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PubMed1999

Visualizing and characterizing white matter fiber structure and architecture in the human pyramidal tract using diffusion tensor MRI.

We used diffusion tensor imaging to assess diffusion anisotropy in the pyramidal tract in ten young, and ten elderly subjects (five males and five females in each group). The purpose of this study was to define normative values for anisotropy at different anatomic levels of the brainstem as well as to assess differences due to age, gender, and laterality. In all subjects, anisotropy was highest in the cerebral peduncle, lowest in the caudal pons, and intermediate in the medulla. In the pons and medulla the regional variability was high, with significant differences in anisotropy even between contiguous slices. Multifactorial ANOVA (performed using the average value of anisotropy within each region of interest) revealed that elderly subjects had significantly lower values than young subjects in the cerebral peduncle, with no differences in the pons and medulla. No significant differences in anisotropy due to gender and side were found. The differences in anisotropy at different levels of the brainstem reflect differences in the local architecture of white matter fibers. Anisotropy is high in the cerebral peduncle because fibers have a highly ordered arrangement, while in the pons and medulla, anisotropy is lower because the local fiber architecture is less coherent due to the presence of other fibers and nuclei. The biologic meaning of the intergroup differences in anisotropy is discussed in light of the structure and architecture of the tissue under investigation. We also consider potential sources of artifacts, such as noise and motion, partial volume contamination, anatomic mismatching, and the use of inappropriate statistical tests. We conclude that the age-related decrease in anisotropy in the cerebral peduncle is not artifactual but rather reflects subtle structural changes of the aging white matter. Our study however shows that caution must be exercised in interpreting diffusion anisotropy data.

Adult↗
PubMed2005

Pyramidal tract imaging in multiple-system atrophy.

A new radiological finding of T2 FLAIR hyperintensities in the pyramidal tracts is described in a patient clinically thought to have idiopathic Parkinson's disease but histologically proven to have multiple-system atrophy.

Adult↗
PubMed1991

Distribution of synapses on fast and slow pyramidal tract neurons in the cat. An electron microscopic study.

Distributions of synapses on various portions of fast and slow pyramidal tract neurons (PTNs) in cat motor cortex were studied with electron microscopy. PTNs were identified by their antidromic invasion following stimulation of the medullary pyramid and were classified into fast and slow PTNs according to conduction velocities of their axons. Two fast and two slow PTNs were intracellularly labeled and, by systematic sampling, electron micrographs from various portions of these neurons were examined to compare the distributions of different types of synapses. It was found that most synapses formed on apical and basal dendrites of fast PTNs were with the dendritic shafts. In slow PTNs, while synapses on apical dendrites were mostly axospinous, about 70% of the sampled synapses on basal dendrites of slow PTNs were established with the dendritic shafts. Virtually all synapses on apical dendrites of slow PTNs belonged to asymmetrical type and most of the synapses sampled from basal dendrites of fast PTNs were also asymmetrical. On the other hand, about 29% of the synapses found on apical dendrites of fast PTNs were symmetrical and a trend was observed for this type of synapses to increase their number with increasing proximity to the cell body. Over 28% of the synapses on basal dendrites of slow PTNs were also symmetrical and seemed to be mainly distributed in layer VI. All synapses formed on the soma were symmetrical both for the fast and slow PTNs.

Animals↗
PubMed1968

An investigation of pyramidal tract cells in the somatosensory cortex of the rat.

1. An electrophysiological study has been made of pyramidal tract (PT) cells in the somatosensory cortex of the rat; the axons of the cells were shown to project either to the dorsal column nuclei or to the corticospinal tract.2. The corticospinal axons had conduction velocities of 7.6-10.8 m/sec. and therefore must have belonged to the large population of PT axons with relatively small diameters.3. PT cells constituted almost a quarter of the units encountered; they were distributed throughout the forepaw area within the deeper layers of the cortex.4. The sizes of the receptive fields of PT cells varied widely and did not differ significantly from those of non-PT cells.5. The latencies of PT cell discharges following peripheral stimulation showed less variation than those of non-PT cells though the mean latencies were identical.6. Most PT cells could be driven from the periphery and exhibited spontaneous activity in addition; they therefore function to maintain a continuous control over the somatosensory input to the brain which can be increased whenever the skin is stimulated.

Animals↗
PubMed1981

Dual activity patterns of fast pyramidal tract cells and their family neurones during EEG arousal in the cat.

