Mossy and climbing fiber collateral inputs in monkey cerebellar paraflocculus lobulus petrosus and hemispheric lobule VII and their relevance to oculomotor functions

Recent lesion studies on monkeys suggest that the cerebellar lobulus petrosus of the paraflocculus (LP) and crura I and II of hemispheric lobule VII (H-7) are involved in smooth pursuit eye movement control. To reveal the relationship between the LP and H-7, we studied mossy and climbing fiber collateral inputs to these areas in four cynamolgus monkeys. After unilateral injections of retrograde tracers into the LP, labeled mossy fibers were seen ipsilaterally in the crura I and II of H-7. A very small number of labeled mossy fiber collaterals were also seen in the dorsal paraflocculus (DP). Labeled climbing fibers were seen exclusively in the ipsilateral crus I. No labeled mossy/climbing fibers were seen in the flocculus, ventral paraflocculus and other cortical areas. Combined injections of fast blue in the LP and cholera toxin subunit B in the posterior crus I and crus II of H-7 resulted in a small number of the double-labeled pontine and principal olivary neurons. Combined injections in the LP and DP induced only a few double-labeled neurons in the pontine nuclei, and no double-labeled neurons in the olivary nuclei. These results suggest that the LP and crura I and II of H-7 may share some of their mossy and climbing fiber inputs and mediate similar functional roles involving smooth pursuit eye movement control.     

Demonstration of axonal branching of fibres from certain precerebellar nuclei to the cerebellar cortex and nuclei: a retrograde fluorescent double-labelling study in the cat

Summary The projections from certain brain stem precerebellar nuclei to the cerebellar cortex and nuclei have been examined in the cat by using the retrograde fluorescent double-labelling technique. Crystalline Fluoro-Gold was implanted into the left cerebellar nuclei from the contralateral side and rhodamine-B-isothiocyanate was injected into the overlying cerebellar cortex. The inferior olive, the lateral reticular nucleus, and the reticular tegmental pontine nucleus all contained double- as well as single-labelled neurons, and it was concluded that these nuclei have a high number of neurons whose axons branch to both the cerebellar cortex and nuclei. The neurons in the paramedian reticular nucleus and the pontine nuclei proper appear to project only to the cerebellar cortex.     

The feline oculomotor nucleus: morphological subdivisions and projection to the cerebellar cortex and nuclei

Summary The cytoarchitecture of the feline oculomotor nucleus was examined in sections stained with thionin and neutral red. Five different subdivisions (caudal central, paramedian, ventral, dorsomedial and dorsolateral divisions) can be identified on each side of the midline. This observation is discussed, and our findings are compared to previous studies of the cytoarchitecture or central muscular representation of the oculomotor nucleus in which different subgroups have been distinguished. Implants or injections of the wheat germ agglutinin-horseradish peroxidase complex have revealed that all five subdivisions project to different parts of the cerebellar cortex and nuclei. Retrogradely labelled cells were found in the oculomotor nucleus in 18 cases following deposition of tracer in the fastigial and interposed nuclei and certain regions of the anterior, posterior and flocculonodular lobes. The projection is bilateral and appears to have its main termination in flocculus. It originates from small neurons, especially from those located along the dorsal border of the oculomotor nucleus.     

The cerebellar projection from the raphe nuclei in the cat as studied with the method of retrograde transport of horseradish peroxidase

