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PubMed1982

Excitatory effect of acetylcholine on different types of neurons in the first somatosensory neocortex of the rat: laminar distribution and pharmacological characteristics.

In rats anaesthetized with either urethane, pentobarbital or fluothane the effects of acetylcholine, cholinergic agonists and antagonists (applied by iontophoresis) were studied on single cortical neurons of first somatosensory region. The laminar distribution of the neurons excited by acetylcholine was determined by the reconstruction of each electrode track based on a dye-deposit made at the last recording site. Neurons were identified using antidromic stimulation of the pyramidal tract, the ventrobasal thalamus and the corpus callosum. Neurons excited by acetylcholine could be segregated into two groups: one encompassing layer Vb and the upper part of layer VI, the other more deeply located at the limit between the cerebral cortex and the subjacent white matter. Neuronal responses to glutamate and nicotine, unlike those to actylcholine were evenly distributed in the cortex. Pyramidal tract neurons had corticothalamic neurons were frequently excited by acetylcholine and were shown to be located with the first group of acetylcholine sensitive neurons. Commissural neurons were rarely excited by acetylcholine and were not restricted to either group. The analysis of neuronal responses to acetylcholine and various agonists (carbachol, nicotine, acetyl-beta-methylcholine, carbamyl-beta-methylcholine, butyrylcholine) and antagonists (atropine, mecamylamine) revealed a prominent but not exclusive muscarine character. It is included (i) that cortical neurons of first somatosensory cortex which are excited by acetylcholine belong to two populations, one consisting, at least in part, of projection neurons (upper group) and the other of interneurons (lower group); (ii) that cortical acetylcholine receptors are of a 'mixed' type strongly weighted toward the muscarinic side.

Acetylcholine↗

PubMed1977

The mode of synaptic linkage in the cerebro-ponto-cerebellar pathway investigated with intracellular recording from pontine nuclei cells of the cat.

1. Intracellular potentials of pontine nuclei (PN) cells were recorded in cats anesthetized with pentobarbitone sodium. 2. Stimulation of the cerebellar nuclear regions or the brachium pontis induced an antidromic action potential composed of IS-SD spikes, after-depolarization and after-hyperpolarization. 3. Cerebellar stimulation produced EPSPs only in a few PN cells. 4. Activation of the corticopontine or pyramidal tract produced in all PN cells an EPSP built up from the unitary components with variable amplitudes and time courses. Paired or repetitive activation revealed a property of the frequency potentiation of the EPSP. 5. Unitary EPSPs also occurred spontaneously. A great majority of these spontaneous EPSPs were cerebral in origin, and had amplitudes and time courses comparable with those evoked by stimulation of the corticopontine or pyramidal tract. 6. The half-width versus time of peak relationship of these unitary EPSPs suggested a dendritic location of the synapses with variable distances from the soma. It is assumed that large, proximal synapses serve for efficient relay of signals while small, distal synapses for their integration.

Action Potentials↗

PubMed2002

White matter mapping using diffusion tensor MRI.

Diffusion tensor MRI is used to define trajectories that reflect the long-range order of in vivo white matter (WM) fiber tracts. Fiber tracking is particularly prone to cumulative error from noise and partial volume along the length of the trajectory paths, but the overall shape of each path is anatomically meaningful. By considering only the long-range similarity of path shapes, a method of constructing 3D maps of specific WM structures has been developed. A trajectory is first computed from an operator-selected seed voxel, located within the anatomical structure of interest (SOI). Voxels from the same structure are then automatically identified based on the similarity of trajectory path shapes, assessed using Pearson's correlation coefficient. The corpus callosum and pyramidal tracts in 14 patients with multiple sclerosis, and in 10 healthy controls were mapped by this method, and the apparent diffusion coefficient (ADC) was measured. The ADC was significantly higher in patients than in controls, and higher in the corpus callosum than in the pyramidal tracts for both groups. Using this method the different functional structures in the WM may be identified and mapped. Within these maps, MRI parameters can be measured for subsequent comparison with relevant clinical data.

Algorithms↗

PubMed2005

Neuropathologic characteristics of spinal cord lesions in sporadic Creutzfeldt-Jakob disease.

