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PubMed1994

Motor impairment in Wilson's disease. 3: The clinical impact of pyramidal tract involvement.

Magnetic brain stimulation was performed on 24 patients with Wilson's disease (WD). Responses to the right and left first dorsal interosseus muscle (FDI) and to the right and left tibialis anterior muscle (TA) were analysed. In 45% of the patients prolonged central motor conduction times (CCTs) to the FDIs were found, whereas only 12% of the patients presented with prolonged CCTs to the TA muscles. No consistent significant correlations between copper metabolism and pyramidal tract function tested by magnetic brain stimulation were found. An improvement of CCTs and response amplitudes with copper elimination therapy was observed only at early phases of therapy. There was no correlation with duration of therapy or neurological symptoms. Thus magnetic brain stimulation turns out to be sensitive to detect subclinical pyramidal tract impairment in WD but seems to test a too specific aspect of motor impairment in WD to reflect the overall neurological status of the patients. Therefore, it has to be combined with other tests to be used for therapy control.

Adolescent↗
PubMed2006

Pyramidal tract maturation after brain injury in newborns with heart disease.

OBJECTIVE: Our objective was to quantify white matter tract development in term newborns with congenital heart disease, a population at high risk for perioperative brain injury, using magnetic resonance imaging diffusion tensor tractography (DTT). METHODS: Twenty-five newborns with congenital heart disease were imaged before and after surgery, with a median of 2 weeks between serial magnetic resonance imaging examinations. DTT was performed to segment bilateral pyramidal tracts using semiautomated fiber tracking software, and manual region of interest measurements were taken for comparison. RESULTS: Significant maturational rates of increasing fractional anisotropy (median, 4.4% per week) and decreasing mean diffusivity (D(av)) (median, -2.0% per week) in the pyramidal tract were measured in infants without brain injury. Fractional anisotropy maturation rates were highest in newborns with normal scans, intermediate (median, 2.4% per week) in those with postoperative injury, and lowest (median, 0.9% per week) in those with preoperative injury, indicating a significant trend across brain injury groups (p = 0.015). D(av) maturation rates did not differ across injury groups (p = 0.15). Manual region of interest measures showed greater variability in serial measurements, and no significant differences were identified between injury groups, suggesting that DTT may provide more sensitive measures. INTERPRETATION: DTT is feasible in term newborns and may help to characterize abnormal white matter tract development following acquired brain injury.

Brain Injuries↗
PubMed1980

Origin of the pyramidal tract determined with horseradish peroxidase.

The origin of the axons contained in the pyramidal tract (PT) of the cat was established using retrograde transport of horseradish peroxidase (HRP). A complete section was made through a PT at the level of the medulla oblongata and HRP was applied to the sectioned axons. Cat brains were cut in frontal and sagittal planes and HRP-labeled cells were plotted in outlines of the brain sections. The entire cortical region containing PT cells was divided into 8 subregions and the percent of PT cells was determined in each. Surface cortex, subregions 1, 3 and 8, contained only 30--40% of PT cells; the majority resided in deep sulcal cortex, in subregions 2, 4, 5, 6 and 7. Subregion 1 (containing 6--12% of PT cells) extends rostral to the cruciate sulcus; subregion 3 (15--22%) extends from the cruciate sulcus caudally to the ansate sulcus; subregion 8 (7--8%) covers cortex laterally adjacent to subregion 3. The hidden banks of the cruciate sulcus contained the greatest concentration of PT cells, 28--34% in the dorsal bank (subregion 5) and 15--20% in the ventral bank (subregion 4). The coronal sulcus contained only 2--5% of PT cells in its dorsal bank (subregion 6) and 1--4% in its ventral bank (subregion 7). The presylvian sulcus contained 8--12% of all PT cells in its lateral bank (subregion 2). This new cortical area is not yet considered part of 'PT cortex'. Qualitative limitations of this study are discussed.

Animals↗
PubMed1979

Projection of individual pyramidal tract neurons to lumbar motor nuclei of the monkey.

