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PubMed2003

Complete and partial lesions of the pyramidal tract in the rat affect qualitative measures of skilled movements: impairment in fixations as a model for clumsy behavior.

Little is known about prenatal and perinatal brain injury resulting in subsequent clumsy behavior in children. One candidate motor system is the pyramidal tract. The tract traverses the entire central nervous system and, through direct and indirect connections to the brainstem and spinal cord sensory and motor nuclei, is involved in the learning and execution of skilled movements. Here, rats, either naive or pretrained on a number of motor tasks, were assessed for acute and chronic impairments following complete or incomplete pyramidal tract lesions. Postsurgery rats with complete lesions were impaired on the qualitative measures of limb aiming, supination, and posture. Impaired movements require fixations, complementary movements in different body segments. The impairment in fixations was manifest acutely and underwent no improvement with subsequent training/testing. The finding that complete and partial pyramidal tract lesions produce chronic impairment in fixations provides insight for understanding clumsy behavior in humans and its potential remediation via specific training in making fixations.

Animals↗
PubMed2005

How to enhance ipsilateral actions of pyramidal tract neurons.

We have shown previously that ipsilateral pyramidal tract (PT) neurons facilitate the actions of reticulospinal neurons on feline motoneurons (Edgley et al., 2004), which indicates that they might assist the recovery of motor functions after injuries of contralateral corticospinal neurons. Nevertheless, stimulation of ipsilateral PT fibers alone only rarely evoked any synaptic actions in motoneurons. The aim of this study was to investigate possible ways of enhancing such actions and of inducing more effective excitation and inhibition of motoneurons. The effects of stimulation of the ipsilateral PT were investigated after eliminating the spinal actions of contralateral PT fibers by hemisecting the spinal cord at a low thoracic level and were estimated from intracellular records from hindlimb motoneurons. Two measures were used to enhance PT actions. The first was to increase the probability of activation of reticulospinal neurons by mutual facilitation of actions of ipsilateral and contralateral PT neurons. The second was to enhance synaptic transmission between PT neurons and reticulospinal neurons, and in pathways between the reticulospinal neurons and motoneurons via commissural interneurons, by systemic application of a K+ channel blocker, 4-aminopyridine (4-AP). The results show that under favorable conditions, ipsilateral PT neurons may induce EPSPs and IPSPs in hindlimb motoneurons, or even action potentials, via the reticulospinal pathway. This study strengthens previous conclusions that ipsilateral PT neurons can potentially replace, at least to some extent, the actions of injured contralateral PT neurons. It also suggests that 4-AP might improve the progress of the recovery.

4-Aminopyridine↗
PubMed1989

Corticostriatal cells in comparison with pyramidal tract neurons: contrasting properties in the behaving monkey.

Antidromically identified neurons projecting to the putamen (CPNs) and pyramidal tract neurons (PTNs) were recorded from motor and premotor cortex of a monkey which performed a load-bearing task with the wrist. CPNs appeared as a uniform population with very slowly conducting axons and low spontaneous activity. In contrast to PTNs, they exhibited weak, mostly insignificant correlation with graded steady-state forces, responded to torque perturbations with remarkably long latency, and seemed to discharge much later with active movement. Collateral branching of PTNs to the putamen was found to be infrequent (1%). We suggest that the putamen receives a cortical message that is strikingly different from that sent down the pyramidal tract.

Animals↗
PubMed1984

Diameter of axons and thickness of myelin sheaths of the pyramidal tract fibres in the adult human medullary pyramid.

After perfusion fixation with a mixture of paraformaldehyde, glutaraldehyde, and potassium-chromate 4 adult human medullary pyramids were examined with the electron microscope. The myelin sheaths showed only mild signs of post mortal destructions. The periodicity of the lamellae is preserved and varies about 17 nm. For quantitative purposes specimens were taken at random from regions with an extend of half a mm2 on the cross section of the pyramid. On the average 62 lamellae (s = 5, n = 200) built up 1 micron myelin sheath in the 4 brains. The myelin sheath thickness and the inner circumference of the myelin sheath are measured. The axon diameter is calculated from the inner circumference. We obtained an average number of 66,000 fibres, s = 11,000 per mm2. Fibres with a total diameter below 4 microns amount to 87.9%, fibres from 4 to 10 microns to 10.77%, and larger than 10 microns to 1.4%. An axon diameter of about 0.5 micron combined with a thickness of the myelin sheath of 0.3 micron was most often found in all 4 cases. The fibres showed a broad variation of myelin thickness. In a given group of the small axons the thickest myelin sheath exceeded 3 to 4 times the value of the thinnest one. The coefficient of correlation between axon diameter and myelin sheath thickness was calculated as r2 = 0.56. No correspondence exists between frequency maxima and the ratio g, axon diameter to total diameter. Below a total fibre diameter of 5 microns the ratio g scatters broadly about 0.6, fibres larger than 5 microns exceed the value of 0.6. From the morphological data only large sized fibres can evoke a strong effect on compound action potentials if the method of reconstruction of the action potential from fibre size frequency distribution is employed.

