Dorsal Lamella Research Articles

Olivocerebellar projections to paramedian lobule in tree shrew ( Tupaia glis): a horseradish peroxidase study

Horseradish peroxidase (HRP) was used as a retrograde tracer to identify the distribution pattern of labeled cells in the inferior olivary nucleus (IO) of Tupaia. Crystallized HRP was implanted into dorsal (DPML) and ventral (VPML) divisions of the paramedian lobule (PML) and, following appropriate survival times, the tissues were processed using diaminobenzidine and tetramethylbenzidine as chromogens. Subsequent to implants into lateral DPML and VPML, HRP-labeling is seen in rostral subgroup a of the medial accessory olive (MAO) and in the medial part of the dorsal accessory olive (DAO m) and ventral lamellae of the principal olive (VLPO) close to their rostral poles. The lateral bend and adjacent dorsal lamella of the principal olive and rostral subgroup c of MAO also contain HRP-reactive somata following lateral DPML implants. Subsequent to implants in central DPML, labeling is seen in rostral DAO m and subgroup a of MAO. Central VPML implants result in additional clusters of labeled cells in VLPO, the lateral bend of the principal olive (PO), and subgroup c of MAO. Following implants of HRP into medial PML reactive somata are found in dorsomedial VLPO and DLPO, and clusters of labeled cells are present in caudal subgroup a of MAO and DAO m. In contrast to implants in central and lateral PML, rostral DAO m and PO are devoid of reactive neurons. These results show that olivocerebellar projections to PML of Tupaia are exclusively contralateral and topographically organized. Collectively these olivocerebellar data corroborate the existence of zones C 1, C 2, C 3 and D in PML of Tupaia and show that their patterns are similar, in their essential features, to those seen in the corticonuclear pathway in this species.

Postnatal development of the inferior olivary complex in the rat. II. Topographic organization of the immature olivocerebellar projection.

The state of organization of the olivocerebellar projection in newborn and 5-day-old rats has been analyzed by autoradiography of anterogradely transported 3H-leucine, as well as by retrograde transport of horseradish peroxidase. The efferent axons of the inferior olivary neurons are already present and already highly organized in the cerebellum of newborn rats. Most of the autoradiographic labelling subsequent to the injection of 3H-leucine into the inferior olive is seen in the subcortical medullary zone. Labelled axons only partially invade the gray matter, where they reach the zone occupied by randomly distributed Purkinje cells. At this immature stage, olivocerebellar projections are already entirely crossed and distributed according to a pattern which is similar to the adult. At the fifth postnatal day olivocerebellar projections have moved from the medullary zone toward the interface between the molecular and the granular layers where Purkinje cells have arranged in a monolayer. Evidence for translocation of climbing fibers from their perisomatic to their peridendritic position is already distinct in these young cerebella. Combination of anterograde and retrograde fiber system tracing experiments discloses the following crossed topography of olivocerebellar projections: The caudal half of the medial accessory olive projects mainly to the vermis of the posterior lobe, whereas its rostral half projects to the flocculus, paraflocculus, and the intermediate cortex. The principal olive, ventral and dorsal lamellae, supplies climbing fiber inputs to the hemispheric cortex. The caudal half of the dorsal accessory olive projects to the lateral portion of the vermis of the anterior lobe, whereas neurons in its rostral half send their axons toward the intermediate cortex. This topographic arrangement is, therefore, similar to that reported for adult mammals. The present results, alone or when compared with those obtained during other studies on the synaptogenesis between climbing fibers and Purkinje cells, allow the following conclusions: The climbing fibers enter the cerebellar cortex before Purkinje cells have reached the developmental phase compatible with synaptogenesis. They wait in the medullary white matter until appropriate maturation of their cellular targets. Olivocerebellar topography is roughly similar in newborn, 5-day -old, and adult rats. Synaptogenesis between climbing fibers and Purkinje cells, which is known not to start before the second postnatal day, is not necessary for the establishment of the topographic organization of the olivocerebellar projection.

