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M Kuno

Publications and source records attributed to M Kuno.

At least 73 records · Page 4Linked to original sources
PubMed1988

Excitatory postsynaptic currents in response to different synaptic inputs of frog spinal motoneurons.

Excitatory postsynaptic currents (EPSCs) evoked by the primary afferents (dorsal root; DR) and the descending lateral column (LC) fibers were studied in frog spinal motoneurons under voltage clamp with two separate electrodes. The average rise time and half-width of the EPSCs were shorter for LC-EPSCs than for DR-EPSCs, though the values of the parameters for LC- and DR-EPSCs were distributed within a similar range. The relation between the amplitudes of the EPSP and EPSC was almost linear. The amount of current required to generate a 1 mV increment in the EPSP was 5.0 +/- 2.3 nA for the DR-EPSC and 3.8 +/- 1.2 nA for the LC-EPSC. The decay time was shortened by hyperpolarization and prolonged by depolarization in DR- and LC-EPSCs and spontaneous EPSCs. The reversal potential ranged from -30 to -5 mV and was almost identical for DR- and LC-EPSCs and spontaneous EPSCs in individual motoneurons. The current-voltage relation was linear from -100 to +50 mV for these EPSCs. Spontaneous EPSCs became more prominent and frequent during a large hyperpolarization or a large depolarization. These results suggest that the ionic mechanisms underlying EPSC are similar for the functionally different excitatory synapses located on motoneurons.

Action Potentials↗
PubMed1988

Voltage-clamp analysis of taurine-induced suppression of excitatory postsynaptic potentials in frog spinal motoneurons.

1. The depressant actions of taurine applications on lumbar motoneurons in the isolated frog spinal cord were studied using conventional intracellular recordings and the two-electrode voltage-clamp technique. 2. With microelectrodes containing K+-acetate, 0.75-2 mM taurine mostly induced a hyperpolarization that often faded or turned into depolarization during the continuous application. A higher concentration (5-7.5 mM) depolarized a majority of cells. The effects on the membrane potential were associated with an increase in input conductance (approximately 285%). 3. The reversal potential of the taurine-induced currents was approximately -70 mV, with microelectrodes containing K+-acetate. In recordings using KCl-filled electrodes, taurine (less than or equal to 2 mM) produced a large depolarization (greater than or equal to 20 mV) at resting potentials near -50 mV, thereby indicating that the reversal potential was positively shifted by loading the cell with Cl-. These results suggest that the taurine potentials were mediated predominantly by an increased Cl- permeability. 4. Voltage-dependent relaxations of taurine currents were observed in 10 of 14 neurons. 5. A linear relation was found between the input conductance and the amount of current required to generate a 1-mV increment in EPSP at resting potential. 6. Polysynaptic excitatory postsynaptic potentials (EPSPs) and currents (EPSCs) were more susceptible to taurine than the monosynaptic responses. Taurine (less than 1 mM) seemed to suppress the interneurons mediating polysynaptic pathways. 7. Monosynaptic EPSPs and EPSCs were decreased with higher concentrations of taurine (greater than 1 mM). The percent reduction of EPSPs and that of the corresponding EPSCs had a positive correlation (r = 0.95), whereas, there was no significant correlation between changes in EPSPs and in input conductance, and between changes in EPSCs and in input conductance. The amount of current required to produce a 1-mV increment of EPSP was increased in the presence of taurine, in association with the increased input conductance. 8. Taurine suppressed synaptic potentiation of EPSPs evoked by paired stimuli, at an interval of 60-180 ms. Gamma-D-glutamylglycine, an antagonist of receptors for excitatory amino acids, greatly reduced the amplitude of EPSPs, but had little effect on synaptic potentiation. 9. Taurine suppressed glutamate currents evoked at membrane potentials, clamped near rest in low Ca2+, high Mg2+ solution. 10. These findings suggest that the taurine-induced reduction of EPSPs is due mainly to suppression of EPSCs, through both presynaptic and postsynaptic mechanisms.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Calcitonin gene-related peptide prevents disuse-induced sprouting of rat motor nerve terminals.

