Inferior olive projection

Apps R (1990) Columnar organization of the inferior olive projection to the posterior lobe of the rat cerebellum. J. Comp. Neurol., 302, 236-254. 

Similar to other projections from the cerebellar nuclei (except those to the inferior olive which are GABAergic), terminals of cerebellar origin in the red nucleus are enriched in Glu (Schwarz and Schmitz, 1997 Fig. 5). Enrichment of Glu has also been detected in terminals in the oculomotor nucleus originating from the abducens and ventral lateral vestibular nuclei (Nguyen and Spencer, 1999 Fig. 5). 

Fig. 101. Diagram of the projections of the dentate and interposed cerebellar nuclei (CN) and the mossy and climbing fiber recurrent circuits. The non-GABAergic projections of the nuclei divide in ascending (A and C) and descending (B) branches. The descending branch terminates in the nucleus reticularis tegmenti pontis (NRTP), one of the main sources of the mossy fiber collateral projection to the nuclei. The ascending branch terminates in the red nucleus (n. ruber), the nuclei of the mesodiencephalic junction MDJ, a relay in the recurrent cerebellomesencepho-olivary loop, and in the ventral tier nuclei of the thalamus (VA/VL). The GABAergic nucleo-olivary projection (2) terminates in the inferior olive (lO). Courtesy of Dr. T.J.H. Ruigrok.

Tolbert s (Tolbert et al., 1978a) and Courville and Cooper s (1970) quantitative analysis clearly showed that all sizes of neurons were present in all central nuclei in monkey and cat. Histograms of the soma diameter of the nuclear neurons projecting to the thalamus and the cerebellar cortex are very similar to the overall size distribution of these neurons. The cells in the cerebellar nuclei of the cat that project to the inferior olive, however, constitute a population of small, spindle shaped neurons (Fig. 109). This... 

Fig. 109. Histograms of the maximum soma diameters of neurons of the cerebellar nuclei of the cat retrogradely labelled with HRP from injection sites in A the thalamus (VL), B the inferior olive (lO), and C the cerebellar cortex (CbS). D is a histogram of the overall size distribution of neurons in the cerebellar nuclei. Note that cerebellothalamic and nucleocortical projections arise from a heterogeneous population of neurons whose diameters correspond to the size spectrum of neurons present in the deep nuclei, whereas the cerebello-olivary pathway arises from a specific population of small neurons. Tolbert et al. (1978a).

Fig. 142, Lateral extension of zone A in the posterior lobe with its projection to the dorsolateral protuberance (dip) of the fastigial nucleus in the rat. The cumulative results of 8 injections of WGA-HRP in the posterior lobe are illustrated. The injection sites are represented as grey areas in B and the corresponding afferent and efferent connections are represented in black in A (inferior olive) and C (cerebellar nuclei), respectively. Dots indicate single labelled neurones in A and few sparsely labelled terminals in C. The lateral extension of the A zone receives a projection from the medial subnucleus c of the caudal medial accessory olive (MAO A2-7). Buisseret-Delmas (1988a)...

Afferent systems of the inferior olive have been reviewed by Brodal and Kawamura (1980) for the cat and by Martin et al. (1980) for the opossum. For the rat the tabulated summary of its afferent connections in the paper of Brown et al. (1977) and the review by Flumerfelt and Hryccyshyn (1985) are useful. Afferent systems of the inferior olive can be subdivided into three groups (1) the GABAergic nucleo-olivary and vestibulo-olivary projections (2) the monoaminergic and cholinergic projections to the inferior olive (3) the specific projections from the spinal cord, certain brain stem nuclei and the cerebral cortex will not be considered in this chapter. Their neurotransmitters are not known. 

The nucleo-olivary and vestibulo-olivary projections The GABAergic afferents of the inferior olive... 

GAD-immunoreactive neurons in the parasolitary and cuneate nuclei could be labelled after injection of retrograde tracers in the inferior olive of the rat (Nelson and Mugnaini, 1989). These nuclei, therefore, provide additional GABAergic projections to the inferior olive. The projection of the ipsilateral parasolitary nucleus was located in the medial subnucleus c of the caudal MAO by these authors. Connections from the parasolitary nucleus (indicated as the lateral solitary nucleus) also were documented in earlier studies by Loewy and Burton (1978) and Molinari (1985) in the cat. The inhibitory connections from the cuneate nucleus in the rat are crossed and terminate in the medial DAO. A similar GABAergic cuneo-olivary pathway appears to be responsible... 

Fig. 164. The nucleo-olivary projection in the rat. Data from Ruigrok and Voogd (1990). Upper and lower block diagrams represent the cerebellar and vestibular nuclei, and the subdivisions of the inferior olive respectively. According to Ruigrok and Voogd (1990) the cerebellar nuclei and their olivary target nuclei can be considered as a continuum, stretching from the rostral medial cerebellar nucleus, projecting to caudal MAO, to the lateral vestibular nucleus, projecting to the dorsal fold of the DAO. DL = dorsolateral protuberance of the medial cerebellar nucleus DMC = dorsomedial cell column IntA = anterior interposed nucleus IntDL = dorsolateral hump IntP = posterior interposed nucleus lOD = dorsal accessory olive lODM = dorsomedial cell column lOM = medial accessory olive lOP = principal olive Lat = lateral cerebellar nucleus LVe = lateral vestibular nucleus Med = medial cerebellar nucleus VL = ventrolateral outgrowth.