Longitudinal and topographical organization of the olivary projection to the cat ansiform lobule

This study on the organization of the olivary projections to the ansiform lobule in the cat was aimed at defining the longitudinal zonal pattern and the internal topography within the zones. The horseradish peroxidase method was used. Two types of injections were made: large injections covering the full extent of small groups of folia, and small injections aimed to be restricted to the single zones proposed by Voogd. It was shown that olivary projections to these parts of the cerebellum originate from the dorsal and medial accessory nuclei and from the principal nucleus, in agreement with previous studies. Moreover it was found that the ventral lamella and the dorsal lamella (and bend) of the principal nucleus give rise to two distinct, non-overlapping, cerebellar projections to D1 and D2 zones, respectively. It is thus concluded that in the cat four separate olivo-cerebellar strips, corresponnding to the C2, C3, D1 and D2 zones of Voogd, are present in the ansiform lobule. In addition a transverse rostro-caudal organization was found, in which discrete regions of each olivary subdivision are connected to discrete areas of the crural cortex, within each olivo-cerebellar strip. The old idea of a point-to-point topography in the olivo-cerebellar system is consequently still valid, being compatible with the now proven longitudinal zonal pattern of the olivo-ansiform projection. The fact that the two subdivisions of the principal olive, here shown to project to separate D1 and D2 zones of the ansiform lobule, receive specific sets of afferents suggests that the two cortical zones are part of two different cerebellar operational units.

Descending projections to the inferior olive from the mesencephalon and superior colliculus in the cat. An autoradiographic study.

Descending projections from the mesencephalon and superior colliculus to the inferior olive were analyzed by an autoradiographic tracing method. Injections of tritium-labelled leucine were placed in regions which had previously been identified as sources of afferents to the olive. These were located adjacent to the central gray and extended from the rostral red nucleus to the posterior thalamus. Additional injections were made in the superior colliculus. Other injections were placed in the basal ganglia and thalamus. Injections restricted to one side of the central mesencephalon resulted in predominantly ipsilateral labelling of the olive. After injections in the caudo-medial parafascicular and subparafascicular nuclei and rostral nucleus of Darkschewitsch, deposits of grains were observed in the rostral pole of the medial accessory olive and adjacent ventral lamella of the principal olive. The medial accessory olive contained grains into its middle third. More caudal injections which involved the interstitial nucleus of Cajal as well as the nucleus of Darkschewitsch and rostral red nucleus resulted in the dense labeling of the entire principal olive (except the dorsal cap), the entire medial accessory olive (except subnucleus beta and the caudo-medial pole) and the caudo-dorsal accessory olive. Injections centered in the caudal magnocellular red nucleus and extending into the rostral parvocellular division labelled the dorsal lamella of the principal olive almost exclusively. When only the caudal part of the red nucleus was involved in the injection, the olive was entirely clear of grains. Minor contralateral distributions were observed in the dorsomedial cell column, the medial tip of the dorsal lamella and in the caudal medial accessory olive. The deep layers of the superior colliculus were found to project strongly to the contralateral medial accessory olive immediately beside subnucleus beta and weakly to the same area ipsilaterally. Four pathways were identified as contributing fibers to the olivary projections. These were the medial longitudinal fasciculus, the medial tegmental tract, the central tegmental tract and tectospinal or tectobulbar fibers. The rubrospinal tract did not contribute projections to the olive. Injections in the caudate nucleus, entopeduncular nucleus and ventral anterior and ventral lateral thalamic nuclei, did not result in any labeling in the olive.

Participation of the principal olivary nucleus in neocerebellar motor control.