1. Intracellular activities of fast pyramidal tract (PT) cells and their family neurones were investigated during the EEG arousal of various degrees in terms of (1) the strength of natural or midbrain reticular stimuli, (2) the length of aroused EEG and (3) the extent of stage shift from EEG synchronization to desynchronization. 2. These cells showed a response pattern of either disfacilitation (DF), disfacilitation followed by excitation (DF + E) or excitation (E). DF and E components in these responses were respectively quantified with their amplitude and incidence, and their relations to the above-listed intensity parameters of EEG arousal were examined. 3. The threshold of eliciting DF response was lower than that for E response to natural and reticular stimuli. On intensifying the parameters of EEG arousal, accompanying increases were observed in E response but not in DF response. Rather, DF response was often masked by E response on application of relatively intense stimuli, or was decreased in a reciprocal manner to the increase of E response in accordance with the degree of EEG arousal. 4. It is postulated that the phasic and tonic phases of EEG arousal manifested, respectively, as the initial DF and late E responses bear different functions, the former representing the cerebral state of a general set on receipt of a novel stimulus, and the latter involving the state of actively responding to the stimulus by encoding its intensity.

Animals↗
PubMed1994

Pyramidal tract Wallerian degeneration and correlated symptoms in stroke.

In order to reveal the precise degree of injury in the pyramidal tract after stroke, we studied 35 patients with motor deficit associated with cerebrovascular disease of the internal capsule using the T2-weighted coronal image along the 'pyramidal line'. According to the severity of the motor deficit, the patients were divided into three groups. The Wallerian index was calculated as: (area of Wallerian degeneration in the pons divided by area of the ipsilateral half of the pons) x 100. There were significant differences between the three groups. It is concluded that the area of Wallerian degeneration is related to the severity of motor deficit.

Adult↗
PubMed1986

Pyramidal tract of the cat: axon size and morphology.

The purpose of this work was to determine the number and morphology of pyramidal tract (PT) axons in the cat, using electron microscopy, modern methods of fixation, and computer-assisted morphometric analysis. Sections taken at the level of the medullary pyramids in three animals were fixed and magnified up to 10,000 X to produce photomicrographs. Morphological data were entered into computer files for analysis by tracing axon perimeters on micrographs mounted on a digitizer tablet. The number of axons per PT averaged 415,000, of which 88% were myelinated and 12% were unmyelinated. 90% of the myelinated axons fell in the diameter range 0.5-4.5 microns. Axons larger than 9 microns diameter accounted for 1% of the total; the largest were 20-23 microns. Myelinated axon mean diameter was 1.98 microns; because of the skewed distribution, with many small axons and a few very large axons, median diameter was 1.60 micron. Size distribution was relatively uniform throughout the PT cross section, with all sizes represented in all regions. However, the more medial regions had a higher proportion of small fibers than the more lateral regions: mean medial diameter was 1.85 micron while mean lateral diameter was 2.09 microns. Myelin sheath thickness averaged 7.9% of fiber diameter for axons up to 11 microns, but was constant at 0.9 micron for larger fibers. Myelinated fibers were distorted from the circular shape in cross section, with a mean circularity index (or form factor) of 0.85, which implies that the fibers could swell about 15% without rupture of the cell membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

Effects of chronic epileptic foci on control of pyramidal tract neurons in monkeys.

Five Macaca mulatta monkeys were operantly conditioned to control the firing patterns of single precentral pyramidal tract neurons. The accuracy with which the monkeys could control normal PTNs from within the focus was significantly poorer than PTNs from contralateral, homotopic cortex. In comparison to nonepileptic monkeys, there was no significant difference in the accuracy with which PTNs from cortex contralateral to interictal foci were controlled. By contrast, comparison of the time necessary to gain accurate control over individual PTNs from contralateral cortex showed the epileptic monkeys to be significantly encumbered when compared to nonepileptic monkeys. These data suggest that interictal foci produce "noise" in remote regions of brain that are involved in an operant task requiring a high degree of discrimination.

Aluminum Hydroxide↗
PubMed1978

Operant control of pyramidal tract neurons: the role of spinal dorsal columns.

A monkey was trained to control the firing patterns of precentral pyramidal tract neurons. The operant task was for the monkey to produce consecutive interspike intervals (ISI) within a requisite range, or target. The mean time off-target (error) is used to quantify the accuracy of control the monkey could assert over each PTN. Following partial destruction of the dorsal funiculi the number of PTNs driven by peripheral stimuli greatly decreased. Those PTNs which remained responsive to peripheral stimuli were as accurately controlled as those tested before column section, whereas, those PTNs unresponsive to peripheral stimuli were significantly less accurately controlled. The conclusion is that the monkey relies heavily upon proprioceptive feedback to operantly control precentral PTNs.

Acoustic Stimulation↗
PubMed1981

Excitation of slow pyramidal tract cells and their family neurones during phasic and tonic phases of EEG arousal.

