Interposed nucleus

The subdivision of Weidenreich-Ogawa received strong support from the localization of the fibers in the superior cerebellar peduncle. A small medial and a large lateral portion can be distinguished in this pathway in most mammals at its exit from the central nuclei (see in Fig. 102). Experiments in cat (Verhaart, 1956 Voogd, 1964) and rat (Haroian et ah, 1981) have shown that the medial part of the superior cerebellar peduncle takes its origin from the nuclei of the caudomedial group, mainly from the ipsilateral posterior interposed nucleus, and the lateral portion from the ipsilateral anterior interposed and lateral cerebellar nucleus. 

Fig. 103. The cerebellar nuclei of the cat. The transitional U-shaped region of the fastigial and posterior interposed nuclei is indicated by double hatching, be = brachium conjunctivum cr = restiform body DV = descending vestibular nucleus F = fastigial nucleus flo = floccular peduncle Ftail = tail of the fastigial nucleus lA = anterior interposed nucleus IP = posterior interposed nucleus L = lateral cerebellar nucleus LV = lateral vestibular nucleus MV = medial vestibular nucleus SV = superior vestibular nucleus u = uncinate tract Y = group y of Brodal and Pompeiano (1957).

Fig. 104. Two transverse, AChE-incubated sections through the cerebellar nuclei of the cat, A. Rostral section. B. Caudal section. Note medium-sized cells of dorsal group y in floccular peduncle and strongly AChE positive ventral group y along dorsal border of restiform body in (A) U-shaped nucleus between IP and F in (B). cr = restiform body F = fastigial nucleus flo-i-y = floccular peduncle with group y lA = anterior interposed nucleus IP = posterior interposed nucleus IP/F = U-shaped nucleus between F and IP L = lateral cerebellar nucleus sad = stria acoustica dorsalis.

Large cells are prominent in the rostral part of the medial nucleus, small cells predominate in its ventromedial and caudal parts (Flood and Jansen, 1961). The lateral border of the medial nucleus is flush with the AChE-positive raphe which forms the lateral border of the medial A-compartment of the anterior vermis. AChE is concentrated in the lateral and ventral parts of the medial nucleus and in the neuropil of cell groups scattered in between the medial and the anterior interposed nucleus. Caudally these AChE-positive clusters coalesce in a U-shaped nucleus located at the transition of the medial and the posterior interposed nucleus (Fig. 104B). The medial limb of the U forms the lateral border zone of the fastigial nucleus, the lateral limb usually is included with... 

The posterior interposed nucleus is best distinguished in horizontal sections. A cell-free zone separates it from the anterior interposed and lateral nuclei. Medially the posterior interposed nucleus is continuous with the fastigial nucleus. Cells at the junction of these two nuclei project to the spinal cord (Matsushita and Hosoya, 1978 and Bentivoglio and Kuypers, 1982). This region was distinguished as the interstitial cell group, the target nucleus of the X zone, by Buisseret-Delmas et al. (1993). 

Deiters nucleus with its large AChE-positive perikarya in an unstained neuropil is wedged in between the AChE-rich areas of the group y and the medial vestibular nucleus and reaches far dorsally into the hilus region of the central nuclei. Purkinje cell fibers enter Deiters nucleus as perforating fibers, passing in between the dorsolateral protuberance and the anterior interposed nucleus, and through the middle part of the medial nucleus. More rostrally, where Deiters nucleus has disappeared, the AChE-rich neuropil of the superior and medial vestibular nuclei meet at the oblique border between the two nuclei. 

According to Tolbert et al. (1978a) the nucleo-olivary neurons in the cat are concentrated in the ventral parts of the dentate and posterior interposed nuclei, they are scarce in the fastigial nucleus. Concentrations of these small neurons were also reported in the rostral and caudal poles and the hilar portion of the dentate nucleus and the lateral parts of the interposed nucleus in the rat (Brown et al., 1977 Chan-Palay, 1977). A more diffuse distribution of these cells was noticed in experiments with retrograde tracing of Martin et al. (1976) in the dentate and interposed nuclei of the opossum and in double labelling studies with fluorescent dyes in rat (Bentivoglio and Kuypers, 1982) and cat (Bharos et al., 1981). 

The GABAergic-nucleocortical cells may be identical to the small nucleocortical neurons that were identified in the posterior interposed nucleus and along the boundaries of the lateral nucleus of the rat by retrograde transport of an antibody to GAD... 

The existence of a rest group of neurons that remains unaffected by large lesions of the efferent cerebellar pathways in the kitten has been claimed as evidence in favour of the presence of intrinsic or nucleocortical neurons in the central nuclei (Jansen and Jansen 1955). Many of these neurons were found to be large and to be located in the posterior interposed nucleus. Intrinsic neurons of the cerebellar nuclei have been observed in Golgi preparations of the rat by Chan-Palay (1973a, 1977) as small multipolar neurons in the dentate nucleus. The terminals of these intrinsic, inhibitory neurons on the soma and dendrites of cerebellar nuclear cells were tentatively identified as small... 

One group of small neurons in the rhesus monkey, which was described by Langer (1985) under the name of the basal interstitial nucleus (see Section 5.1.), displays uniform and strong AChE activity. These small cells lie dispersed in the white matter of the flocculus and the nodulus and ventral to the dentate and the posterior interposed nucleus, in the roof of the fourth ventricle. The presence of strongly AChE-positive but ChAT-negative small cells in the white matter of the flocculus of the rat, that may correspond to Langer s interstitial nucleus, was noticed by Komei et al. (1983). 

Rg. 117. Localization of serotonin-like immunoreactivity in transverse sections through the cerebellar nuclei of the opossum. DN = dentate nucleus FN = fastigial nucleus IPA = anterior interposed nucleus IPP = posterior interposed nucleus. Bishop et al. (1985). 