We investigated the neuropathologic features of spinal cord lesions in 23 patients with sporadic Creutzfeldt-Jakob disease (sCJD), paying particular attention to neuronal loss and gliosis, pyramidal tract degeneration and prion protein (PrP) deposition. The study included 9 cases of subacute spongiform encephalopathy, 13 cases of panencephalopathic-type sCJD and 1 case of sporadic fatal insomnia (sFI). In the spinal gray matter, although gliosis was present in some patients with disease of relatively long duration, the number of neurons, including large motor neurons, was well preserved regardless of disease duration. Pyramidal tract degeneration was observed in some patients with disease lasting more than 14 months but not in the patient with sFI. PrP deposition was present in the spinal cord of all sCJD patients, and was identified predominantly in the posterior horn, particularly in the substantia gelatinosa, regardless of disease duration or disease classification based on cerebral pathology. Relatively prominent PrP deposition was also observed in Clarke's column. The density of PrP deposition in the sCJD spinal cord was not associated with disease duration or neuronal degeneration. Our results indicate that PrP deposition in the spinal cord is an early pathologic event in sCJD and may remain to the end stage. Although no VV1, VV2 or MV2 cases were included in our study, we suggest that stereotypic accumulation of PrP is a consistent pathologic feature of sCJD and that the spinal cord remains relatively resistant to the pathologic process of sCJD, at least in patients with MM1 sCJD.

Adult↗

PubMed1998

Does a C3-C4 propriospinal system transmit corticospinal excitation in the primate? An investigation in the macaque monkey.

1. Synaptic responses to electrical stimulation of the contralateral pyramidal tract were measured in intracellular recordings from 206 upper limb motoneurones in ten chloralose-anaesthetized macaque monkeys. The objective was to search for evidence of a disynaptic excitatory pathway via C3-C4 propriospinal interneurones similar to that in the cat. 2. In monkeys with intact spinal cords, only a small proportion of motoneurones (19%) responded with late EPSPs to repetitive stimulation of the pyramid; only 3% had segmental latencies that were appropriate for a disynaptic pathway. 3. From previous studies in the cat, it was expected that a lesion to the dorsolateral funiculus (DLF) at C5 would interrupt the corticospinal input to the spinal segments supplying upper limb muscles, whilst leaving intact excitation transmitted via a C3-C4 propriospinal system, the descending axons of which travel in the ventral part of the funiculus. In five of the monkeys a lesion was made to the DLF at C5 which spared the ventrolateral columns. It severely reduced the monosynaptic EPSPs and disynaptic IPSPs evoked from the pyramidal tract that were present in the intact monkey spinal cord, and which might have masked the presence of disynaptic EPSPs. However, even after the lesion the proportion of motoneurones with such late EPSPs was still low (18%); 14% of motoneurones had EPSPs within the disynaptic range. 4. In addition, some EPSPs with relatively long segmental latencies (> 1.1 ms) were recorded before and after the C5 lesions, but since these effects could be evoked by single stimuli, had stable latencies and did not facilitate with repetitive shocks, it is likely that they represent monosynaptic EPSPs evoked by slowly conducting corticospinal fibres which survived the lesions. 5. In seven of the monkeys motoneurone responses to stimulation of the ipsilateral lateral reticular nucleus (LRN) were also tested. Most motoneurones showed EPSPs with short latencies (1.2-2.5 ms) and other properties characteristic of monosynaptic activation. This is consistent with the presence of collaterals of C3-C4 propriospinal neurones to the LRN, as demonstrated in the cat. 6. These short-latency EPSPs evoked from the LRN were just as common before (77%) as after (75%) the C5 lesion. They had small amplitudes both before (mean +/- s.d. 1.1 +/- 0.59 mV) and after (1.2 +/- 0.72 mV) the lesion. Unlike the situation in the cat, only a small proportion (16%) of motoneurones activated from the LRN showed late EPSPs after repetitive stimulation of the pyramid. 7. The results provide little evidence for significant corticospinal excitation of motoneurones via a system of C3-C4 propriospinal neurones in the monkey. The general absence of responses mediated by such a system in the macaque, under experimental conditions similar to those in which they are seen in the cat, show that extrapolation of results from the cat to the primate should be made with considerable caution.

Animals↗

PubMed1976

The development of motor control in the rhesus monkey: evidence concerning the role of corticomotoneuronal connections.

