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Biomedical subjects

N Kudo

Publications and source records attributed to N Kudo.

At least 127 records · Page 7Linked to original sources
PubMed1985

Development of the monosynaptic stretch reflex in the rat: an in vitro study.

The properties and development of the stretch reflex pathway were investigated in new-born and fetal rats using the isolated spinal cord-hind limb preparation. Muscle afferent discharge was elicited by small stretch of the triceps surae muscle in the new-born rat and in the fetus. It appeared as early as embryonic day 18.5. Ramp-and-hold stretch elicited only phasic discharges in most afferent fibres. A phasic reflex response was evoked in the triceps surae muscle by brief or ramp-and-hold stretch of the muscle in the new-born rat. The threshold stretch required for evoking the reflex response was close to that for eliciting the afferent discharge. A reflex response in the triceps surae muscle was also evoked by electrical stimulation of the triceps surae muscle nerve or the sciatic nerve in the new-born rat. Excitatory post-synaptic potentials (e.p.s.p.s) in the triceps surae motoneurones were evoked by stimulation of the muscle nerve in the new-born rat. The amplitude of the e.p.s.p.s was large enough to generate spike potentials. Homonymous e.p.s.p.s were significantly larger than heteronymous e.p.s.p.s. The amplitudes of the e.p.s.p.s were very susceptible to the rate of stimulus repetition. At a stimulus frequency of 10 Hz they were depressed to less than 10% of the control value. Presynaptic impulses evoked by stimulation of afferents in the muscle nerve appear in the motor nucleus less than 1.0 ms before the onset of synaptically evoked field potentials. The interval between the arrival of impulses evoked by dorsal root stimulation and the onset of e.p.s.p.s in motoneurones was 0.56 +/- 0.16 ms, indicating monosynaptic transmission from the primary afferents to the motoneurones. In the fetus, a reflex response in the triceps surae muscle was observed following a small stretch of the muscle (or electrical stimulation of the sciatic nerve) in all preparations at embryonic day 20.5 and in about half of those examined at embryonic day 19.5. Neither stimulation evoked a reflex response at embryonic day 18.5. Latencies of the reflex responses evoked by muscle stretch or by nerve stimulation were similar to those in the new-born rat. It is concluded that the monosynaptically evoked stretch reflex response in the triceps surae muscle first appear at embryonic day 19.5. Natural and electrical stimulation of the plantar skin evoked a reflex response with long latencies in flexor muscles. Such a cutaneous reflex was first present at embryonic day 17.5, two days earlier than the onset of the stretch reflex.

Action Potentials↗
PubMed1984

Firing of spinal motoneurones due to electrical interaction in the rat: an in vitro study.

The excitatory interaction between spinal motoneurones was investigated by means of electromyogram (EMG) recordings from hindlimb muscles as well as intracellular ones from their innervating motoneurones in the isolated preparation of immature rats. Stimulation of the muscle nerve to biceps femoris or medial gastrocnemius or of the L5 ventral root evoked early and late EMG responses in the muscle of the preparations with the dorsal roots cut. The early response was produced directly by volleys in the motor nerve. The late response was of spinal origin, since it disappeared after the severance of the ventral root. The thresholds and the conduction velocities of nerve fibres, which conducted the centripetal impulse causing the late response, were compatible with those of motor nerve fibres. The amplitude of the late response was 5-10% of that of the maximum early EMG response. Intracellular recordings from spinal motoneurones revealed that stimulation of the ventral root elicited the double discharge composed of antidromic and delayed spike potentials. The delayed spike was never evoked after the spike potential elicited directly by a short depolarizing pulse. The double discharge was observed in about 6% of the motoneurones examined. The threshold of the stimulus intensity evoking the double discharge was in the range of those of motor nerve fibres. The latencies of the delayed excitation were 7.0-9.0 ms, comparable to the intraspinal delays of the late EMG response. Stimulation of the ventral root at intensities subthreshold for antidromic activation was found to produce a small depolarizing potential in about 60% of the motoneurones examined. The amplitudes were 0.5-5.0 mV, and the onset and the peak latencies 2.0-7.0 ms and 5.0-8.0 ms, respectively. The potential was unaffected by the deficiency of calcium ions in the perfusing medium and persisted after the degeneration of the afferent fibres in the ventral root.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1982

Aggregation of plant protoplasts by artificial lipid vesicles.

Sonicated unilamellar lipid vesicles, consisting of egg lecithin, stearylamine, and cholesterol in 7:2:1 molar ratios, promoted the aggregation of tobacco (Nicotiana glutinosa) protoplasts with the aid of mono- or divalent cations.A reaction mixture containing liposomes (0.4 micromoles lipid per milliliter), 50 millimolar CaCl(2), 0.5 molar mannitol, and 5 x 10(5) protoplasts per milliliter resulted in approximately 25% protoplast aggregation. To achieve the maximum protoplast aggregation, 1.6 x 10(8) liposomes per protoplast per hour would be required.The kind of liposomes effective in protoplast aggregation were positively charged, small-size vesicles which were obtained either by 60-minute sonication or by membrane filtration in conjunction with sonication.

Journal Article↗