The projection of individual pyramidal tract (PT) neurons from the hindlimb area in the precentral gyrus of the cerebral cortex to the lumbar spinal cord was studied in the monkey by systematically searching for sites within identified regions of the spinal gray from which the PT neurons could be antidromically activated by local stimulation. All investigated neurons belonged to the fast conducting fraction of PT neurons. The following results were obtained. 1. Each PT neuron could be activated from more than one region of the spinal gray matter, including identified spinal motor nuclei and areas dorsomedial to these nuclei, but do not the intermediate nucleus or regions dorsal to it. "Passage areas" and "termination areas" were defined. 2. Half of the PT neurons with termination areas within motor nuclei had these areas in more than one nucleus. There were thus strong suggestions for synaptic contacts of some PT neurons with motoneurons of more than one muscle. 3. Four groups of three or four neurons were recorded simultaneously by the same cortical electrode. Comparisons of passage and termination areas within groups revealed both similarities and differences in projections of neighboring neurons. Every neuron was activated from some region(s) where others of the group were not. Common passage areas, or passage and termination areas, for two or three neurons of a group within at least one motor nucleus were found for all groups. Termination areas in the same motor nucleus have been found for the majority of the neurons of only one group. These common projection areas are compatible with, but not prove, that group of adjacent PT neurons has common target cells in the spinal cord.

Animals↗
PubMed1976

Blockade by amino acid antagonists of neuronal excitation mediated by the pyramidal tract.

1. The responses to glutamate and amino acid antagonists of cells in the cuneate nucleus of anaesthetized rats have been examined.2. 1-hydroxy-3-amino-pyrrolidone-2 (HA-966) and glutamic acid diethylester applied by micro-iontophoresis reduced glutamate excitation of the neurons. HA-966 WAS EFFECTIVE ON MORE CELLS THAN GLUTAMIC ACID DIETHYLESTER AND WAS MORE POTENT. HA-966 DID NOT AFFECT EXCITATORY RESPONSES TO ACETYLCHOLINE.3. Spike activity of cuneate cells was evoked by stimulating the cerebral cortex. Spikeswhich could be attributed to monosynaptic activation of the cells were studied. The pyramidal tract is the only corticofugal pathway known to be capable of short latency activation of dorsal column nucleus neurones.4. HA-966 reversibly blocked the evoked activity in twenty-eight (70%) of forty units in which monosynaptically evoked spikes were induced.5. The results raise the possibility that the neurotransmitter released by neurones of the pyramidal tract may be an excitatory amino acid.

Action Potentials↗
PubMed2002

Fiber tracking from DTI using linear state space models: detectability of the pyramidal tract.

Diffusion tensor imaging (DTI) is an emerging and promising tool to provide information about the course of white matter fiber tracts in the human brain. Based on specific acquisition schemes, diffusion tensor data resemble local fiber orientations allowing for a reconstruction of the fiber bundles. Current techniques to calculate fascicles range from simple heuristic tracking solutions to Bayesian and differential equations approaches. Most methods are based only on local diffusion information, often resulting in bending or kinking fiber paths in voxels with reduced diffusion properties. In this article we present a new tracking approach based on linear state space models encompassing an inherent smoothness criterion to avoid too wiggly tracked fiber bundles. The new technique will be described formally and tested on simulated and real data. The performance tests are focused on the pyramidal tract, where we employed a test-retest study and a group comparison in healthy subjects. Anatomical course was confirmed in a patient with selective degeneration of the pyramidal tract. The potential of the presented technique for improved neurosurgical planning is demonstrated by visualization of a tumor-induced displacement of the motor pathways. The paper closes with a thorough discussion of perspectives and limitations of the new tracking approach.

Adult↗
PubMed1984

Unmyelinated axons in the pyramidal tract of the cat.

Ultrastructural preparations revealed the presence of unmyelinated axons in the pyramidal tract (PT) of the adult cat. At the level of the medulla oblongata, unmyelinated axons constituted 8-15% of the total PT population. Axon diameters ranged from 0.05 to 0.06 micron with a mean of 0.18 micron. Although axons were distributed throughout the PT, their density was highest in the medial part.