Corticospinal fibres terminate in three areas in the spinal grey matter of the rhesus monkey: the nucleus proprius of the dorsal horn, the intermediate zone and directly upon motoneurons, particularly those inervating limb muscles. It was suggested at their earliest discovery that direct corticomotoneuronal (CM) connections might constitute a critical anatomical substrate for the type of fractionated movement exemplified by relatively independent finger movements (RIFM). The present study was undertaken in an attempt to provide further evidence in support of this idea. The evidence is based upon the anatomical finding that few CM connections are present at birth in the monkey, the bulk being formed postnatally to reach an adult density at approximately 8 months of age. There were two experimental approaches: in the first it was argued that if RIFM are dependent upon the presence of CM connections it would be expected that such movements would appear only gradually postnatally, developing in parallel with the development of the connections. In 2 normal monkeys studied from this point of view discrete distal movements did develop only gradually with RIFM reaching an adult level at 7 to 8 months of age. The second experimental appraoch was based upon the fact that pyramidal lesions in newborn animals interrupt corticospinal fibres before CM connections are formed. It was argued that such a situation might provide a better opportunity for other descending pathways to establish the connections necessary for RIFM. Five infant monkeys had bilateral pyramidal tract lesions made from 5 days to 4 weeks after birth and were observed for a period of three years. In the 4 animals in which the lesions were complete, RIFM failed to develop. In the fifth animal, in which the lesions were incomplete, there was development of some degree of RIFM. It was concluded that the development of RIFM is dependent upon fibres passing in the pyramidal tracts and that in infant monkeys, as well as in adults, other descending pathways are unable to form the connections necessary for these movements. The possible contribution to RIFM of the corticospinal fibres arise in the somatosensory cortex and terminate in the dorsal horn was studied by bilateral removal of the arm and leg area of the somatosensory cortex in one animal. Since RIFM were only minimally and transiently altered, it was concluded that such movements are not dependent upon these fibres. The different lines of evidence presented in the study are interpreted as giving further support to the idea that corticomotoneuronal connections constitute an essential anatomical substrate for fractionated movements such as RIFM. Observations were also made of the development of general locomotor activity in normal and pyramidotomized infant monkeys.

Age Factors↗

PubMed1999

Profile of non-compressive myelopathy in eastern India: a 2-year study.

Eighty-two patients with non-compressive myelopathy have been studied from July 1994 to June 1996 in Bangur Institute of Neurology and S.S.K.M. Hospital, Calcutta, of which 48 patients were men and 34 patients were women. Presentation was acute in 40 patients (48.78%), subacute in 7 (8.53%), chronic in 27 (32.92%) and history of relapse and remission in 8 (9.75%) patients. Preceding as well as simultaneous fever was observed in 16 cases (19.5%); vaccination (anti-rabies) in 1 case (1.21%); drug abuse in 1 case (1.21%); arthralgia-myalgia and rash in 2 cases (2.42%) and history of electrocution in 2 cases (2.42%). Only pyramidal tract involvement was present in 24 cases (29.26%) and remaining 58 cases (70.73%) had pyramidal tract affection with other sites of involvement. CSF study carried out in 60 cases, revealed rise of protein in 31 (37.8%); oligoclonal band had been detected in 6 (7.31%), pleocytosis in 18 cases (21.95%) and increased IgG index greater than 6.66 in 2 cases (2.42%). CT myelogram done in 23 cases revealed no abnormality. MRI study carried out in 59 cases showed myelomalacia in 1 (1.21%); demyelination plaque in 14 cases (17.07%); atrophy of cord in 3 (3.65%); infarction of cord in 1 (1.21%) and in 40 cases (48.78%) no abnormality could be detected. Etiological diagnosis could be established in 59 (71.95%) cases such as transverse myelitis or myelopathy (post infectious) in 24 (29.26%); demyelination in 16 (19.51%); vascular and vasculitis in 3 (3.65%); toxic in 1 (1.21%); physical (electrocution) in 2 cases (2.42%). In the remaining 23 cases (28.04%) no aetiological factors could be found.

Adult↗

PubMedDate not supplied

Computed tomographic findings of good prognosis for hemiplegia in hypertensive putaminal hemorrhage.

Computed tomography (CT) findings were analyzed in 17 patients with hypertensive putaminal hemorrhage accompanied by hemiplegia which had subsided almost completely by conservative therapy within one month after the onset. In such patients a high density area was not seen at the level of the lateral ventricles on CT scan. To study the reason for this, the relationship between the extent of a hematoma and the level at which the pyramidal tract was destroyed was investigated. From consideration of the process of destruction of the pyramidal tract by a hematoma, it seemed that CT findings at the level of the bodies of the lateral ventricles, rather than at the level of the posterior limb of the internal capsule, were of value in evaluating the prognosis of hemiplegia in putaminal hemorrhage.