A new method for reversible cooling of the inferior olivary nucleus has been used in chronically prepared monkeys. Local olivary cooling depressed discharge of complex spikes of Purkinje cells in contralateral cerebellar cortex. Selective cooling of the principal olive (lateral and dorsal lamellae) produced movement oscillations at about 3-5 Hz of the contralateral arm during cooling in a monkey trained to make prescribed arm movements in the horizontal plane. The effects resemble those of dentate dysfunction. Selective cooling of the dorsal accessory olive and/or the overlying reticular formation, in 3 monkeys, produced during cooling a tendency for postural drift of the contralateral arm and for reduction of its movement amplitudes. These changes tended to vary together according to the degree of cooling. Arm oscillations did not occur. It is concluded that climbing fiber projections from the principal olivary nucleus are essential in the primate for optimal neocerebellar control of arm movements.

Further observations on the olivocerebellar projection in the monkey.

The distribution of retrogradely labeled cells in the inferior olive was studied following cerebellar injections of horseradish peroxidase in four experiments in macaque monkeys. The flocculus was found to receive its main projection from the dorsal cap and a minor projection from the medial accessory olive. The uvula receives fibers from the nucleus beta, the dorsomedial cell column and from an area of the medial accessory olive. The paramedian lobule is supplied from the dorsal and ventral lamella of the principal olive and from an area in each of the accessory olives. The findings are considered in the light of our more extensive information of the olivocerebellar projection in the cat and with reference to present knowledge of the longitudinal subdivision of the cerebellum in the cat. In general the principal organization appear to be the same in the cat and the monkey, in spite of some species differences. Thus the olivary area projecting to zone C2 (rostral part of the medial accessory olive) appears to be relatively larger in the monkey than in the cat. The same appears to be the case for the dorsal lamella of the principal olive and its cerebellar projecting zone D (probably zone D1).

A re-examination of the rubro-olivary tract in the cat, using horseradish peroxidase as a retrograde and an anterograde neuronal tracer

Most authors using free horseradish peroxidase as a retrograde tracer have had difficulties in demonstrating a rubro-olivary tract. Injections of this tracer into the inferior olive in animals of different species resulted in only a few retrogradely labelled rubral cells within the rostral part of the ipsilateral nucleus. The present study, which is based on the highly sensitive technique of Mesulam (1978), confirms this observation. Injections of free horseradish peroxidase (Serva or Sigma VI type) into the dorsal lamella of the principal olive in eleven cats gave a positive retrograde labelling of rostral rubral cells in only three animals, with a very few cells in each case. In contrast to this, olivary injections of horseradish peroxidase labelled lectin (wheat germ agglutinin) result in an abundance of retrogradely labelled cells within the rostral part of the ipsilateral red nucleus, the great majority of these cells being of the small and medium-sized type. Many of the retrogradely labelled rubral cells are only faintly stained. However, free horseradish peroxidase appears to be well suited as an anterograde tracer for a demonstration of the rubro-olivary tract. The findings are discussed in relation to the observation that in the cat only peroxidase conjugated to lectin can be used successfully as a retrograde tracer for a visualization of the rubro-olivary connection.

The olivocerebellar projection in the monkey. Experimental studies with the method of retrograde tracing of horseradish peroxidase.

