The brain stem in a lizard, Varanus exanthematicus.
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Animals↗
Biomedical subjects
G C Bangma
Publications and source records attributed to G C Bangma.
The fasciculus longitudinalis medialis in the lizard Varanus exanthematicus. 2. Vestibular and internuclear components.
In the present study the vestibular components of the fasciculus longitudinalis medialis (flm) were investigated in the lizard Varanus exanthematicus with various tracing techniques: anterograde transport of horseradish peroxidase to study vestibulo-oculomotor and vestibulospinal projections, the multiple retrograde fluorescent tracer technique for the cells of origin of such projections. Internuclear projections between the oculomotor and abducens nuclei could also be studied in this way. Rather extensive vestibulo-ocular projections passing via the flm were demonstrated. Mainly ipsilateral ascending projections arise in the dorsolateral vestibular nucleus, mainly contralateral ascending projections in the ventromedial vestibular nucleus and adjacent parts of the ventrolateral and descending vestibular nuclei. Furthermore, distinct bilateral ascending projections of the nucleus prepositus hypoglossi were demonstrated. Extensive vestibulospinal projections pass via the flm and form the medial vestibulospinal tract. This largely contralateral descending pathway arises predominantly in the ventromedial and descending vestibular nuclei. Terminal structures presumably arising in the ventromedial and descending vestibular nuclei were found on contralateral neurons, probably motoneurons innervating neck muscles. Vestibular neurons with both ascending (presumably to extra-ocular motoneurons) and descending projections to the spinal cord are present in all vestibular nuclei, although preferentially in the ventromedial vestibular nucleus and adjacent parts of the ventrolateral and descending vestibular nuclei. However, also in the dorsolateral vestibular nucleus a substantial number of double labeled neurons were found. These vestibular neurons with both vestibulomesencephalic and vestibulospinal projections are probably involved in combined movements of eyes and head. Evidence for reciprocal internuclear connections between the oculomotor and abducens nuclei was found. Neurons in the dorsal part of the oculomotor nucleus probably project to the ipsilateral abducens nucleus, while neurons in the abducens nucleus most likely project to the contralateral oculomotor nucleus. These reciprocal internuclear connections between the oculomotor and abducens nuclei probably play an important role in conjugate horizontal eye movements.
Animals↗
Cerebellar efferents in the lizard Varanus exanthematicus. II. Projections of the cerebellar nuclei.
The projections of the cerebellar nuclei have been studied in the lizard Varanus exanthematicus with various experimental anatomical techniques. In anterograde degeneration experiments (lesions of the cerebellar peduncle) both ascending and decending contralateral projections were found. Ascending fibers which could be traced from the cerebellar commissure ventralward decussated at the level of the trochlear and oculomotor nuclei. These fibers coursed rostralward to the mesodiencephalic junction. With anterograde tracing techniques (3H-leucine and HRP) this tract was found to terminate in the nucleus ruber and the interstitial nucleus of the fasciculus longitudinalis medialis. Moreover, retrograde tracer studies (HRP, "Fast Blue") showed that this tract appeared to arise mainly in the lateral cerebellar nucleus. With both anterograde degeneration and tracing techniques (3H-leucine and HRP) a bundle of fibers could be followed, which decussates in the basal part of the cerebellum and passes dorsally around the contralateral medial cerebellar nucleus to the lateral side of the brainstem. This contralaterally descending projection system was found, lateral to the vestibular nuclear complex, and as far caudally as the descending vestibular nucleus, to terminate on various vestibular nuclei. Horseradish peroxidase studies showed that this contralaterally descending projection system originates mainly in the medial cerebellar nucleus, but ipsilaterally descending projections were also found. With the fluorescent double labeling technique ("Fast Blue" and "Nuclear Yellow") the projections of the cerebellar nuclei described above were confirmed. Furthermore, double labeling revealed neurons in both cerebellar nuclei (especially the medial nucleus) that project to both the mesencephalon and the cervical spinal cord. The present results indicate that the efferent connections of the cerebellar nuclei in the lizard Varanus exanthematicus are organized as two main projections, an ascending projection comparable to the mammalian brachium conjunctivum arising in the lateral cerebellar nucleus, and a descending projection comparable to the mammalian hook bundle (fasciculus uncinatus), originating mainly in the medial cerebellar nucleus. Such projections are common for terrestrial vertebrates.
