Secondary vestibulocerebellar projections to flocculonodular lobe in a prosimian primate, Galago senegalensis

Abstract

The organization of vestibulocerebellar projections to the flocculonodular and adjacent cortices were studied in Galago using horseradish peroxidase (HRP). Implants of HRP pellets or injections (0.14-0.95 microliter) were placed in floccular, parafloccular, nodular, and uvular cortices. Following survival times of 18-25 hours animals were killed via transcardiac perfusion of heparinized saline followed by a buffered solution of paraformaldehyde and glutaraldehyde. Tissues were processed using DAB as the chromogen. Consequent to floccular implants HRP-positive cells are found bilaterally in medial (MVN), spinal (SpVN), and superior (SVN) vestibular nuclei. Labeled neurons are present in the ipsilateral subgroup y and interstitial nucleus of the eighth nerve. The prepositus hypoglossal nuclei also contained HRP-positive somata. A column of labeled cells is present exclusively in dorsomedial MVN subsequent to injection of the paraflocculus. Injections of nodular cortex reveal a distinct bilateral projection to this cortical area. Many labeled cells are located in SpVN, MVN, SVN, subgroups x and y, the interstitial nucleus, and the ganglion of the eighth nerve. Labeled somata are concentrated in dorsal and dorsolateral SpVN and in a bandlike configuration in subgroup x. HRP-reactive cells appear to have a differential rostrocaudal distribution in MVN, while the majority of positive cells in SVN are found in central portions of the nucleus. After HRP injection into the transition area between nodular and uvular cortices, labeled neurons are present in MVN, SpVN, and the prepositus hypoglossal nucleus. A similar distribution of HRP-positive cells is seen following injections of ventral uvula; however, cells are markedly fewer in number. In no case, subsequent to injection of the flocculonodular lobe and adjacent cortices, are HRP-labeled neurons found in the lateral vestibular nucleus.

The Vestibular Complex in a Prosimian Primate <i>(Galago senegalensis): </i>Morphology and Spinovestibular Connections (Part 2 of 2)

“…The present study substantiates this observa tion and further shows that the shape and size of cells located in this subgroup of Galago is comparable to that reported for the cat [12]. The close relationship between subgroup y and the cerebellum is further accentuated by the fact that these cells pro ject to [53] and receive input from [27] the flocculonodular cortex.…”

“…The existence of subgroup 1 is further substantiated by the fact that it appears to selectively receive corticovestibular input from the vermis of the anterior [26] lobe and rostral portions of the posterior lobe [24], Subgroup x in Galago is an identifiable group of cells located in the lateral SpVN adjacent to the restiform body in a posi tion similar to that reported for the cat [12]. In Galago these cells receive spinovestibular input [present report], project to the flocculonodular cortex [53], and re ceive direct cerebellar corticovestibular in put from the vermis lobule VI [24]. As hy pothesized for the cat [!0], subgroup x in Galago may function as an important re lay in secondary spinocerebellar circuits.…”

“…3). These cells, which provide a discrete ves tibulocerebellar projection to the dorsal paraflocculus in the lesser bushbaby [53], may comprise a hitherto undescribed and unnamed subgroup in the MVN.…”

Central projections of the saccular and utricular nerves in macaques

“…In rhesus macaques, Langer et al (1985b) refer to the ventral portion of nucleus y as the supravestibular nucleus and demonstrate afferent projection to the flocculus (ipsi- lateral greater than contralateral). Ipsilateral but not contralateral nucleus y projections to the flocculus and bilateral nucleus y projections to the uvula were reported in galagos (Rubertone and Haines, 1981). The physiologic role of ventral nucleus y is not clear.…”

“…Little is known about this nucleus, other than its input from vestibular afferents. Input from the cerebellar cortex of the vermis has been reported in galagos (Haines, 1977) and the nucleus projects to the flocculus (Rubertone and Haines, 1981;Langer et al, 1985b) and nodulus (Rubertone and Haines, 1981) …”