Non-reciprocal connections between the perihypoglossal nuclei and the cerebellar paramedian lobule in rabbits and their relationship to the climbing fiber zones.

Retrogradely transported horseradish peroxidase (HRP) was used to investigate the organization of projections from the perihypoglossal nuclei to the cerebellar paramedian lobule, and possible reciprocal corticoperihypoglossal connections in rabbits. The absence of labeled Purkinje cells in the paramedian lobule after HRP injections of the perihypoglossal nuclei, compared with labeling in the nodulus, ipsilateral flocculus and adjacent ventral paraflocculus, strongly suggests that corticoperihypoglossal projections do not originate in the paramedian lobule. Comparison of labeling patterns in the perihypoglossal nuclei following HRP injections into various sublobules of the paramedian lobule suggests that projections from the perihypoglossal nuclei to the paramedian lobule exist and that some degree of topographic organization is present exclusively in bilateral projections from the caudal part of nucleus prepositus hypoglossi. All perihypoglossal projections end in deep parts of sublobules e-b of zones C2 and D1 (as defined by inferior olivary labeling). It is significant that in the ipsilateral nucleus prepositus hypoglossi, two groups of cells projecting to zone C2 are arranged rostrocaudally between three other groups projecting to zone D1.

The dentatorubral projection in the rabbit with emphasis on distinction from the interpositorubral connectivity: an HRP retrograde tracer study.

The projection from the lateral (dentate) cerebellar nucleus (NL) to the red nucleus in the rabbit was investigated using free horseradish peroxidase (HRP). Following injections of this tracer into the red nucleus (RN), the distribution patterns of retrogradely labeled cells were checked in the NL. The projection from the NL was found to extend rostrocaudally throughout the contralateral RN except for the predominant part of the rostral one-quarter and the caudalmost part of the RN, i.e. the regions described to receive projections exclusively from the interpositus nuclear complex (NI). On the other hand, the only region of the RN receiving projection exclusively from the NL appeared to be rostralmost parvocellular region of the RN (RN-PA). This study suggested that, in contrast to other species, the projection from the NL is not confined to the most rostrally localized RN-PA but is distributed throughout predominant part of the nucleus and to a great extent overlapped with projection from the NI. This overlapping projection pattern parallels the absence of clear differentiation between parvo- and magnocellular parts of the rabbit RN.

Spatial arrangement of the interpositorubral projection in the rabbit. A retrograde HRP study.

The objective of this investigation was to analyse the organization of rubral afferents from the cerebellar interpositus nuclear complex (NI) in the rabbit. Free HRP was employed as a retrograde tracer to identify the distribution patterns of labeled cells in the anterior and posterior interpositus nuclei. The interpositus projections distribute throughout nearly the entire contralateral red nucleus (RN) except for its rostralmost parvocellular region (RN-PA) which does not correspond to the usually distinguished parvocellular subdivision of the red nucleus (RN-P). The central and lateral regions of the posterior interpositus nucleus (NIP) project (nearly exclusively) to the medial region of the RN. The lateral region of the anterior interpositus nucleus (NIA) sends projections to both the lateral and medial regions of the caudal three-quarters of the RN. Thus, the lateral region of the RN appears to be under nearly exclusive control of NIA. The rostral one quarter of the RN receives cerebellar afferents from the NIP only and caudal pole of RN from the NIA exclusively. Comparison of labelling patterns indicates absence of topogrophic differentiation of projections from the NIP, whereas dorsoventral topography in the NIA can correlate to the rostrocaudal and mediolateral arrangement of the RN. Collectively, interpositorubral projections in the rabbit are similar to those in other species only in basic features.

Non-reciprocal connections between the vestibular nuclei and the cerebellar paramedian lobule, with special reference to the climbing fiber zones: an analysis in the rabbit using the retrograde horseradish peroxidase method.

