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PubMed1991

Physiological studies of electric and magnetic stimulation of the human brain.

It is suggested that transcranial electric stimulation can activate pyramidal tract projections both directly and indirectly in a manner similar to that described after direct stimulation of the exposed cortex in the monkey. This produces both D- and I-waves in the pyramidal tract. At high intensities of stimulation, the stimulus can spread into the brain and activate pyramidal tract axons several centimeters below the cortical surface. Magnetic stimulation at moderate intensities produces electromyographic (EMG) responses with latencies 1-2 msec longer than those after electric stimulation. Two possible explanations have been put forward to account for this effect: (1) because of the difference in the direction of electric current flow induced in the brain by the 2 forms of stimulation, magnetic stimulation preferentially excites pyramidal tract cells indirectly, and hence evokes only I-waves in the pyramidal tract. (2) Electric stimulation (even at threshold) activates pyramidal axons deep in the white matter, whereas magnetic stimulation activates the pyramidal cells in the gray matter, probably at their initial segment. There is one interesting consequence common to both explanations. Whether magnetic stimulation activates the pyramidal neurons transsynaptically or at their initial segment, the size of the descending volley evoked will depend on the level of excitability of the motor cortex. In contrast, the response to electric stimulation will be less affected, since a proportion of the descending volley is initiated directly at the axon of the pyramidal cell. This differential effect of cortical excitability on the responses to electrical and magnetic stimulation can be useful in describing excitatory or inhibitory influences on motor cortex from other structures.

Action Potentials↗

PubMed2006

[Function magnetic resonance imaging and diffusion tensor tractography in patients with brain gliomas involving motor areas: clinical application and outcome].

OBJECTIVE: To explore the role of preoperative blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) and diffusion tensor tractography (DTT) to identify the relationship between motor cortical area, pyramidal tracts with brain gliomas in neurosurgical treatment of intraoperative electrical stimulation for gliomas involving motor areas at 3T. METHODS: Twenty-eight patients with brain gliomas involving motor areas were included. They underwent MRI examination, which included conventional T1WI, T2WI, BOLD-fMRI of bilateral hands movement paradigm and diffusion tensor imaging (DTI). The data of BOLD-fMRI and DTI were transferred to the workstation (Leonardo syngo 2003A, Siemens) and analyzed. Activation mapping of hands movement, fractional Anisotropy (FA) Color and three dimensional pyramidal tracts were produced. The relationship between motor cortical area, pyramidal tracts and brain gliomas was demonstrated, which was used to optimize the pre-surgical planning. With guidance of the result of BOLD-fMRI and DTT, all patients received microsurgery under anaesthesia retaining consciousness using intraoperative motor functional brain mapping with the method of direct electrical stimulations. The brain lesions were removed as far as possible in the case of eloquent areas and sub-cortical important white matters preservation. The preoperative and postoperative KPS of all patients were operated to evaluate the state of patients. RESULTS: BOLD-fMRI, DTI were performed successfully in 28 patients. The relationship between the primary motor cortex, premotor area, supplementary motor area, pyramidal tracts and brain gliomas localized by preoperative fMRI and DTI. Under anaesthesia retaining consciousness, the primary motor area was monitored by the method of direct electrical stimulations with the guidance of preoperative BOLD-fMRI. There was good correlation between preoperative fMRI and intraoperative cortical stimulation. Furthermore, the preoperative mappings and DTT could make up for the un-monitored motor areas and pyramidal tracts during operative cortical stimulation. Comparing the preoperative KPS, the postoperative KPS was advanced. CONCLUSIONS: BOLD-fMRI and DTT could non-invasively localize the relationship between brain motor cortex, pyramidal tracts and brain gliomas in vivo to optimize the surgical planning, guide the microsurgery under anaesthesia retaining consciousness using intraoperative motor functional brain mapping with the method of direct electrical stimulations and remove brain tumors as far as possible in the case of eloquent areas and sub-cortical important white matters preservation.

