The fiber projections from the dentate nucleus to the reticular formation of the brain stem in the rabbit

Summary The projections from the dentate nucleus to the reticular formation of the brain stem in rabbit have been examined by means of the Fink-Heimer technique. The fibers arising from the dentate nucleus primarily project to the reticular formation via the contralateral and ipsilateral descending limbs of the brachium conjunctivum. The descending fibers project bilaterally to the parvocellular reticular nucleus, the ventral reticular nucleus, the gigantocellular reticular nucleus, the nucleus raphe magnus, the oral and caudal pontine reticular nuclei, and the reticulo-tegmental nucleus.     

Olivary afferents from the brain stem reticular formation

Summary The projections from the brain stem reticular formation to the inferior olive have been studied in cats in which microinjections of horseradish peroxidase have been made into the inferior olive from a ventral approach. Retrogradely labelled cells were observed within the reticular formation proper of the medulla, pons and mesencephalon (within the nucleus reticularis parvicellularis, reticularis ventralis, reticularis gigantocellularis, reticularis lateralis, reticularis pontis caudalis, reticularis pontis oralis, cuneiformis and subcuneiformis). Labelled cells were also found within the lateral reticular nucleus (the nucleus of the lateral funiculus), the paramedian reticular and the perihypoglossal nuclei. The connections are bilateral (the projection from the lateral reticular nucleus is only contralateral). The observations demonstrate a more widespread origin for the reticulo-olivary fibres than has previously been shown and indicate that the medullary reticular formation is the area with the highest number of cells projecting to the olivary complex.Abbreviations ß nucleus ß - Br.c. superior cerebellar peduncle (brachium conjunctivum) - Br.p. middle cerebellar peduncle (brachium pontis) - C.i. inferior colliculus - C.r. inferior cerebellar peduncle (restiform body) - Cu nucleus cuneiformis - D dorsal accessory olive - dl dorsal lamella - dors.c. dorsal cap - dorsomed.c.col. dorsomedial cell column - F.l.m. medial longitudinal fasciculus - Ic or ic nucleus intercalatus - l lateral - M medial accessory olive - m medial - N.III,V,VI,VII,X,XII root fibres of cranial nerves - N.c. nucleus cuneatus - N.c.e. external (accessory) cuneate nucleus - N.c.t. nucleus of corpus trapezoideum - N.l.l. nucleus of lateral lemniscus - N.m.X dorsal motor (parasympathetic) nucleus of vagus - N.mes. mesencephalic trigeminal nucleus - Nr nucleus ruber - Nrl or N.r.l lateral reticular nucleus (nucleus of lateral funiculus) - Nrp or N.r.p. nucleus reticularis paramedianus - N.r.t. nucleus reticularis tegmenti pontis - nucl. nucleus ß - Ol.s. superior olive - P principal olive - ph or P.h. nucleus praepositus hypoglossi - PN perihypoglossal nuclei - Pp nucleus peripeduncularis - Py pyramid - Rg or R.gc. nucleus reticularis gigantocellularis - Rl or R.l. nucleus reticularis lateralis (of Olszewski) - Rp or R.pc. nucleus reticularis parvicellularis - Rpc or R.p.c. nucleus reticularis pontis caudalis - Rpo or R.p.o. nucleus reticularis pontis oralis - Rv or R.v. nucleus reticularis ventralis - Scu nucleus subcuneiformis - S.n. substantia nigra - Tr.sp.V. spinal tract of trigeminal nerve - T.s. tractus solitarius surrounded by nucleus of solitary tract - vl ventral lamella - vlo or ventrolat outgr. ventrolateral outgrowth - V.m. medial vestibular nucleus - I-XV transverse sections through the olive from caudal (I) to rostral (XV) - III,IV,V,VI,VII,X and XII motor nuclei of cranial nerves (X: nucleus ambiguus)     

The cerebellar projection from the lateral reticular nucleus as studied with retrograde transport of horseradish peroxidase

Summary The cerebellar projection from the lateral reticular nucleus (NRL) was studied in cats by means of retrograde axonal transport of horseradish peroxidase (the projection to the paramedian lobule was not included, see Brodal, 1975, for afferents to this cortical region). The entire cerebellar cortex and all cerebellar nuclei receive fibres from the NRL. The strongest connection is with the anterior lobe and lobulus VIIIB of the posterior lobe vermis. As concerns the anterior lobe the observations confirm the previous finding by Brodal (1975) that there is a clearcut topical pattern in the nuclear projection to this part of the cerebellum. The observations furthermore show that crus II is the only cerebellar region devoid of fibres from the subtrigeminal part of the NRL.The cerebellar projection from the NRL is bilateral with a heavy ipsilateral preponderance. The large majority of the labeled cells within the NRL are of the small category (<25 m in size). This and the other findings are discussed in relation to previous studies on the efferent and afferent connections of the nucleus.     

