Biomedical subjects

H Asanuma

Publications and source records attributed to H Asanuma.

At least 127 records · Page 7Linked to original sources

PubMed1987

The physiological identification of pyramidal tract neurons within transplants in the rostral cortex taken from the occipital cortex during development.

Axons from neurons in the occipital cortex transiently extend to the pyramidal tract (PT) during the early postnatal development of rats. Normally, these axons are eliminated by the end of the third postnatal week. However, if a portion of fetal occipital cortex is transplanted to the parietofrontal region in newborn hosts then some neurons in the transplant will extend pyramidal tract axons and maintain them. Intracortical microstimulation and electrophysiological recording techniques were used to identify the physiological characteristics of the transplanted pyramidal tract cells and to determine if motor effects could be elicited from the occipital transplant. Microstimulation of the transplant did not reliably evoke movement but the low density and disarray of PT cells within the transplant might account for this. Recording from within the transplant revealed that the overall cell activity was depressed. We were able to identify neurons within the transplant which responded antidromically to stimulation of the pyramidal tract, indicating that their axons have the capacity to conduct impulses and are therefore likely to have developed some viable connections. The functional significance of such projections remains uncertain.

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PubMed1987

Long-lasting potentiation of synaptic potentials in the motor cortex produced by stimulation of the sensory cortex in the cat: a basis of motor learning.

A long-lasting increase in the efficiency of synaptic transmission in the central nervous system has been thought to be one of the bases of learning and memory. To explore the possibility that the motor cortex (area 4 gamma) itself is involved in motor learning, the existence of long-term potentiation (LTP) was examined by recording excitatory postsynaptic potentials (EPSPs) from motor cortical neurons. Short tetanic intracortical microstimulation (ICMS) of the somatic sensory cortex produced a marked potentiation of the EPSPs in a small group of motor cortical neurons. The results raised the possibility that the input from the sensory cortex participates in motor learning and retention of the learned motor skills.

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PubMed1986

Effect of disuse of hand for recovery of motor function following dorsal column section in the monkey.

A question of whether use or disuse of the hand affects the recovery of motor function following dorsal column (DC) section was examined in monkeys. The hand was immobilized by a cast for 16 and 18 days after the section. When the cast was removed, the motor deficit was severer than that observed immediately after the DC section in control animals clearly indicating that the usage of the hand was necessary for the recovery. However, the impairment was not permanent. The hand skill started improving following the removal of the cast and reached the same level as the control although it took longer than for control animals. Neuronal mechanisms for the recovery are discussed in relation to the formation of new synapses.

Afferent Pathways↗

PubMed1985

Caudal cuneate nucleus projection to the direct thalamic relay to the motor cortex: an electrophysiological study.

We previously reported that injection of horseradish peroxidase (HRP) into a physiologically identified region of the thalamus between the ventrolateral nucleus and ventroposterolateral nucleus, VL-VPL, in cat results in labeled cell bodies in the caudal cuneate nucleus (CCN) of the dorsal column nuclei (DCN). We recognized, however, that the spread of HRP to localized regions of less than 1.0 mm distance from the injection site and subsequent uptake by neighboring fibers might have accounted for the resulting label in CCN. In the present study, therefore, we reexamined the DCN input to VL-VPL using a more sensitive physiological method. First, we used the microstimulation technique and corroborated the previous result. In 5 additional preparations, a modified collision procedure was used to ascertain that the same VL-VPL neuron which projects to the motor cortex also receives input from CCN. We report, for the first time, evidence of a lemniscal input to neurons in VL-VPL which are physiologically identified as projecting to the motor cortex.

Afferent Pathways↗

PubMed1985

Anatomical and physiological properties of the projection from the sensory cortex to the motor cortex in normal cats: the difference between corticocortical and thalamocortical projections.