Adult↗

PubMed1986

Short latency inputs to phrenic motoneurones from the sensorimotor cortex in the cat.

Short latency responses were recorded from C5 phrenic roots and intracellularly from phrenic motoneurones following stimulation of the pericruciate cortex or medullary pyramids in cats anaesthetized with Nembutal or chloralose-urethane. Focal stimulation of the cortical surface (single pulses, 0.5-2 ms, 0.3-8 mA) during inspiration evoked EPSPs (latency 4.7 +/- 1.7 ms, rise time 1.9 +/- 1.1 ms, amplitude 0.22 to 3.94 mV) in 42% of motoneurones studied (n = 107). The EPSPs were absent, or on average 60% smaller, following stimulation during expiration. In all but two motoneurones, during both inspiration and expiration, hyperpolarizing potentials were observed either following the initial depolarization or alone. They could be reversed by hyperpolarizing current or chloride injection. Stimulation of the pyramidal tract at mid medullary level (1 to 3 pulses, 0.2 ms) evoked short latency excitation in phrenic motoneurones only with currents of more than 200 microA. Smaller stimuli applied to the medial reticular formation above the pyramidal tract evoked excitation (onset latency 1.5-3.2 ms) in which the earliest part was probably monosynaptic. These results show that the corticospinal responses in phrenic motoneurones are both excitatory and inhibitory. They are not transmitted through the pyramidal tract and are at least disynaptic. Excitation evoked from the medullary pyramidal tract can be explained by current spread beyond the pyramidal tract fibres.

Animals↗

PubMed1997

Primary motor cortex influences on the descending and ascending systems.

The motor cortex plays a crucial role in the co-ordination of movement and posture. This is possible because the pyramidal tract fibres have access both directly and through collateral branches to structures governing eye, head, neck trunk and limb musculature. Pyramidal tract axons also directly reach the dorsal laminae of the spinal cord and the dorsal column nuclei, thus aiding in the selection of the sensory ascendant transmission. No other neurones in the brain besides pyramidal tract cells have such a wide access to different structures within the central nervous system. The majority of the pyramidal tract fibres that originate in the motor cortex and that send collateral branches to multiple supraspinal structures do not reach the spinal cord. Also, the great majority of the corticospinal neurones that emit multiple intracraneal collateral branches terminate at the cervical spinal cord level. The pyramidal tract fibres directed to the dorsal column nuclei that send collateral branches to supraspinal structures also show a clear tendency to terminate at supraspinal and cervical cord levels. These facts suggest that a substantial co-ordination between descending and ascending pathways might be produced by the same motor cortex axons at both supraspinal and cervical spinal cord sites. This may imply that the motor cortex co-ordination will be mostly directed to motor responses involving eye-neck-forelimb muscle synergies. The review makes special emphasis in the available evidence pointing to the role of the motor cortex in co-ordinating the activities of both descending and ascending pathways related to somatomotor integration and control. The motor cortex may function to co-operatively select a unique motor command by selectively filter sensory information and by co-ordinating the activities of the descending systems related to the control of distal and proximal muscles.

Afferent Pathways↗

PubMed1982

Pericruciate cortex unit activity during intentional movement. Effect of subcortical electrical stimulation.