Following injections of horseradish peroxidase (HRP) in various lobes and lobules of the macaque cerebellum the occurrence of retrogradely labeled cells in the inferior olive was mapped. Only cortical areas showing staining of the molecular layer were considered as sites of uptake of HRP. To facilitate comparisons between cases and presentation of findings, a diagram of the macaque inferior olive as imagined unfolded was constructed (Fig. 1). Attempts were made to compare the findings made with data on the olivocerebellar projection in the cat and the pattern of a longitudinal zonal subdivision of the cerebellum. In general there appears to be a remarkably close correspondence between the organization of the olivocerebellar projection in the monkey and the cat. The projection is precisely organized and appears to be purely crossed. Within the projections to some of the cerebellar cortical zones a topical pattern can be demonstrated. Olivary afferents to vermal lobules V, VII, and VIII are derived from the caudal half of the medial accessory olive, projecting to Voogd's zone A. The topical pattern resembles that in the cat (Fig. 8). after injections covering the lateral zone of the anterior lobe vermis (zone B), labeled cells are seen in the caudal part of the dorsal accessory olive. In some cases staining of the intermediate part of the anterior lobe and of the paramedian lobule is followed by labeling of cells in the rostral part of the dorsal accessory olive (zones C1 and C3) or in the rostral half of the medial accessory (zone C2). When the injected area covers lateral parts of the cerebellum, there is labeling in the principal olive (projecting to zones D1 and D2). Although not entirely decisive, the findings lend support to the view that the ventral lamella of the principal olive supplies zone D2, whereas the dorsal lamella supplies zone D1. The relatively sparse data in the literature on the afferents to the monkey olive are briefly considered. On may points the projections appear to be as in the cat. However, there is possibly a species difference between cat and monkey as concerns their receipt of afferents from the red nucleus.

The inferior olivary connections to the cerebellum in the rat studied by retrograde axonal transport of horseradish peroxidase

Olivocerebellar projections were investigated in the rat using retrograde axonal transport of horseradish peroxidase. Discrete cell groups of the inferior olive were labelled, subsequent to injections in the paravermal region, the vermis, or the caudolateral hemisphere. Injections in the midrostrocaudal third of the paravermal area resulted in labelling of cells in the medial accessory olive (MAO), in cell group “b” at caudal levels, and in its lateral portion at mid-rostrocaudal levels. The rostral pole of the principal olive (PO), the dorsal accessory olive (DAO), and the dorsomedial cell column, were heavily labelled. By comparison, caudal paravermal injections resulted in labelling in the medial part of the mid-rostrocaudal levels of the MAO, but not in its caudal portion. The PO lamellae were labelled in their lateral half, excluding the lateral bend connecting them. Injections slightly lateral within this paravermal area gave no caudal MAO labelling, but did label cells in segments of both PO lamellae, medial to those in the previous case. From vermal injections, cell groups “b” and “c” of the caudal MAO were labelled, but no labelled cells were present in the PO. Subsequent to injections in the paramedian lobule, cells in the dorsal lamella of the PO were labelled. No cells of the MAO were labelled. These results are discussed in terms of specific labelling patterns and the general concepts of organization presently held for the Olivocerebellar system.

The olivocerebellar projections to the flocculus and paraflocculus in the cat, compared to those in the rabbit. A study using horseradish peroxidase as a tracer

The projections from the inferior olive to the flocculus and paraflocculus in the cat have been mapped by means of the method of retrograde axonal transport of horseradish peroxidase. The findings show that the afferents to the flocculus are derived from the dorsal cap, ventrolateral outgrowth, the principal olive (the caudal parts of the ventral and dorsal lamella) and from the rostral part of the medial accessory olive. The fibers to the paraflocculus come from the caudal part of the principal and from the rostral part of the medial accessory olive. Details in the projections are seen from Figs. 1 and 2. Concerning some points the findings are at variance with those made in the rabbit by Hoddevik and Brodal 9, and suggest that there are species differences hitherto not known.

The parieto-rubro-olivary pathway in the cat.

