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PubMedDate not supplied

[Effect of stimulation of "emotiogenic" brain structures on pyramidal tract responses].

In experiments with stimulation of emotiogenic zones (lateral and medial hypothalamus, raphe nuclei), as a conditioning agent, a study was made of summary responses of the pyramidal tract to electrical stimulation of the sensorimotor cortex in immobilized and freely moving rats. The responses exhibited a positive early direct P-component (mean latency 0.8 +/- 0.3 ms) and a late synaptic N-component (mean latency 1.8 +/- 0.5). Reduction of the N-component amplitude was observed during stimulation of the lateral hypothalamus, and its enhancement during stimulation of the medial hypothalamus. Stimulation of the raphe nuclei produced variable, statistically non-significant changes. The experiments have shown that the identified pyramidal neurones tend to reciprocal reactions during stimulation of positive and negative emotiogenic structures. Inhibitory and excitatory influences of the respectively positive and negative emotiogenic structures on pyramidal neurones are due to indirect modulating actions on presynaptic structures.

Animals↗
PubMed1975

Pyramidal tract control over cutaneous and kinesthetic sensory transmission in the cat thalamus.

In the thalamic ventrobasal complex (VB) of the cat, effects of electrical stimulation of the pyramidal tract (PT) upon activities of 112 relay cells and 18 internuncial cells were examined. Single PT shocks to the cerebral peduncle elicited short-latency discharges in 31 relay cells (mean latency, 1.4 +/- 0.5 msec). When weak PT stimuli were employed as conditioning shocks, facilitatory effects upon responses to medial lemniscal (ML) stimulation were observed. It was revealed that VB relay cells were excited monosynaptically via collaterals of the fast PT fibers. Among 31 PT-excited cells 22 were fired by movements of joints (joint-movement units) and they made up 88% of all the joint-movement units. A majority of the relay cells responding to stimulation of hairs (hair units) did not receive excitatory effects from PT, except some special ones which represented long hairs at the distal or proximal end of the forearm-forepaw. In 44 relay cells repetitive PT shocks suppressed both evoked responses to ML stimulation and spontaneous discharges for 70--100 msec. Of these, 34 were hair units. The PT-induced inhibition in the hair units increased as their receptive fields shifted from the trunk towards the digits. Some intracellular recordings showed that the PT-induced inhibition was due to IPSPs generated disynaptically. Among 18 interneurons presumed to be inhibitory 10 responded with short latencies to PT stimulation. These were mostly the interneurons which presumably subserve the recurrent collateral inhibition in VB.

Animals↗
PubMed1976

Prolonged inactivation of cortical pyramidal tract neurones in cats by distension of the carotid sinus.

1. We have investigated the effects of stimulating carotid sinus baroreceptors upon the activity of single cortical pyramidal tract cells (PT-cells) in anaesthetized cats.2. Extracellular potentials were recorded from PT-cells, which were driven orthodromically (1/sec) by stimulating thalamic nuclei (N. ventralis lateralis, N. ventralis posterolateralis) or afferent nerves in the contra-lateral forepaw. Baroreceptors were stimulated by inflating small balloons placed in the bifurcations of one or both common carotid arteries.3. Distension of the carotid sinus caused a prolonged depression of the orthodromically evoked discharge of eighteen of thirty-two PT-cells, the effect ranging from a 15% reduction in firing to complete cessation of activity (average reduction, 39%). The depression of firing outlasted the period of balloon inflation by an average of 85 sec; in some experiments inhibition persisted for as long as 2-3 min.4. Inflation of the balloon caused a reflex fall in arterial pressure (mean decrease, 29 mmHg), pressure reverting to the control level as soon as the balloon was deflated. Single fibre recording from the carotid sinus nerve confirmed that stimulation was confined to baroreceptors and that carotid chemoreceptors were unaffected by balloon distension.5. Depression of PT-cell activity could not be explained simply by a fall in cerebral blood flow resulting from the reflex fall in arterial blood pressure. When a comparable or greater degree of hypotension was produced by bleeding or peripheral vagal stimulation, PT-cell firing fell in a third of experiments but reverted immediately to the control level when arterial pressure was restored. Thus some factor other than a decrease in cerebral perfusion pressure was responsible for the prolonged inhibition evoked by carotid sinus distension.6. Our results are consistent with the hypothesis that baroreceptor input to the reticular formation exerts an ascending influence on cortical mechanisms, with prolonged inhibitory effects comparable to those previously demonstrated at spinal level.