Details of the distribution of terminal sites of the projection fibers from area 2 of the sensory cortex to the motor cortex were studied and compared with the distribution of terminals from the ventrolateral (VL) nucleus of the thalamus to the motor cortex. The results obtained were as follows: Intracortical microstimulation (ICMS) in area 2 produced measurable short-latency EPSPs only in neurons located in layers II and III of the motor cortex, whereas VL stimulation produced short-latency EPSPs in neurons throughout the depths of the motor cortex. The time from the beginning to the peak of the EPSPs was not significantly different for area 2- and VL-elicited EPSPs suggesting that there was no systematic difference between effective terminal sites for both inputs. However, there was a difference when a given neuron received both inputs suggesting that there was a segregation between the two inputs within a given cell. The majority of area 2-elicited EPSPs were smooth and monophasic, but some (40%) of them showed double peaks indicating that some neurons received mono- and disynaptic inputs from area 2. Intracellular injections of HRP suggested that neurons receiving input from area 2 were predominantly multipolar non-pyramidal neurons in layers II and III whereas neurons receiving thalamic input were pyramidal as well as non-pyramidal cells. Field potentials in the motor cortex evoked by area 2 stimulation did not change polarity in the depths of the cortex and therefore, differed from the VL-evoked potentials suggesting differences in the mechanisms of generating the electrical fields. It is concluded that association fibers effective for producing EPSPs terminate primarily on non-pyramidal cells in layer II and III whereas VL fibers terminate not only on pyramidal but also on non-pyramidal cells in layers III and V. This study provided a basis for examining the modifiability of association fibers after elimination of VL input to the motor cortex which is reported in the following paper.

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PubMed1985

Modification of the projection from the sensory cortex to the motor cortex following the elimination of thalamic projections to the motor cortex in cats.

Examination of the projection from area 2 of the sensory cortex to the motor cortex revealed substantial changes following lesion of the ventrolateral nucleus of the thalamus. These observed changes were as follows. (1) The polarity of the evoked potentials elicited by area 2 stimulation reversed in the depth of the motor cortex whereas in normal animals, there was no reversal. (2) The amplitude of area 2-elicited EPSPs in the motor cortical neurons became greater following the lesion of VL. (3) The shape of the observed EPSPs was characterized by multiple peaks whereas in normal animals, the EPSPs were generally smooth and monophasic. (4) Neurons receiving a short-latency input from area 2 were distributed throughout the depths of the motor cortex whereas in normal animals, they were located only in the upper layers (layers II and III). (5) Intracellular injection of HRP revealed that the neurons receiving short-latency input were not restricted to typical stellate type cells, but also included bipolar or bitufted neurons with elongated cell bodies and polarized arborizations. These neurons were located in the superficial (II and III) as well as in the deep (V) layer. It is concluded that the elimination of thalamic input resulted in the reinforcement of the corticocortical input to the motor cortex. The subsequently observed corticocortical projection extended to neurons did not originally innervated by the association fibers. The results suggested that functional recovery following thalamic lesion is partly due to reorganization of projections from the sensory cortex to the motor cortex.

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PubMed1985

Distribution of corticocortical and thalamocortical synapses on identified motor cortical neurons in the cat: Golgi, electron microscopic and degeneration study.

Details of the terminal connection of corticocortical and thalamocortical fibers on pyramidal and stellate neurons in the cat motor cortex were studied using the electron microscope in combination with the Golgi and axonal degeneration techniques. Corticocortical terminals were examined in 23 identified neurons of which 11 were pyramidal and 12 were stellate. Stellate neurons located in layer III received many degenerating terminals (average 8.4 +/- 2.2 per unit length of dendrite (ULD)) and the majority of these (95%) were found on the proximal dendrites or on the cell bodies. The pyramidal neurons received fewer degenerating terminals (average 2.1 +/- 0.27/ULD) and these were located on more distal dendritic shafts or on dendritic spines. The majority of these synapses were of the asymmetric type. Thalamocortical terminals were examined in 9 pyramidal and 9 stellate neurons. Pyramidal neurons received many terminals (average 6.0 +/- 1.23/ULD) and these were found on the basal as well as the apical dendrites and on dendrite spines. Stellate neurons received fewer terminals (average 4.2 +/- 0.64/ULD) and were located primarily on proximal dendritic shafts. The majority of these synapses were of the asymmetric type. The functional role of these synapses is discussed in relation to the physiological results reported in the preceding paper.