Adult↗

PubMed2005

An autopsy case of caudate nucleus lobulation accompanied with diaphragmatic eventration.

We describe an autopsy female case of multiple anomalies with lobulation of caudate nucleus tail, diaphragmatic eventration, skeletal anomalies, pyramidal tract anomaly, and meningothelial meningioma. Her psychomotor development was delayed, and she developed bilateral eventration of the diaphragms on X-ray film in her third decades. Right hemi-colonectomy was performed for volvulus at the age of 44 years, and meningioma was incidentally identified. She died at the age of 47 years. Autopsy demonstrated the partial deficiency of the muscular tissue in the circular thinned membranous area predominantly on left side including the central tendon of the diaphragm. The tails of the bilateral caudate nucleus demonstrated excessive lobulations, and the brainstem pyramidal tract showed hypoplasia. Immunoreactivity for tyrosine hydroxylase was deficient in the lobulated tail of caudate. We believe that this case is characterized by a rare combination of eventration, skeletal and nervous anomalies.

Abnormalities, Multiple↗

PubMed1976

Disynaptic inhibition of spinal motoneurones from the motor cortex in the monkey.

1. The neuronal mechanism of disynaptic inhibition of spinal motoneurones by the corticospinal tract was investigated in Macaca irus. Surface stimulation or weak intracortical stimulation was used in order to evoke the inhibition. Intracellular records were taken from motoneurones in lumbar segments. 2. Both the disynaptic i.p.s.p.s evoked from group Ia afferents and the disynaptic i.p.s.p.s evoked from corticospinal fibres were found to be depressed by conditioning stimulation of motor axons to antagonistic muscles. Mutual facilitation of the actions from these two fibre systems occurred when nerve impulses set up in them reached the explored spinal segment synchronously. These observations led to the conclusion that disynaptic i.p.s.p.s from group Ia afferents and from the motor cortex are mediated by common interneurones. 3. No evidence either for or against projections of the same pyramidal tract cells to motoneurones of one motor nucleus and to interneurones interposed between group Ia afferents and motoneurones of an antagonistic muscle could be obtained by comparing cortical areas from which monosynaptic e.p.s.p.s and disynaptic i.p.s.p.s were evoked in the different motor nuclei. 4. The areas from which the disynaptic i.p.s.p.s were evoked in individual motoneurones appeared to be similar in size to the areas of cortical monosynaptic projections to motoneurones and showed similar degrees of overlap, indicating that the projections of pyramidal tract cells to Ia inhibitory interneurones are as extensive as to motoneurones and that they are similarly organized.

Animals↗

PubMed1986

Effective stimulation distance for current from macroelectrodes.

Effective spread of stimulating current from macroelectrodes was measured using antidromic responses of axons of the pyramidal tract as an indicator of excitation. Both monopolar and concentric bipolar electrode configurations were tested with stimulating distances as large as 7mm. The effective stimulation distance was greater from monopolar electrodes especially at greater current strengths, but differences between the two configurations were frequently small and reversals of this trend occurred. There was no statistically significant difference between the estimates of effective stimulation distance made using large and small axons. The shape of current-distance curves was approximately parabolic using both bipolar and monopolar stimulation. A current strength of 0.5 to 1.0 mA will confine effective current from a monopolar electrode to a sphere of 2-mm radius, but will not stimulate all elements within that area. Even in a brain area as homogeneous as the pyramidal tract, there is still a great deal of variability from mean values in effective stimulation distance. Presumably, the variability would be even greater in more heterogeneous regions.

Animals↗

PubMed1995

[Chorea with prominent spasticity associated with an expansion of the CAG trinucleotide repeat in the IT15 gene: a case report].

A 60-year-old female, who had been noted to have slowly progressive mental changes since the age of 40, subsequently developed irregular, abrupt, jerking movements of her limbs, and coordination and walking difficulty after 15 years. Her father, aunt and sister had also been suffering from similar involuntary movements and changes of personality. Neurological examination revealed slight dementia, choreic movements and the evidence of pyramidal tract signs; i.e., she showed general hyperreflexia of extremities, bilateral ankle clonus, and extensor plantar responses of lower extremities. laboratory data were all within normal ranges except iron deficiency anemia. Axial MRI showed moderate cortical atrophy, however, without dilatation of the frontal hours of lateral ventricles and the caudate head appeared normal. Our initial impression was dentatorubropallidoluysian atrophy (DRPLA). However, the genetic analysis of her peripheral leukocytes disclosed an expansion of the CAG repeats (43 copies) in the IT15 gene in chromosome 4p, indicating the diagnosis of Huntington's disease (HD). CAG repeats in chromosome 12, known to link with DRPLA, was not expanded. Thus, this case is unique in that the classical symptomatologies of HD was betrayed by the presence of prominent pyramidal tract signs. This patient may be of importance in demonstrating the diversity of neurological symptoms and neuropathologies caused by CAG trinucleotide repeats in HD.

