Central projections of the saccular and utricular nerves in macaques

Abstract

The central projections of the utricular and saccular nerve in macaques were examined using transganglionic labeling of vestibular afferent neurons. In these experiments, biotinylated dextran amine was injected directly into the saccular or utricular neuroepithelium of fascicularis (Macaca fascicularis) or rhesus (Macaca mulatta) monkeys. Two to 5 weeks later, the animals were killed and the peripheral vestibular sensory organs, brainstem, and cerebellum were collected for analysis. The principal brainstem areas of saccular nerve termination were lateral, particularly the spinal vestibular nucleus, the lateral portion of the superior vestibular nucleus, ventral nucleus y, the external cuneate nucleus, and cell group l. The principal cerebellar projection was to the uvula with a less dense projection to the nodulus. Principle brainstem areas of termination of the utricular nerve were the lateral/dorsal medial vestibular nucleus, ventral and lateral portions of the superior vestibular nucleus, and rostral portion of the spinal vestibular nucleus. In the cerebellum, a strong projection was observed to the nodulus and weak projections were present in the flocculus, ventral paraflocculus, bilateral fastigial nuclei, and uvula. Although there is extensive overlap of saccular and utricular projections, saccular inputs to the lateral portions of the vestibular nuclear complex suggest that saccular afferents contribute to the vestibulospinal system. In contrast, the utricular nerve projects more rostrally into areas of known concentration of vestibulo-ocular related cells. Although sparse, the projections of the utricle to the flocculus/ventral paraflocculus suggest a potential convergence with floccular projection inputs from the vestibular brainstem that have been implicated in vestibulo-ocular motor learning.

Central projections of the utricular nerve in the gerbil

“…In squirrel monkeys, Naito et al (1995) did not see a projection to Y from the utricle, nor was this connection seen in the guinea pig (Gstoettner et al, 1992). The same BDA technique described in this report (Newlands et al, 2001) has demonstrated utricular and saccular projections to Y in macaques.…”

New understanding on the contribution of the central otolithic system to eye movement and skew deviation

“…6,7 Polysynaptic pathways also have a critical role in mediating the utriculo-ocular reflex. [8][9][10] Signals from the lateral utricle ipsilateral to the direction of head translation are transmitted to the ipsilateral vestibular nucleus, via an extensive network of projections within the cerebellum (including the nodulus, ventral uvula, fastigial nucleus, anterior vermis, and flocculus/ventral paraflocculus). Polysynaptic pathways are also responsible for generating ocular counterroll movements during static head tilt.…”

Lack of the Central Nervous System- and Neural Crest-Expressed Forkhead Gene Foxs1 Affects Motor Function and Body Weight

“…This test measures the ability to learn, sustain, and execute complex coordinate movements, processes in which the cerebellum and its processing of incoming and outgoing signals plays a crucial role. In this context, it is interesting that other Foxs1-positive regions, such as the fastigial nucleus, vestibular nuclei, and external cuneate nucleus, have been implicated as targets for cerebellar projections (37,45). Thus, it is possible that alterations in processing and integration of cerebellar afference/ efference, at several levels, might be altered in response to lack of Foxs1, rendering null mutants more capable in the rotarod test.…”