena (the third otolith endorgan in vertebrates)

Abstract

In this review, the structure and functions of the lagena (the third otolith organ) in an evolutionary lineage of the vertebrates are described and discussed. The lagenar macula appears first in the posterior part of the sacculus of elasmobranchs; in these animals, the lagena is considered to be involved in the balance support (orientation with respect to the gravitation force). The lagena as a separate endorgan has been described in teleost fishes; in some species, the lagena is connected with the sacculus, while in other species the interrelations of these structures can be dissimilar. The lagena supplements the functions of the sacculus; in fishes (animals with no special organ of hearing), it is involved in discrimination of sound oscillations, identification of the gravitation vector, and orientation in the course of movements within the vertical plane. In amphibians, the lagena is localized in the posterior part of the sacculus, near the auditory structures; it performs mostly vestibular and (to a much lesser extent) auditory functions. In amniotes, the lagena was first separated from the sacculus; it is localized in the cochlear canal, distally with respect to the hearing organ. Information on the functions of the lagena in amniotes is rather limited and contradictory. Central projections of this organ have been examined practically only in birds. Lagenar afferents project to the vestibular nuclei and cerebellum, while some fibers come to the auditory nuclei of the medulla. The lagena in birds can be related to their navigation abilities (birds are supposed to be capable of orienting within the magnetic field of the Earth due to the magnetic properties of the lagenar otoconia; this structure can also provide detection of movements along the vertical axis. The close proximity between the otolithic and auditory endorgans in the cochlear canal of amniotes can be indicative of the functional significance of these interrelations. This aspect, however, remains at present undiscovered. In mammals (except Monotremata), there is no lagena as an independent endorgan.

信鸽瓶状囊耳石中磁性元素的电感耦合等离子体质谱分析

“…The lagena may play a similar role in sensing gravitational and acceleration signals as the utricle does. Current evidences from morphological and anatomical studies [8,11] indicate that the avian lagena mainly sends neural projections to the vestibular nuclei and the cerebellum, and at an obviously lesser extent to the auditory nuclei. It is also reported that lagenal hair cells are insensitive to sound signals [24] .…”

“…The macula lagena is another otolithic organ in the inner ear in non-mammalian vertebrates [7] and has distinct functions across species [8] . In the fish, the lagena is mainly involved in sensations of acoustic oscillations and orientation in the vertical plane.…”

Central projections of the lagena (the third otolith endorgan of the inner ear) in the pigeon

“…Despite the fact that the vestibular system in vertebrates is, from the evolutionary aspect, rather conservative, otolith endorgans in different animals demonstrate certain variability [1][2][3]. In most mammals, two otolith endorgans, the utriculus and the sacculus, are found, while in many vertebrates of other classes there is the third otolith endorgan (called the lagena).…”

“…In most mammals, two otolith endorgans, the utriculus and the sacculus, are found, while in many vertebrates of other classes there is the third otolith endorgan (called the lagena). The receptor apparatus of the lagena includes a group of hair sensory cells localized in a certain cavity (chamber) of the membranous labyrinth of the inner ear and covered by the otoconium membrane [1][2][3]. Among vertebrates, the lagena as an independent endorgan was described for the first time in elasmobranch cartilaginous fishes (sharks and rays) [4] in which this structure is considered to be the equilibrium organ [5].…”

“…In reptiles (crocodiles), birds [1,2,9], and monotremate mammals (platypus and echidna) [10], organization of the lagena demonstrates substantial similarity, despite the fact that sizes of the animal's body and living conditions of representatives of the above-mentioned different classes of vertebrates are dissimilar. The functions of the lagena in amniotes, including birds, remain unclear in detail, although there are a number of hypotheses on the functional role of the sensory apparatus of this organ [3]. Our experimental study was aimed at elucidating the central projections of the lagena in birds; we believed that the data would help one to interpret the function of this sensory structure in a more scientifically grounded manner.…”