Animals↗
PubMed1988

Changes in pyramidal tract conduction with experimental brain-stem ischaemia in the monkey.

The effect of graded ischaemia on intracranial nerve fibre conduction has not previously been studied quantitatively. We measured pyramidal tract (PT) discharges evoked by electrical stimulation of the ipsilateral motor cortex, together with local blood flow (by hydrogen clearance), in the internal capsule and ventral pons of baboons anaesthetised with alpha-chloralose. Changes in conduction time and amplitude of the motor volley were monitored over this PT segment as it was subjected to progressive ischaemia in controlled stages. Conduction time increased significantly, with attenuation of the volley, at average brain-stem tissue flows below 30 ml/100 g/min. Using paired stimuli, we demonstrated relative refractory and supernormal characteristics of PT conduction. In mild ischaemia, the conduction time of the test response decreased, much more than with single stimulation, and in denser ischaemia it increased, relatively more so at smaller inter-stimulus intervals. The data demonstrate the impairment of conduction in a population of CNS axons with reduced local blood flow and indicate that the transmission of relatively rapid sequences of impulses would be the first aspect of conduction to suffer in ischaemia prior to conduction block.

Animals↗
PubMed1986

Pattern of pyramidal tract collateralization to medial thalamus, lateral hypothalamus and red nucleus in the cat.

Stimulating electrodes were placed in the red nucleus, lateral hypothalamus and medial thalamus in order to determine whether pyramidal tract (PT) neurons send collaterals to those sites. The red nucleus projections are well-known, but it was discovered that PT neurons also project into the other two sites. All of the fibers that sent collaterals to all three sites originated from fast PT neurons. Those that responded to stimulation of the skin and that sent collaterals to two or three sites were predominantly fast PT neurons. Those neurons that responded only to cerebral peduncle stimulation were predominantly slowly-conducting, when compared with the set of PT neurons in response to cerebral peduncle stimulation. The patterns of collateral branching to red nucleus and to lateral hypothalamus were similar, suggesting a similar synaptic effect of the pyramidal system in the two sites. Measurement of the speed of conduction from three sites along the length of corticospinal fibers revealed large changes on some, but not all, fibers; there was no evident pattern to these changes that might be associated with collateral branching. A new hypothesis concerning the functional role of fast PT neurons in regulating movement is presented.

Anesthesia↗
PubMed1988

[Reactions of the neurons of the parietal association cortex in the cat that send axons into the pyramidal tract to peripheral stimuli].

Experiments were performed on cats anaesthetized with nembutal and immobilized with myorelaxin. Excitatory responses to somatic, light and auditory stimulation were recorded in 73.8, 57.7 and 65.4% of pyramidal tract (PT) neurons, respectively, whereas inhibitory responses--in 26.2, 42.3 and 34.6% of PT neurons. Among 64 PT neurons studied, trisensory cells accounted for 64.0%, bisensory--for 26.6%, monosensory--for 9.4%. The broad convergence of different-modality signals on PT neurons favoured their integration.

Acoustic Stimulation↗
PubMed1991

Conduction velocities of pyramidal tract fibres and lumbar motor nerve roots: normal values.

Measurements of spinal cord and individual lumbar nerve root lengths were performed in 20 dissected cadavers. These data were correlated with the pyramidal tract and motor root conduction times obtained in 53 healthy subjects using motor evoked potentials. The distance between motor cortex and the level of the anterior horn cells ranged from 50.2 +/- 3.0 cm (mean +/- standard deviation) for the L1 segment to 54.4 +/- 3.6 cm for the L5 segment. The length of the motor roots from their exit from the myelon to their exit from the intervertebral foramen ranged from 10.3 +/- 1.7 cm in the L1 root to 17.5 +/- 1.9 cm in the L5 root. The central motor conduction velocity calculated for the distance motor cortex - anterior horn cells of the L5 segment was 50.1 +/- 4.5 m/s. The proximal peripheral conduction velocity of the motor nerve root between its exit from the spinal cord and its exit from the intervertebral foramen was 75.9 +/- 29.0 m/s. The overall conduction velocities between motor cortex and exit of the nerve roots from the intervertebral foramen were 57.4 +/- 6.3 m/s for the L4 fibers to the quadriceps femoris and 57.3 +/- 6.1 m/s for the L5 fibers to the anterior tibial muscle.

