Corticopontine Research Articles

Cerebral embryopathy in late first trimester: possible association with swine influenza vaccine.

An infant girl was born with cerebral malformations characterized by developmental arrest late in the first trimester of gestation. These features included persistent pontine flexure, cerebellum developed only around the rhombic lip, failure of migration of inferior olive, absence of basis pontis and of corticospinal and corticopontine tracts, and agenesis of olfactory bulbs. The cerebral cortex was thin and poorly laminated, and primary and secondary sulci had failed to form. The choroid plexus contained vascular malformations, hemorrhages, and infarcts. The leptomeninges contained foci of primitive mesenchyme. The mother had received an inoculation of swine influenza vaccine six weeks after conception, followed by a 2-week illness. The temporal relation to the timing of the cerebral malformation suggests a teratogenic effect of the vaccine, but may have been coincidental.

An anatomical investigation of the corticopontine projection in the primate ( Macaca fascicularis and Saimiri sciureus)—II. The projection from frontal and parietal association areas

In continuation of a previous study on the corticopontine projection from sensorimotor areas of the cerebral cortex in primates, the projection from frontal and parietal association areas has been investigated with degeneration and autoradiographic tracing techniques. Since the connexions are ipsilateral the projection from peri-Rolandic areas was also studied on the contralateral side of the same animals as a control. It was found that association areas have only a modest contribution to the corticopontine system as compared to the massive projection from sensorimotor areas. Of those association areas studied in the present experiments, area 5 of the parietal cortex and the premotor cortex contributed most corticopontine fibres. The prefrontal cortex and area 7 were found to have only very weak connexions. It is evident, especially from autoradiographic studies, that the corticopontine system has an intricate organization, with one particular cortical area projecting to multiple small target zones in the pontine nuclei interdigitating with target zones or ‘patches’ receiving fibres from other cortical areas. The distribution of these zones may be rather widespread, especially those receiving afferents from the motor cortex, thus providing ample opportunities for integration of motor command signals with sensory, mainly somatosensory, signals. The fact that the pontine nuclei receive chiefly signals from primary cortical areas, rather than from high-order association areas, may be taken to indicate that the cortico-ponto-cerebellar system subserves rapid corrections of movements and ‘triggered actions’, a proposition which is also supported by behavioural studies in monkeys subjected to reversible cooling of the dentate nucleus.

The pontocerebellar projection in the rhesus monkey: An experimental study with retrograde axonal transport of horseradish peroxidase

The pontocerebellar projection has been studied in the Rhesus monkey by use of the retrograde axonal transport of horseradish peroxidase. The parts of the cerebellum investigated receive afferents from pontine cell groups arranged as rostro-caudally oriented lamella or slab-like regions. As a rule labelled cells are found at all rostro-caudal levels in discrete groups, but their number at various levels, and particularly their distribution in the transverse plane, differ according to which part of the cerebellum has been injected. Although the same cell group may apparently be labelled after injections of different parts of the cerebellum, each cerebellar region has its own characteristic territory in the pontine nuclei. The anterior lobe receives fibres from lamella-like regions mainly in the caudal half of the pons, with cells projecting to the vermis and intermediate parts of the anterior lobe somewhat differently situated. Crus I is connected mainly with a region rostromedially in the pons, while crus II receives fibres from all levels of the pons, the cells being located medially and ventrally at caudal levels and more laterally at rostral levels. The paramedian lobule is supplied from pontine cells restricted to the rostral two-thirds of the pons and located more laterally than those projecting to crus II. Lobules VII and VIIIA (the main part of the vermal visual area) receive fibres mainly from two long column-like regions located dorsomedially and dorsolaterally, while lobulus VIIIB is supplied mainly from other areas in the pons. Counting of labelled cells indicates that about 30% of the fibres to the vermis, and about 10% to the hemispheres, are uncrossed. The density of the projection to the cerebellar hemispheres is found to be about three times as high as to the vermis. In two cases injections of horseradish peroxidase were placed in the cerebral cortex as well as in the cerebellum, enabling a direct comparison of sites of termination of corticopontine fibres (orthograde transport of horseradish peroxidase) with location of pontocerebellar neurons. It is suggested that the cortico-ponto-cerebellar pathway is organized so as to bring about convergence in the cerebellar cortex from several parts of the cerebral cortex, and that this takes place in a highly organized manner so that each small part of the cerebellar cortex has its own characteristic set of inputs.