Extracellular unitary activity of pericruciate cortex neurons (CPCns) was recorded in cats performing a learned flexion--extension movement of the contralateral forearm. The present report concerns solely those cells showing firing changes on electrical stimulation of nucleus medialis dorsalis thalami (DM). These CPCns responding to DM stimulation (CPCdmns) were classified as either pyramidal tract or non-pyramidal tract neurons (CPCdm PTns, CPCdm non-PTns) by antidromic activation of the medullar pyramid. In addition, convergence of DM and other subcortical structures (lateral hypothalamus HL, basal amygdala AB, and dorsal amygdala AD) on CPCdmns was tested by means of single and paired electrical stimulation. On the bases of the obtained data, CPCdmns had been grouped in the following different types. Type I: thirty-two neurons activated by stimulation of all the studied subcortical structures. All these cells are PT neurons and 20 of them (62.5%) are task-related, showing firing frequency increase before movement onset. Type II: forty-six neurons also activated by stimulation of all subcortical structures. All are non-PT cells and 17 of them (36.9%) are task-related, showing firing decrease or firing arrest at movement onset. Type III: twenty-one neurons activated exclusively by DM stimulation (and therefore non-PT cells). Four of them (19%) being task-related, and showing firing increase after movement onset. Type IV: twenty neurons responding exclusively to DM stimulation with firing frequency increase frequency decrease. None of them was movement-related. It is concluded that the cat's CPC agranular cortex receives effective inputs from such subcortical structures as DM, AB, AD and HL and that these subcortical structures play an important role in the regulation of motorcortical cell activity.

Afferent Pathways↗

PubMed1988

[Neurophysiological analysis of efferent-afferent interaction of neurons of the parietal associate cortex in cats].

Neuronal responses of the parietal associate cortex (field 5) was recorded in waking cat during electrical stimulation of the pyramidal tract axons and afferent stimulation. The electrical stimulation of the pyramid evoked marked responses in 39% of neurons. 87% of these neurons increased spike activity during sematic nociceptive stimulation, 61% of test neurons were activated by light or tonal stimulation. Neuronal activity was recorded during defensive conditioning to the pyramidal tract axons stimulation. It has been shown that conditioned stimulation of the pyramidal tract evoked plastic changes of responses in 66% of neurons of the parietal cortex. These data are discussed relative to the possible functional role of the efferent-afferent interaction to field 5.

Animals↗

PubMed1993

Electrophysiological characterization of different types of neurons recorded in vivo in the motor cortex of the cat. I. Patterns of firing activity and synaptic responses.

1. Patterns of firing activity and characteristics of antidromic and synaptic responses to stimulation of the pyramidal tract at peduncular level [peduncular pyramidal tract (PP)] and the ventrolateral thalamic nucleus (VL) were studied in neurons of area 4 gamma of the motor cortex of awake, chronic cats using intracellular microelectrode techniques. The results offer a new functional classification of neocortical neurons based on electrophysiological properties of the 640 recorded cells. 2. Four classes of neurons were distinguished: (class i) inactivating bursting (ib) neurons (n = 60) including fast antidromic response PP (fPP) (n = 0), slow antidromic response PP (sPP) (n = 11), and no antidromic response PP cells (nPP) (n = 49); (class ii) noninactivating bursting (nib) neurons (n = 79), including fPP (n = 23), sPP (n = 0), and nPP cells (n = 56); (class iii) fast-spiking (fsp) neurons (n = 56), including fPP (n = 0), sPP (n = 0), and nPP cells (n = 56); and (class iv) regular-spiking (rsp) neurons (n = 445), including fPP (n = 96), sPP (n = 38), and nPP cells (n = 311). (Neurons in each classification were further separated by their antidromic responses to PP stimulation: fast PP (fPP) slow PP (sPP), or nPP cells, the latter not responding antidromically to electrical stimulation of the peduncle.) 3. Recurrent monosynaptic excitatory postsynaptic potentials (EPSPs) followed antidromic spikes elicited by PP stimulation in most (96%) fPP but much fewer (24%) sPP cells. In fPP cells, it was possible to separate the PP EPSPs into two monosynaptic EPSP components that were generated by other fPP and sPP cells, respectively. VL stimulation evoked monosynaptic EPSPs in 100% of fPP cells (vs. 63% of sPP cells) and antidromic action potentials in 16% of fPP cells (vs. 12% of sPP cells). 4. Firing activity consisted of single spike discharges in most PP cells; however, noninactivating bursting was observed in 19% of fPP cells, and inactivating bursting was observed in 23% of sPP cells (see below). In 18% of ib and 11% of nib/nPP neurons, VL stimulation elicited antidromic action potentials. Other bursting neurons proved to be PP cells with characteristic differences in axonal conduction velocity (see above). All PP cells among the nib cells were fPP, and all PP cells among the ib cells were sPP cells. All fsp neurons were found to be nPP cells, and none could be activated antidromically by VL stimulation. Thus the fsp pattern of discharge distinguished a unique class of nPP cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1985

Critical stages for growth in the development of cortical neurons.