The cerebellar projection from locus coeruleus as studied with retrograde transport of horseradish peroxidase in the cat

Summary The cerebellar afferent projection from locus coeruleus has been studied in the cat by means of retrograde axonal transport of horseradish peroxidase. Labelled cells are present bilaterally in locus coeruleus only following injections in the cerebellar vermis (especially its anterior and posterior parts), the ventral paraflocculus and the flocculus. The labelled cells are restricted to the caudal half of the nucleus.A few labelled cells are also present in locus coeruleus following injections in the fastigial nucleus, and in nucleus interpositus anterior. The findings are discussed in relation to other studies on the efferent and afferent connections of the locus coeruleus.On leave from the Laboratory of Neurobiology and Department of Anatomy, Faculty of Science, Mahidol University, Bangkok, Thailand, under the Fellowship Program of the Norwegian Agency for International Development (NORAD)     

Brain stem afferents to the periabducens reticular formations (PARF) in the cat

Summary Six injections of HRP were placed in the periabducens reticular formation (PARF). Two were placed ventromedial to the caudal half of the abducend nucleus (VIn), two were placed further laterally and ventral to the rostral half of the nucleus, and two were placed rostral to the nucleus. Most injections in PARF produced cell labeling in the vestibular and perihypoglossal nuclei bilaterally and labeled cells in the reticularis gigantocellularis (Rgc) and reticularis pontis caudalis (Rpc) nuclei contralateral to the injection site. Few labeled neurons were found in the caudal part of the paramedian pontine reticular formation (PPRF). In the mesencephalon, bilateral but more numerous ipsilateral labeled cells were found in the medial mesodiencephalic region including the nuclei of Cajal, Darkschewitsch and the posterior commissure. Injections placed caudomedial to VIn resulted in a characteristic concentration of labeled cells in the ipsilateral nucleus cuneiformis and rostral half of the contralateral superior colliculus (SC). Injections placed rostral to VIn in PARF produced cell labeling in the nucleus campi Foreli. The results are related to physiological evidence which suggests that PARF is an important premotor center for coordination of oculomotor, head and body movements.     

The projection from nucleus reticularis tegmenti pontis onto the cerebellum in the cat

Summary Following stereotactically performed lesions in nucleus reticularis tegmenti pontis (N.r.t.) degenerating fibers are traced to the contralateral N.r.t., to the pontine nuclei, through brachium pontis to restricted areas of the cerebellar nuclei and to most parts of the cerebellar cortex where they terminate in the granular layer. Most degenerating fragments are found in the contralateral half of the cerebellum with the greatest density in the vermal lobules VI and VIIA and in the flocculus.Following injections of HRP in the various cerebellar lobules labeled cells are mainly present within limited groups in the N.r.t.. Injections in vermal lobules VI-VIII B give rise to labeled cells within circumscribed areas in the dorsal and ventral parts throughout the rostrocaudal extent of the N.r.t.. In cases with injections in lobule IX or the ventral paraflocculus labeled cells are found ventrally in the rostral half of the N.r.t., while following injections in the vermal lobules I-V labeled cells are mainly found in the ventral and caudal part of the N.r.t.. Following injections in the intermediate and lateral parts of the anterior lobe, Crus I and II, the paramedian lobule and the dorsal paraflocculus labeled cells occur within groups in medial and lateral parts throughout the rostrocaudal extent of the N.r.t.. Following injections in the flocculus labeled cells are found in a very distinct group in the dorsal and rostral part of the N.r.t., While an injection in the nodulus (lobule X) gave rise to a smaller group of labeled neurons in the dorsolateral corner in the caudal part of the N.r.t.. Labeled cells within processus tegmentosus lateralis (p.t.l.) are only found following injections in lobules VI-VIIIA, Crus I and II and the dorsal paraflocculus.From what is known about afferents to the N.r.t., it is concluded that no cerebellar lobule gets information from one only of these sources via the N.r.t.. Visual information can probably be mediated from the superior colliculus via the N.r.t. to the flocculus and to a minor extent to the vermal lobules VI-VIII B, and from the pretectum via the N.r.t. to both vermal and lateral parts of the cerebellum.     