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PubMed1985

Motor effects produced by stimulation of secondary somatosensory (SII) cortex in the monkey.

Threshold for evoking movements by microstimulation of the second somatosensory area of the cynomolgus monkey's cortex to intracortical microstimulation was examined. Motor effects were obtained contralateral to the side of stimulation, in a region histologically verified to be in grey matter deep in the sylvian cortex, and which corresponds to the second somatosensory cortex. The thresholds were low but higher than for movements evoked by stimulation of the motor cortex. The results are explained in terms of increased specialization of the motor cortex for movements in the monkey compared with the cat.

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PubMed1984

Caudal cuneate nucleus projection to the direct thalamic relay to motor cortex in cat: an electrophysiological and anatomical study.

The input to the border region between the ventrolateral nucleus (VL) and ventroposterolateral nucleus (VPL) of the thalamus, VL-VPL, was studied in cats using a combined electrophysiological and anatomical technique. Neurons within this border region receive somatic afferent input and project to a region of the motor cortex having similar receptive fields. In this study we asked the question whether neurons in the VL-VPL border receive input from the dorsal column nuclei (DCN). To answer this question we delivered intra-cortical microstimulation (ICMS) to the motor cortex while a second electrode inserted into the VL-VPL border, filled with a 20% solution of HRP dissolved in KCl, was used to record antidromically activated neurons. When an antidromically activated neuron was encountered and the neuron responded to natural peripheral stimulation, HRP was iontophoretically injected through the recording electrode. After a 48-72 h survival time, cats were sacrificed, and the brain tissue processed according to the method of Hardy and Heimer. Labeled cell bodies were found in the caudal cuneate nucleus (CCN) in all injected animals. These results suggested that neurons in CCN project to cells in VL-VPL which in turn project to the motor cortex.

Animals↗

PubMed1984

Focal and diffuse metabolic changes in the spinal cord of the monkey elicited by microstimulation of differing motor cortical foci.

The pattern of projections from identified motor cortical efferent zones onto the spinal cord was examined in the monkey using a combination of microstimulation and [14C]2-deoxyglucose metabolic labeling. Regional differences were found in the branching patterns between the projections of proximal and distal forelimb foci of the motor cortex onto the spinal cord. Cortical efferent zones related to proximal movements project extensively within the spinal cord activating numerous motor nuclei. In contrast, the corticospinal projection of a distal movement zone was found to be significantly more restricted in overall rostrocaudal extent projecting with greatest density onto a small focal region of the ventrolateral horn.

Animals↗

PubMed1984

Corticocortical connections to the motor cortex from the posterior parietal lobe (areas 5a, 5b, 7) in the cat demonstrated by the retrograde axonal transport of horseradish peroxidase.

Neurons in the parietal region of the cerebral cortex, projecting to the ipsilateral distal forelimb area of the motor cortex (area 4 gamma) were identified in the cat brain using the horseradish peroxidase (HRP) retrograde tracing method. After making microinjections of HRP into the distal forelimb area of the motor cortex, clusters of HRP-labeled cell bodies were observed in different regions of the ipsilateral parietal cortex. In particular these clusters of labeled cells were found in areas 5a, 5b and 7. The area 5a cluster is formed from closely packed irregularly-shaped cells, the area 5b cluster is made up of dispersed medium-sized pyramidal cells, while area 7 contains a cluster of widely dispersed small pyramidal cells. Typically, labeled cell bodies were found in lamina III of cortex. Labeled cell bodies were neither observed in the contralateral cortex nor in the visual cortex (areas 17, 18 and 19). Since parietal cortex receives projections from primary somatosensory and visual cortex, the projections from parietal to motor cortex may well form the neural substrate for the processing of convergent sensory information used in voluntary movements.