In order to study the role of efferent connectivity in the development of CNS neurons, the growth of pyramidal tract neurons within the hamster sensorimotor cortex was studied during normal development and after early postnatal lesions of the pyramidal tract. We first determined, by a combination of Nissl and retrograde HRP techniques, that within the lumbar representation of cortical layer 5B in adult animals two cell populations exist: a large-celled population (40% of the total) projecting to the spinal cord and a small-celled population (60% of the total) projecting intracortically and to targets rostral to the medulla. We could not determine whether large layer 5B cells in the infant sensorimotor cortex also represent the corticospinal population. Nevertheless, measurements of the growth in cross-sectional area of the large cells from 7 days postnatal to adulthood showed that these cells continue to grow until 51 days of age. The most rapid rate of growth occurs between 7 and 14 days, during which time the cross-sectional area of the cell bodies triples, coincident with the arrival of corticospinal axons in the lumbar cord and the beginning of target innervation (Reh and Kalil, '81). The growth of the large neurons in layer 5B was then charted after the pyramidal tract was cut ipsilaterally in the medulla at various postnatal ages. Early lesions of the tract (4-8 days postnatal) interrupt lumbar projection fibers before they establish synapses in the cord. Nevertheless, cortical cell bodies in the lumbar representation continue to grow normally after axotomy until 11 days after birth. At this time, large cells are arrested in development and their cell size remains in the 11-day stage (50% of normal adult large cell size) indefinitely. In contrast, adult lesions of the tract cause a 60% shrinkage of large cells, which in the adult represent corticospinal neurons. No evidence for cortical cell death was found after pyramidal tract lesions at any age. The results of axotomy reveal a turning point in the development of layer 5B cortical neurons. Before the age of 11 days the large cells have an independent program of cell growth that proceeds despite axotomy. After this time, the large cortical neurons appear to require intact axons for further growth and, in the absence of normal connectivity, are arrested in development.

Age Factors↗

PubMed1996

A quantitative analysis of rat central nervous system myelination using the immunohistochemical method for MBP.

The temporal order of the myelination of the nervous pathways in 0-42-day-old Wistar rats was quantitatively analyzed using immunohistochemistry with anti-myelin basic protein (MBP) antibody. Immunohistochemistry was performed on paraffin-embedded tissue according to the standard ABC technique. For the objective evaluation of myelination, we converted the level stained with the immunohistochemical method into continuous numbers of 0-256 giving the intensity of myelination, using an image analyzing system. We analyzed nine nervous pathways: corpus callosum, optic tract, internal capsule, spinal tract of trigeminal nerve, inferior cerebellar peduncle, cerebellar white matter, pyramidal tract, medial longitudinal fasciculus, and cuneate fasciculus. The onset of the myelination of the spinal tract of the trigeminal nerve, inferior cerebellar peduncle, medial longitudinal fasciculus and cuneate fasciculus was day 7 (postnatal). That of the corpus callosum, optic tract, internal capsule and cerebellar white matter was day 14, and that of the pyramidal tract was day 21. The time required to reach the level of myelination of day 42 was day 21 for the spinal tract of the trigeminal nerve and the inferior cerebellar peduncle, day 28 for the internal capsule, day 35 for the corpus callosum, optic tract, cerebellar white matter and pyramidal tract, and day 42 for the medial longitudinal fasciculus. Our method using immunohistochemistry with anti-MBP antibody provided a highly sensitive and objective criterion for judging precisely the time and the progress of myelination in each nervous pathway and compare one nervous pathway with another.