The organization of the secondary vestibular projections onto the cerebellar paramedian lobule (PML) and possible reciprocal corticovestibular connections were investigated by the retrograde horseradish (HRP) technique in the rabbit. Following injections of the tracer into the vestibular nuclear complex (VNC), an ill-defined, sagittal band composed of numerous labelled Purkinje cells was found ipsilaterally throughout the length of the lateral portion of the vermis, the ventral paraflocculus and the flocculus. However, no labelled Purkinje cells were found in the cortex of the PML. The results indicate that zone B, considered to give rise to cerebellar corticovestibular projections, is not present in the rabbit PML. After injections of HRP into the PML, the retrograde labelling pattern in the VNC was analyzed, in relation to the climbing fiber zones identified by retrograde labelling in the inferior olive. No clear-cut correspondence could be found between the vestibular subdivisions and climbing fiber zones in the PML, except that only the interstitial nucleus of the vestibular nerve projects into zone D1 in sublobules e and d. There were no vestibular projections to zone D2. The only salient feature was that cells projecting onto zones C2, C1 and C3 of the PML were arranged rostrocaudally in the inferior vestibular nucleus and the caudal portion of the medial vestibular nucleus. In addition, a topical relationship was found between parts of the VNC and sublobules of the PML.

The neurons of origin of non-cortical afferent connections to the oculomotor nucleus. A retrograde labeling study in the rabbit.

The cellular origin of the brainstem projections to the oculomotor nucleus in the rabbit has been investigated by using free (HRP) and lectin-conjugated horseradish peroxidase (WGA-HRP). Following injections of these tracers into the somatic oculomotor nucleus (OMC), retrogradely labeled cells have been observed in numerous brainstem structures. In particular, bilateral labeling has been found in the four main subdivisions of the vestibular complex, predominantly in the superior and medial vestibular nuclei and the interstitial nucleus of Cajal, while ipsilateral labeling was found in the rostral interstitial nucleus of the medial longitudinal fascicle (Ri-MLF), the Darkschewitsch and the praepositus nuclei. Neurons labeled only contralaterally have been identified in the following structures: mesencephalic reticular formation dorsolateral to the red nucleus, abducens internuclear neurons, group Y, several areas of the lateral and medial regions of the pontine and medullary reticular formation, ventral region of the lateral cerebellar nucleus and caudal anterior interpositus nucleus. This study provides also information regarding differential projections of some centers to rostral and caudal portions of the OMC. Thus, the rostral one-third appears to receive predominant afferents from the superior and medial vestibular nuclei, while the caudal two-thirds receive afferents from all the four vestibular nuclei. Finally, the group Y sends afferents to the middle and caudal, but not to the rostral OMC.

Subcortical afferents to the interstitial nucleus of Cajal: an anatomical retrograde tracing study in the rabbit.

Organization of brainstem projections to the interstitial nucleus of Cajal (INC) in the rabbit has been studied using the method of retrograde transport of horseradish peroxidase or wheat germ agglutinin-horseradish peroxidase conjugate. Injections of tracers into INC resulted in bilateral labelling in the medial terminal nucleus of the accessory optic tract, medial region of the zona incerta, vestibular nuclei (superior, medial, inferior), rostral portion of the prepositus nucleus and several nuclei of the pontine and medullary reticular formation. Retrograde labelling on the contralateral side was noted in all 4 deep cerebellar nuclei, the lateral vestibular nucleus, group Y, the rostral interstitial nucleus of the medial longitudinal fascicle, INC and mesencephalic reticular formation dorsal and lateral to the red nucleus. Cells of origin for the ipsilateral afferents of INC were found only in the nucleus of the posterior commissure. These data are discussed in relation to other morphological and physiological studies of afferent connectivity of INC in other species.

Topographic and zonal pattern of olivocerebellar projection to the paramedian lobule in the rabbit: an experimental study with an HRP retrograde tracing method.

Distribution of neurons in the inferior olive (IO) projecting to the paramedian lobule (PML) was studied in rabbits by means of retrograde transport of horseradish peroxidase (HRP). HRP was injected into various regions of different folia of the PML. Findings indicate zonal and to some extent topographic organization in olivocerebellar projections to PML folia. The neurons in corresponding areas of dorsal (dlPO) and ventral lamina (vlPO) of the principal olive (PO) project to composite zones D (D1 + D2) in sublobule f: medial, intermediate and lateral. In addition, the caudal part of the medial accessory olive (MAO) projects to the most laterally located zone (C2-lateral) and the caudal part of the dorsal accessory olive (DAO) to the most lateral zone (C3) in sublobule f. The middle part of the DAO sends projections to zone C1 located medially in sublobules d-a. The rostral and caudal parts of the DAO send projections to zone C3 in sublobules a and f, respectively. The rostral, middle and adjacent caudal parts of MAO, with no clear topographic organization, project to broad zone C2 in sublobules e-b. The neurons in restricted areas of the caudomedial part of the dlPO and vlPO, probably intermingled with those supplying the composite medial zone D in sublobule f, project to sublobules e-b to terminate in zones D1 and D2, respectively.