Animals↗
PubMed1982

Pyramidal tract neurons in somatosensory cortex: central and peripheral inputs during voluntary movement.

Recordings with pyramidal tract neurons (PTNs) in the primary somatosensory cortex of the monkey show that these neurons have 3 properties in common with PTNs of primary motor cortex: (1) they exhibit discharge prior to the onset of voluntary movement, (2) their discharge frequency varies as a function of strength of muscular contraction, and (3) they show reflex responses to afferent stimuli that occur during movement. These findings support the view that in addition to its widely recognized role in somesthetic perception, somatosensory cortex has a direct role in the control of movement.

Afferent Pathways↗
PubMedDate not supplied

Pyramidal tract responses (PTR) during hypoxia and hypotension.

In rats with unilateral carotid artery ligation pyramidal tract responses were studied during hypoxia and during trimethaphan-induced hypotension. Observations on EEG activity during hypoxia suggest that unilateral carotid artery ligation produces a more severe perfusion defect in lateral portions of the hemisphere. During hypoxia and during trimethaphan-induced hypotension indirect PTRs disappeared first from the hemisphere on the side of carotid artery ligation and next from the opposite hemisphere. This was followed by loss of direct PTRs in the same order. Animals could not be resuscitated once the direct PTR from the non-ligated hemisphere had disappeared. Hypotension appears to be a late contributing factor in impairing electrocerebral activity during hypoxia in this study.

Animals↗
PubMed1984

Sensory response properties of pyramidal tract neurons in the precentral motor cortex and postcentral gyrus of the rhesus monkey.

Pyramidal tract neurons (PTNs) were identified in precentral motor cortex (MI) and in postcentral cortex (PoC) of a monkey trained to pronate and supinate its forearm. PTN responses to passive, ramp-form displacements of the forearm were examined in relation to the size of the neuron (as reflected by its antidromic latency). Larger PTNs tended to exhibit transient responses to passive limb displacement, whereas smaller PTNs more frequently showed sustained responses. These findings suggest that smaller PTNs, that make up the majority of the total PTN population, receive continuous feedback during posture as well as during the dynamic phase of movement.

Afferent Pathways↗
PubMed2001

Dopaminergic inhibition of excitatory inputs onto pyramidal tract neurons in cat motor cortex.

The role of dopamine (DA) on motor cortical pyramidal tract neurons (PTNs) was studied in anesthetized cats with in vivo extracellular recordings in response to transcallosal (TC) and ventrolateral (VL) thalamic stimulations. An antidromic PT potential was evoked to recognize PTNs. In most PTNs, iontophoretic application of DA significantly reduced the spike activity exerted by 20 single-pulse stimulations. Both D(1)-like and D(2)-like receptor antagonists blocked (disinhibited) the effect in a similar way regardless of TC and VL stimulations, suggesting colocalization of two receptors. Except for the presence of jittering, the mean latency was usually fixed and short. These findings indicate that ventral midbrain DA imposes an intense suppression in modulating PTNs response to both callosal and thalamocortical excitatory inputs in motor cortex. Such DAergic suppression could play pivotal role to improve motor and sensorimotor signal integration.

Action Potentials↗
PubMed1960

Effect of pyramidal tract activity on dorsal column nuclei.

The response of single units in cuneate and gracile nuclei to cutaneous stimulation can be modified by prior stimulation of the motor cortex of the cat. Both excitation and inhibition of these neurons can be effected via the pyramidal tract.

Animals↗
PubMed1983

Properties of the spike afterhyperpolarization in pyramidal tract neurons.

Features of the spike afterhyperpolarization (AHP) recorded intracellularly have been analyzed in fast pyramidal tract neurons of cats. Cell input conductance increases during the AHP, possibly because of a change in potassium conductance, as suggested by an AHP equilibrium potential 10--15 mV negative to the resting membrane potential. When more spikes are evoked in succession, AHPs following the first one are strongly reduced in amplitude. The effect is virtually maximal (30--50% of the control) after a single spike and fades out by 200-400 ms after the last spike. At short interspike intervals the initial time course of the depression is hidden by summation occurring between consecutive AHPs.

