Cerebellar Projections of the Lagena (the Third Inner Ear Otolith Endorgan) in the Pigeon

Abstract

We studied cerebellar projections of primary afferents coming from the lagena, the third inner ear otolith endorgan of the pigeon, using a technique of anterograde axonal transport of biotinylated dextran amine, BDA, applied to the region of the lagenar epithelium. Labelled fibers were found ipsilaterally in different lobules of the cerebellum, but mostly in caudoventral regions of the latter (lobules IX and X) and in lobule І. Among the cerebellar nuclei, labelled fibers were observed only in the lateral nucleus, and they passed along its lateral edge. Localization of the predominant part of primary lagenar afferents in the caudoventral cerebellar regions (which are classified as the vestibulocerebellum where primary and secondary vestibular fibers terminate) shows that the lagena in birds is functionally related to the vestibular system.

Central projections of lagenar primary neurons in the chick

“…Direct lagenar afferents to the cerebellum of different vertebrate taxa has been reported (Barry, ; Tomchik and Lu, ; Racz et al, ; Khorevin, ). Our study showed that the primary lagenar afferents in the chick projected to all of the cerebellar nuclei.…”

“…However, there are also several instances of inconsistency of the findings among previous reports that cannot be explained on the basis of species difference. For example, different results for the lagenar afferents to the brainstem and cerebellum in pigeon were obtained when different techniques were used (Boord and Karten, ; Dickman and Fang, ; Khorevin, , ). It seems likely that the limitation of surgical approaches in these studies made it difficult to reproduce the site of lesion in degeneration technique or tracer injection site in more recent studies.…”

“…Some found that lagenar projections were confined to the cerebellar nuclei (Boord and Rasmussen 1963;Dickman and Fang, 1996). In contrast, Khorevin (2010) reported lagenar afferents in pigeons in the cerebellar cortex in the uvula and nodulus. Our results partially agree with the latter view and with other reports for rodents showing that the otolith organs project primarily to the uvula (Kevetter and Perachio, 1986;Maklad and Fritzsch, 2003a).…”