Summary Following injections of horseradish peroxidase (HRP) in the cerebellar cortex and nuclei of the cat, the distribution of labeled cells in the raphe nuclei was mapped. The findings confirm those made previously in studies of retrograde cell degeneration following cerebellar ablations (Brodal et al., 1960a), and in addition reveal new details in the projection of the raphe nuclei onto the cerebellar cortex and nuclei.All the raphe nuclei except nucleus linearis intermedius and nucleus linearis rostralis project onto the cerebellar cortex. The nuclei raphe obscurus and pontis contribute the greatest number of afferents to the cerebellum.With the exception of lobule VI which probably is the recipient of a weak projection, all parts of the cerebellar cortex receive afferents from the raphe nuclei. The heaviest projection is to the vermis of lobules VIIA and X, and to crus II. The afferents to the cerebellar nuclei are few in number (Tables 2–6).The observations indicate that each raphe neuron probably projects to more than one terminal site in the cerebellum.The findings are discussed with reference to other efferent and afferent studies of the raphe nuclei. All these studies indicate that the raphe nuclei have widespread efferent and afferent connections, making them capable to participate in a variety of regulatory functions.List of abbreviations f.apm. Ansoparamedian fissure - f.icul. Intraculminate fissure - f.in.cr. Intercrural fissure - fl. Flocculus - f.pc. Preculminate fissure - f.pfl. parafloccular fissure - f.ppd. Prepyramidal fissure - f.pr. Fissura prima - f.prc. Precentral fissure - f.prc.a Precentral fissure a - f.p.l. Posterolateral fissure - f.p.s. Posterior superior fissure - f.sec. Fissura secunda - HII–HX Hemispheral lobules II–X - HVIIA cr.I, cr. II Crus I and II of lobule HVIIA - HVIIIA,B Sublobules A and B of lobule HVIII - Li Nucleus linearis intermedius - Lr Nucleus linearis rostralis - l.ans. Ansiform lobule - N.f. Nucleus fastigii - N.i.a. Nucleus interpositus anterior - N.i.p. Nucleus interpositus posterior - N.l. Nucleus lateralis - pfl.d. Dorsal paraflocculus - pfl.v. Ventral paraflocculus - Rd Nucleus raphe dorsalis - Rm Nucleus raphe magnus - Rob Nucleus raphe obscurus - Rpa Nucleus raphe pallidus - Rpo Nucleus raphe pontis - Sc Nucleus raphe centralis superior - s.int.cr.1 Intracrural sulcus 1 - s.int.cr.2 Intracrural sulcus 2 - I–VI Vermian lobules I–VI - VIIA,B Anterior and posterior sublobule of lobule VII - VIIIA,B Anterior and posterior sublobule of lobule VIII     

The cerebellar corticonuclear and nucleocortical projections in the cat as studied with anterograde and retrograde transport of horseradish peroxidase

Summary The cerebellar paramedian corticonuclear and nucleocortical connections in the cat were studied by means of anterograde and retrograde transport of HRP.Previous experimental studies have given evidence that the paramedian cortex in a lateromedial direction can be subdivided, into six longitudinal zones. These are recognized as zones D₂, D₁, C₃, C₂, C₁ and B. An analysis of our material suggests that each cortical zone has its own field of termination in the cerebellar nuclei and that the Purkinje fibres from one zone have only one terminal region. The nuclear terminal areas for the fibres from the described cortical zones are the ventral nucleus lateralis (the D₂ zone), the transition area between the nucleus lateralis and nucleus interpositus anterior (the D₁ zone), the dorsolateral nucleus interpositus posterior (the C₂ zone), the ventromedial nucleus interpositus posterior (the C₁ zone), and the dorsomedial nucleus interpositus anterior (the B zone). A separate nuclear terminal region for the fibres from a cortical C₃ zone could not be positively demonstrated, but a comparison of cases makes it likeky that it is located in the transition area of nucleus lateralis and nucleus interpositus anterior, medially to the D₁ zone.The rostral folia of the paramedian lobule project more laterally in the cerebellar nuclei than do the caudal folia. Furthermore, our findings indicate that the axons of the Purkinje cells in one folium from medial to lateral terminate along a mediolateral nuclear band which loops from the dorsomedial nucleus interpositus anterior down into the ventral nucleus interpositus posterior, and from a bend in this part to the dorsal nucleus interpositus posterior, and hence into the transition zone of nucleus interpositus anterior and nucleus lateralis, from here to proceed caudally to its end.The nucleocortical projection shows with some exceptions the same zonal arrangement as the corticonuclear, but a few labelled nuclear neurons were in some cases found in the fastigial nucleus. This nucleus does not receive Purkinje axons from the paramedian lobule. This shows that although retrogradely labelled nuclear cells usually were located among or just adjacent to anterogradely filled terminal fibres, there is not a complete reciprocity in the corticonuclear and nucleocortical projections. The observations furthermore indicate that the cortical afferents terminate as mossy fibres.The advantages and problems encountered with the use of HRP as an anterograde tracer are discussed and the observations are related to previous observations on the corticonuclear and nucleocortical cerebellar projections.     