Brain↗

PubMed1986

[Postsynaptic reactions of neurons of the sensomotor cortex of the cat during evoked and self-sustained rhythmic activity of the "peak-wave" type].

Intracellular correlates of evoked rhythmic cortical "spike-and-wave" potentials produced in sensorimotor cortex during 3/s stimulation of the thalamic relay nucleus (VPL) and of self-sustained "spike-and-wave" afterdischarges following 8-14/s stimulation of the same nucleus were studied in acute experiments on cats immobilized by myorelaxants. Intracellular recordings of pyramidal tract neurons revealed that different components of evoked "spike-and-wave" potentials, i. e. the spike-like negative wave and the long lasting negative wave, are postsynaptic in origin: the first is due to EPSPs with spike discharges, and the latter--to IPSPs of cortical neurons. Components of "spike-and-wave" afterdischarge mostly reflect the paroxysmal depolarizing shifts of the membrane potential of cortical neurons. After cessation of sustained "spike-and-wave" activity the long-lasting hyperpolarization accompanied by inhibition of spike discharges and subsequent recovery was observed in cortical neurons. It is presumed that the negative wave of the evoked "spike-and-wave" potential as well as slow negative potentials of direct cortical and primary responses reflect IPSPs of deeper parts of pyramidal tract neurons, while the waves of the sustained "spike-and-wave" afterdischarges are due to paroxysmal depolarizing shifts in cortical neurons.

Animals↗

PubMed1998

An investigation of the intrinsic circuitry of the motor cortex of the monkey using intra-cortical microstimulation.

The motor cortex contains a distributed map of muscles, with a single muscle represented over a wide cortical area. We have searched for inter-connections between distant sites projecting to common muscles by delivering pairs of 20-microA single-pulse intracortical microstimuli (ICMS) to sites separated by 1.5-2 mm in the hand-area primary motor cortex of two macaque monkeys performing a precision grip task. The facilitation of hand- and forearm-muscle rectified EMG was measured. When stimuli were delivered simultaneously, responses were quantified using a technique to correct for non-linearities inherent in the use of averaged, rectified EMG. A spatial facilitation was seen for such simultaneous stimuli; however, it was of the same magnitude as that occurring when ICMS was paired with stimulation of corticospinal axons in the pyramidal tract (PT), so that it was likely to be spinal in origin. When two such distant sites were stimulated separated by a 10- or 20-ms delay, the second response scaled with the level of background EMG in the same way as a response to the PT stimulus. By contrast, when the same site was stimulated twice with these delays, the second response showed a facilitation compared with a similarly timed PT response. There would therefore appear to be a local facilitation of the cortical output at these intervals, which is not seen between distant sites. Antidromically identified pyramidal-tract neurones (PTNs) were recorded whilst stimuli were delivered to a cortical site, with a distance between stimulating and recording electrodes of also 1.5-2 mm. The most common response was a facilitation followed by a suppression. Six of eleven PTNs showed a facilitation in their discharge following this stimulation (maximum connection strength s=0.19), 8/11 showed a suppression (maximum s=0.16). It is concluded that powerful inter-connections do exist between distributed parts of the motor output and that there is widespread cortical activation after even a single ICMS pulse. However, these inter-connections do not lead to interactions between cortical outputs following stimulation, as assessed from the EMG. It is proposed that this is likely to reflect differences in the summation of output cells to local versus remote stimulation.

Animals↗

PubMed1984

Cerebellar targets of visual pontine cells in the cat.