Calcitonin gene-related peptide (CGRP) coexists with acetylcholine (ACh) in motor nerve terminals. Externally applied CGRP has been shown to increase the synthesis of ACh receptors in cultured myotubes by a mechanism independent of muscle activity. Thus, CGRP is suggested to be a neurotrophic factor that may regulate the expression of several long-term events occurring at the neuromuscular junction. We have examined the effect of CGRP on the sprouting of motor nerve terminals induced by chronic block of nerve-muscle activity in adult rats. Daily treatment with CGRP suppressed the disuse-induced terminal sprouting in a dose-dependent manner, whereas the morphology of motor nerve terminals in active muscles was unaffected by CGRP. CGRP may be a possible candidate for an antisprouting agent which has been postulated to exist in nerve terminals. The disuse-induced outgrowth of terminal sprouts was accompanied by an increase in the mean quantum content of end-plate potentials, as well as in the frequency of spontaneous miniature end-plate potentials. This increased transmitter release was still maintained at the junctions in which disuse-induced terminal sprouting had been suppressed by CGRP. It is suggested that the formation of terminal sprouts per se is not responsible for the plastic change of transmitter release induced by prolonged disuse of the neuromuscular junction.

Animals↗
PubMed1987

Responses of intracranial pressure (ICP) produced by stimulating the pressor area in the brainstem at various levels of blood pressure and ICP in cats.

An increase in intracranial pressure (ICP) was produced by stimulating brainstem pressor sites in cats anesthetized with alpha-chloralose. The ICP responses were augmented by lowering prestimulus BP and reduced by elevating prestimulus BP. In contrast, stimulus-induced pressor response of BP showed no consistent correlation to prestimulus BP. When the mean amplitude of stimulus-induced ICP responses at the control prestimulus ICP (within 18 mmHg) was plotted against the mean of the prestimulus BP levels for each site examined, the sites were classified into 2 groups by the regression line; sites generating a marked ICP response above the line and those generating a small ICP response on and under the line. The former sites were located in the paramedian region of the reticular formation including nuclei parvocellularis and gigantocellularis. The latter sites scattered throughout the brainstem pressor area. The ICP response at the former sites was markedly increased at an elevated prestimulus ICP. The peak ICP response at 30-50 mmHg of prestimulus ICP was 70-100 mmHg, similar to plateau waves. The ratio of ICP response size to BP response size was negatively correlated to prestimulus BP and the regression line was 2-5 times steeper at an elevated prestimulus ICP (18-60 mmHg) than at the control ICP. On the other hand, the negative relation between the response ratio and the BP for the latter sites produced no such change at the increased prestimulus ICP. These findings suggest that the ICP response is produced primarily by neurogenic intracranial vasodilation, which works most effectively at moderately decreased cerebral perfusion pressure. This mechanism may be involved in a series of events that results in plateau waves.

Animals↗
PubMed1987

Cell death of axotomized motoneurones in neonatal rats, and its prevention by peripheral reinnervation.

1. Motoneurone death induced by axotomy in the rat was studied following section of the medial gastrocnemius nerve near the muscle 4 days after birth. 2. The maximum twitch tension of the medial gastrocnemius muscle achieved by motor reinnervation after section of its nerve was about 70% of that measured on the contralateral, intact side. 3. The number of motor units counted at 35-45 days of age in the animals whose medial gastrocnemius nerves had been sectioned on day 4 was 62% of that observed in normal rats. 4. The number of medial gastrocnemius motoneurones retrogradely labelled with horseradish peroxidase (HRP) 30-40 days after section of the medial gastrocnemius nerve was 77% of that labelled on the contralateral, intact side. 5. When the medial gastrocnemius nerve had been sectioned on day 4 and prevented from peripheral reinnervation, the number of medial gastrocnemius motoneurones labelled with HRP was, on the average, only 18% of that labelled on the control side. 6. Decreased number of medial gastrocnemius motoneurones labelled with HRP following prevention of peripheral reinnervation was associated with a decrease in the neurone density of the motor cell column, indicating the occurrence of motoneurone death. 7. The majority of medial gastrocnemius motoneurones axotomized 4 days after birth appear to maintain their survival for about 2 weeks without target contact. 8. The area of the compound action potential of medial gastrocnemius motor fibres once decreased after axotomy on day 4 began to recover from the 12th day after the operation if reinnervation by the cut peripheral nerve had been allowed, whereas the compound action potential continued to decrease in those axotomized motoneurones whose reinnervation had been prevented. 9. It is concluded that target dependence of motoneurone survival previously observed at embryonic stages is still present during the early post-natal period.