Typical and atypical neurovascular relations of the trigeminal nerve in the cerebellopontine angle: an anatomical study

The aim of the present study was to anatomically evaluate in adults the neurovascular trigeminal relations in the cerebellopontine angle (CPA), from a morphological and topographical perspective and thus to improve, detail and debate the pre-existing information, with educational and surgical implications. For the present anatomical study we performed bilateral dissections on 20 human adult skull bases, in formalin-fixed cadavers, at the level of the cerebellopontine angle, using the anatomical superior approach; we also studied 20 additional drawn specimens—cerebellum and brainstems, from autopsied cadavers, in order to better document the vasculature at the trigeminal root entry zone (REZ). The most constant but not exclusive neurovascular relations of the trigeminal nerves were those with the superior cerebellar artery (SCA) and the superior petrosal vein (the petrosal vein of Dandy). The regular possibility for the SCA to appear divided into a medial and a lateral branch and these to represent individual trigeminal relations at the level of the pontine cistern or REZ must not be neglected. The petrosal vein tributaries can also represent superior, inferior, or interradicular trigeminal relations. Arterioles emerging from the SCA or the anterior inferior cerebellar artery (AICA) represented trigeminal relations either at the REZ or were coursing between the trigeminal roots. A dissected specimen presented a radicular trigeminal artery emerging from the basilar artery and entering the trigeminal cavum inferior to the nerve. Another specimen presented two bony lamellae superior to the trigeminal nerve at the entrance in the trigeminal cavum—these lamellae were embedded within the lateral border of tentorium cerebelli and the posterior petroclinoid ligament. So we bring here an evidence-based support extremely useful not only for specialists dealing with this area but also for educational purposes. It appears important not only to consider the typical anatomy at this level but also to take into account the atypical and hardly predictable morphologies that may alter the diagnoses and the specific surgical procedures.     

The cerebellar corticonuclear and nucleocortical projections in the cat as studied with anterograde and retrograde transport of horseradish peroxidase

Summary The cerebellar corticonuclear and nucleocortical connections of lobulus simplex, crus I and II in the cat were studied by means of anterograde and retrograde transport of HRP. Previous experimental studies give evidence that the cortex of the cerebellar hemisphere in a lateromedial direction can be subdivided into five longitudinal zones. These are recognized as zones D₂, D₁, C₃, C₂ and C₁. Our observations indicate that each cortical zone has its own field of termination in the cerebellar nuclei, and that these nuclear fields are similar to those receiving afferents from the corresponding zones within the paramedian lobule (Dietrichs and Walberg, 1979).The Purkinje axons from each folium terminate from medial to lateral along a continuous band which loops through the cerebellar nuclei from the ventromedial part of nucleus interpositus posterior to the dorsolateral part of the same nucleus, from where it proceeds into the lateral part of nucleus interpositus anterior and the transition area between nucleus interpositus anterior and the dentate nucleus, to end within the latter. In addition to this arrangement there is a rostrocaudal organization within the hemispheral cortex so that the nuclear bands receiving Purkinje axons from the rostral folia (lobulus simplex) are situated slightly ventral to those receiving terminal fibres from the middle folia (crus I), which again are situated ventral to the terminal bands for the caudal folia (crus II).The nucleocortical projection shows largely the same zonal arrangement as the corticonuclear, but labelled nuclear neurons are in some cases found bilaterally within the fastigial nucleus. This nucleus does not receive Purkinje axons from lobulus simplex, crus I and crus II.The findings are discussed with reference to previous investigations on the cerebellar corticonuclear and nucleocortical connections, and some comments are made concerning the use of HRP as an anterograde tracer.Research Fellow, The Norwegian Research Council for Science and the Humanities     

Relation of callosal and striate-extrastriate cortical connections in the rat: Morphological definition of extrastriate visual areas