Fig. 123. Diagram of the corticonuclear projection in the cat. Based on retrograde labelling of Purkinje cells and their axons after injections of HRP in their target nuclei. A = A zone A = Anterior interposed nucleus ANS = ansiform lobule B = B zone C1-C3 = C1-C3 zones CRII = crus II of the ansiform lobule D1-D2 = D1-D2 zones DV = descendng vestibular nucleus F = fastigial nucleus FLOC = flocculus IP = posterior interposed nucleus L = lateral eerebellar nucleus LOB POST = posterior lobe LOB ANT = anterior lobe LV = Deiters nucleus MVmc = magnocellular medial vestibular nucleus MVpc = parvicellular medial vestibular nucleus PFL = paraflocculus PFLD = dorsal paraflocculus PFLV = ventral paraflocculus PMED = paramedian lobule SV = superior vestibular nucleus I-X = lobules I-X. Bigare (1980).

Fig. 124. Comparison of bands of AChE reaction product in the molecular layer of the anterior vermis of cat cerebellum and retrograde labelling of Purkinje cells in B and lateral A zones after an injection of HRP in the vestibular nuclei (A-C) and in the B and X zones after an injection in the lateral fastigial nucleus and the B compartment (D-F). Note different size of Purkinje cells in B and X zones. A = A zone B = B zone Deit = Deiters nucleus DV = descending vestibular nucleus F = fastigial nucleus lA = anterior interposed nucleus MV = medial vestibular nucleus X = X zone. I-V = lobules I-V. Voogd (1989).

V takes its origin from the posterior interposed nucleus. 

Fig. 125. White matter compartments Cj, D, and D2 in the paraflocculus of the cat in transverse, AChE-reacted sections. Note concentric arrangement of the compartments in the dorsal and the ventral paraflocculus. A = caudalmost section D = rostralmost section. ANS = ansiform lobule brp = brachium pontis Cl-3 = Cl-3 compartments crest = restiform body D = dentate nucleus D (1,2) = D (1,2) compartments F = fastigial nucleus FLO = flocculus lA = anterior interposed nucleus IP = posterior interposed nucleus PFLD = dorsal paraflocculus PFLV = ventral paraflocculus PMD = paramedian lobule.

The C2 compartment is clearly related to the posterior interposed nucleus. Rostrally it is located dorsal to the anterior interposed nucleus, in the intermediate part of the hemisphere. From the posterior interposed nucleus the C2 compartment extends dorso-laterally into the ansiform lobule, caudally into the paramedian lobule and ventrolater-ally into the paraflocculus and the flocculus (Fig. 148). In the anterior lobe C2 is located between the C, and C3 compartments. Ventrally C, and C3 fuse and are related to the... 

Fig. 127. Distribution of acetylcholinesterase at the borders of white matter compartments in the anterior lobe of Macaco fascicularis A-C3 = A-C, zones be = brachium conjunctivum bp = brachium pontis FLO = flocculus lA = anterior interposed nucleus m = midline PFLV = ventral paraflocculus.

Fig. 128. Diagrammatic representation of the corticonuclear projection of lobule V in Galago. There are at least six identifiable corticonuclear projection zones in the lobule V cortex. The vermis consists of zones A and B, the intermediate cortex of three zones C, - C3 and the lateral cortex of a single D zone, f = flocculus IC = intermediate cortex LC = lateral cortex Ivn = lateral vestibular nucleus 1-nia = lateral anterior interposed nucleus m - nia = medial anterior interposed nucleus m - nip = medial posterior interposed nucleus nl = lateral cerebellar nucleus nm = medial nucleus vc = vermal cortex. Haines and Rubertone (1979)...

Fig. 129. Schematic drawing of the distribution of motilin-immunoreactive (M-i) Purkinje cells (open triangles) and glutamic acid decarboxylase-immunoreactive (GAD-i) Purkinje cells (filled circles) in a coronal section of rat cerebellum. M-i cells and GAD-i cells are both more concentrated in the flocculus and the paraflocculus than elsewhere. Both cell types occur in the vermis and participate in the formation of the sagittal microzones (arrows). M-i terminal axon projections in the deep cerebellar nuclei are heaviest in the dentate (D left side) and GAD-i projections are heaviest in the lateral vestibular nucleus (LV right side). 1 = interposed nucleus F = fastigial nucleus. Chan-Palay et al. (1981).

Fig. 143. Comparison between Purkinje cells of the A and B zone (open circles) retrogradely labelled from the vestibular nuclei (left side) and retrograde labelling of Purkinje cells of the X zone after an injection of WGA-HRP in the transitional region of the fastigial and posterior interposed nucleus the rat (right side). Purkinje cells of the X zone occupy the Zebrin-positive P2+ zone labelled Purkinje cells of the lateral A zone and the B zone are located in the Zebrin-negative PI- and P2- zones. Graphical reconstructions of transverse sections double labelled for HRP reaction product and Zebrin 1 immunocytochemistry. COP = copula pyra-midis CrI and II = crus I and II of the paramedian lobule PMD = paramedian lobule SI = simple lobule I-X = lobules I-X. Voogd et al. (1991b).

The white matter compartments of the flocculus do not simply continue as components of the floccular peduncle, but a reorganization takes place, that directs Purkinje cell axons from the compartments 2 and 4 to the medial vestibular nucleus and of the compartments 1 and 3 to the superior vestibular nucleus. The C2 compartment does not contribute to the floccular peduncle, but leads its fibers towards the posterior interposed nucleus. In monkeys the equivalent of compartment 1 of the rabbit extends in the roof of the fourth ventricle, along the basal interstitial nucleus of the cerebellum (Fig. 148). 

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