Cerebellar afferents from the paramedian reticular nucleus studied with retrograde transport of horseradish peroxidase

Summary Details in the cerebellar projections from the paramedian reticular nucleus (PRN) were studied in cats and monkeys by means of retrograde axonal transport of horseradish peroxidase (HRP). In the cat the majority of the fibres projects to the anterior lobe and to the vermis of the posterior lobe (with the exception of lobules VIIB and VIIIA). A less conspicuous projection was found to the lobulus simplex, the crura and the flocculus. The cerebellar nuclei, the paramedian lobule and the paraflocculus appear to be weakly connected with the PRN. A similar distribution of the cerebellar afferent fibres was found in the monkey material. The three subgroups of the PRN in the cat are not equal in their projection. The dorsal group appears to be connected with the greater part of the cerebellar cortex and with all nuclei. The ventral group lacks a connection with lobulus IX, the flocculus and the paraflocculus, and the accessory group appears to have its strongest connection with lobulus I (lingula), the flocculus and the vermal lobules VII–X. The findings are discussed in relation to other studies on the efferent and afferent connections of the nucleus.On leave from the Laboratory of Neurobiology and Department of Anatomy, Faculty of Science, Mahidol University, Bankok, Thailand, under the Fellowship Program of the Norwegian Agency for International Development (NORAD)     

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     

The projection from the nucleus reticularis tegmenti pontis to the cerebellum in the rhesus monkey

Summary Following injections of horseradish peroxidase in various parts of the monkey cerebellum, the distribution of labelled cells in the nucleus reticularis tegmenti pontis (NRT) has been studied. As a rule, labelled cells are found at all rostrocaudal levels of the NRT regardless of the injection size and site. The densest projection from NRT seems to reach the vermal visual area (lobulus VII), a less dense projection supplies the anterior lobe while the paramedian lobule receives a more sparse projection than the anterior lobe. Very few labelled cells were found in the NRT after injections of crus I and II. The projection is topographically organized so that the dorsomedial part of the NRT supplies lobulus VII, a large central region sends fibres to the anterior lobe (and the cerebellar hemispheres), while the lateral extension of NRT (processus tegmentosus lateralis) is connected with the paramedian lobule.The results of the present study are compared with those of a preceding one of cortical afferents to NRT. It is concluded that the cortical areas projecting to the NRT seem likely to exert their influences on largely different parts of the cerebellum via the NRT. The present results are also discussed inrelation to termination of other afferent contingents in the NRT, and it is concluded that the NRT is not homogenous anatomically, and consequently different parts of the nucleus would be expected to play somewhat different functional roles.     

Synaptic action of the fastigiobulbar impulses upon neurones in the medullary reticular formation and vestibular nuclei

Summary In anaesthetized cats, the fastigial nucleus of cerebellum was stimulated with electric pulse currents, and the effects thereby induced were investigated by recording intracellularly from cells in the medullary reticular formation, the nucleus of Deiters and the descending vestibular nucleus. The early effect commonly seen in these cells was initiation of excitatory postsynaptic potentials (EPSPs) with monosynaptic latencies from both sides of the fastigial nuclei. These EPSPs appeared to be produced in part by a kind of axon reflex through cerebellar afferent fibres, but a certain portion of them was ascribable to the crossed fastigiobulbar axons, as they were influenced by stimulation of the cerebellar cortex in the manner to be expected from the previous study on cerebellar nuclei. These EPSPs were followed by a sequence of a prolonged disfacilitatory hyperpolarization and a late facilitatory depolarization, which apparently reflected the inhibition and disinhibition, respectively, produced in fastigial neurones via Purkinje cell axons of the corticonuclear projection. Either EPSPs or IPSPs were also induced in both reticular and vestibular neurones through polysynaptic pathways in which the fastigiobulbar projection might have been involved.     