Summary The main purpose of this study was to correlate the tangential distributions of visual callosal and striate-extrastriate connections in the rat. Cells of origin and terminations of the visual callosal pathway of one hemisphere were labeled by the anterograde and retrograde transport of horseradish peroxidase (HRP) after multiple injections of this enzyme in the contralateral hemisphere, while ipsilateral striate-extrastriate projection fields were revealed by using the autoradiographic method following single injections of 3H-proline in striate cortex. A remarkable complementarity in the distribution of both cortico-cortical pathways was revealed by superimposing in a camera lucida the patterns of callosal and striate-extrastriate projections from consecutive tangential sections processed for HRP and autoradiography, respectively. Projections from striate cortex are distributed into multiple extrastriate fields which are partially or totally surrounded by cortical strips containing dense and overlapping accumulations of labeled callosal cells and terminations. In addition to projections to the following striate recipient areas described in previous reports: posterior (P), posterolateral (PL), lateromedial (LM), laterolateral (LL), anterolateral (AL) and anteromedial (AM); projections to laterointermediate (LI), laterolateral anterior (LLa), anterior (A), medial (M) and pararhinal (PR) areas were defined in the present study. Striate-extrastriate projection fields occupy only a portion of the acallosal islands that contain them, and the location of the fields within these islands correlates with the retinotopic location of the isotope injection in striate cortex. When compared to previous physiological and anatomical maps of extrastriate visual areas in the rat, the present results indicate that the distribution of callosal connections correlates with the borders of extrastriate visual areas, and that the projection from striate cortex into these areas is retinotopically organized. Surprisingly, a direct projection from striate cortex to the head representation region in somatosensory cortex was labeled, a finding that challenges the view that primary sensory areas do not connect directly.Supported by NIH grants EY 02877 to V.M.M. and HD 3352 to the Waisman Center     

The cerebellar nuclear afferent and efferent connections with the lateral reticular nucleus in the cat as studied with retrograde transport of WGA-HRP

Summary The cerebellar nuclear projection from the lateral reticular nucleus (NRL) was studied in 29 cats by means of retrograde axonal transport after implantation of the crystalline wheat germ agglutinin-horseradish peroxidase (WGA-HRP) complex in the cerebellar nuclei. It was confirmed that all the cerebellar nuclei receive afferent fibres from the NRL with the strongest termination in the ipsilateral interposed nuclei. In addition, these experiments give evidence of a previously unrecognized topical pattern in the projection to the interposed nuclei, arranged according to the same principle as in the projection to the immediately overlying cerebellar cortex. Thus, the anterior interposed nucleus receives fibres from all parts of the main NRL, its rostral part especially from laterally situated neurons, while subsequent more caudal parts from more medially situated neurons, while the posterior interposed nucleus receives fibres mainly from the dorsomedial part of the main NRL.The cerebellar nuclear projection to the NRL was investigated in 15 cats using retrograde transport after ventral microiontophoretical ejections of the WGA-HRP complex in the main NRL. The contralateral rostral fastigial nucleus was confirmed as the main origin of this projection, but projecting neurons were, in addition, discovered rostrally in the anterior interposed and dentate nuclei on the same side. No topical differences could be observed following ejections in different parts of the NRL; the majority of the projecting neurons were always concentrated along the ventral and lateral borders of the fastigial nucleus and in the adjacent medial part of the anterior interposed nucleus.     

The cerebellar corticonuclear and nucleocortical projections in the cat as studied with anterograde and retrograde transport of horseradish peroxidase

Summary The cerebellar parafloccular corticonuclear and nucleocortical connections were studied in the cat by means of anterograde and retrograde transport of horseradish peroxidase.Previous investigations have given evidence that the cortex of the paraflocculus can be subdivided into three zones. These zones are recognized as C₂, D₁ and D₂. The material presented is compatible with the findings from previous reports with other methods that each of these zones sends its Purkinje axons to separate regions within the cerebellar nuclei. These terminal fields are the lateral part of nucleus interpositus posterior (the alleged nuclear zone C₂) and the dentate nucleus and its transition area with nucleus interpositus anterior (the supposed nuclear D zones). The parafloccular corticonuclear fibres appear to terminate along a continuous mediolateral band extending from the NL through the NL-NIA transition area into the lateral NIP. This observation is in concordance with our previous findings concerning the termination of the cerebellar corticonuclear fibres (Dietrichs and Walberg 1979, 1980; Dietrichs 1981). Within the NL and NL-NIA transition area the Purkinje axons from the ventral paraflocculus terminate ventral to those from the dorsal paraflocculus.The nucleocortical projection shows the same zonal arrangement as the corticonuclear connection, indicating the presence of a corticonuclear-nucleocortical reciprocity.The findings are discussed with reference to previous studies on the parafloccular corticonuclear and nucleocortical connections, and some comments are made concerning the cerebellar zonal subdivision of this cortical area.     