Age Factors↗

PubMedDate not supplied

[Callosal neurons: monosynaptic connection between them and their descending projections].

Antidromic and monosynaptic unit responses to the stimulation of the corpus callosum and the symmetrical cortical area as well as antidromic responses to pyramidal tract and thalamic nuclei stimulation were recorded in the sensorimotor cortex of unanaesthetized rabbits. Out of 182 callosal neurones 13 exhibited transcallosal monosynaptic responses. 8 out of 56 callosal units responded antidromically to pyramidal tract or thalamic stimulation. Thus callosal neurones may be monosynaptically excited by callosal units via the corpus callosum and by the pyramidal tract units. It was also found that a pyramidal tract neurone may send a collateral through the corpus callosum and at the same time have a transcallosal monosynaptic input. The role of monosynaptic transcallosal excitation of callosal neurones is discussed.

Animals↗

PubMed2002

GABA-B-related activity in processing of transcallosal response in cat motor cortex.

GABA-ergic characteristics of transcallosal (TC) responses were studied with specific antagonists of both GABA-A and GABA-B receptor subtypes. We used a paired-pulse paradigm to get insight into the role of GABA in interhemispheric interactions between motor cortices. 3-Amino-2-(4-chlorophenyl)-propylphosphonic acid (phaclofen) and 3-aminopropyl-diethoxymethyl-phosphinic acid (CGP 35348) were used as GABA-B antagonists and bicuculline methiodide (BMI) was used to block the GABA-A receptor. Although both GABA-A and GABA-B antagonists increased spike discharge upon transcallosal stimulation, in both pyramidal tract and non-pyramidal tract neurons, they had different effects on the responses to the first and second stimuli of paired-pulse stimulation (200 msec interval). Although the inhibition seen with the second stimulus was greatly attenuated by antagonists of the GABA-B receptor, it was maintained in the presence of the GABA-A antagonist. These finding support a presynaptic regulation of callosal transmission by GABA-B receptors in the callosal synapse of the cat motor cortex.

Animals↗

PubMed1990

Central motor conduction time to bulbocavernosus muscle: evaluation by magnetic brain stimulation and testing of bulbocavernosus reflex.

Magnetic brain stimulation and bulbocavernosus reflex (BCR) testing were performed to evaluate the central motor conduction time (CMCT) to the bulbocavernosus muscle (BC). In six healthy subjects CMCT ranged from 13.81 ms to 16.9 ms with a mean value of 15.77 ms (SD 1.38 ms). This equals a central motor conduction velocity of about 40 m/s, which can only be realized in fast conducting pyramidal tract fibres. Testing of pyramidal tract function by BC-CMCT might improve the diagnosis of male sexual dysfunction.

Adult↗

PubMed1989

[Secondary degeneration of substantia nigra following massive basal ganglia infarction].

Two autopsied cases of massive unilateral cerebral infarction due to occlusion of the middle cerebral artery (MCA) were reported with special reference to presence of the secondary degeneration of the substantia nigra. Case 1 was a 70-year-old male who suddenly suffered from left hemiplegia 3 years and 2 months prior to death. CT scan showed massive infarction involving basal ganglia and fronto-parietal white matter on the right side. Some parkinsonian features such as oily face and rigidity of limbs were noted during the course. At autopsy, the proximal portion of rt MCA was found occluded and the right substantia nigra was found depigmented. Case 2 was a 71 year-old male who suddenly became hemiplegic 4 years prior to death. CT scan revealed a low density area in the corona radiata of the right cerebral hemisphere. On carotid antiography, complete obstruction of the horizontal portion of right MCA at its distal end was observed, which was confirmed at autopsy. Histologically, the right substant a nigra in case 1 showed marked neuronal loss with gliosis as well as presence of many extracellular melanin pigments. These changes were more prominent in its medial portion where chromatolytic neurons were occasionally seen. The adjacent fronto-pontine tract and pyramidal tract showed secondary degeneration. The left substantia nigra appeared normal. In case 2, the substantia nigra on both sides appeared normal. The whole right cerebral peduncle, on the other hand, showed diffuse myelin pallor.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1992

[Studies on motor neuron disease with cranial magnetic resonance imaging].