Do the same subdivisions of the nucleus reticularis tegmenti pontis project onto longitudinal zones of the paramedian lobule? An anatomical study in the rabbit with retrograde tracing technique (HRP).

Rabbits were subject to iontophoretic injections of HRP into various sites of mediolateral extent of the cerebellar paramedian sublobules (PML). The distribution of retrogradely HRP-labelled neurons was mapped within the subdivisions of the pontine reticular tegmental nucleus (NRTP). Clear evidence for absence of correlation between the distribution of labelled cells within the NRTP longitudinal subdivisions and mediolateral location of HRP injection sites in PML has been obtained. The present findings suggest that there is no longitudinal compartmentalization of the NRTP-PML connectivity and the same NRTP longitudinal subdivisions project onto several sagittal zones of the PML.

Afferent fiber connections from the raphe nuclei to the cerebellar paramedian lobule. A histochemical study in the rabbit utilizing horseradish peroxidase as a retrograde marker.

The distribution of labelled cells within the raphe nuclei has been studied after iontophoretic injections of horseradish peroxidase into various folia of the cerebellar paramedian lobule. Retrogradely marked neurons of all sizes and shapes were found in more caudally located raphe nuclei: obscurus, pallidus, magnus and pontis, as well as single neurons in nucleus centralis superior and dorsal raphe nucleus. The nuclei raphe pontis and obscurus send the greatest number of fibers to the paramedian lobule. Most of the projection takes origin from raphe neurons located in midline and ipsilaterally. Folia c and d are the recipients of most afferents from the raphe nuclei (pallidus, obscurus, pontis, magnus). On the other hand, folia f and e appear to receive contribution from nuclei raphe pontis and pallidus, while folia a and b from nuclei obscurus and magnus. Additionally single neurons in nucleus raphe dorsalis contribute to the projection onto the folia f and e, and from nucleus centralis superior to the folia c, d and occasionally to the sublobule a. The studies are discussed in relation to other investigations of afferent-efferent connections and already known functional role of the raphe nuclei.

The pontocerebellar efferents from the pontine reticular tegmental nucleus in the rabbit: differential projections to the paramedian sublobules as revealed with tracing of retrograde axonal transport of horseradish peroxidase.

Projections from the nucleus reticularis tegmenti (NRTP) pontis to the cerebellar paramedian lobule were studied using a horseradish peroxidase retrograde transport technique. The rabbit's NRTP consists of a medial principal part (the nucleus papillioformis: PLF) and smaller lateral part (the processus tegmentosus lateralis: PTL). The PLF can be subdivided into a dorsomedial part--zone A, a ventrolateral part--zone C, and a main part--zone B. Zone B is furthermore divisible into the subzones: B1, B2, and B3. In addition, some cells of zone B3 invade the fiber bundles of the medial lemniscus. Experimental data have indicated a topographically organized bilateral projection from the NRTP to the anterior, the middle and the posterior folia of the paramedian lobule with some degree of contralateral dominance. In contrast to an earlier report in cats we find that not only the ventral, but also the dorsal region of the NRTP send projections onto the paramedian lobule. The neurons sending axons to the paramedian lobule are localized mainly in the middle and to a some degree in the posterior thirds of the NRTP. Zones A, B1 and B3 project onto all of sublobules of the paramedian lobule. While zone A projects primarily onto the anterior sublobules (e, f), zone B1 emanates to the middle paramedian sublobules (c, d), Zone B3 sends fibers mainly into the posterior sublobules (a, b) and to a some degree to the middle paramedian sublobules. Zone B2 distributes a few axons exclusively to the middle folia of the paramedian lobule, while the middle part of the PTL gives rise to small bilateral projection to sublobules c and d of the paramedian lobule. Neurons of zone C send projections into the middle folia of the paramedian lobule. These findings are discussed in relationship to other morphological and physiological data on neurons of the pontine reticular tegmental nucleus.