The cerebellar corticonuclear projection from lobule Vb/c of the cat anterior lobe: a combined electrophysiological and autoradiographic study

Summary The present study examines the projection to the cerebellar nuclei of Purkinje cells in particular sagittal zones within the intermediate region of the cerebellar cortex. The boundaries between the zones were delimited electrophysiologically on the basis of their climbing fibre input so that a small volume (10–120 nl) of ³H-leucine could be injected into the centre of a chosen zone. The subsequent uptake and orthograde transport of labelled material by the Purkinje cells was studied autoradiographically. It was found that the smallest injections resulted in injection sites restricted to a single cortical zone and extremely reproducible results could be obtained using such a combined electrophysiological/autoradiographic technique. Larger injections sometimes spread to a neighbouring zone but the resultant terminal labelling within the deep nuclei was invariably consistent with the results obtained from smaller injections. The c₁ and c₃ olivocerebellar zones, which are known to receive climbing fibre input transmitted from the ipsilateral forelimb via a dorsal funiculus spino-olivo-cerebellar pathway (DF-SOCP), were found to project to partially overlapping regions within nucleus interpositus anterior (NIA). No projection to nucleus interpositus posterior (NIP) was demonstrated for either zone. No distinction could be seen between the terminal fields for the medial and lateral halves of the c₁ zone which are, however, known to receive their climbing fibre input from quite separate regions within the inferior olive. The c₂ zone, which was delimited on the basis of its climbing fibre input which is transmitted from both forelimbs via a lateral funiculus SOCP, was found to project exclusively to interpositus posterior. The hemispheral d₁ zone was found to project to the transitional region where interpositus anterior and the dentate nucleus adjoin.     

The cerebellar corticonuclear and nucleocortical projections in the cat as studied with anterograde and retrograde transport of horseradish peroxidase

Summary The cerebellar corticonuclear and nucleocortical connections of the anterior lobe were studied in the cat by means of anterograde and retrograde transport of HRP.Previous experimental studies have given evidence that the cortex of the anterior lobe can be subdivided in a mediolateral direction into seven longitudinal zones: A, B, C₁, C₂, C₃, D₁ and D₂. An analysis of the present material shows that the Purkinje axons from each cortical zone have their own terminal region within the cerebellar nuclei, and that these areas correspond to those receiving terminal corticonuclear fibres from the same zones in other parts of the cerebellum (Dietrichs and Walberg 1979, 1980). The terminal fields are the rostral part of the fastigial nucleus (the nuclear A zone), the medial nucleus interpositus anterior (the nuclear B zone), the ventromedial nucleus interpositus posterior (the nuclear C₁ zone), the dorsolateral nucleus interpositus posterior (the nuclear C₂ zone), the lateral nucleus interpositus anterior and the medial part of the transition area between the dentate nucleus and nucleus interpositus anterior (the nuclear C₃ zone), the lateral part of this transition area and the medial dentate nucleus (the nuclear D₁ zone) and the lateral part of the dentate nucleus (the nuclear D₂ zone). The nuclear zones have no sharp borders. The seven main terminal fields are connected by areas where scanty terminal fibres occur, indicatin that the Purkinje axons from each folium of the anterior lobe from medial to lateral terminate along a continuous band which loops through the cerebellar nuclei.With few exceptions the nucleocortical projection shows the same zonal arrangement as the corticonuclear, but there is in addition a weak nucleocortical connection to the anterior lobe from the middle and caudal parts of the fastigial nucleus.These and other findings are discussed with reference to previous studies on the corticonuclear and nucleocortical projections, and some comments are made concerning the zonal subdivision of the anterior lobe.     