Animals↗
PubMed1981

Dendritic spikes induced in fast pyramidal tract neurons by thalamic stimulation.

In deeply anesthetized cats the synaptic events induced in fast pyramidal tract cells (Pt cells) by ventrolateral (VL) stimulation were analyzed with intracellular recordings. In 40% of the fastest conducting Pt neurons it was found that VL stimulation induced fast depolarizing potentials (FPPs) with or without underlying excitatory postsynaptic potentials (EPSPs). These FPPs were all or non fast rising events lasting about 2 ms. They could be induced by brachium conjunctivum stimulation or they could also occur spontaneously. Those occurring spontaneously had amplitude and time course similar to those evoked by VL stimulation suggesting that they were of thalamic origin. On the basis of their amplitude and lack of collision with antidromic action potentials FPPs were neither axonal nor IS events. Passage of hyperpolarizing currents could block them in an all or none manner. It is concluded that FPPs represent electronically attenuated dendritic spikes generated in small side branches (oblique ascending dendrites) or fast Pt neurons where VL terminals most probably establish their synaptic contacts.

Animals↗
PubMedDate not supplied

[Reactions of cat motor cortex neurons to stimulation of the pyramidal tract and ventroposterolateral thalamic nuclei].

Responses of neurons of motor cortex evoked by stimulations of pyramidal tract (PT) and ventroposterolateral (VPL) nucleus of thalamus were studied in cats immobilized by Myorelaxin. Antidromic spikes were found in 22.6% and in 9.9% of cortical cells when PT and VPL were stimulated, respectively. Fast- and slow-conducting PT-neurones could be differentiated according to antidromic excitation latencies. PT stimulation evoked EPSPs in 46.3% of studied neurones and VPL stimulation--in 48.2% ones. Monosynaptic EPSPs were identified in responses of fast- and slow-conducting PT-units and of neurones projecting in VPL; mechanisms and functional role of such reactions are discussed. Di- and polysynaptic IPSPs were evoked in 74.5% of units by PT stimulation and in 94.4%--by VPL stimulation. Three groups of IPSPs were classified with durations to 120, 130-280 and more than 300 ms. Duration of PT-evoked IPSPs was higher in cortical neurones from surface layers and VPL-evoked ones--in units localized in deep layers.

Action Potentials↗
PubMed1985

Two different mechanisms control inhibition of spike discharge in neurons of cat motor cortex after stimulation of the pyramidal tract.

Intracellular recordings were made from neurons of the motor cortex of awake cats while the pyramidal tract (PT) was stimulated at the level of the facial nucleus. In some neurons IPSPs of 35-120 ms peak latency were recorded that diminished in size or reversed with hyperpolarizing current. During these IPSPs a decrease in input resistance reflective of a conductance increase was measured. More often, however, PT stimulation produced IPSPs with comparable latencies that increased in size with hyperpolarizing current. These IPSPs diminished with depolarizing current, and in some instances they appeared to reverse with strong depolarization. During these IPSPs an increased input resistance reflective of a decreased conductance was measured. The results indicate that two different mechanisms control rapid inhibition of spike discharge in neurons of the motor cortex after PT stimulation.

Animals↗
PubMed1982

Impulse coding of ramp currents intracellularly injected into pyramidal tract neurones.

Relationships between the repetitive discharge and dynamic aspects of the input were analyzed in pyramidal tract neurones of the cat. Inputs were intracellularly injected currents reaching a steady level after ramps of different slopes (from 0.02 to 1.5 nA ms-1). Output was the instantaneous frequency of the discharge. During the transient phase, instantaneous frequency appeared to be related both to the velocity of rise and to the intensity of the stimulating current. The dynamic component of the cell response was estimated by subtraction of the intensity-bound component (derived from the steady-state response to current steps). After subtraction, the instantaneous frequency of interspike intervals following the first one became proportional to the ramp slope. The instantaneous frequency of the first interval also increased with the current slope, but at a lower rate than the frequency of other intervals. Moreover its dynamic component virtually stopped growing when the ramp slope exceeded 0.3-0.5 nA ms-1.

Animals↗