The nucleo-olivary projection is not completely crossed. Some fibers from the dorsolateral hump, IP and the ventromedial lateral nucleus recross at the level of the inferior olive, and terminate in the ipsilateral DM, rostral MAO and ventral leaf of the PO respectively. Ipsilateral labelling was sparse or absent in other parts of the inferior olive. 

Fig. 171. Termination zones in the anterior lobe of the dorsal (A, DF-SOCPs), ventral (B, VF-SOCPs), dorsolateral (C, DLF-SOCPs) and lateral (D, LF-SOCP) spino-olivo-cerebellar paths. The diagrams represent those parts of lobules IV and V in the left half of the anterior lobe which are accessible at the cerebellar surface. Borders between zones a-d, are indicated with lines. Areas activated from hindlimb and forelimb nerves through direct and indirect paths from the dorsal funiculus nuclei (DFN) or spinal cord to the inferior olive (10) are indicated (see key). The DF-SOCP projection (from forelimb nerves) and the LF-SOCP projection to the C2 zone, and the VF-SOCP projection to the b zone are bilateral, whereas all other projections are ipsilateral. B-D based on Larson et al. 1969a, 1969b and Oscarsson and Sjolund 1977a, 1977b. Ekerot and Larson (1979a)...

Fig. 179. Diagram of lamellar and zonal distribution of olivary afferents and efferents in the rat. The two lamellae (folds) of the dorsal accessory olive (DAO, 1 and 2) and the horizontal lamella of the medial accessory olive (MAO, 3) appear to receive afferents mainly from the spinal cord and dorsal column nuclei while projecting to anterior vermis and parts of intermediate cerebellum. The medial MAO (vertical lamella, 4) receives afferents from the vestibular and visual areas and projects to the posterior vermis as well as the flocculus. The rostral lamella of MAO and both lamellae of the principal olive (PO) receive projections from higher centers and send fibers to the lateral hemispheres. In the lower part of the figure, three drawings of the inferior olive demonstrate the lamellae corresponding to their sagittal zones of projection in the cerebellum. Azizi and Woodward (1987).

Fig. 185. The olivocerebellar projection to the pyramis and the uvula (lobules 8 and 9) of tbe rat cerebellum. A,B- Olivocerebellar projection zones of the lobules 8 and 9. C. Origin of these projections, indicated in diagrams of transverse sections through the inferior olive, a = subnucleus a of the medial accessory olive b = subnucleus b of the medial accessory olive beta = group beta c = subnucleus c of the medial accessory olive d = dorsal accessory olive dm = dorsomedial subnucleus m = medial accessory olive pr = principal olive 8 and 0 = lobules VIII and IX of Larsell. Relabelled and reproduced from Eisenman (1984).

Fig. 187. Olivocerebellar projection to the uvula based upon retrograde tracing experiments in the cat (Kanda et al. 1989). The bottom diagrams of the flattened inferior olive were reconstructed from their data, beta = subnucleus beta cMAO = caudal medial accessory olive dc = dorsal cap dlPO = dorsal leaf of the principal olive dmcc = dorsomedial cell column DU = dorsal folia uvula rMAO = rostral medial accessory olive vlo = ventrolateral outgrowth vlPO = ventral leaf of the prineipal olive VU = ventral folia uvula.

Zonal projections of the inferior olive to the nodulus (lobule X) and the flocculus have been substantiated in different species. Purkinje cells of these lobules are uniformly Zebrin-positive in rat, mouse, opossum, squirrel monkey (see Section 6.1.3.) and rabbit (Jaarsma unpublished observations). A compartmental subdivision of the white matter of the nodulus and the flocculus was demonstrated with AChE-histochemistry in the rabbit and the monkey (Section 6.1.5.) and correlated with the olivocerebellar projection to these lobules (Voogd et al., 1987a,b Tan et al., 1995a,b). 

Fig. 189. Diagram of the projection from the inferior olive to the flocculus and the ventral paraflocculus in the rat. The medial accessory olive (MAO) and the principal (PO) are drawn as diagrams of the unfolded inferior olive the cortex of the flocculus and the ventral paraflocculus are unfolded. Different climbing fiber zones are indicated with different symbols. The climbing fiber zones of the rat flocculus corresponds to those in the rabbit (Fig. 188). FD corresponds to zone 1 of the rabbit FE to zone 2 FD to zone 3 and FE to zone 4. FD and FD continue as zone D of the paraflocculus. C2 = C2 zone caud = caudal dc = dorsal cap FD, FD = FD ( ) zone (projections of vlo and PO) FE, FE = FE ( ) zone (projections of dc) FLOd and v = dorsal and ventral surface of the flocculus MAO = medial accessory olive PO = principal olive rost = rostral vlo = ventrolateral outgrowth VPFL = ventral paraflocculus. Ruigrok et al. (1992)...

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