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Biomedical subjects

S Homma

Publications and source records attributed to S Homma.

At least 361 records · Page 20Linked to original sources
PubMed1979

Conductance changes during bath application of beta-alanine and taurine in giant interneurons of the isolated lamprey spinal cord.

(1) Input conductances of giant interneurons in the isolated spinal cord of lampreys were measured with two separate intracellular electrodes. Bath applications of 0.4--3 mM beta-alanine and taurine produced large, reversible conductance increases which were Cl-dependent. (2) Strychnine at 1--2.5 microM might be a competitive antagonist of both amino acids, but had a stronger effect on taurine. Bicuculline and picrotoxin were weak antagonists of beta-alanine and taurine in some cells. (3) A few giant interneurons desensitized after repeated application of the amino acids, but most became more sensitive. Responses to the amino acids also increase at low temperatures in in Na-free fluid, suggesting effect of uptake mechanisms.

Alanine↗
PubMed1979

Coding process in human stretch reflex analysed by phase-locked spikes.

The Achilles tendon of man was tapped by triangular pulsatory waves with stimulus intervals from 10 to 100 Hz, while single motor unit spikes were recorded from the soleus muscle. The discharge probability of the motor unit spikes in relation to the triangular taps was analysed by means of cross-correlograms. A summation of the results of cross-correlograms of motor unit spikes with 10--100 Hz taps revealed one prominnet kernel, the primary correlation kernel. From the summated correlograms, it became clear that the mean width of the primary correlation kernel, the correlation time, was 8.3 +/- 2.5 msec. The correlation time is interpreted as representing the time-to-peak of the excitatory postsynaptic potential of an alpha-motoneuron.

Humans↗
PubMed1979

Measurements of excitatory postsynaptic potentials in the stretch reflex of normal subjects and spastic patients.

The patellar tendon was tapped by random impulses of triangular waveform and motor unit spikes were recorded from the quadriceps femoris muscle. The cross-correlogram of the taps and the motor unit spikes revealed a primary correlation kernel, the width of which was interpreted as an indicator of the mean time-to-peak of excitatory postsynaptic potentials (EPSPs) elicited monosynaptically in an alpha-motoneurone by the triangular taps. The mean time-to-peak was 7.6 +/- 1.3 ms in normal subjects and 9.0 +/- 1.8 ms in spastic patients (P less than 0.005). The prolonged time-to-peak of EPSP in spastic patients is consistent with the hypothesis that as a result of degeneration of the corticomotoneuronal tract the Ia axons sprout and form more synaptic contacts on distal portions of the dendrites of alpha-motoneurones.

Achilles Tendon↗
PubMed1978

Conductance increases produced by glycine and gamma-aminobutyric acid in lamprey interneurones.

1. Conductances of individual neurones in the isolated lamprey spinal cord were measured with separate intracellular electrodes for recording potentials and for passing current pulses during application of glycine or GABA (0.1-1.0 MM) in Ca-free bathing fluid. Large, reversible increases in conductance were produced in giant interneurones by both amino acids, but Müller axons and sensory dorsal cells were unaffected. 2. Conductance increases produced by glycine and by GABA were selective for Cl. Both conductance increases were linearly related to external Cl concentrations and repeated exposure to the amino acids in Cl-free fluid progressively reduced the conductance increases to less than 1% of their values in normal Cl. 3. Strychnine was a competitive antagonist of glycine, while GABA was antagonized competitively by bicuculline and non-competitively by picrotoxin. 4. The sensitivity of giant interneurones to glycine and GABA increased at low temperatures, in Na-free fluid, and after repeated exposure to the amino acids. Sensitization may have been produced by inhibition of uptake mechanisms for glycine and GABA in the spinal cord. 5. Discharges of interneurones recorded extracellularly were inhibited by bath-applied glycine and GABA, but directly elicited action potentials of axons were unaffected. Strychnine and Cl-free fluid in the presence of Ca produced seizures in lamprey spinal cord. 6. The conclusions of these experiments are that different receptors for glycine and for GABA are present on giant interneurones, that glycine is the better candidate for an inhibitory transmitter in the lamprey spinal cord, and that GABA produces effects similar to those which have been well studied in arthropod muscle.

Action Potentials↗
PubMed1976

Crossed inhibition as revealed by cross-correlogram between bilateral homonymous motor unit spikes in man.

Neuromuscular unit (NMU) spikes activated during the tonic vibration reflex (TVR) in man were studied by means of the cross-correlogram test. Those NMUs which preferredly fired at some definite interval with good correlation with vibration were called "locked" spikes. The amount above zero correlation level seen in the cross-correlogram was expressed as ipsilateral "excitatory frequency", Ef. TVR contraction of the ipsilateral quadriceps femoris muscle was stimulated by voluntary contraction of the contralateral quadriceps femoris. I. Cross-correlogram test of the contralateral voluntary NMU spikes with ipsilateral vibration revealed "contralateral inhibitory modulation". Such inhibitory modulation was observed in 24% of the contralateral NMUs during voluntary tracking contraction with visual feed-back and in 22% of NMUs during blind simulated contraction without visual feed-back. The "subtracted" amount, i.e., contralateral inhibitory modulation, was also expressed as the contralateral "inhibitory frequency", If, which was calculated from the indentations of the cross-correlogram. 2. When varied vibratory frequency was applied to the muscle both Ef and If attained their maximum value around an "optimal frequency" of vibration, i.e., 80-95 HZ. 3. The ratio Ef/If was proposed as the reciprocal co-activation ratio which was fairly independent of the change of vibratory frequency. An average value of Ef/If ratio was calculated at 2.2 +/- 0.9 from 19 experiments.

Adult↗
PubMed1975

Participation of mono- and polysynaptic transmission during tonic activation of the stretch reflex arcs.

Through intracellular observations of the cat spinal motoneuron both mono- and polysynaptic reflex arcs were shown to participate in repetitive activation of stretch reflex. Experiments were performed on 25 cats anesthetized by intraperitoneal (i.p.) injection of 3 cc/kg of a mixture of 1% chloralose and 10% urethane. Driving of the motoneuronal discharges accomplished by electric stimulation (16-100 Hz) of the gastrocnemius lateralis and medialis nerves. Repeated electric stimulation of muscle nerves elicited monosynaptic "vibratory" EPSPs and a polysynaptic "augmenting" EPSP in the motoneuron. The firing of the motoneuron occurred when a temporal summation of the "vibratory" EPSPs was sufficiently obtained. The discharge frequency of motoneuron, MNf, was expressed as a product of electrostimulus frequency, Sf, and reciprocal of an integer, n, i.e. MNf=(1/n)Sf. An increase in the stimulus intensity resulted in a dimimution of the vibratory EPSP and a remarkable increase of n. This was assumed to be due to an inhibitory process produced by the Group II fibers. The minimum value of integer n was always a determinant factor for the maximum value of MNf which was referred to as the "preferred" frequency of the motoneuron. Long-lasting electric stimulation of muscle nerves was followed by a more remarkable recruitment of the augmenting EPSP which made the motoneuron attain its critical threshold of firing. Motoneuronal spikes elicited by such a large augmenting EPSP were not locked to the Ia impulses. Unlocked spikes were observed only in a later stage of electric stimulation of Ia fibers.

Animals↗