Afferent Pathways↗

PubMed1984

Experiments on functional role of peripheral input to motor cortex during voluntary movements in the monkey.

The functional role of sensory input to the motor cortex was studied by interrupting two major input pathways. One was the dorsal column, which sends the input directly through the thalamus to the motor cortex, and the other was the sensory cortex, which transfers its input through association fibers. Removal of the sensory cortex produced very little motor disturbances and the function recovered within a week. Section of the dorsal column produced some motor deficit, but the deficit was not severe and the animals recovered nearly completely within 2 wk. Combination of dorsal column section and sensory cortex removal produced severe motor deficits. These consisted of loss of orientation within extrapersonal space and loss of dexterity of individual fingers. These deficits never recovered within the duration of observation, which lasted 4-5 wk. It is concluded that the direct sensory input from the thalamus plays an important role in the control of voluntary movements, but loss of its function can be compensated by the input from the sensory cortex. The possible neuronal basis for the observed motor deficits is discussed and it is proposed that the sensory input functions by selectively changing the excitability of cortical efferent zones before and during the execution of voluntary movements. Recovery of motor function following dorsal column section occurred in parallel with the recovery of sensory input to the motor cortex. The recovered function and sensory input disappeared again following section of the association fibers from the sensory cortex. Neuronal mechanism for this observation is also discussed.

Afferent Pathways↗

PubMed1983

Low threshold motor effects produced by stimulation of area preinsularis (2 pr.i) of the secondary sensory cortex in the cat; input-output relationship.

Intracortical microstimulation (ICMS) delivered to area 2 perinsularis (area 2 pr. i) of the second somatosensory cortex, SII, elicited contralateral distal limb movements with threshold currents as low as 2 microA. The effective sites for a particular movement were located in a small area within the depth of the cortex extending along the direction of the radial fibers. Neurons in an area for a particular movement generally received peripheral input from the skin overlying the muscle to which the area projected. ICMS in area 2 pr.i produced powerful monosynaptic as well as disynaptic activation of pyramidal tract neurons, suggesting that the effect was mediated by the pyramidal tract. Ablation of the motor cortex did not eliminate or otherwise reduce the low threshold responses from area 2 pr.i suggesting that the described effect is independent of the motor cortex.

Animals↗

PubMed1983

Movement of facial muscles following intra-cortical microstimulation (ICMS) along the lateral branch of the posterior bank of the ansate sulcus, areas 5a and 5b, in the cat.

The lateral branch of the posterior bank of the ansate sulcus within the parietal cortex, areas 5a and 5b, was mapped using intracortical microstimulation (ICMS). Motor effective sites for contraction of facial muscles were identified using ICMS currents of less than 30 microA. Of the 177 effective sites, 78% were activated with threshold currents of less than 20 microA, and of these, 33% responded to stimulus strengths of less than 10 microA. Since neurons in this portion of the ansate region send projections to the face region of motor cortex, area 4 gamma, the possibility existed that the motor effects might be mediated through area 4 gamma. To examine this possibility we ablated both the anterior sigmoid gyrus (ASG) and the second somatosensory cortex, SII, including area 2pri, a region shown to contain a low threshold motor component, and report that the motor effect recorded from the ansate region is independent of both the ASG and area 2pri.

Animals↗

PubMed1982

Pattern of projection and physiological properties of cortico-cortical connections from the posterior bank of the ansate sulcus to the motor cortex, area 4 gamma, in the cat.