Action Potentials↗
PubMed1987

Expression of two different tachykinin receptors in Xenopus oocytes by exogenous mRNAs.

Three tachykinins, substance P (SP), neurokinin A (NKA), and neurokinin B (NKB), have been isolated from the mammalian nervous system. In accordance with the presence of multiple tachykinins, the existence of multiple tachykinin receptors has been suggested. These receptors differ in binding specificities for different tachykinins. However, it is not known whether these receptors are indeed made of different molecules or whether the same receptor molecule undergoes posttranslational modification at different destination tissues, thereby altering its binding specificity. We examined whether mRNAs isolated from different tissues may synthesize different types of tachykinin receptors in the same expression system. For this purpose, Xenopus oocytes were injected with poly (A)+ RNAs extracted from rat brain or bovine stomach, and their responses to different tachykinins were examined under voltage-clamp. On the basis of potency ranking of 6 tachykinin agonists, the receptor induced by rat brain mRNA was found to correspond to a tachykinin receptor subtype currently classified as the NK-1 (SP-P) receptor, whereas that synthesized by bovine stomach mRNA corresponded to the NK-2 (NK-A) receptor. Thus, each of the 2 receptors can be induced in the same expression system, depending upon the source of exogenous mRNA injected. Therefore, the difference in the nature of the 2 receptors does not seem to be due to the possible posttranslational modification alone. However, the ionic mechanisms underlying activation of the 2 receptors translated in oocytes were similar. It is likely that activation of the 2 receptors uses the same internal mediator in oocytes.

Animals↗
PubMed1986

Induction of beta-lactamase in Proteus vulgaris.

Various beta-lactam antibiotics, including monocyclic beta-lactams, induced the beta-lactamase of Proteus vulgaris; when clinical isolates were induced by benzylpenicillin, each strain produced a single beta-lactamase but the activity per milligram dry weight differed from strain to strain. The beta-lactamases of the P. vulgaris strains were heterogeneous with respect to their isoelectric points, but had almost the same specific activities, substrate specificities and Michaelis constants. The kinetics of beta-lactamase formation were investigated in three strains, each with a different beta-lactamase activity. Differential rates of enzyme synthesis and peak activity depended on the concentration of inducer. The plots of the reciprocals of the differential rates versus the reciprocals of the inducer concentrations were linear, and the maximum rate of enzyme synthesis and the concentration of the inducer giving half-maximum induction were determined from this double reciprocal plot. The maximum rates of enzyme synthesis were different in the three strains. The kinetic analysis of beta-lactamase formation revealed that the beta-lactamase activities in a single bacterial species were determined by differences in the rate of enzyme synthesis and not by differences in the properties of the enzyme.

Cephalosporins↗
PubMed1986

Effects of calcium and magnesium on transmitter release at Ia synapses of rat spinal motoneurones in vitro.

The lumbar spinal cord excised from neonatal rats was superfused with an oxygenated saline, and monosynaptic excitatory post-synaptic potentials (e.p.s.p.s) were recorded from the lumbar motoneurones following stimulation of muscle nerves of the hind leg. The amplitude of monosynaptic e.p.s.p.s increased with an increase in the external Ca2+ concentration ([Ca2+]o). In [Ca2+]o of 0.5-2 mM, the relation between the e.p.s.p. amplitude and [Ca2+]o was linear with a slope of 1.6 on double logarithmic co-ordinates. An increase in [Mg2+]o in a range of 1-5 mM reduced the e.p.s.p. amplitude without affecting the slope of the relation between log e.p.s.p. amplitude and log [Ca2+]o, suggesting competitive interaction between Ca2+ and Mg2+. When [Ca2+]o was increased to 4-12 mM, the latency of monosynaptic e.p.s.p.s was prolonged, and the antidromic action potential failed to invade the cell body or initial segment of motoneurones. Under these conditions, the monosynaptic e.p.s.p.s were still present. It is concluded that at near-normal levels of [Ca2+]o the effects of Ca2+ and Mg2+ on the e.p.s.p. amplitude are accounted for entirely by their competitive interaction for the probability of transmitter release without altering the mode of impulse propagation at central terminals of the Group Ia sensory fibres. It is suggested that impulses of Ia sensory fibres normally invade their terminals without intermittent blocks at their terminal branch points.