Adult↗
PubMed1997

[An autopsy case of amyotrophic lateral screlosis (ALS): magnetic resonance imaging and pathological findings of the pyramidal tract].

A 59-year-old woman was diagnosed as amyotrophic lateral screlosis (ALS) on the basis of neurological and electromyographical findings, and died after about 4 years course. Magnetic resonance imaging (MRI) on coronal planes through the internal capsule revealed high signal area almost limited to the pyramidal tract; the high signal area was more restricted in proton weighted imaging than in T2 weighted imaging. Histological lesion of the precentral gyrus was slight, while loss of myelinated fibers in the posterior limb of the internal capsule was remarkable. Extent of the pathological lesion in the posterior limb of the internal capsule well corresponded to the high signal area in proton weighted imaging. Comparison of the pyramidal tract pathology in the corona radiata and the internal capsule in Klüver-Barrera preparations with the MRI findings obtained 2 years and 8 months before the autopsy suggests us that the T2 weighted imaging of ALS brains may detect involvement of the pyramidal tract as early as or even earlier than histological changes become manifest.

Amyotrophic Lateral Sclerosis↗
PubMed1986

A transient pyramidal tract projection from the visual cortex in the hamster and its removal by selective collateral elimination.

During the early postnatal development of the neocortex in rats there is an axonal projection from the occipital cortex (which includes the visual cortex) to the spinal cord which is subsequently completely removed through a process of selective collateral elimination. In order to determine whether a similar phenomenon occurs during the development of the hamster cortex, we have injected the retrogradely transported fluorescent dye Fast Blue (FB) into the pyramidal decussation of hamsters at various ages. In adult hamsters such an injection results in a band of labeled neurons confined to layer V and to about the rostral two-thirds of the neocortex; no labeled cells are seen in the occipital cortex. However, a similar FB injection made during the first postnatal week results after a 4-day survival in a continuous band of FB-labeled layer V neurons spread throughout the tangential extent of the neocortex, including the occipital cortex. A similar continuous band of FB labeled layer V neurons is seen throughout the tangential extent of the neocortex including the occipital region in hamsters injected during the first postnatal week but allowed to survive until the fourth week (i.e., after the restriction of the widespread neonatal pattern has occurred). Injections of the anterograde tracer wheat germ agglutinin conjugated to horseradish peroxidase made into the occipital cortex, or for comparison, into more rostral cortical regions in hamsters ranging in age from neonates to adults, reveal that the extension of pyramidal tract axons is staggered along the anterioposterior axis of the cortex such that axons originating from the posterior regions lag behind those arising from more rostral areas. The transient occipital projection appears to reach a maximum around the end of the first postnatal week: a large number of labeled occipital axons is seen in the medullary pyramidal tract, and some of these can be followed through the pyramidal decussation and into the dorsal funiculus of the spinal cord. Injections into the occipital cortex on P16 label only a few fibers in the medullary pyramidal tract, and none is labeled in hamsters injected as adults.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Direct synaptic linkage of ventrolateral nucleus of thalamus terminal with cat fast pyramidal tract neuron.

An electron microscopic study on the synaptic connections between neurons of ventrolateral nucleus of thalamus (VL) and pyramidal tract neurons (PTNs) in cat motor cortex was conducted by means of the anterograde degenerating procedure coupled with horseradish peroxidase (HRP) intracellular staining. Following VL lesions, a large majority of the degenerating terminals were found to terminate on dendritic spines and a few on the dendritic shaft. An asymmetric type synapse formed by a VL degenerating terminal and the dendritic shaft of a branch of apical dendrite of a labeled fast pyramidal tract neuron was demonstrated.

Animals↗
PubMed1993

[A case of hereditary motor and sensory neuropathy type I with optic atrophy, neural deafness and pyramidal tract signs].