Properties of pyramidal tract neuron system within a functionally defined subregion of primate motor cortex

Properties of pyramidal tract neuron system within a functionally defined subregion of primate motor cortex

The mode of synaptic linkage in the cerebro-ponto-cerebellar pathway investigated with intracellular recording from pontine nuclei cells of the cat

1. Intracellular potentials of pontine nuclei (PN) cells were recorded in cats anesthetized with pentobarbitone sodium. 2. Stimulation of the cerebellar nuclear regions or the brachium pontis induced an antidromic action potential composed of IS-SD spikes, after-depolarization and after-hyperpolarization. 3. Cerebellar stimulation produced EPSPs only in a few PN cells. 4. Activation of the corticopontine or pyramidal tract produced in all PN cells an EPSP built up from the unitary components with variable amplitudes and time courses. Paired or repetitive activation revealed a property of the frequency potentiation of the EPSP. 5. Unitary EPSPs also occurred spontaneously. A great majority of these spontaneous EPSPs were cerebral in origin, and had amplitudes and time courses comparable with those evoked by stimulation of the corticopontine or pyramidal tract. 6. The half-width versus time of peak relationship of these unitary EPSPs suggested a dendritic location of the synapses with variable distances from the soma. It is assumed that large, proximal synapses serve for efficient relay of signals while small, distal synapses for their integration.

Sprouting of the corticopontine fibres after neonatal cerebellar lesion in the albino rat

Sprouting of the corticopontine fibres after neonatal cerebellar lesion in the albino rat

Histological findings after hemicerebellectomy in man: anterograde, retrograde and transneuronal degeneration

Histological changes are described in the brain of a patient in whom a hemicerebellectomy had been performed 14 years before death. There is cell and fibre loss, partial or total, in nuclei known to have direct connections with the cerebellum. In some nuclei the sequel to cell loss is marked fibrillary gliosis. In other nuclei the cells have disappeared without trace. The degeneration of these tracts with a direct connection with the cerebellum has also led to degeneration of other tracts in synaptic relationship with them. This transneuronal degeneration has occurred in the corticopontine tracts and in the central tegmental tract, in the former definitely, and in the latter probably, retrogradely. It is probable that transneuronal degeneration has also occurred in other tracts. The extent of the degeneration and, in particular, the occurrence of overt transneuronal degeneration, suggest that the examination of material after a very long term of survival might be of value in experimental work concerned with mapping neuroanatomical networks.

Responses of pontocerebellar neurones to stimulation of the parietal association and the frontal motor cortices

The corticopontine projections from the paruetal association cortex (the anterior portion of the middle suprasylvian gyrus) were electrophysiologicaly investigated and compared with those form the frontal motor cortex (the anterior sigmoid gyrus) in cats under light Nembutal anaesthesia. It was indicated by field potential study that the pontine nucleus (PN) neurones receive a significant amount of the direct corticopontine fibres from both the parietal and frontal cortical areas. In extracellular unitary study, out of 107 PN neurones identified by antidromic activation due to the brachium pontis stimulation, 33 responded with firings to stimulation of the parietal association area and 64 to the frontal motor area. Only 10 of them were excited by both parietal and frontal stimulations, but they were not estimated to receive the dual monosynaptic projections from both cortical areas. There were found data suggesting that the pontocerebellar neurones with faster conduction velocities respond at shorter latencies to the cortical stimulation and those with slower conduction velocities fire at longer latencies on the cortical stimulation. No remarkable difference was observed between the topographical localization of the PN neurones receiving the projection fibres from the parietal association and the frontal motor cortical areas. It was concluded that a vast majority of the pontocerebellar neurones possibly receive monosynaptic contacts differentially with the corticopontine fibres originating from the parietal association and the frontal motor areas.

The basilar pontine gray of the opossum: a correlated light and electron microscopic analysis.

