Central projections of lagenar primary neurons in the chick

Abstract

Perception of linear acceleration and head position is the function of the utricle and saccule in mammals. Nonmammalian vertebrates possess a third otolith endorgan, the macula lagena. Different functions have been ascribed to the lagena in arboreal birds, including hearing, equilibrium, homing behavior, and magnetoreception. However, no conclusive evidence on the function of the lagena in birds is currently available. The present study is aimed at providing a neuroanatomical substrate for the function of the lagena in the chicken as an example of terrestrial birds. The afferents from the lagena of chick embryos (E19) to the brainstem and cerebellum were investigated by the sensitive lipophilic tracer Neuro Vue Red in postfixed ears. The results revealed that all the main vestibular nuclei, including the tangential nucleus, received lagenar projections. No lagenar terminals were found in auditory centers, including the cochlear nuclei. In the cerebellum, the labeled terminals were found variably in all of the cerebellar nuclei. In the cerebellar cortex, the labeled fibers were found mostly in the uvula, with fewer afferents in the flocculus and paraflocculus. None was seen in the nodulus. The absence of lagenar afferent projections in auditory nuclei and the presence of a projection pattern in the vestibular nuclei and cerebellum similar to that of the utricle and saccule suggest that the primary role of the lagena in the chick lies in the processing of vestibular information related to linear acceleration and static head position.

Magnetic field-driven induction of ZENK in the trigeminal system of pigeons ( Columba livia )

“…The problem for a hypothesis suggesting that the magnetic activation in PrV and SpV could have come from putative magnetoreceptors in the vestibular system (lagena) is that, although the vast majority of neuronal connections within the brain show reciprocal innervations, no projections backwards from the N. basalis to either the superior vestibular nuclei (D in figure 5) or to PrV (E in figure 5) have been described yet. However, a recent neuronal tracing study in domestic chicken reported a direct projection from the lagena not only to medial and spinal vestibular nuclei [47] (F in figure 5), but also to SpV (G in figure 5). Thus, a putative neuronal connection seems to exist in a different bird species, which could support an explanation, where the magnetically induced neuronal ZENK activation we observed in PrV or SpV would be owing to primary magnetic sensors located in the lagena.…”

Origin of Neuroblasts in the Avian Otic Placode and Their Distributions in the Acoustic and Vestibular Ganglia

“…Regarding the anatomical aspect of the vestibular and acoustic ganglia, studies of otic neuron segregation and axonal projections in both mammals and birds have considered the division of the vestibular ganglion into two portions, one superior portion and another inferior portion [ 10 , 54 , 73 , 74 ]. Judging from a preliminary anatomical study of the vestibular and acoustic ganglia in chicks using HuC/D immunoreactions, which labeled the postmitotic neuronal phenotypes [ 75 ], the vestibular ganglion can be considered to be divided into two portions (lobes), anterior ( a -VG) and posterior ( p -VG) ( Figure 1 a,b; Supplementary Figure S1 ), according to the anterior-to-posterior axis of the hindbrain.…”

“…All sensory elements of this intricate organ are composed of mechano-transducing hair cells that transform mechanical stimuli into electric signals and supporting cells that offer cellular and mechanical support to the hair cells, with both types of cells having an extremely specific cytoarchitectonic arrangement [ 6 , 7 ]. Neurons of the acoustic and vestibular ganglia connect the hair cells of the developing otic epithelium with their targets, the vestibular and auditory nuclei in the hindbrain, with a topographically well-defined pattern of connections [ 8 , 9 , 10 , 11 ]. Both hair cells and otic neuroblasts have a clonal relationship, these cells being derived from a population of common progenitor cells [ 12 , 13 ].…”

A novel cerebellar commissure and other myelinated axons in the Purkinje cell layer of a pond turtle (Trachemys scripta elegans)

“…Physiological recordings in fish and frogs have demonstrated that lateral cerebellar regions have neurons that respond to head rotation (Ansorge & Grüsser‐Cornehls, ; Blanks, Precht, & Giretti, ; Montgomery, ). Although these reports suggest that the myelinated commissure can, in part, mediate vestibular signals, CN VIII also carries afferents from several other sensory neuroepithelia in the turtle's temporal bone (papilla neglecta, sacculus, utricle, lagena, and the basilar papilla) that mediate nonvestibular signals (Mahmoud, Reed, & Maklad, ).…”