A case of hereditary motor and sensory neuropathy (HMSN) type I with optic atrophy, neural deafness and pyramidal tract signs was described. The patient was a 53-year-old man who had suffered from difficulty in walking, decreased visual acuity since age 16 years. These symptoms were slowly progressive. At the age of 37, he was pointed out optic atrophy, positive pyramidal tract signs. Distal muscle weakness with atrophy of four limbs was prominent at the age of 50. Since then, he noticed progressive hearing loss with blindness. His elder sister was diagnosed Charcot-Marie-Tooth disease. On neurological examination, he showed to have optic atrophy without retinitis pigmentosa and neural deafness. Also he showed mild degree of muscle weakness and atrophy in four limbs, severe in the distal part of lower limbs. Deep tendon reflexes were absent in all limbs with right Babinski sign. Superficial sensation was decreased slightly in the distal parts of four limbs. Deep sensation was markedly decreased in the leg. There were no cerebellar signs. Audiometric examination revealed bilateral neural hearing loss. There were no findings of spinal cord compression on spinal MRI. On the nerve conduction studies, sensory nerve action potential was not elicited in all nerves tested. Motor nerve conduction velocity of the right median was 41.1 M/sec, also ulnar nerve 44.7 M/sec, but M-wave was not elicited with the electrical stimulation of other tested nerves. On sural nerve biopsy, the density of myelinated fibers was severely decreased. Well-myelinated axon surrounded by onion bulb formation was observed in electron microscopic examination.(ABSTRACT TRUNCATED AT 250 WORDS)

Charcot-Marie-Tooth Disease↗
PubMed1991

Junctional specializations between growth cones and glia in the developing rat pyramidal tract: synapse-like contacts and invaginations.

The ultrastructure of contacts between axonal growth cones and glial cells in the developing pyramidal tract was examined by serial sectioning at the third cervical spinal cord segment in 0-, 2-, and 4-day-old rats. Junctional specializations, composed of synapse-like contacts and invaginations, were frequently observed at the contact zone between growth cones and glial elements. The synapse-like contacts consist of clear, round vesicles of 43 +/- 6 nm in the presynaptic growth cone, a pre- and a postsynaptic density, separated by a cleft of 12.1 +/- 0.9 nm. The invaginations consist of small protrusions of the growth cone into the glial element. The invaginated glial membrane is coated. Within the glial element, close to the invagination, frequently organelles were observed that closely resemble endosomes and prelysosomes. Therefore, it is suggested that the invagination represents a stage in endocytosis or possibly phagocytosis of the protruding part of the growth cone by the glial cell. The junctional specializations are formed by growth cones and, less frequently, by axon shafts. The targets of these specialized contacts are, in general, immature glial cells located within the tract area. Occasionally, however, invaginations were also observed into myelinating oligodendrocytes, suggesting that the population of immature target cells includes oligodendrocyte precursors. With regard to the functional significance of these temporary growth cone-glial contacts, several possibilities are discussed, including the suggestion that outgrowing pyramidal tract axons provide immature glial cells with chemical messages, which may influence the timing of glial cell maturation in the tract.

Animals↗
PubMed1990

A quantitative analysis of axon outgrowth, axon loss, and myelination in the rat pyramidal tract.

A quantitative analysis of the development of the pyramidal tract (PT) was carried out at the level of the caudal medulla oblongata and at the sixth cervical spinal segment (C6), in rats ranging in age from embryonic day 20 (E20) to the adult of 90 days postnatally (P90). The axon number in the right medullary PT rises from 27,000 axons at E20 to 391,000 axons at P4. Growth cones are abundant during this period, but can still be observed occasionally at P7. After P4, the axon number is reduced by 62%, to 150,000 in the adult. A rapid axon loss until P14 is followed by a gradual axon loss, continuing beyond the third postnatal week. A similar biphasic axon loss was observed in the cervical PT. At P2 and at P7, concentrations of electron-dense material were observed in 0.5-0.7% of the axon profiles in the medullary PT. Since at P21 this feature was only observed in 0.2% of the axons, it might represent an early sign of axon loss. Myelination starts in the medullary PT at P7. Especially during the third postnatal week, the number of myelinated axons increases rapidly. In the adult rat PT, both at medullary and cervical levels, about one third of the axons are still unmyelinated. The results indicate that the development of the rat PT is characterized by a gradual outgrowth of its fibers and by a protracted, biphasic axon loss. Furthermore, comparing the PT at the medulla, at C3, and at C6, a rostrocaudal decrease in axon number was observed during development as well as at the adult stage. Therefore, no evidence was found for increased axon branching in the tract in the cervical intumescence.