Neurons within the basilar pontine gray (BPG) of the American opossum can be subdivided into four major nuclei which are named medial, lateral, ventral and peripeduncular in accordance with previous studies. In addition, several smaller subnuclei, such as the median and dorsolateral cell groups, are present, as well as two longitudinal columns of neurons within the ventral nucleus. Neurons in the BPG range in size from 9 to 35 mu and appear randomly distributed so that none of the subdivisions contains exclusively nerve cells of the same perikaryal dimension. Projection neurons as shown in Golgi impregnations have a variable dendritic pattern; those in peripeduncular zones exhibit dendrites closely applied to the surface of the cerebral peduncle, whereas those in other regions generally have a radial type of arrangement. Certain projection neurons can be distinguished on the basis of their dendritic surface, which bears either claw-like protrusions or stalked appendages. Smaller nerve cells measuring less than 18 mu may be intrinsic neurons, since axon-like processes arise from their dendrites and course for some distance near the parent cell before becoming thin and beaded. Ultrastructural observations show profiles of neurons comparable in size to those seen in Golgi impregnations and suggest at least four classes of presynaptic profiles. One category ranges in size from 2 to 8 mu, contains round vesicles (average diameter 450 A) and characteristically forms multiple asymmetric synaptic contacts with several small postsynaptic profiles, some of which appear to be the dendritic claws mentioned above. The other three types of axon terminals measure less than 2 mu in their greatest dimension and are distinguished by their synaptic vesicles; one group containing round vesicles with an average diameter of 380 A, a second group exhibiting larger round vesicles with an average diameter of 500 A and a third group containing flatened or eliptical vesicles. Transection of the superior cerebellar peduncle produces early filamentous and later electron dense degenerative changes in some, but not all, of the larger types of presynaptic profiles. Subsequent to large motor-sensory cortex ablations both filamentous and dark degenerating profiles are simultaneously observed at all survival times. In one case with a cortical lesion restricted to the motor-sensory cortex, mainly dark degenerating terminals are apparent in the ipsilateral pontine gray, whereas in a lesion confined to the visual cortex only filamentous degeneration was observed. It is suggested, therefore, that some of the dark degenerating profiles represent the terminals of collaterals of corticospinal axons and the filamentous boutons are terminal expansions of direct corticopontine fibers.

Cerebrocerebellar communication systems.

Cerebrocerebellar communication systems.

The corticopontine projection in the cat. The projection from the auditory cortex.

The corticopontine projection in the cat. The projection from the auditory cortex.

The corticopontine projection from the visual cortex in the cat. I. The total projection and the projection from area 17

Summary Large lesions of the whole visual cortex (areas 17, 18 and 19) and small lesions (in most cases bilateral) of area 17 were made in adult cats, and the ensuing degeneration in the pontine nuclei was studied with the silver impregnation methods of Nauta and of Fink and Heimer. Most of the lesions were made by thermocoagulation. The main results are as follows. (1) The visual cortex as a whole projects onto several sharply delimited, mainly transverse bands in the rostral half of the pontine nuclei. The exact localization of these bands has been compared with the terminal areas of the corticopontine fibers from other cortical regions as determined by the present author. Only a modest degree of overlap is possible between the projection areas of the visual cortex and of the sensorimotor cortex. (2) All parts of area 17 project onto the pontine nuclei. The projection from middle parts (representing roughly the central visual field) is sparse, whereas it is heavy from rostral and caudal parts (representing peripheral parts of the visual field). (3) The total projection from area 17 covers the same pontine region as does the projection from the visual cortex as a whole (areas 17, 18 and 19). (4) A topical localization is present within the pontine projection from area 17. Rostral parts (representing the lower visual field) project more laterally within the pontine nuclei than do caudal parts (upper visual field). Medial and lateral parts of area 17 also project differently onto the pontine nuclei.