The nucleus "k" of Meessen and Olszewski efferents to the cerebellar paramedian lobule: a retrograde tracing histochemical (HRP) study in the rabbit and the cat.

The group "k" of Meessen and Olszewski (1949) was identified in the brain stems of normal rabbits and cats. In the rabbit, a topographical subdivision of the group "k" into the well defined cell aggregations k1, k2 and k3 was found. In the cat, the nucleus corporis pontobulbaris was subdivised into a posterodorsal and a anteroventral part. The former was located ventrally to the motor and principal sensory trigeminal nuclei, the latter was wedgeshaped and situated more anteriorly at the lateroventral margin of the pons. In 9 rabbits and 7 cats the neurons of origin for cerebellar paramedian lobule afferents were identified with retrograde transport of horseradish peroxidase within the nucleus "k" and nucleus corporis pontobulbaris, respectively. In both species, most projections to the paramedian lobule were seen as originating ipsilaterally with only a small contralateral component. The study suggests that there are certain segregated projections of the nucleus "k" or the nucleus corporis pontobulbaris to the cortex of the anterior and posterior parts of the paramedian lobule, with some valid species differences. In the cat, the whole projection was found to originate in the more anterior and ventral parts of the nucleus "k" (nucleus corporis pontobulbaris). The posterior part of the paramedian lobule in the rabbit receives afferents from the homolateral subdivisions k3 and, to a minor degree, from k2; while in the cat, afferents are bilateral with an ipsilateral preponderance and originate from the posterior cellular group of the nucleus corporis pontobulbaris dispersed among and medially to the exiting motor root of the trigeminal nerve. The anterior part of the paramedian lobule afferents in the rabbit originates bilaterally within subdivision k1, to a minor degree ipsilaterally in the dorsal region of subdivision k3, and occasionally in subdivision k2, whereas in the cat afferents originate from the anterior and posterior levels of the corpus pontobulbaris. Additionally, some afferents for the rabbit anterior paramedian lobule originate within the homolateral nucleus "n". No evidence for a longitudinal zonal pattern of the projection onto the paramedian lobule was found. The study is discussed in the light of present information on the connections of the nucleus "k" (nucleus corporis pontobulbaris).

Evidence for cerebellar efferents to the ventral lateral geniculate nucleus and the lateral terminal nucleus of the accessory optic system in the rabbit. A morphological study with comments on the organizational features of visuo-oculomotor-trunco-cerebellar loops.

The efferent ascending connections of the cerebellar nuclei and afferent optic projections to the ventral lateral geniculate nucleus and the terminal nuclei of the accessory optic tract were traced in the 26 rabbits using the technique of experimental anterograde degeneration. Following eyeball enucleation, within the ventral lateral geniculate nucleus terminal degeneration was found mostly contralaterally and was restricted to both the sublayers (external and internal) of the lateral division, while ipsilaterally only scanty and confined to the dorsal region of the external sublayer of the lateral (sector alpha) division. After cerebellar lesions degeneration was found within the ventral region of the medial division (sector gamma) of the contralateral LGv and within contralateral LTN. From the localization of the lesions in the cerebellar nuclei, as well as from the distribution of degenerations in the area of the LGv, it was postulated that the parent neurons for the cerebello-LGV fibers are located in the contralateral posterior interposed nucleus, although the anteroventral lateral cerebellar nucleus, the Y group and the infracerebellar nucleus have been not excluded. Within the all terminal nuclei of the accessory optic tract the retinal fibers were found to terminate bilaterally with contralateral preponderance, mostly in the MTN, while ipsilateral fibers terminate most extensively in the lateral terminal nucleus of the accessory optic tract (LTN). In this means the retinal afferents of both sides seem to subserve the contralateral lateral cerebellar nucleus control. Taken together, the findings indicate that the extrageniculate visual inputs might be subjected to direct reciprocal cerebello-nuclear control. The visual extrageniculate cerebellopetal pathways and their correlations with the vestibulo-ocular and optokinetic reflex loops are discussed.

Cerebellar afferent projection to the inferior colliculus of the mesencephalic tectum. An anterograde degeneration study in the rabbit.