1. Intracellular activities of slow pyramidal tract cells and their family neurones were investigated during the EEG arousal of various intensities. 2. By assessing the intensity of midbrain reticular or natural stimuli, the arousal length of EEG and the extent of EEG stage shift, these neurones were identified as the recipient of enduring excitation (E + E) during both the phasic and tonic phases of EEG arousal, and were termed E + E cells. 3. These cells were located in all the cortical laminae. E + E responses took the form of continuous depolarization in most of the deep cortical layer cells, but separated initial and late peaks of depolarization were seen in most of the superficial initial and late peaks of depolarization were seen in most of the superficial layer cells. 4. The E + E response versus stimulus intensity or arousal length relationship consisted of plateau and rising limbs, which would characterize the initial and late E components, respectively. 6. The excitatory tonus was revealed in E + E cells with mean levels of resting membrane potential, being most hyperpolarized during highly synchronized EEG and gradually depolarized according to stage shift towards desynchronization.

Animals↗
PubMed1986

Response properties of the non-pyramidal tract neuron in the kitten motor cortex during early postnatal development: an intracellular HRP study.

Response properties of the non-pyramidal tract neurons (non-PTNs) of the kitten motor cortex were examined with intracellular horseradish peroxidase (HRP) staining under Nembutal anesthesia. Thirty-one neurons were identified as non-PTNs and their responses were analyzed with stimulation of the cerebellar nuclei (CN) and/or the medullary pyramid (Py). Excitatory postsynaptic potentials (EPSPs) were induced both by CN and Py stimulation even at birth, whereas inhibitory postsynaptic potentials (IPSPs) were first detected during the third postnatal week in layers II-III pyramidal neurons, which is much later than in PTNs. This indicates that the intracortical circuits responsible for IPSPs in the superficial cortical layers develop later than in layer V.

Animals↗
PubMedDate not supplied

Synaptic processes in pericruciate cortical neurons evoked by pyramidal tract stimulation in cats.

In cats anesthetized with chloralose and pentobarbital and immobilized with D-tubocurarine activity of 423 pericruciate cortical neurons was recorded (342 extra- and 81 intracellularly); 78 neurons had spontaneous activity. Stimulation of the pyramidal tract evoked antidromic action potentials in the pyramidal neurons with a latent period of 0.5-16.0 msec. Recurrent and lateral PSPs also developed both in pyramidal and in unidentified neurons in all layers of the cortex; IPSPs were recorded in 46.7% of neurons, EPSPs in 21.0%, mixed responses in 26.0%, and no visible changes were found in 6.3%. The latent period of the IPSPs was 1.5-14.0 msec, ther amplitude 1.3-17.0 mV, their rise time from 4 to 18 msec, and their duration 18-120 msec (sometimes up to 250-500 msec). In 30% of cases in which IPSPs appeared, their course was divided into two phases: fast (duration 10-20 msec) and slow. EPSPs developed after a latent period of 2.6-29.0 msec; their amplitude was 1.0-7.8 mV and their duration from 10.0 to 50.0 msec. In 51.2% of spontaneously active neurons the antidromic volley inhibited their activity in the course of 200-400 msec, in 19.5% it stimulated their activity, in 7.4% it had a mixed effect, and in 21.9% no visible change took place in their activity. The role and participation of axon collaterals of pyramidal neurons and of the interneuronal system in the formation of these processes are discussed.

Animals↗
PubMed1988

Relationships between axonal diameter, soma size, and axonal conduction velocity of HRP-filled, pyramidal tract cells of awake cats.

Relationships between axonal diameter, soma size, and axonal conduction velocity were examined in intracellularly recorded pyramidal tract (PT) cells of conscious cats using pressure injection of horseradish peroxidase. Positive linear correlations were found between axonal conduction velocities and axonal diameters as well as between axonal conduction velocities and soma sizes. All PT cells had somata located in layer V. Slow PT cells had high densities of dendritic spines in layer III; however, so did some fast PT cells, making this morphologic feature unacceptable for distinguishing between slow and fast conducting PT neurons.

Animals↗
PubMedDate not supplied

[Changes in pyramidal tract response to direct stimulation of the sensomotor cortex of the rabbit during formation of a conditioned reflex].

Changes of pyramidal tract (PT) response were analyzed, reflecting the final result of cortical interaction in the process of combinations of direct stimulations of cortical surface in nonimmobilized and unanaesthetized rabbits. It has been shown that in a situation, modelling conditioning, changes take place of the first direct component--the D-component--of the PT response (reflecting the excitability of the PT neurones), as well as changes of the successive indirect synaptic component--I-component (reflecting the excitability of presynaptic cortical elements and of intracortical synaptic connections). I-component changes were significantly more expressed. In most cases the I-component of the response was increased. The obtained data testify to an increase of synaptic efficiency in the process of temporary connection formation and to possible change (increase or reduction) of excitability of PT neurones.

Animals↗