Stimulation of the parietal association cortex as well as the frontal motor cortex elicited clearly extracellular unitary activities or field potentials in the ipsilateral inferior olive in the cat. The parietal-induced responses came out generally at a longer and more variable latency than the frontal-induced ones. This suggested the existence of an indirect pathway from the parietal association cortex to the inferior olive. The recording sites for the parietal-induced responses were located not only in the dorsal lamella but also in the ventral lamella of the principal olive and in the medial accessory olive. Such olivary sites were exclusively in the rostral half of the inferior olive, and these areas in the olive were considered to give projection fibres predominantly to the hemispherical parts of the cerebe-lar cortex (neocerebellum). Small neuronal cells were labelled with horseradish peroxidase (HRP) homolaterally in the midbrain tegmentum, after HRP was injected through recording glass microelectrodes into the inferior olive where only the parietal-induced responses were evidently recorded. These small cells were distributed in the rostral one-third of the red nucleus and/or around the adjacent midbrain reticular formation close to the lateral border of the red nucleus. In referring to recent anatomical and physiological data, such small neurones labelled with HRP could be identified as the parvocellular red nucleus neurones. The present results indicate the existence of the parieto-rubro-olivary pathway system in the cat and suggest, in association with our previous studies, that the parvocellular red nucleus neurones participate in control of highly co-ordinated posture and movement predominantly through the neocerebellum.

The olivocerebellar projection in the cat studied with the method of retrograde axonal transport of horseradish peroxidase. VII. The projection to lobulus simplex, crus I and II.

The olivocerebellar projection to lobulus simplex, crus I and II in the cat was investigated by means of retrograde axonal transport of horseradish peroxidase (HRP). The distribution of labeled cells in the inferior olive following HRP injections in lobulus simplex, crus I and II confirmed the findings by Brodal ('40b) that the rostral half of the principal olive projects to these areas of the cerebellar hemisphere. However, concerning details there are some differences in so far as the heaviest contribution to crus I comes from the medial parts of the ventral and dorsal lamella, that to crus II from its lateral part, especially the ventral bend. The present findings show that in addition the rostral part of the medial and the rostromedial part of the dorsal accessory olive project to these areas of the cerebellar cortex. Further details in the projection are shown in figure 8B. The findings agree fairly well with the electrophysiological results of Armstrong et al. ('74) and the experimental anatomical data of Groenewegen and Voogd ('77a,b). An attempt is made to correlate the findings with the pattern of longitudinal zonal subdivision of the cerebellum. There is evidence for a topical organization within the projection to crus I and II and parts of their projection areas in the principal olive. The distribution of the labeled cells which project to lobulus simplex, crus I and II is discussed in relation to afferent pathways to the inferior olive.

The synaptic terminations of certain midbrain-olivary fibers in the opossum.

The nuclear origin and distribution of midbrain-olivary fibers has been described in a previous study utilizing axonal transport techniques (Linauts and Martin, '78a). The present report extends their results to the electron microscopic level and details the postsynaptic distribution of such fibers. Lesions within the ventral periaqueductal grey and adjacent tegmentum, the red nucleus or the nucleus subparafascicularis result in electron dense axon terminals within the olive at survival times of 48, 72 and 96 hours. At 72 hours, many degenerating presynaptic profiles shrink, become irregular in shape and are totally or partially surrounded by glial processes. The principal olivary nucleus contains the majority of these profiles. However, the subparafascicular terminals are more abundant in the rostral and intermediate parts of the medial accessory nucleus and the rubral terminals are concentrated within the dorsal lamella of the principal nucleus. The nuclear location of the degenerating terminals was determined by examination of 1 micrometer plastic sections cut in the transverse plane from each block face prior to thin sectioning. Degenerating terminals were counted in three cases, one from each of the three lesion sites described above. When taken together these cases show that just over 50% of the degenerating terminals are presynaptic to spiny appendages and are located within the synaptic clusters (glomeruli) described previously (King, '76). The percentage of degenerating terminals in the glomeruli increases to 70% when the lesion is in the ventral periaqueductal grey and adjacent tegmentum. The remaining degenerating terminals contact dendritic shafts outside the astrocytic boundaries of the synaptic clusters. The synpatic vesicle populations within the degenerating terminals vary with the location of the lesion. Lesions in the ventral periaqueductal grey and the adjacent tegmentum result in the degeneration of terminals with either clear spherical vesicles or endings with both clear spherical vesicles and a variable number of large dense core vesicles. In contrast, the primary degenerative changes that occur after destruction of the red nucleus or the nucleus subparafascicularis are in terminals with clear spherical vesicles. When the synaptic complex was present in the plane of section, regardless of the site of the lesion, the degenerating terminals could be classified as Gray's type I. Thus, we have demonstrated that afferents from the mesencephalon terminate within synpatic clusters located in the principal and medial accessory (part A) subnuclei of the inferior olive. Although the mesencephalic afferents have multiple origins (Linauts and Martin, '78a), many of their synaptic terminals contact spiny appendages within the synaptic clusters. This postsynaptic site also receives cerebellar terminals (King et al., '76). The origin of presynaptic profiles within the synaptic clusters that contain clear pleomorphlic vesicles is yet to be determined.