Electrophysiological studies of the pontine nuclei

Summary Responses of neurones in the pontine nuclei (PN) to stimulation of the sensorimotor cortex were recorded by microelectrodes inserted in the nuclei. Extracellular and intracellular recordings from individual neurones as well as systematic field potential analysis revealed features of neuronal activities in the nuclei. PN neurones sending their axons to the cerebellum, the ponto-cerebellar neurones, could be fired not only antidromically but also trans-synaptically by stimulation of the cerebellar folium. The results require us to postulate that axon collaterals of ponto-cerebellar neurones may feed back to the neurones themselves and excite them. A volley produced by stimulation of the sensorimotor cortex could arrive in the PN at a latency of about 0.5 msec. Cortico-pontine fibres may have direct synaptic as well as polysynaptic connections with PN neurones. Excitation of PN neurones due to stimulation of the sensorimotor cortex was usually replaced at a latency of 15–25 msec by suppression. EPSP-IPSP sequences were recorded in PN neurones, corresponding in time course to the excitation and suppression. Somatotopical organization of the cortico-pontine projection could not be shown definitively. Activation of the medial part of the PN was, in general, more marked than that of the lateral part on the same stimulation, and stimulation of the medial part of the anterior sigmoid gyrus (area 6a beta) was most powerful among various parts of the sensorimotor cortex in exciting PN neurones.

Neocortical projections to the pons and medulla of the nine-banded armadillo (Dasypus novemcinctus).

AbstractThe pattern of neocortical projections to the pons and medulla was determined by employing the Nauta‐Gygax technique ('54) on the brains of armadillos subjected to neocortical ablations. The results of this study indicate that the pretrigeminal basilar pontine gray receives input from a considerable portion of the neocortex. Degenerating fibers resulting from a lesion of the frontal tip of the neocortex terminated within the dorsal medial, the medial and the ventral medial areas of the rostral basilar pontine gray. Corticopontine fibers from the mid‐presupraorbital neocortex ended throughout the rostral to caudal extent of the basilar pontine gray, and terminated within the dorsal medial, the medial and the ventral medial areas; whereas degenerating fibers resulting from a lesion of the neocortex immediately rostral to the supraorbital sulcus terminated within the medial, the ventral and the ventral lateral areas of the basilar pontine gray. The neocortex immediately caudal to the supraorbital sulcus distributed corticopontine fibers to the ventral, the ventral lateral, the dorsal lateral and to the dorsal areas of the basilar pontine gray, while degenerating fibers resulting from lesions of the caudal one‐third and most caudal tip of the neocortex projected to the ventral and lateral portions of the basilar pontine gray.Neocortical projections to the pontine and medullary reticular formation originated mainly from cortical areas rostral and immediately caudal to the supraorbital sulcus. The neocortex rostral to the supraorbital sulcus distributed to the rostral and medial portions of the pontine reticular formation, whereas corticoreticular fibers from the neocortex immediately caudal to the suprarbital sulcus, also distributed degenerating fascicles to the spinal trigeminal nucleus, the nucleus of the solitary tract and to the nucleus cuneatus. No degenerating fibers were seen to terminate within motor nuclei of cranial nerves located within either the pons or medulla.

Electronmicroscopic observations on the structure of the pontine nuclei and the mode of termination of the corticopontine fibres. An experimental study in the cat.

The electron microscopical changes occurring in the pontine nuclei following unilateral lesions of the primary sensorimotor cortex have been studied in 7 cats with a survival time from 2–23 days. A description is also given of the fine structure of the pontine regions in receipt of the fibres. These regions are shown in Fig. 1.

Collateral pyramidal influences on the corticorubrospinal system.

Collateral pyramidal influences on the corticorubrospinal system.

The corticopontine projection in the cat. Demonstration of a somatotopically organized projection from the second somatosensory cortex.

The corticopontine projection in the cat. Demonstration of a somatotopically organized projection from the second somatosensory cortex.

The projection of the forebrain on the pons and cerebellum

Although the existence of the cortico-pontine fibres has long been recognized and their functions partially elucidated in more recent times, there has as yet been no solution of the problem of their distribution in the pons and projection on the cerebellum. The thorough investigation of the problem requires prolonged and tedious experimental work and has, probably on that account, hitherto been largely neglected. But experiments are not performed only by man. In obscure recesses of the animal kingdom lie hidden experiments of Nature which, confined within the limits of the direction of evolution chosen for them, have been condemned to carry their eccentricity to its logical conclusion. Experiments of an even more casual nature have been performed by the indiscriminate invasion of every part of the human brain by pathological processes; but it is only by the patient collection and examination of vast masses of records that any continuous narrative can be extracted from the chaotic whole. Of the three types of experiment available it is more economical of time and material to chose that which comes ready-made: the method of comparative neurology. This, even if it does not supply a complete answer, at least provides valuable clues for the more accurate direction of the other methods.