Branching projection of the nucleus “k” neurons to the rabbit cerebellar paramedian lobule: a retrograde fluorescent tracing study

The nucleus "k", in the reticular core of the rabbit caudal pons, is divided into a large medial (composed of dorsal k1 and ventral k2) and a small lateral (k3) subdivision. In this study, the nucleus "k" subdivisions were examined in the rabbit with respect to projections to the cortex of rostral (rPML; face-forelimb region) and caudal (cPML; hindlimb region) paramedian lobule of the cerebellum. The retrograde fluorescent labeling method with Fast Blue (FB) and Diamidino Yellow (DY) was used. Numerous single FB or DY labeled neurons were found in defined regions of all nucleus "k" subdivisions bilaterally, with an ipsilateral preponderance. The distribution of these neurons indicated that afferents originating from different nucleus "k" subdivisions terminated in overlapping regions within the rPML and the cPML rather than in separate domains. Apart from this, double FB + DY labeled neurons (n = 104) were intermingled within a common region of single labeling, but exclusively on the ipsilateral side. Such neurons occupied predominantly the central and lateral regions of the caudal two thirds of the k1 subdivision, and were scattered in the caudal half of k2 as well as throughout the entire rostrocaudal extent of the k3 subdivision. The size of labeled perikarya varied from 20 to 40 microm in diameter. The number of neurons with branching axons was considerably lower than those with single projections to the rPML and the cPML. It amounted to about 3% in k1 and k3, and 2% in the k2 subdivision. However, this population may form an intralobular link between two somatotopically non-corresponding PML regions. The present study provides a morphological basis for further investigations for comparison with other species using both anatomical and electrophysiological methods, also with respect to other connections of the nucleus "k".     

Organization of afferent connections to the lateral and interpositus cerebellar nuclei from the brainstem relay nuclei: a horseradish peroxidase study in the cat

Afferent projections to the lateral (dentate) and interpositus cerebellar nuclei from the brainstem relay nuclei were studied in cats using the horseradish peroxidase (HRP) method. In the first series of experiments, HRP was injected into the brachium pontis. Mossy fiber terminals were anterogradely labeled, predominantly in the lateral (hemispherical) part, moderately in the intermediate part, and slightly in the vermal part of the cerebellum. Besides these terminals in the cerebellar cortex, axon terminals labeled anterogradely were also found in the cerebellar nuclei. The labeled terminals appeared almost exclusively in the lateral nucleus and rarely in the interpositus nucleus. Cells labeled retrogradely were found both in the pontine nuclei and the tegmental reticular nucleus, but not in other brainstem nuclei. In the second series of experiments, HRP was injected into the lateral and interpositus nuclei, and retrograde labeling was examined in the brainstem relay nuclei. After HRP injection into the lateral nucleus, the number of labeled cells was significantly large in the pontine nuclei, but fairly small in the reticular or vestibular nuclei. The number of labeled cells was generally large in the inferior olive, mainly in the principal olive. After HRP injection into the interpositus nucleus, the number of labeled cells was moderate in the reticular or vestibular nuclei, but small in the pontine nuclei. The number of labeled cells in the inferior olive was also large, being distributed mainly in the accessory olives. These results indicate that the pontine nuclei and the principal olive provide major afferent inputs to the lateral nucleus, whereas the reticular nuclei, the vestibular nuclei and the accessory olives are the major afferent sources to the interpositus nucleus.     

Brain afferents to the lateral caudal ventrolateral medulla: a retrograde and anterograde tracing study in the rat

The ventrolateral medulla (VLM) modulates autonomic functions, motor reactions and pain responses. The lateralmost part of the caudal VLM (VLMlat) was recently shown to be the VLM area responsible for pain modulation. In the present study, the brain sources of VLMlat afferent fibers were determined by tract-tracing techniques. Following injection of cholera toxin subunit B into the VLMlat, retrogradely labeled neurons in the forebrain occurred at the somatosensory, insular, motor, limbic and infralimbic cortices, and at the central amygdaloid nucleus. Retrogradely labeled neurons in diencephalic regions were observed in the lateral hypothalamus, posterior hypothalamus and paraventricular nucleus. In the brainstem, retrograde labeling occurred at the periaqueductal gray, red nucleus, parabrachial area, nucleus raphe magnus, nucleus tractus solitarii, lateral reticular nucleus and dorsal and ventral medullary reticular formation. In the cerebellum, retrogradely labeled neurons occurred at the lateral nucleus. Following injections of the anterograde tracer biotinylated dextran amine (BDA) into the lateral hypothalamus or paraventricular nucleus, anterogradely labeled fibers were mainly observed in the VLMlat. Injections of BDA into the periaqueductal gray, red nucleus or lateral nucleus of the cerebellum resulted in anterograde labeling in the VLMlat and lateral reticular nucleus.The present study gives an account of the brain regions putatively involved in triggering the modulatory actions elicited from the VLMlat. These include areas committed to somatosensory processing, autonomic control, somatic and visceral motor activity and affective reactions. The findings suggest that the VLMlat may play a major homeostatic role in the integration of nociception with other brain functions.     