The nucleus reticularis tegmenti pontis and the adjacent rostral paramedian reticular formation: differential projections to the cerebellum and the caudal brain stem

Summary The projection of the nucleus reticularis tegmenti pontis and the adjacent tegmental area, to the caudal brain stem and the cerebellum were investigated by means of anterograde transport of tritiated leucine. The nucleus reticularis tegmenti pontis was found to be exclusively connected with the cerebellum. Mossy fiber terminals were absent only from lobule X and most abundant in lobule VII and the hemispheres with a slight contralateral predominance. The paramedian pontine reticular formation projects with bilateral symmetry to the cerebellar lobules VI, VII and the crura I and II, and heavily to the medial aspect of predominantly the ipsilateral reticular formation in the lower brain stem including specific targets as the nucleus reticularis paramedianus, the nucleus prepositus hypoglossi, the nucleus intercalatus, the nucleus of Roller, the nucleus supragenualis and the dorsal cap of the inferior olive. The nucleus vestibularis medialis receives a very weak projection. The connections are discussed in the light of their possible involvement in pathways for the execution of voluntary and reflex eye movements.Abbreviations bp brachium pontis - CBL cerebellum - cr I, II crus I, II - ct corpus trapezoides - dc dorsal cap of Kooy - dl dorsal lamina of the principal olive - FL flocculus - flm fasciculus longitudinalis medialis - gVII genu of the facial nerve - H VI hemisphere of lobule VI - IO inferior olivary nucleus - ll lemniscus lateralis - ml lemniscus medialis - NCS nucleus centralis superior - NIC nucleus intercalatus - NP nuclei pontis - NPH nucleus prepositus hypoglossi - NRaP nucleus raphe pontis - NRGc nucleus reticularis gigantocellularis - NRL nucleus reticularis lateralis - NRo nucleus of Roller - NRP nucleus reticularis paramedianus - NRPoC nucleus reticularis pontis caudalis - NRPoO nucleus reticularis pontis oralis - NRTP nucleus reticularis tegmenti pontis - NSG nucleus supragenualis - NVM nucleus vestibularis medialis - N VI nucleus abducens - n XII nervus hypoglossus - ped pedunculus cerebri - PFLD dorsal paraflocculus - PFLV ventral paraflocculus - PMD paramedian lobule - PPRF pontine paramedian reticular formation - vl ventral lamina of the principal olive - vlo ventrolateral outgrowth - X nucleus dorsalis vagi - XII nucleus hypoglossus - I-X lobules I to X     

Inhibitory reticular neurons related to the quick phase of vestibular nystagmus — Their location and projection

Summary The medial brain stem was explored mainly in the vicinity of the abducens nucleus to find interneurons related to the quick phase of vestibular nystagmus in the cat. Most neurons exhibiting a burst of spikes specifically at the quick phase of nystagmus directed to the ipsilateral side were found in the dorsomedial part of the reticular formation caudal to the abducens nucleus and lateral to the medial longitudinal fasciculus. The burst spikes were preceded by a negative field potential which was fairly localized in the above region. These neurons were activated antidromically from the contralateral and not from the ipsilateral abducens nucleus. The effective sites for antidromic activation showed a patch-like distribution in the abducens nucleus, indicating their axonal branching within the nucleus.Simultaneous recording of spikes of these neurons and the field potential in the contralateral abducens nucleus showed that a spike burst of each neuron began fairly synchronously with the onset of steep positive field potential in the abducens nucleus at the quick inhibitory phase of motoneurons. Microstimulation at the region where these neurons were located induced monosynaptic IPSPs in the contralateral abducens motoneurons. It is thus postulated that these neurons are inhibitory in nature and cause the IPSPs in contralateral abducens motoneurons at the quick inhibitory phase of vestibular nystagmus. The burst inhibitory neurons were activated polysynaptically from the ipsilateral vestibular nerve and monosynaptically from the contralateral superior colliculus or the ipsilateral pontine reticular formation at the level of P2–P6.     

Afferent connections of the mesencephalic reticular formation: A horseradish peroxidase study in the rat

The afferent connections of the mesencephalic reticular formation were studied experimentally in the rat by the aid of the retrograde horseradish peroxidase tracer technique. The results suggest that the rostral portion of the mesencephalic reticular formation receives its main input from the cerebral cortex, the zona incerta and the fields of Forel, the central gray substance, the nuclei reticularis pontis oralis and caudalis, and the deep cerebellar nuclei. Substantial input to the same territory of the mesencephalic reticular formation appears to come from the superior colliculus, the substantia nigra, the parabrachial area, the spinal trigeminal nucleus, and the nucleus reticularis gigantocellularis, whereas several other brain structures, among which the locus coeruleus and the raphe complex, seem to represent modest but consistent additional input sources. The afferentation of more caudal portions of the mesencephalic reticular formation appears to conform to the general pattern outlined above with only three exceptions: the cerebral cortex, the deep cerebellar nuclei and the spinal trigeminal nucleus seem to be relatively modest sources of projections to these levels.Considering that the mesencephalic reticular formation is a critical structure in the “ascending activating systems”, the present results, confirming and extending those of many other investigators, characterize a set of pathways that seem to be an important part of the anatomical substrate of the sleep-waking cycle.     

