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Biomedical subjects

S Murakami

Publications and source records attributed to S Murakami.

At least 865 records · Page 48Linked to original sources
PubMed1981

Motor unit activities during maintained voluntary muscle contraction at constant levels in man.

Activities of motor units of human tibialis anterior muscle were studied when the subject maintained the force of the muscle at a constant level voluntarily. Motor units were classified into two main groups according to their discharge frequencies and their tensions. Those units which were recruited from the beginning of the contraction and discharged tonically throughout yielded low tensions and units which showed discharge only for a limited period produced higher tensions.

Adult↗
PubMed1981

Adult T-cell leukemia in Japan: an ultrastructural study.

An electron microscopic study of adult T-cell leukemia, which might be a new distinct disease entity of T-cell malignancies, is presented. The most characteristic feature of adult T-cell leukemia was an extremely irregular nucleus with condensed heterochromatin in the nuclear periphery, the greater part of which was very similar to the small-cell variant form of Sézary syndrome, although some nuclei were similar to normal-appearing lymphocytes or atypical lymphoid cells with slightly indented nuclei or Sézary cells. Nuclear pockets containing tubuloreticular structures and filamentous structures etc., were also characteristic. Regarding the cytoplasmic features, the appearance of clustered dense bodies seemed to be a distinguishing feature of adult T-cell leukemia. Tubuloreticular structures were also observed in some cases. The nature of the test tube-shaped or ring-shaped forms in rough endoplasmic reticulum, which appeared in one case, is not clear.

Adult↗
PubMed1981

Effects of stimulation of frontal cortex, superior colliculus, and neck muscle afferents on interstitiospinal neurons in the cat.

Interstitiospinal neurons were activated by antidromic stimulation of the spinal cord ventromedial funiculus at C1 and C4 in cerebellectomized cats under chloralose anesthesia. Neurons responding only to C1 were classified as N cells and those responding both to C1 and C4 were classified as D cells, as in previous experiments (Fukushima et al. 1980a). Vestibular branching interstitiospinal and reticulospinal neurons were also identified as in the previous experiments. Stimulation of the ipsilateral pericruciate cortex evoked firing in 31% of N cells, 41% of D cells and 35% of the vestibular branching neurons, while stimulation of the contralateral cortex excited 6% of N cells, 29% of D cells and 14% of vestibular branching neurons. Response latencies ranged from 2 to 15 ms after the effective pulse. By measuring the thresholds of activation of these neurons while changing the depth of the stimulating electrodes, and by mapping the cortical areas, it was shown that the lowest threshold areas were in the frontal eye fields and the anterior sigmoid gyrus near the presylvian sulcus (Area 6). Stimulation of the latter area often evoked neck or shoulder muscles contraction. Stimulation in the deep layers of the ipsilateral superior colliculus evoked firing in about 20% of interstitiospinal neurons and about 42% of vestibular branching neurons, with typical latencies 2-3 ms after the effective pulse, while stimulation of the contralateral superior colliculus was rarely effective. N cells and D cells responded similarly. Thresholds for activation were high in the intermediate tectal layers and declined as the electrodes entered the underlying tegmentum. This suggests that the superior colliculus is not the main source of synaptic inputs to these neurons. Low threshold points were found above the deep fiber layer when stimulating electrodes were inserted into the pretectum. Stimulation of the C2 biventer cervicis nerve excited about 8% of N cells, 18% of D cells, and 15% of vestibular branching neurons bilaterally with typical latencies around 10 ms. Similar results were obtained when C2 splenius nerves were stimulated. The fibers responsible for such excitation are probably group II, since stimuli stronger than 1.8 times threshold of the lowest threshold fibers were needed to evoke excitation. Response decrement was often observed when stimuli were repeated at 1/s, while no such decrement was observed at the rate of 1/3 s. When the convergence of cortical and labyrinthine excitatory inputs was studied, 36% of interstitiospinal neurons received single inputs either from the pericruciate cortex or from the labyrinth, 22% of neurons received convergent excitation from both and the remaining 42% did not respond to either stimulus. Although vestibular branching neurons rarely received labyrinthine inputs, they frequently showed convergence of excitation to stimulation of the frontal cortex, superior colliculus and vestibular nuclei.

Afferent Pathways↗
PubMed1981

Ataxic hemiparesis with trigeminal weakness.

We experienced a most unusual case of right-sided ataxic hemiparesis with left masticatory involvement, in which we confirmed the responsible lesion in the basis pontis by computerized tomography.

Ataxia↗
PubMed1980

Properties of mesencephalic reticulospinal neurons in the cat.

Neurons that project to the spinal cord were located in the mesencephalic reticular formation outside the interstitial nucleus of Cajal in cerebellectomized cats under chloralose anesthesia. Of these neurons 40% responded only at C1 (reticulospinal N cells) and the remaining 60% responded at C4 also (reticulospinal D cells). Conduction velocities of N cells were significantly slower than those of D cells. N cells and D cells responded similarly to stimulation of the whole vestibular nerves and vestibular nuclei. However, they differ in semi-circular canal inputs; N cells were more responsive to canal stimulation. Comparison of properties between mesencephalic reticulospinal and interstitiospinal neurons (Fukushima et al. 1980) showed that many reticulospinal and interstitiospinal neurons have similar properties, suggesting that functionally similar neurons may be found distributed over more than one anatomically defined cell group.