Pallidal inputs to thalamocortical neurons projecting to the supplementary motor area: an anterograde and retrograde double labeling study in the macaque monkey

Summary The relationship between thalamocortical neurons projecting to the supplementary motor area (SMA) and pallidothalamic projection fibers was examined with an anterograde and retrograde double labeling technique in macaque monkeys (Macaca fuscata). In each monkey, Fast Blue (FB) was injected into the handarm area of the SMA after mapping the somatotopy using intracortical microstimulation, and horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) was injected into the ipsilateral internal segment of the globus pallidus (GPi). As a result, numerous projection neurons labeled with FB were distributed in pallidal terminal areas labeled with WGA-HRP in the ventral nuclear group of the thalamus. The present findings indicate that the SMA receives strong indirect projections from the GPi via the thalamus.     

The total number,time of origin and kinetics of proliferation of neurons comprising the deep cerebellar nuclei in the rhesus monkey

Summary The genesis of the neurons that form the cerebellar nuclei was studied by autoradiographic methods in 30 postnatal rhesus monkeys which were exposed to ³H-thymidine at various embryonic (E) and postnatal (P) ages. As a basis for this quantitative analysis, five 2–3 month old monkeys were used for cell counting and estimation of the total number of neurons in each of the cerebellar nuclei. The results show that the cerebellar nuclei on each side contain 131,000 neurons. There are 68,000 neurons in the dentate nucleus, 25,000 neurons in the posterior interposed nucleus, and 19,000 neurons in both the anterior interposed and fastigial nuclei. All of the neurons comprising the deep nuclei are generated during the first half of the 165 day gestation period in this species. Although neurogenesis lasts from E30 through E70, approximately 81% of the neuron population is generated during a one week period between E36 and E40, with the peak of proliferation occurring at E36. Before E45 both large (maximum diameter greater than 35 m) and small (maximum diameter 35 m or less) neurons are produced simultaneously; after this period only small neurons are generated. Although no clearcut spatio-temporal gradients of neurogenesis could be discerned along any of the cardinal axes, each cerebellar nucleus has a somewhat distinctive developmental history in terms of the onset and cessation of neurogenesis and the tempo of cell proliferation. Thus, genesis of neurons destined for the dentate nucleus begins earlier and ends later than proliferation of the neurons that ultimately comprise the fastigial nucleus. Generation of the neurons destined for the anterior and posterior interposed nuclei follows an intermediate time course. The present data on neurogenetic sequences in the deep nuclei could not be correlated with the zonal pattern of reciprocal axonal connections that link the deep nuclei and overlying cerebellar cortex.This work was supported by U.S.P.H.S. Grant NS 14841 and Postdoctoral Fellowship NS 06061     

A comparison of the distribution of the cerebellar and cortical connections of the nucleus of Darkschewitsch (ND) in the cat: a study using anterograde and retrograde HRP tracing techniques