Animals↗
Cerebellar efferents in the lizard Varanus exanthematicus. I. Corticonuclear projections.
The organization of the cerebellar corticonuclear projections, i.e., the projections from the Purkinje cell layer to the cerebellar nuclei and the vestibular nuclear complex, was investigated with the horseradish peroxidase (HRP) technique in the lizard Varanus exanthematicus. After HRP slow-release gels were implanted in the cerebellar nuclei or various parts of the vestibular nuclear complex, the following longitudinally oriented zones of labeled Purkinje cells could be distinguished: a medial zone projecting to the medial cerebellar nucleus; an intermediate zone projecting to the vestibular nuclear complex, especially the ventrolateral vestibular nucleus, but probably also the dorsolateral vestibular nucleus; a caudolaterally located area of the cerebellar cortex projecting to the lateral cerebellar nucleus; and the flocculus and the adjacent lateral part of the Purkinje cell layer with projections to the middle and caudal parts of the vestibular nuclear complex, i.e., the descending and ventromedial vestibular nuclei. All projections of the Purkinje cells appeared to be strictly ipsilateral. It can be concluded that in reptiles a longitudinal organization of cerebellar corticonuclear projections exists, which may be basic for terrestrial vertebrates.
Animals↗
A crossed rubrobulbar projection in the snake Python regius.
In the present study a distinct crossed rubrobulbar projection has been demonstrated in the snake Python regius, a limbless vertebrate which lacks a rubrospinal tract. This rubrobulbar projection is presumably involved in the neural control of mastication. The red nucleus may relay cerebellar influence to the trigeminal and facial nuclei.
Animals↗
Some afferent and efferent connections of the vestibular nuclear complex in the red-eared turtle Pseudemys scripta elegans.
In the present study some afferent, commissural, and efferent connections of the vestibular nuclear complex in the turtle Pseudemys scripta elegans were demonstrated with the HRP tracing technique. Afferent projections to the vestibular nuclei were found to arise in the nucleus of the basal optic root, the interstitial nucleus of the fasciculus longitudinalis medialis, the medial and lateral cerebellar nuclei, the perihypoglossal nuclear complex, and the reticular formation. Distinct commissural projections appeared to arise in the dorsolateral, ventromedial, and descending vestibular nuclei. The commissural projection arising in the ventrolateral vestibular nucleus appeared to be only sparsely developed. Both ascending and descending efferent projections were demonstrated to arise from the vestibular nuclear complex. The ascending vestibulo-oculomotor projection was found to be organized in an ipsilateral pathway arising in the dorsolateral vestibular nucleus and in a contralateral pathway, arising mainly in the medial vestibular nucleus. These projections appeared to be directed to the interstitial nucleus of the fasciculus longitudinalis medialis, the oculomotor, trochlear, and abducens nuclei. Also the perihypoglossal nuclear complex appeared to be an important target of vestibular efferents. The origin and course in the brainstem of the descending vestibular projections, i.e., the lateral and medial vestibulospinal tracts, as demonstrated in previous anatomical and experimental studies in reptiles, were confirmed. However, in addition a direct projection of the vestibulospinal tracts to presumably neck motoneurons was found. THe organization of the vestibular connections observed in the turtle Pseudemys scripta elegans appeared to be basically comparable to the organization of the vestibular connections in birds and mammals.
Animals↗
Cerebellar corticonuclear projections in the red-eared turtle Pseudemys scripta elegans.