The cerebellum receives visual mossy fiber input from the cerebral cortex via visual cells in the pons. We identified the regions of cat cerebellum that receive cerebral visual input by injecting orthograde tracers among physiologically identified visual pontine cells. Cerebellar labeling following these injections indicates that the contralateral paraflocculus and the rostral folium of the uvula (vermal lobule IX) receive the heaviest projection from cortically activated pontine visual cells. Lighter visual input reaches much of the rest of the contralateral posterior lobe. A second experiment combined, in the same animal, orthograde tracing of the visual corticopontine pathway with retrograde tracing of the pontocerebellar projection. The results of this experiment confirm that the paraflocculus and uvula receive more cortical visual input than do other regions of the cerebellum. This experiment also shows that uvula-projecting and paraflocculus-projecting cells occupy different parts of the ventromedial pons. Uvula-projecting cells cluster immediately adjacent to the ventral and medial borders of the pyramidal tract and near the midline. Paraflocculus-projecting cells lie ventral and medial to the pyramidal tract but displaced from its border. There are few paraflocculus-projecting cells near the midline.

Animals↗

PubMed1992

Myopathic changes in schistosomal hepatosplenomegaly; histopathological, histochemical and immunopathological studies.

Eighteen patients suffering mainly from schistosomal hepatosplenomegaly (B.H.S.M.) were selected & classified into 3 groups according to the degree of B.H.S.M. Muscle biopsy for histopathological, histochemical and immunopathological studies were taken. The results showed that fatiguability as a symptom was present in all cases but motor weakness was present in four cases. Twelve cases had peripheral neuropathy in the form of glove and stocking hypothesia, while pyramidal tract lesion was present in four cases. Two cases, however, showed both peripheral neuropathy and pyramidal tract lesions. Histopathological and histochemical assessment revealed frank myopathic changes in 14 cases while only one case showed definite neuropathic changes. The remainder cases were inconclusive. Immunopathological examination revealed marked deposition of IgG in 50% of cases, while IgM and IgA showed mild to moderate reactions. It was concluded that muscular changes in schistosomal patients are myopathic in nature and that immunological mechanisms could be considered as a factor in the pathogenesis of this muscular disorder.

Adolescent↗

PubMed1995

Space-occupying lesions of the sensori-motor region.

Successful surgery of the sensori-motor region requires precise pre- and intraoperative localization of the sensori-motor region and pyramidal tract. Important aids are the landmarks of cranio-cerebral topography, coronal suture and bregma and the sulcal anatomy of the sensori-motor region, which can be identified in CT or MR images. Due to considerable displacement and distortion of the anatomical structures, elicited by mass lesions, these aids often fail to render reliable support. In this situation, identification of the motor area can be achieved by electrical stimulation of the precentral gyrus in association with the recording of somatosensory evoked potentials of the pre- and postcentral gyrus. The localisation of the "motor mosaics" in relation to the lesion, enable determination of the direction of displacement of the motor strip and the fan of the pyramidal tract. Based on this information the most appropriate route of access to the lesion is selected, either transcortical or transsulcal. Lesion-specific operative techniques as well as location-specific approaches are discussed. With consequent application of these principles the risk of a new persistent motor deficit was as low as 4%. Thus, the indication for surgery in this area can now be set with greater confidence and far more generously than in the past.

Brain Abscess↗

PubMed1984

Cerebral response to medullary pyramid stimulation in the rabbit.

The response evoked in the cerebral cortex of the rabbit by stimulation of the medullary pyramid was studied electrophysiologically. The response was everywhere surface-positive and began 2-3 ms after the stimulus. It exceeded 1 mV in amplitude and generally lasted 2-4 ms. Maps of the response showed it to extend throughout the anterior one-third of the cortex (in the 'motor' cortex) and into adjacent tissue, including the limbic cortex. Although it depended on antidromic conduction in pyramidal tract fibers for its production, it varied in amplitude, configuration and latency at different sites and at the same sites on repeated trials. It was found to reverse polarity deep in the cortex, to become a large, negative wave in layer V and to maintain that polarity into the underlying white matter. The response disappeared during a spreading depression, though it recovered more rapidly than the primary response evoked by skin stimulation. Maps of the primary response showed a strong overlap with the 'antidromic' response, though the response was largest slightly caudal to the maximal focus of the 'antidromic' response and extended more caudally through transitional and into limbic cortex. The 'antidromic' response showed two major foci on the cortex, with an additional minor focus located more laterally. It is argued that the 'antidromic' response in the rabbit is the same as that found in the opossum, woodchuck, rat and slow loris, and is markedly different from that found in the cat and macaque monkey. It is postulated that this response reflects synaptic action in pyramidal tract axon collaterals, probably onto cell bodies in layer V, rather than being a purely antidromic event.

Animals↗