Action Potentials↗
PubMed1986

Generator potentials and spike initiation in auditory fibers of goldfish.

Responses were recorded extra- or intracellularly from single, small afferent fibers of the goldfish saccule, that is, S2 fibers, to clarify how the spontaneous and sound-evoked firings in these fibers are initiated from generator potentials. Spontaneously active units randomly selected from the saccular nerve of five goldfish (total 78 units) were classified by the coefficient of variation (CV) of interspike intervals into irregular (59 units; CV greater than 0.3), intermediate (10 units), and regular types (9 units; CV less than 0.23). The irregular type showed a burst (38 units) or random (21 units) pattern of firing in spontaneous activity. In cases where a clear generator potential could be recorded in response to each sound wave, spontaneous generator potentials could also be observed in the absence of stimulus sound. These spontaneous potentials were irregular in amplitude and time course, and often contained components much slower than the sound-evoked generator potentials. The sound-evoked generator potentials in S2 fibers were produced with a delay of 0.4-0.85 ms following each sound wave, and had a time course comparable to the sound-evoked excitatory postsynaptic potentials (EPSPs) of large S1 fibers. They also shared other properties such as adaptive decline in amplitude, incremental and decremental responses, and off-suppression. The mean amplitude of the sound-evoked generator potentials in S2 fibers was linearly related to the rate of afferent firing. There was no apparent difference in the action potential threshold amplitude for spontaneous and sound-evoked generator potentials. It may be concluded that the generator potentials that underlie the spontaneous and sound-evoked firing of S2 fibers are produced by the release of transmitter by hair cells.

Adaptation, Physiological↗
PubMed1986

Changes in intracranial pressure and arterial blood pressure following electric stimulation to restricted regions in the cat brainstem.

The brainstem of anesthetized cats was electrically stimulated to examine the changes in the intracranial pressure (ICP). There were pressor and depressor sites, which preferentially produced an immediate increase and decrease in ICP in association with the arterial pressor and depressor responses, respectively. A preferential increase in ICP was also observed by stimulation of some depressor sites. The stimulus-induced ICP responses were usually different from the secondary ICP changes due to nonneurogenic alteration of arterial blood pressure (BP) as evoked by arterial bleeding and infusion of saline solution; the stimulus-induced increase in ICP was greatly enhanced when the stimulation to the pressor sites was applied at lowered BP levels and at moderately elevated ICP levels. In addition, when a gradual elevation in ICP was spontaneously observed with the lowering of the BP level, the pressor site-induced increase in ICP exceeded 70-100 mmHg at the peak plateau-like waves, regardless of the magnitude of accompanying arterial pressor response. We propose that the stimulus-induced ICP responses cannot be explained merely by the metabolic changes, the decreased intracranial compliance, and the secondary transmural action on the intracranial space of the arterial pressor and depressor responses. A neurogenic mechanism that directly affects intracranial blood diameter may be involved in the ICP responses, especially those observed at a lower BP level, in addition to extracranic action of sympathetic and parasympathetic nerve activities.

Animals↗
PubMed1986

Effects of nerve growth factor on differentiation of muscle spindles following nerve lesion in neonatal rats.

Central synaptic function of Group Ia sensory fibers has been shown to be enhanced by daily applications of NGF in neonatal rats. In the periphery, Group Ia sensory fibers are known to trigger the differentiation of muscle spindles. In the present study we examined, in neonatal rats, whether daily NGF treatment affects the number or structure of spindles formed in muscle whose nerve has been crushed. The results show that 25-35 d after nerve crush, de novo supernumerary spindles were formed by treatment with NGF in the temporarily denervated muscle. The number of spindles in the corresponding muscle on the contralateral, intact side was not affected by NGF treatment. Following nerve crush alone, the mean number of spindles in the muscle was not significantly different from the normal value. It is suggested that treatment of neonatal rats with NGF may facilitate the outgrowth of excessive peripheral collaterals of regenerating Group Ia sensory fibers, which, in turn, contributes to the formation of de novo spindles as a result of interaction with myotubes.

Animals↗