Taxonomy and World Distribution of Campylopus introflexus and C. pilifer (= C. polytrichoides): A New Synthesis

Campylopus introflexus (Hedw.) Brid. sensu lato comprises two widespread, closely related species: tropical and warm-temperate C. pilifer Brid. (= C. polytrichoides DeNot.) and temperate southern hemispheric C. introflexus (Hedw.) Brid., which was recently introduced in Europe. Main differences are in the height of the dorsal lamellae of the leaves, in spore size and in seta length. In C. pilifer lamellae are more pronounced in tropical mountains than in lowland areas. An extreme form with lamellae up to seven cells high is C. pilifer var. lamellatus (Mont.) comb. nov. from Bolivia.

The olivocerebellar projection in the cat studied with the method of retrograde axonal transport of horseradish peroxidase. VI. The projection onto longitudinal zones of the paramedian lobule

Microinjections (30-50 nl) of a horseradish peroxidase (HRP) suspension of 25% (wt./vol.) were made in different folia of the paramedian lobule of cats, and the sites of occurrence of labeled cells in the inferior olive were precisely determined. In each case only a small number of cells are labeled, aggregated in a minute area. The labeled cells are found within three only of the four olivary areas previously determined (Brodal et al., '75) to project onto the paramedian lobule (fig. 1): one area in the rostral half of the medial accessory olive, another in the dorsal accessory olive (except its caudalmost part), and a third in part of the caudal half of the dorsal lamella of the principal olive. Labeled cells were never found in the fourth area, the ventral lamella. A distinct zonal pattern in the projection is demonstrated (figs. 3, 5B): a middle longitudinal zone of the paramedian lobule receives olivary afferents from the area in the medial accessory olive, a medial zone from part of the projection area in the dorsal accessory olive, a lateral zone from part of the projection area in the dorsal lamella. This zonal projection appears to extend throughout the length of the paramedian lobule (the two caudalmost folia could not be studied). tthe somatotopical pattern in the projections from the accessory olives described previously (Brodal et al., '75) is confirmed. The pattern of a zonal projection obtained with the HRP-method (fig 5B) is simpler than that deduced by Armstrong et al ('74) from recordings of antidromic potentials in the olive (fig 5A). Concerning main points there is satisfactory agreement. The phenomenon that following microinjections of HRP in superficial parts of the folia labeled cells occur within parts only of the regions of the olive which contain labeled cells following large HRP-injections in the paramedian lobule is discussed.

The olivocerebellar projection studied with the method of retrograde axonal transport of horseradish peroxidase. V. The projections to the flocculonodular lobe and the paraflocculus in the rabbit.

HRP was injected in the flocculonodular lobe and the paraflocculus in the rabbit to determine the areas of the inferior olive which project onto these cerebellar regions. Following injections in the flocculus labeled cells occurred in the dorsal cap and the rostralmost tip of the medial accessory olive. Following injections in the nodulus labeled cells were likewise found in the dorsal cap, but in addition in the rostralmost part of the dorsomedial cell column and the adjoining part of the medial accessory olive. Injections in the dorsal paraflocculus gave rise to labeling in the rostrolateral part of the medial accessory olive, while injections in the ventral paraflocculus resulted in labeling in the principal olive, mainly in the lateral part of the ventral lamella. Injections in the lateral third of the dentate nucleus gave rise to labeling mainly in the dorsal lamella of the principal olive. The results are discussed with reference to those obtained by previous authors. There are both similarities and discrepancies. It appears from what is known of afferents from areas mediating visual impulses to the inferior olive that the olivary areas projecting onto the flocculonodular lobe, and possibly the dorsal paraflocculus, may mediate visual impulses to these lobules.