Summary Bidirectional transport of lectin conjugated horseradish peroxidase was employed to investigate the relative distribution qf the cerebellar and cortical connections of the nucleus of Darkschewitsch in the cat. Injection of horseradish peroxidase into the deep cerebellar nuclei produced terminal labeling which extended throughout the length of the contralateral nucleus of Darkschewitsch and into the perifascicular region. Injection of horseradish peroxidase into the pericruciate cortex produced both ipsilateral terminal labeling which extended throughout the length of the nucleus of Darkschewitsch and into the perifascicular region, and ipsilateral retrograde neuronal labeling. Labeled neurons displayed a variety of shapes and sizes, were more numerous in sections cut at rostral levels of the nucleus of Darkschewitsch, and were located both within and outside fields of terminal labeling. Comparison of the distribution of labeling following cerebellar and cortical injections indicates that convergence and overlap of input from these two sources occur in the nucleus of Darkschewitsch. These findings provide the morphological basis for integration of cerebellar and cortical information in this nucleus which may, in turn, influence output from neurons which project to the cortex or to the inferior olivary nucleus.Abbreviations ASG Anterior sigmoid gyrus - CA Cerebral aqueduct - CoS Coronal sulcus - CrS Cruciate sulcus - dCN Deep cerebellar nuclei - FR Fasciculus retroflexus - INC Interstitial nucleus of Cajal - ION Inferior olivary nucleus - IP _A Interposed anterior nucleus - IP _P Interposed posterior nucleus - L Lateral nucleus - LV Lateral vestibular nucleus - M Medial nucleus - ND Nucleus of Darkschewitsch - PAG Periaqueductal gray - PSG Posterior sigmoid gyrus - PSS Presylvian sulcus - V ₃ Third ventricle - y Cell group y A preliminary report of this study was presented at the Seventeenth Meeting of the Society for Neuroscience in New Orleans, LA, November 1987     

Origin of projections from the midbrain raphe nuclei to the hypothalamic paraventricular nucleus in the rat: A combined retrograde and anterograde tracing study

A number of neuronal functions governed by the hypothalamic paraventricular nucleus are influenced by serotonin, and it is generally believed that the moderate density of serotonin-immunoreactive fibres and terminals within the paraventricular nucleus originates from the midbrain dorsal and median raphe nuclei. To further evaluate the intricate anatomy of projections from brain stem raphe nuclei of the rat, a combination of retrograde and anterograde tracing experiments were conducted to determine the medullary raphe nuclei projection to the paraventricular nucleus. Rhodamine-labelled latex microspheres, Cholera toxin subunit B and FluoroGold we used as retrograde tracers. Intracerebroventricular injections into the third ventricle of all retrograde tracers labelled a distinct population of neurons in the dorsal raphe situated in the subependymal stratum adjacent to the cerebral aqueduct indicating that these cells take up the tracer from the cerebrospinal fluid. Very few retrogradely labelled neurons were seen in the median raphe after i.c.v. administration of the tracers. Retrograde tracers delivered into the medial part of the paraventricular nucleus labelled no further cells in the midbrain dorsal and median raphe nuclei, whereas a substantial number of retrogradely labelled cells emerged in the pontine raphe magnus. However, when the retrograde tracers were delivered into the lateral part of the paraventricular nucleus, avoiding leakage of the tracer into the ventricle, very few labelled neurons were seen in the dorsal and median raphe, whereas the prominent labelling of raphe magnus neurons persisted. The anatomical organization of nerve fibres terminating in the area of paraventricular nucleus originating from midbrain raphe nuclei was studied in a series of anterograde tracing experiments using the plant lectin Phaseolus vulgaris leucoagglutinin. Injections delivered into the dorsal raphe or median raphe labelled but a few fibres in the paraventricular nucleus proper. A high number of fine calibered nerve fibres overlying the ependyma adjacent to the paraventricular nucleus was, however, seen after the injections into the subependymal rostral part of the dorsal raphe. Injections delivered into the raphe magnus gave rise to a dense plexus of terminating fibres in the parvicellular parts of the paraventricular nucleus and moderately innervated the posterior magnocellular part of the paraventricular nucleus as well as the magnocellular supraoptic nucleus. Concomitant visualization of serotonin-immunoreactive neurons and retrograde FluoroGold-tracing from the paraventricular nucleus revealed that none of the serotonergic neurons of the raphe magnus projects to this nucleus, while a few of the neurons putatively projecting to the paraventricular nucleus from the median raphe are serotonergic.

The current observations suggest that the raphe magnus constitute by far the largest raphe input to the paraventricular nucleus and strongly questions the earlier held view that most raphe fibres innervating the paraventricular nucleus are derived from the midbrain dorsal and median raphe. However, the source of serotonergic innervation of the paraventricular nucleus remains elusive.