In the present study the organization of the corticonuclear projections of the cerebellum in the red-eared turtle Pseudemys scripta elegans was investigated. To find out whether a zonal pattern exists in the cerebellar cortex, a topological analysis was made of the Purkinje cell layer of a Nissl-stained series of the cerebellum. This analysis showed a distinct, longitudinally oriented zonal pattern of Purkinje cells. In each cerebellar half a medial, an intermediate, and a lateral zone could be distinguished. This pattern appeared to correspond in part to an earlier subdivision of the reptilian cerebellum suggested by Larsell ('26, '32, '67). In the experimental part of this study, the corticonuclear projections to the cerebellar nuclei and the vestibular nuclear complex were demonstrated with the horseradish peroxidase (HRP) technique. All projections of the Purkinje cells appeared to be strictly ipsilateral. After HRP slow-release gel implantations at various levels of the vestibular nuclear complex, longitudinally oriented areas of labeled Purkinje cells were found in the lateral part of the medial zone, the intermediate zone, and the lateral zone. Two strips of Purkinje cells remained unlabeled: One in the rostrolateral part of the intermediate zone, and another in the medial part of the medial zone. After HRP gel implantations in the cerebellar peduncle aimed at the medial and lateral cerebellar nuclei, respectively. Purkinje cells in the latter two strips were labeled. The present results indicate that the corticonuclear projections to the medial cerebellar nucleus arise in the medial part of the medial zone and those to the lateral cerebellar nucleus in the rostrolateral part of the intermediate zone. It can be concluded that cerebellar zones as demonstrated in the turtle Pseudemys scripta elegans, are phylogenetically very old and may represent the basic functional circuit of the cerebellum.
Animals↗
Reticulospinal and vestibulospinal pathways in the snake Python regius.
In the present HRP study extensive reticulospinal projections and more modestly developed vestibulospinal pathways have been demonstrated in the snake Python regius. The funicular trajectories of the main reticulospinal pathways have been shown: via the lateral funiculus pass spinal projections of the nucleus reticularis superior pars lateralis, the nucleus reticularis inferior and nucleus raphes inferior; via the ventral funiculus fibers arising in the nucleus reticularis superior and nucleus reticularis medius. Spinal projections of the locus coeruleus and subcoeruleus area reach their targets via both the lateral and ventral funiculi. Two vestibulospinal pathways have been demonstrated: an ipsilateral tractus vestibulospinalis lateralis arising in the ventrolateral vestibular nucleus, and a contralateral tractus vestibulospinalis medialis from the descending and ventromedial vestibular nuclei. After HRP gel implants into the vestibular nuclear complex direct vestibulocollic projections to motoneurons in the rostral spinal cord were observed. Spinal projections from the ventral part of the nucleus reticularis inferior and the descending and ventromedial vestibular nuclei are mainly aimed at the thin "neck area" (approximately the first 50 spinal segments). This area is extensively used in such acts as orientation and prey-catching, requiring a rather delicate brain stem control.
Afferent Pathways↗
Afferent connections of the cerebellum in various types of reptiles.
The origin of cerebellar afferents was studied in various types of reptiles, viz., the turtles Pseudemys scripta elegans and Testudo hermanni, the lizard Varanus exanthematicus, and the snake Python regius, with retrograde tracers (the enzyme horseradish peroxidase and the fluorescent tracer "Fast Blue"). Projections to the cerebellum were demonstrated from the nucleus of the basal optic root, the interstitial nucleus of the fasciculus longitudinalis medialis, the vestibular ganglion, and the vestibular nuclear complex, two somatosensory nuclei, viz., the descending nucleus of the trigeminal nerve and the nucleus of the dorsal funiculus, the nucleus of the solitary tract, the reticular formation, and throughout the spinal cord. A distinct bilateral projection to the cerebellum was found to arise in a nucleus previously called nucleus parvocellularis medialis (Ebbesson, '67). In the present study this cell mass is termed the perihypoglossal nuclear complex, considering its comparable position and fiber connections to the perihypoglossal nuclei in mammals. In all reptilian species studied a contralateral cerebellar projection of a cell mass located in the caudal brainstem adjacent to the nucleus raphes inferior was observed. It seems likely that this cell mass represents the reptilian homologue of the mammalian inferior olive. Most of the spinocerebellar fibers appeared to arise in neurons located in area VII-VIII of the gray matter. In this respect the origin of the spinocerebellar projection in reptiles resembles the origin of the rostral and ventral spinocerebellar tracts in mammals. No indications for the existence of a column of Clarke or a central cervical nucleus in the reptilian spinal cord were obtained. On comparison of the cerebellum afferents in reptiles with the known connections of the cerebellum in amphibians, birds, and mammals, a basic pattern of cerebellar afferent projections appears to exist in these vertebrate classes, including retinal, vestibular, precerebellar, somatosensory, and spinal afferents.
Afferent Pathways↗