The physiological properties of neurons lying along the posterior bank of the ansate sulcus and the projection of these neurons to area 4 gamma of the motor cortex of the cat were studied and the following results were obtained: (1) Short latency antidromic responses were recorded from neurons along the medial-lateral bank of the posterior ansate sulcus following intracortical microstimulation (ICMS) delivered to motor cortex, area 4 gamma. (2) The posterior ansate region projects topographically to the motor cortex. Neurons in the most medial part of the ansate region project to the medial part of 4 gamma, while neurons in the central and lateral parts of the ansate region project to the more lateral parts of area 4 gamma. (3) In 33 cases, receptive field information was available for both the antidromically activated ansate neuron and from neurons around the stimulating site in 4 gamma. In 58% of the cases, both cortical sites received afferent input from within the same part of the periphery. (4) Afferent input to the motor cortex was examined following combined ablations of the primary somatosensory cortex (SI) and third somatosensory cortex (SIII) including all of area 5. We conclude that the integrity of these cortical regions is not necessary for afferent input to reach the motor cortex.

Afferent Pathways↗

PubMed1982

Physiological properties and pattern of projection of cortico-cortical connections from the anterior bank of the ansate sulcus to the motor cortex, area 4 gamma, in the cat.

The physiological properties of neurons in the postsigmoid gyrus lying along the anterior bank of the ansate sulcus and the pattern of projection of these neurons to the motor cortex, area 4 gamma, were investigated in the cat and the following results were obtained. (1) Neurons lying along the anterior bank of the ansate sulcus receive somatotopically organized afferent input from the skin and deep structures on the contralateral side of the body. (2) Short latency antidromic responses were recorded from all regions along the bank of the sulcus following intra-cortical microstimulation (ICMS) of area 4 gamma. (3) The projection of neurons to area 4 gamma was topographically organized. Neurons in the lateral portions projected to more lateral parts of 4 gamma, whereas neurons in the medial region of the postsigmoid gyrus sent axons to the more medial regions of the motor cortex. (4) In 50 cases, receptive fields were recorded from both the antidromically identified postsigmoid gyrus neuron and from neurons around the activation site in area 4 gamma. In 62% of these instances, both cortical sites received afferent input from within the same part of the periphery.

Animals↗

PubMed1982

Physiological properties of neurons projecting from area 3a to area 4 gamma of feline cerebral cortex.

1. The corticocortical projection from area 3a to area 4 gamma was restudied using tranquilized cats. 2. Intracortical microstimulation (ICMS) of a given locus in area 3a produced effects on neurons in area 4 gamma that were located in a small area extending along the direction of the radial fibers constituting a columnar shape. 3. Cortical neurons in area 3a that projected to a particular neuron in area 4 gamma were located in a region that extended along the direction of the radial fibers and constituted a columnar shape. 4. Two-thirds of the projection neurons in area 3a had different receptive fields from those of neurons in the projected area in 4 gamma, thus suggesting that the 3a neurons are not simply transferring peripheral information to the 4 gamma neurons. 5. ICMS delivered to area 3a rarely excited 4 gamma neurons but rather facilitated their evoked discharges. 6. It is suggested that the activity of corticocortical projection from area 3a to 4 gamma can influence the activity of 4 gamma neurons only when combined with other inputs to the motor cortex.

Animals↗

PubMed1982

Motor deficit following interruption of sensory inputs to the motor cortex of the monkey.

The possible functional role of sensory inputs in voluntary movements was examined by severing the sensory input pathways to the motor cortex. The somatic sensory cortex and the dorsal column, which are known to be the two major sources of the peripheral inputs to the motor cortex, were ablated or sectioned. The deficit produced by sensory cortex ablation or dorsal column section was not prominent and the function recovered within a week or two as long as the other input was intact, but elimination of both inputs produced severe impairment in movements such as loss of orientation in space and of manipulation of individual fingers. The possible role of the afferent input is discussed and it is proposed that it participates in the smooth pursuit of movement by continuously changing the excitability of cortical efferent zones.

Animals↗