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.     

Influence of rubrospinal tract and the adjacent mesencephalic reticular formation on the activity of medullary respiratory neurons and the phrenic nerve discharge in the rabbit

Suprapontine brain sites acting on the central respiratory system have been demonstrated to give rise to inspiratory as well as expiratory facilitatory effects. In the present study the inspiratory inhibitory effect which has been reported in the cat to be elicited consistently by electrical stimulation of the rubrospinal tract and the adjacent mesencephalic reticular formation was examined in the urethane-anaesthetized rabbit. Stimulation of these sites with single electrical shocks of moderate intensity induced a short latency (onset after 3.0 ms) transient (duration: 29 ms) inhibition of the phrenic nerve activity (PHR). Short volleys of stimuli applied in mid- to late-inspiration led to a premature off-switch of inspiration. The extracellularly recorded discharge activity of the different types of medullary respiration-related units (RRU) reflected these alterations, accordingly. Axonal connections of RRU with mesencephalic structures were evaluated. Examination of orthodromic responses of medullary RRU to stimulation of this pathway revealed that most bulbospinal inspiratory neurons (10 out of 13) were paucisynaptically inhibited after short latency (at least 1.2 ms). The conduction time from bulbospinal inspiratory neurons to the recording site of PHR was 1.6 ms. Thus, a disynaptic pathway — including bulbospinal inspiratory neurons — is suggested inducing inspiratory inhibition 3.0 ms after single shock midbrain stimulation. This inhibition results in disfacilitation of phrenic motoneurons. The fact that extensive electrolytic lesions of the pneumotaxic center in rostral pons did not abolish the observed inspiratory inhibitions excludes these structures from being involved. A direct pathway from the red nucleus and the adjacent reticular formation to phrenic nuclei of the spinal cord, however, can not be excluded from being involved in the demonstrated inspiratory inhibition. The described effects may play a role in behavioral or voluntary control of respiration.     

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.     

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.     

Monosynaptic innervation of facial motoneurones by neurones of the parvicellular reticular formation

In order to determine whether neurones in the parvicellular reticular formation are in direct synaptic contact with motoneurones innervating facial muscles, a combined retrograde and anterograde transport study was carried out in the rat. Animals received injections of the retrograde tracer cholera toxin B conjugated to horseradish peroxidase into facial muscles and of the anterograde tracer biocytin into the parvicellular reticular formation. The facial motor nucleus was then examined for anterograde and retrograde labelling in the light and electron microscopes. Retrogradely labelled neurones were found in the facial motor nucleus with a distribution that was dependent on the muscles injected. Terminals anterogradely labelled with biocytin from the parvicellular reticular formation were observed in the motor nucleus amongst the retrogradely labelled neurones. At the electron microscope, the retrogradely labelled cells were found to receive input from unlabelled terminals and from terminals that were anterogradely labelled from the injections of biocytin in the parvicellular reticular formation. The labelled terminals were 1–2 m in diameter at the active zone and packed with spherical vesicles. They formed both symmetrical and asymmetrical synapses with their labelled or unlabelled targets. It is concluded that neurones in the parvicellular reticular formation form direct synaptic contact with motoneurones of facial muslces. This may represent a pathway by which the basal ganglia can directly influence orofacial movement, as the substantia nigra is known to project to that part of the reticular formation.     

The projection of visceral afferents to the cerebellar cortex of the cat

Summary After stimulation of the superficial radial nerve and the splanchnic nerve, evoked potentials were recorded on the surface of the cerebellum and their distribution mapped. It was shown, that the potentials of both afferents were quite different from each other. The differences in shape indicate that both afferents are differentially organized by the cerebellar cortex. This conclusion was reached through interaction experiments, frequency studies, and input-output-relation.