Aging↗
PubMed1998

Spontaneous regeneration of the pyramidal tract after transection in young rats.

Spontaneous regeneration of the pyramidal tract after transection of the medullary pyramid was examined in young rats by the anterograde tracing method with wheat germ agglutinin-conjugated horseradish peroxidase. Care was taken to cut the tract as sharply as possible to minimize traumatic injuries. A very sharp cut produced edema-free lesions without subsequent formation of either cysts or scars, whereas a relatively blunt cut produced edema and later scars and/or cysts in the lesion. Regenerated projections in the latter cases were sparse, short, dispersed and largely aberrant as described in previous reports. By contrast, regenerated projections in the former cases were very much similar to normal in various respects: the amount, extension, path, formation of a compact bundle and termination. There was, however, a decisive difference from normal, that is, the additional aberrant projections.

Age Factors↗
PubMed1980

[Role of the pyramidal tract in the mechanism of dyspnea and hyperventilation].

Hypoxia evoked by mechanical asphyxia first of all disturbs the generation of potentials in pyramidal tract neurons. Hypoxic work, therefore, causes inadequate contraction of somatic muscles, a difficulty in work performance and respiratory discomfort. Concurrently, the disturbance of the pyramidal tract disinhibits the respiratory center of the brain stem with a result of excessive hyperventilation during hypoxic work.

Afferent Pathways↗
PubMed1982

A re-evaluation of the question of ascending fibers in the pyramidal tract.

In 1952 we published a study in the cat with the Glees method, demonstrating the occurrence of degenerating fibers in the pyramidal tract rostral to transections of the tract in the spinal cord. These fibers were interpreted as spinocortical fibers, which have also been described in man. However, other authors have disputed the existence of such fibers. In an attempt to provide more information about this subject, multiple injections of horseradish peroxidase (free and lectin-labeled) were made in the sensorimotor cortex of 4 cats. No retrogradely labeled cells were found in the spinal cord in these cases. Our present and previously reported findings are discussed in the light of other studies of pathological changes in fiber tracts within the central nervous system. Although the present experiments were negative, the degenerating axons previously observed by us in silver sections from the pyramid, pons and internal capsule after lesions of the pyramidal tract in the spinal cord, can not be satisfactorily explained as evidence of retrograde, indirect Wallerian, degeneration of corticospinal fibers.

Animals↗
PubMed1989

A quantitative analysis of the development of the pyramidal tract in the cervical spinal cord in the rat.

A quantitative electron microscopic analysis was undertaken of the development of the pyramidal tract, at the level of the third cervical spinal segment, in rats ranging in age from the day of birth to three months old. The axon number was calculated as the product of axon density, determined in a systematic random sample of electron micrographs, and tract area. During the first postnatal week the tract contains thin unmyelinated axons and growth cones. Growth cones are abundant in neonatal rats, but can still be observed occasionally at the end of the first postnatal week, indicating a continuous addition of pyramidal tract axons during the first postnatal week. Myelination starts around P10. By the end of the first postnatal month approximately 50% of the axons have already been myelinated. Myelination proceeds during further maturation, but in the three month old rat 28% of the axons are still unmyelinated. The total number of axons increases rapidly after birth up to 153,000 at the fourth postnatal day. Subsequently, the number of axons is reduced by nearly 50% to 79,000 in the adult rat. The axon loss is most prominent during the second postnatal week, when 32,000 axons are eliminated, but continues for several weeks at a slower rate.

Animals↗
PubMed1982

Convergent inputs from the dentate and the interpositus nuclei to pyramidal tract neurons in the motor cortex.

Effects of stimulation of the cerebellar nuclei were investigated by intracellular recordings from fast and slow pyramidal tract neurons and thalamocortical neurons in the cat. The present study demonstrated that: (1) the interpositus and the dentate nuclei excite PTNs in the motor cortex; (2) single pyramidal tract neurons receive convergent inputs from both nuclei, and (3) the convergence of the inputs from both nuclei occurs at the level of the ventrolateral nucleus of the thalamus.

Animals↗
PubMed1978

The intraspinal branching patterns of fast and slow pyramidal tract neurons in the cat.

Antidromic activation of single pyramidal tract neurons (PTNS) was obtained in cats by stimulating either the dorso-lateral funiculus with ball-electrodes, or the spinal gray matter with microelectrodes. The results indicate that the distribution area of single PTNS is much wider than the area of a single motor nucleus, suggesting that single PTNS may influence different motor nuclei.

Animals↗