Adult↗
PubMedDate not supplied

Coronal MR imaging for visualization of wallerian degeneration of the pyramidal tract.

A coronal image taken along a straight line between the front edge of the medulla and the deepest point of the interpeduncular cistern clearly displayed wallerian degeneration of the segment of the pyramidal tract between the internal capsule and the pons, the medulla, or the decussation. This visualization was verified in 21 patients with moderate or severe hemiparesis following a stroke episode.

Adult↗
PubMed1978

Properties of the pyramidal tract neuron system within the precentral wrist and hand area of primate motor cortex.

1. To obtain basic anatomical data that will be useful in interpreting the results of studies of primate pyramidal tract neurons (PTNs), extracellular, single-unit recording techniques were used to determine a number of the properties of the PTN population within the electrically defined, precentral wrist zone of the monkey's motor cortex. 2. Recordings were obtained from a total of 1,375 antidromically identified PT and corticospinal tract (CST) cells. A mathematical model was then used to correct the statistics of the sample for variations in the probability of unit detection, which arise from variations in neuronal size and extracellular field dimensions. 3. Both the experimentally observed and theoretically corrected results suggest that the PT projection from this cortical zone is derived principally from slowly conducting, and presumably small to medium-sized cells (an estimated 85% of the resident PTN population). 4. Both the fast and slow cell subpopulations were found to be concentrated within cortical layer V, where they tend to congregate in small, mixed clusters of 2 to 5 neurons. Estimates of the total packing density of PTNs within layer V of this cortical zone suggest that they account for only 10-20% of the neurons within this major efferent layer. 5. 70% of the slow and 82% of the fast PT neurons within this cortical area were found to send their axons into the contralateral, lateral corticospinal tract. Thus, in futur functional studies of PTNs in this cortical area, it can be assumed that three of every four neurons will in fact influence segmental cells of one category or another directly. 6. Extensive data are also presented on the incidence of axon collateral branching from PT and CST cells to the red nucleus, the medial medullary reticular formation and the cuneate nucleus. 7. Some general implications of these findings for the design of future functional studies of anatomically identified motor cortex cell systems are then discussed.

Action Potentials↗
PubMed1991

The electrophysiological assessment of the pyramidal and non-pyramidal tracts of the spinal cord of rats.

The present paper summarizes our experience with the use of motor evoked potentials (MEP) and cerebellar evoked potentials (CEP) to assess the physiological integrity of the motor tracts of the spinal cord in a rat model. The MEP elicited by intracortical microstimulation of motor cortex reflected activity only in the pyramidal tracts; in contrast the MEP obtained by extradural cortical stimulation with a macroelectrode also reflected activity in a number of non-pyramidal pathways including the lateral vestibulospinal and rubrospinal tracts. The CEP was principally conducted in ventral spinal cord tracts and may reflect direct activation of brainstem nuclei. Data are presented which correlate the relationship between the MEP and axonal integrity after cord injury.

Animals↗
PubMed1995

Pyramidal tract fiber spectrum in rats, with comments on cats and man.

Most CNS fiber spectrums are unimodal and strongly positively skewed, with many small and few large fibers. This study shows that the pyramidal tract (PT) fiber spectrum of a rat can be calculated as the sum of three distributions of myelinated axons, each derived by normal Gompertzian growth from three normal distributions of protoaxons. Histological measurement of the rat PT determined the values entered into the model, thus forcing a unique solution. The model was generalized to cats and man by assuming values for which no experimental data was available; the simulated PT fiber spectrums closely matched the observed PT fiber spectrums, in both species. It is concluded that normal Gompertzian growth is sufficient to account for the specific shape of the fiber spectrum, with no recourse to morphogenetic sculpting. The overproduction of cells during growth, and death of cells during development, may regulate the total number of neurons in different areas of cortex, but plays no role in determining the specific shape of the PT fiber spectrum.