Acetylcholinesterase staining in subdivisions of the cat's inferior olive.

The present paper describes a unique distribution of true AChE activity in the IO. In the dorsal accessory olive three areas with high AChE activity can be distinguished. The medial accessory olive can be subdivided into a caudal part which shows rostro-caudally directed bands with different enzymatic activity, and a rostral part which shows a more uniform, medium activity. In the nucleus beta and the dorso-medial cell column, AChE activity is low. The ventral and dorsal lamellae of the principal olive contain areas with high, medium, and low activity. The dorsal cap is strongly positive, while the ventrolateral outgrowth is negative for AChE. Enzyme distribution cannot be fully explained on the base of the known afferent and efferent connections with the IO. However, histochemical results provide evidence that generally supports a subdivision of the IO that mirrors these connections (Brodal, '40; Armstrong et al., '74' Boesten and Voogd, '75; Groenewegen et al., '75).

The olivocerebellar projection in the cat studied with the method of retrograde axonal transport of horseradish peroxidase. IV. The projection to the anterior lobe.

Following injections of horseradish peroxidase (HRP) in the cerebellar cortex of the anterior lobe of the cat, the distribution of labeled cells in the inferior olive was mapped. The findings largely confirm those made previously in studies of olivary retrograde cell loss following cerebellar ablations (Brodal, '40b). In addition, they reveal further olivary areas projecting onto the anterior lobe, and permit a more detailed analysis of the pattern in this projection. Concerning major points the results are in agreement with physiological studies by Armstrong et al. ('74). They bring supporting evidence for a longitudinal zonal pattern in the anterior lobe (fig. 6C). The middle zone of the vermis receives its fibers from a large central area in the caudal half of the medial accessory olive, a lateral zone of the vermis from the lateral half of the dorsal accessory olive. Both olivary areas project to the corresponding cerebellar zone throughout lobules V-I. The lateralmost part of the anterior lobe (lobules IV-V) receives afferents from an area in the dorsal lamella of the principal olive. The intermediate part of lobules IV-V receives afferents from the medial half of the dorsal accessory olive and from an area in the rostral half of the medial accessory olive. There is suggestive evidence that the latter projects to a middle zone, the former to a medial and a lateral zone within the intermediate part as found physiologically. Conclusions concerning projections to the intermediate part of lobules III-II could not be made. The findings in this and preceding studies with the HRP-method show that the concept of a longitudinal pattern in the cerebellum is scarcely generally valid of the entire olivocerebellar projection. Within the projections of the lateral half of the dorsal accessory olive and the area in the rostral part of the medial accessory olive there appears to be a topical relation with the folial pattern in the anterior lobe. An analysis of the findings with reference to the afferents traced anatomically to the various olivary areas permits some conclusions as to the functional role of the olivary areas. Comparison with Oscarsson's ('73) diagram of the sites of termination of two of the spinal-olivary pathways (his DF-SOCP) and VF-SOCP) permits an anatomical explanation as concerns the projections to the vermis, while correlations as concerns the intermediate part are less satisfactory.

The olivocerebellar projection in the cat studied with the method of retrograde axonal transport of horseradish peroxidase.