Animals↗
PubMed1980

Vestibular responses and branching of interstitiospinal neurons.

1. Interstitiospinal neurons were activated by antidromic stimulation of the ventromedial funiculus of the spinal cord at C1 and C4 in cerebellectomized cats under chloralose anesthesia. 46% of these neurons responded only at C1 (N cells) and the remaining 54% responded at C4 also (D cells). There is no topographical difference in the location of N and D cells. Conduction velocities of N cells were significantly slower than those of D cells. 2. Stimulation of the contralateral whole vestibular nerve evoked firing of 31% of both N and D cells; some responded early enough to suggest disynaptic connections, many responded late. Stimulation of the ipsilateral whole vestibular nerve evoked firing of several cells, one spontaneously discharging D cell was inhibited. 3. Stimulation of the contralateral individual semicircular canal nerves evoked firing of 33% of N cells and 13% of D cells. Most of these responses were late. N cells responded not only to the vertical canals but also to the horizontal canal, whereas D cells responded to the horizontal canal, but seldom to the vertical ones. Most canal responding neurons received specific input, only two N cells received convergent input from both the anterior and horizontal canals. Stimulation of the ipsilateral canals did not evoke excitation of any cells tested; one D cell was inhibited by stimulation of the horizontal canal nerve. 4. Stimulation of the rostral medial vestibular nucleus evoked characteristic negative field potentials centered in the contralateral interstitial nucleus of Cajal (INC). Approximately 60% of both N and D cells received excitation from the contralateral vestibular nuclei. About 17% of these responding neurons received monosynaptic excitation, most frequently from the rostral medial nucleus. Stimulation of the ipsilateral vestibular nuclei evoked firing of 12% of both N and D cells. 5. Twenty-nine neurons were fired antidromically by weak stimuli applied to the ipsilateral vestibular nuclei. Twenty-seven of the 29 were activated only from C1 and were found in the INC (10 cells) and in the reticular formation dorsal to the INC (19 cells). Measurement of the spread of the effect of stimulus current and comparison of latencies to stimulation of the vestibular nuclei and C1 indicated that these neurons have axon collaterals going to the ipsilateral vestibular nuclei. Only one of them received excitation from the contralateral posterior canal, others did not respond to the labyrinth. Some were activated by stimulation of the vestibular nuclei.

Animals↗
PubMed1980

[Projection of neck muscle afferents to the brain stem of the cats (author's transl)].

In order to investigate the afferent projection of neck muscles biventer cervicis, splenius and occipitoscapularis, extremities were performed on cats anaesthetized with chloralose urethane. 246 neurons were found to respond to electrical stimulation of these muscle nerves and they were located mainly in the ipsilateral external cuneate nucleus (242; 98.3%) and the remaining 4 neurons were in the rostral tip of the main cuneate nucleus. It was found that 241 neurons responded to only one of these afferent nerves, 3 neurons received convergent inputs from biventer cervicis and occipitoscapularis nerve and one neuron from biventer cervicis and great auricural nerve. Out of 241 neurons studied, 97 neurons (40.3%) responded to biventer cervicis, 88 (36.5%) to splenius and 56 (23.2%) to occipitoscapularis. 40 out of the 97 biventer cervicis responded neurons showed the monosynaptic firing. 51 out of the biventer cervicis responded neurons, 35 out of the splenius and 34 out of the occipitoscapularis responded neurons fired the first spike response at stimulus strength below 1.7 times the threshold of the largest afferents of each nerves suggesting group I afferents are responsible for the discharges. The monosynaptically activated neurons showed somatotopic distribution in the nucleus; biventer cervicis responded neurons locate in the most lateral part, splenius locate in the middle and occipitoscapularis locate in the medial part of the external cuneate nucleus. Antidromic discharges were evoked in 43/143 (30.1%) of the external cuneate neurons by electrical stimulation of the ipsilateral inferior peduncle and anterior lobes IV and V of the cerebellum. No such and antidromic discharges could be evoked by electrical stimulation of the contralateral thalamus. It was concluded that the relay neurons of the external cuneate nucleus from biventer cervicis, splenius and occipitoscapularis neck muscles projected their axons to the ipsilateral cerebellum but not to ventral posterolateral (VPL) and ventral posteromedial (VPM) nucleus of the contralateral thalamus.

Action Potentials↗
PubMed1979

De- and remyelination and onion bulb in cerebrotendinous xanthomatosis.

In a case of cerebrotendinous xanthomatosis (CTX), confirmed biochemically and histologically quantitative histological studies of the biopsies sural nerve revealed significantly higher incidence of de- and remyelination and onion bulb than in controls. The density of total myelinated fibers fell within the range of controls, although the density of large myelinated fibers seemed to be slightly decreased. It was suggested that the preferential involvement of the myelin sheath and Schwann cell may exist in CTX.

Adult↗