The present study was performed to examine the pyramidal tracts of the brain in both 51 normal subjects (21 male and 30 female subjects; mean age of 43.5 +/- 16.1 years) and 12 patients with motor neuron disease (6 male and 6 female patients; mean age of 57.4 +/- 7.9 years), using the magnetic resonance imaging (MRI). The 12 patients with motor neuron disease (MND) comprised 7 suffering from spinal progressive muscular atrophy (SPMA) and 5 from amyotrophic lateral sclerosis (ALS). The MRI used in this study was of both short spin echo and long spin echo sequence. Of the 52 normal subjects, 24 of them (47%) had the T2 prolonged small areas (high signal intensity areas) at the posterior limb of internal capsule. These findings were not found in the normal subjects over fifty years old. No similar finding was detected in the pyramidal tracts except the posterior limb of internal capsule. On the other hand, 8 patients with MND (67%) proved to have the high signal intensity areas in the pyramidal tracts. Moreover, these high intensity areas were extended from the crus cerebri to corona radiata in 7 patients (58%). In all patients with ALS, these areas were extended in whole areas of the pyramidal tracts, and the similar findings were also found in two patients with SPMA. These findings were demonstrated to be more extensive than those in the normal subjects. The results thus obtained warrant us to conclude that cranial MRI is useful to detect the degeneration of the pyramidal tracts of MND patients.

Adolescent↗

PubMed1987

Branching cortical neurons in cat which project to the colliculi and to the pons: a retrograde fluorescent double-labeling study.

The fluorescent double-labeling technique has been used to determine whether the corticopontine and the corticotectal fibers in the cat are derived from two different sets of neurons or whether they are derived from branching neurons which distribute collaterals to the pontine grey and the colliculi. After unilateral DY.2HCl injections in the pontine grey and FB injections in the ipsilateral colliculi, large numbers of FB-DY.2HCl double-labeled neurons were present in the cortex of the ipsilateral hemisphere. However, the labeled neurons in its rostral part may have represented pyramidal tract neurons which were labeled retrogradely because their fibers descended through the DY.2HCl injection area. Therefore, also DY.2HCl injections were made in the pyramid (i.e. caudal to the pons) and the cortical pyramidal tract area, containing the retrograde DY.2HCl-labeled neurons, was delineated. In the rest of the experiments only the DY.2HCl-labeled neurons in the caudal two thirds of the hemisphere (outside the pyramidal tract area) were taken into account because only these neurons could, with confidence, be regarded as corticopontine neurons. In some anterograde HRP transport experiments the trajectories of the corticotectal and the corticopontine fibers were visualized. On the basis of the findings the DY.2HCl injections in the pontine grey were placed such that they could not involve any of the corticotectal fibers passing from the cerebral peduncle to the colliculi. Thus artifactual double-labeling of cortical neurons was avoided. However, also under these circumstances many double-labeled neurons were present in the caudal two thirds of the hemisphere. This led to the conclusion that in the cat a large proportion of the corticopontine neurons in the caudal two thirds of the hemisphere represent branching neurons which also distribute collaterals to the colliculi. The parietal (anterior part of the lateral gyrus, middle and posterior suprasylvian gyri) and the cingulate areas together contained three quarters of all labeled corticopontine neurons outside the pyramidal tract area. In the parietal areas roughly 25% of them were double-labeled and in the cingulate area 14%. However, in the visual areas 18 and 19 a much larger percentage (30-60%) was double-labeled.(ABSTRACT TRUNCATED AT 400 WORDS)

Amidines↗

PubMed2005

Constant and severe involvement of Betz cells in corticobasal degeneration is not consistent with pyramidal signs: a clinicopathological study of ten autopsy cases.