The distribution of labeled cells in the inferior olive of the cat has been mapped following injections of small amounts of horseradish perosidase in the paramedian lobule of the cerebellum. The distribution of labeled cells was plotted in drawings of approximately serial transverse sections. The findings in each case were transferred to a standard diagram of the olive to facilitate comparison of cases. Previous studies of the distribution of retrograde cell loss in the inferior olive following cerebellar lesions (Brodal, '40b) showed that fibers ending in the paramedian lobule come from the caudal part of the ventral lamella of the principla olive. This was confirmed with the peroxidase method, but in addition three other separate and well circumscribed area of the olive showed labeling: one in the dorsal accessory olive, another in the rostral part of the medial accessory olive, a third in the caudal part of the dorsal lamella of the principal olive (fig. 7). There is some degree of topical arrangement within the projection of each of these olivary areas to the paramedian lobule. It is particularly striking that the projection areas of the caudal one-third of the lobule are different from and overlap only little with those of the orstral two-thirds. On account of diffusion of the injected perosidase solution in the folia it could not be decided whether the different olivary areas project to particular longitudinal zones in the paramedian lobule. The main findings can be correlated with the physiological observations of Armstrong et al. ('74). Some of the "paramedian" olivary areas are labeled also following peroxidase injections in other cerebellar parts, among them the nuclei interpositus anterior and posterior. The findings are compatible with the notion that olivocerebellar fibers branch to supply more than one cerebellar region. It is confirmed that the olivocerebellar projection, including that of the nuclei, is almost completely crossed. In the discussion it is emphasized that afferents from several sources converge on all four olivary regions projecting onto the paramedian lobule. The olivocerebellar projection obviously allows for divergence as well as convergence of impulses from the olive to the cerebellum. For further insight into the anatomical organization of the inferior olive, the entire olivocerebellar projection has to be mapped with the peroxidase methods, and further studies of the afferents to the olive are needed. In such studies, as well as in physiological ones, it is essential that findings are described with meticulous reference to the topography of the olivary subdivisions.

The structure and connections of the developing inferior olivary nucleus of the rhesus monkey (Macaca mulatta).

AbstractStructural and morphological changes were examined in the inferior olivary complex of 25 rhesus monkeys that were 60 days gestation to three months after parturition. At different ages, one‐half brain stem was sectioned sagittaly, and when possible the symmetrical half was sectioned in either the coronal or the horizontal plane. Serial sections were stained by the silver reduction method of Stotler ('51).The olivary complex undergoes its major development between 60 and 129 days gestation when its length, cellular morphology, and afferent patterns resemble those of the adult organ. Structurally, the three major divisions—the principal nucleus, the dorsal accessory nucleus, and the medial accessory nucleus—can be identified at 60 days gestation. At that time, the medial accessory nucleus, the largest of the three, can be subdivided into a ventrolateral and a dorsomedial section; as it develops, it extends caudally and acquires a small cap of cells on its dorsomedial part. By 80 days, the dorsal lamella of the principal nucleus, initially smaller than the ventral, equals the ventral lamella in size and continues to enlarge until by 100 days it has developed two large sulci. The dorsal accessory nucleus, the smallest of the three divisions, initially has a distinct connection with the caudal part of the dorsal lamella of the principal nucleus but it is lost by 92 days.Major afferents to the inferior olive could easily be identified in the early fetal tissue—before the development of the dense neuropil. Afferents first arise from the lateral funiculus of the spinal cord at 60 days and project primarily onto the ventrolateral part of the medial accessory. As they develop, they gradually project more rostrally along the ventrolateral section, onto the dorsomedial section of the medial accessory, onto the caudal part of the ventral lamella, and along the caudomedial part of the dorsal accessory. At 92 days gestation the central tegmental fasciculus, most of which originates from the red nucleus projects into the rostral and later into the middle section of the dorsal lamella, into the rostral ventral lamella, and a few into the rostrolateral part of the dorsal accessory and to the rostral third of the medial accessory. A few fibers arising from the corticospinal tract enter the caudal section of medial accessory, and a few fibers project vertically from the dorsomedial tegmental region of the medulla into the medial section of the dorsal accessory.