Animals↗
PubMed1979

A comparative study of ventrolateral and recurrent excitatory postsynaptic potentials in large pyramidal tract cells in the cat.

In acute cats deeply anesthetized with Nembutal, monosynaptic excitatory postsynaptic potentials (EPSPs) triggered by stimulation of the ventrolateral (VL) thalamic nucleus and the pes pedunculus were recorded in large pyramidal tract cells (PT cells). Deep anesthesia, low intensities of stimulation and an averaging technique were used in order to get VL and recurrent EPSPs free of polysynaptic potentials. Comparison of the time course of both EPSPs revealed a much faster rise time and shorter half-width for VL EPSPs than for recurrent EPSPs. This would suggest a more proximal location for VL synaptic contacts than for recurrent ones with respect to the soma of PT cells. The separation of the sites of origin of both EPSPs is further suggested by their almost perfect linear summation. It is suggested that VL EPSPs are produced on the apical dendritic tree, while recurrent EPSPs could originate on the basilar dendritic branches.

Animals↗
PubMedDate not supplied

Monkey pyramidal tract neurons and changes of movement parameters in visual tracking.

During a single-step visual tracking task of monkeys, parametric changes of the wrist extension-flexion movement and related discharge rate changes of pyramidal tract neurons (PTNs) of hand-arm motor area were studied. The task consisted of preparatory, precontraction, contraction and target periods. If the displacement amplitude was changed from narrow (10-20 degrees) to moderate (40 degrees) range, peak velocity, peak acceleration and contraction period increased linearly but precontraction period decreased slightly. In 61 movement-related PTNs, no linear relationships were found between PTN discharge rate during precontraction or contraction period and displacement amplitude, velocity, acceleration, precontraction period or contraction period. In less than 20% of PTNs, however, correlations between PTN discharge rate during precontraction period and velocity or acceleration were found in the moderate range task. It occurred less frequently in narrow range task. It is said in a visual tracking task that PTN activity is not dependent upon factors related to the task parameters, such as velocity, acceleration. Possible related factors were discussed.

Animals↗
PubMed1985

Synaptic organization of the cerebello-thalamo-cerebral pathway in the cat. I. Projection of individual cerebellar nuclei to single pyramidal tract neurons in areas 4 and 6.

The neural connections of the dentate (DN) and the interpositus (IN) nuclei to the motor cortex and area 6 were investigated by recording intracellular postsynaptic potentials from fast and slow pyramidal tract neurons (PTNs) in the anesthetized cat. Localized stimulation of DN and IN produced di- or polysynaptic EPSPs in fast and slow PTNs in the "forelimb area" of the motor cortex and area 6. The effects of stimulation of the two cerebellar projections were essentially the same, although some regional difference of their relative strength was noted. In these cortical areas, the majority of fast and slow PTNs received convergent inputs from both DN and IN. By examining the interaction of DN- and IN-evoked EPSPs, spatial facilitation and occlusion at the level of the thalamus were demonstrated. Therefore, it was concluded that at least a portion of the convergence of the dentate and the interpositus inputs occurred at the level of the ventrolateral nucleus of the thalamus.

Animals↗
PubMedDate not supplied

[Evaluation of the pyramidal tract state in patients with brain stem tumors].

The tumors of the brain stem include those of the midbrain, pons, and medulla oblongata. The main purpose of the study was to evaluate the motor system (the motor cortex and pyramidal tract) before and after surgery in patients with brain stem tumors. The study was conducted in 104 patients. In all the patients, motor evoked potentials (MEP) under transcranial magnetic stimulation were recorded before and 2-3 weeks after surgery. Comparing the mean values of MEP indicated a statistically significant decrease in the latent time and the time of central motor conduction, the amplitude of responses being statistically insignificantly changed.

Adolescent↗