Studies were conducted on twelve rabbits which were lesioned in various regions of the cortex and cerebellar nuclei. The survival time, in ten animals, was found 4 to 10 days and in one animal 375 days. In the twelfth rabbit further lesions were made in the fastigial nucleus, 380 days after multiple lesions of the posterior cerebellar region. Survival time, in this case, was 9 days. Frozen sections of the cerebellum and brain stem were impregnated according to the Nauta-Gygax modified method (NAUTA 1957, Fink-Heimer 1967, Loewy 1969) and the course and termination of the nerve fibres into the inferior colliculus of the mesencephalic tectum has been studied. Degenerative fibres in this region of the brain stem were seen only after lesion of the fastigial nucleus or of its efferent fibres. The nucleus fastigii project the fibres to the inferior colliculus nuclei on both sides in the ascending ramus of the uncinatus fasciculus. These fibres reach the inferior colliculus nuclei mainly on the contralateral side and, to a lesser degree, on the same side. Results of the studies are discussed in the light of the latest neurophysiological researches.

The medial geniculate body afferents from the cerebellum in the rabbit as studied with the method of orthograde degeneration.

The brain stems of 10 rabbits subject to operation of several lesions of cerebellar cortex and nuclei were examined. Survival time was 4 to 10 days. The course and termination of degenerating nerve fibres into the medial geniculate nuclei (MGN) of both sides were analyzed in frozen sections of the cerebellum and the brain stem impregnated according to various modifications of Nauta method. Degenerated nerve fibres in the MGN were found only when the fastigial nucleus of heterolateral side, or fibres originating in this nucleus were damaged. Cerebellofugal fibres run in two bundles to their termination spot in the magnocellular part of the medial geniculate nucleus. The first bundle separates from the main trunk of the uncinate fascicle, and running medially to the vestibular nuclei, terminates in the MGN after passing through the lateral lemniscus and the ventral lemniscal nucleus. The second bundle separates from the ascending branch of the uncinate fascicle and after passing through the dorsal lemniscal nucleus, also in composition of the lateral lemniscus, it terminates in the same region of the MGN.

The spinal cervical way of afferent innervation of the tongue motor apparatus. An experimental investigation in the dog.

The studies were performed on 24 young, adult dogs. In 16 of the animals sections were made of the descending ramus of the hypoglossal nerve and of the stem of the hypoglossal nerve at various levels: at the base of the skull (superior hypoglossectomy), proximally from the descending ramus (middle hypoglosectomy), and at the entrance to the tongue (inferior hypoglossectomy). Phantom operations were performed in 4 animals and material from 4 others (not operated on) was used for control purposes. The post-operative survival rate ranged from 10 to 29 days. In all 4 cases rostral spinal cervical ganglia were collected. In half of the cases the materials were stained with cresyl violet and further quantitative and qualitative studies of retrograde neuronal changes were performed. The remaining half of the material, prepared with Gomori method on acid phosphatase, was subject to statistical analysis of the degree of acid phosphatase activity. The increase or decrease in number of neurons of definite degree of activity was taken as an index of the increase or decrease of enzymatic activity. As a result of transection of the hypoglossal nerve and its descending ramus, in cresyl violet material, qualitative and quantitative degenerative changes were found in dorsal root ganglia C1 to C3 on the operated side. It was also found that corresponding to the tigrolytic changes in the neurons of the above mentioned ganglia there was an increase of activity for acid phosphatase. The same kinds of changes were found in the spinal ganglia C2 and C3 after transection of the hypoglossal nerve at the entrance to the muscles of the tongue. These results lead the authors to suggest that the tongue motor apparatus receives afferent innervation from neurons locates homolaterally in spinal ganglia C2 and C3.

[Afferents of vagus nerve to intercalary nucleus]. / Afférences du nerf vague an noyau intercalé

In 11 rabbits operations of intracranial transection of IXth and Xth cranial nerves and transections of vagal nerve on its several levels were performed. After survival 271-327 days karyometric investigations of neurons, astrocytes and oligodendrocytes contained in intercalary nuclei of both sides of medulla were performed. It was stated that after transection of the vagus nerve on the levels proximally to the arising of the recurrent laryngeal nerve the volume of cross-area of neurons and nuclei of astrocytes decreases on the operated side. The authors concluded that atrophic changes found in the intercalary nucleus may be probable of transsynaptic in character. It indicated, that intercalary nucleus receives afferents from the vagus nerve.