This report concerns a clinicopathological study of three additional patients with corticobasal degeneration (CBD), described here for the first time, and a clinicopathological correlation between pyramidal signs and upper motor neuron involvement, in ten autopsy cases of CBD, including seven cases reported by us previously. We investigated pyramidal signs, including hyperreflexia, Babinski sign, and spasticity, and involvement of the primary motor cortex and pyramidal tract, focusing on the astrocytosis of the fifth layer of the primary motor cortex. Pyramidal signs were observed in six (60%) of the ten cases. Hyperreflexia was evident in six patients (60%), with spasticity being observed in three patients (30%). Loss of Betz cells associated with prominent astrocytosis and presence of ballooned neurons in the fifth layer of the primary motor cortex was observed in all ten cases. In all cases, involvement of the pyramidal tract was obvious in the medulla oblongata, without involvement of the pyramidal tract in the midbrain. Constant and severe involvement of the fifth layer of the primary motor cortex, including the Betz cells, has not previously been reported in CBD. We suggest that the pyramidal signs in CBD have been disregarded.

Aged↗

PubMed1983

Effect of triiodo-L-thyronine on axonal regeneration in the rat spinal cord after acute compression injury.

Studies were performed on the effect of triiodo-L-thyronine (T3) on clinical recovery and axonal counts in the pyramidal tract of 56 rats subjected to an acute spinal cord compression injury at T-7. The T3 was given at a daily dose of 5 micrograms/kg for 4 weeks to 28 rats in the treatment group. The treatment and control animals were tested weekly for clinical recovery, and cord function as determined by the inclined-plane technique. Groups of animals were killed at 4 weeks and 12 weeks, and the axons in the pyramidal tract cephalad and caudad to the injury site were counted in sections prepared with Holmes' silver stain. There was no difference in clinical recovery between the treatment and control groups. This negative result contrasts with other studies which showed improved recovery of cord-injured animals treated with thyroid hormones. The possible explanations for this discrepancy are discussed. Similarly, there was no difference in the axon counts between the treated and control groups. Thus, T3 did not improve recovery or axonal regeneration in the pyramidal tract of rats after acute spinal cord compression injury. Between 4 and 12 weeks, there was a marked reduction in the cephalad axon counts in the pyramidal tract in both groups, indicating that approximately 50% of the axons in the pyramidal tract had undergone retrograde degeneration or dying back by 12 weeks after this degree of injury. The T3 did not affect the degree of retrograde degeneration.

Animals↗

PubMed1991

Postnatal development of the pontine projections from the visual cortex of the mouse.

We studied the postnatal development of the corticopontine tract in mice by the injection of the axon tracer DiI into the visual cortex. In the postnatal day (P) 0.5 mouse, labeled pyramidal tract fibers pass through the internal capsule and cerebral peduncle, grow over the basilar pontine gray, and enter into the medullary pyramid (in this study, P0 refers to the first 24 hours after birth). Small collateral branches arise from these pyramidal tract fibers on P0.5-1.0, and elongate quickly into the basilar pontine gray around P2-4. These collateral branches give off many secondary branches on P4 and form the bright terminal zone in the rostral portion of the lateral basilar pontine gray on P9. In the P16 mouse, this terminal zone is more restricted, suggesting, on the basis of the anterograde DiI labeling technique, that the visual corticopontine projection matures by P16. DiI-labeled pyramidal tract fibers distal to the branching point of the pontine collaterals are found during the postnatal two weeks, but disappear by the later stages. We conclude that the visual corticopontine tract develops as collateral branches of the transient pyramidal tract fibers arising from the visual cortex of the mouse, as just described in the rat (O'Leary and Terashima, Neuron 1:901-910, 1988).

Animals↗