Biomedical subjects

M Kuno

Publications and source records attributed to M Kuno.

At least 55 records · Page 3Linked to original sources

PubMed1993

[Motoneuronal cell death and neurotrophic factors].

At early developmental stages, the survival of motoneurons is maintained by some as yet unidentified neurotrophic factors derived from their target muscles. As the animal matures, motoneuronal survival becomes less dependent on the innervated muscle. Yet, the dependence of motoneuronal survival on the target muscle does not abolish completely even in adults. In man, more than 50% of the lumbar motoneurons die several years after leg amputation. Thus, in principle, motoneuron disease can result from prolonged impairment of the neurotrophic supply from the target muscle. Several candidates have been proposed for the trophic factor of motoneurons; these include CNTF (ciliary neurotrophic factor), the FGF (fibroblast growth factor) family, the neurotrophin family and CADF (choline acetyltransferase development factor). CNTF is now considered to be a lesion factor rather than a neurotrophic factor. In the FGF family, FGF-5 remains as a possible neurotrophic factor for motoneurons. Three neurotrophins, BDNF (brain-derived neurotrophic factor), neurotrophin 3 (NT-3) and NT-5, may support the survival of both sensory neurons and motoneurons. CADF is a strong candidate, but its primary structure remains unknown.

Animals↗

PubMed1992

Glutamate-induced inhibition of paired pulse facilitation of monosynaptic excitatory post-synaptic potentials in frog spinal motoneurons.

To evaluate actions of glutamate on excitatory synaptic transmission in the central nervous system, we examined glutamate-induced changes in the paired pulse facilitation of monosynaptic excitatory post-synaptic potentials evoked by stimulation of the lateral column fibers (LC-EPSPs) on lumbar motoneurons in the frog spinal cord. Glutamate (1 mM) depolarized motoneurons both in the presence and absence of Mg2+. In most cells perfused with Mg(2+)-free or high Ca(2+)-Mg2+ solutions, the glutamate potential was accompanied by a reduction in peak amplitude of EPSPs, although the degree of change varied with the cells. Glutamate enhanced the EPSP amplitude in a few cells with Mg(2+)-free and high Ca(2+)-Mg2+ solutions, and in most cells with high Mg2+ medium. In 3/5 cells tested, the paired pulse facilitation of EPSPs was reduced by glutamate when the EPSP amplitude either increased or decreased. NMDA (50 microM), kainate (50-100 microM), quisqualate (5-50 microM) and L-2-amino-4-phosphonobutyrate (L-AP4, 1 mM) also decreased the facilitation in about half of the cells tested. The glutamate-induced decrease in the facilitation was observed in both the presence and absence of Mg2+ and was not affected by the concomitant application of glutamate and antagonists for non-NMDA or NMDA receptors, such as 6-cyano-7-nitro-quinoxalinediones (CNQX, 60 microM) or 2-amino-5-phosphonovalerate (APV, 250 microM). Glutamate reduced the facilitation of excitatory post-synaptic currents (EPSCs) recorded at a constant membrane potential under voltage clamp, when the EPSC amplitude either increased or decreased and when the input conductance either increased or decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗

PubMed1992

Degeneration of motor nerve fibers enhances the expression of calcitonin gene-related peptide in rat sensory neurons.

Calcitonin gene-related peptide (CGRP) in skeletal muscle is of neural origin. After degeneration of sensory fibers induced by removal of the lumbar dorsal root ganglia (DRG), the CGRP content in the rat soleus muscle was reduced to about 5% of the normal level. In contrast, degeneration of motor fibers induced by sectioning of the lumbar ventral roots markedly increased the CGRP content in the soleus muscle and CGRP levels in the lumbar DRG. It is suggested that the expression of CGRP in sensory neurons is up-regulated by some humoral factor induced by degeneration of motor nerve fibers.

Animals↗

PubMed1992

Noise of secretagogue-induced inward currents dependent on extracellular calcium in rat mast cells.

We analyzed the noise of the inward currents induced by stimulation of rat peritoneal mast cells with compound 48/80 (48/80), a secretagogue, and examined the role of extracellular Ca2+ in generation of the large noise. In the presence of 2 mM Ca2+ in the external solution, the power density spectra of the 48/80-induced inward currents in most cells were fitted with the sum of two Lorentzian functions. The cut-off frequencies (fc) at -50 mV for the low and high frequency components were 16.3 +/- 7.3 (n = 10) and 180 +/- 95 (n = 9) Hz. Involvement of a cation-selective channel in the large noise was identified in some cells, but the single channel current amplitude estimated from parameters of the noise varied among cells (0.20-2.47 pA at -50 mV), thereby indicating that the currents were mediated by more than two classes of channel. The low frequency component of the 48/80-induced currents was suppressed by lowering the extracellular Ca2+ concentration to 1 microM with the addition of EGTA, without appreciable changes in the high frequency component. When the extracellular Ca2+ was reduced to 1 microM by EGTA 1 min prior to stimulation, 48/80 induced little or no currents in most cells and small currents in some cells. The power density spectra of the small currents were fitted mainly by a single Lorentzian curve with an fc of 150 +/- 5.8 Hz (n = 3). Re-admission of 1.3 mM Ca2+ produced a low frequency part of current noise with an fc of 18.8 (n = 2) Hz.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Calcium-dependent inactivation of inwardly rectifying K+ channel in a tumor mast cell line.

Antigenic stimulation of rat basophilic leukemia (RBL-2H3) cells, a tumor mast cell line, is associated with an increase in intracellular free Ca2+ concentrations ([Ca2+]i) and membrane polarization. We recorded whole cell and single-channel currents through the inwardly rectifying K+ channel, a major resting conductance of cells, using the patch-clamp technique, and we examined interactions between channel activity and [Ca2+]i. With 10 microM Ca2+ in the pipette, the amplitude of whole cell currents gradually declined within 5 min to 48 +/- 13% of that immediately after rupture of the patch membrane, in the presence of 1 mM ATP which minimized intrinsic rundown. In inside-out patches, activity of the channel was reduced by increasing the concentration of Ca2+ in the internal medium, both in the presence and absence of 1 mM ATP, with no apparent change in single-channel conductance. Time-averaged mean current activity in inside-out patches in the presence of 5 microM Ca2+ was less than 50% of that with Ca2+ of 100 nM or less. These results suggest that a rise in [Ca2+]i leads to a closure of the inwardly rectifying K+ channel. In some inside-out patches, inward currents characterized by burst composed of rapid transitions between open and closed states were observed (flickering currents). Single-channel properties of the flickering currents are similar to the inwardly rectifying K+ channel except for kinetics (single-channel conductance of 24.5 +/- 7.9 pS, inward rectification, and permeability to K+).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

[Changes in myocardial blood flow and systemic hemodynamics during hypotensive anesthesia induced by adenosine triphosphate with or without dipyridamole].

The changes in myocardial blood flow and systemic hemodynamics during hypotensive anesthesia with adenosine triphosphate (ATP) or ATP with dipyridamole (0.5 mg.kg-1) were studied in 20 mongrel dogs anesthetized with 0.7% halothane in 100% oxygen. In both groups, mean arterial blood pressure (MAP) was reduced to 60 mmHg by intravenous administration of ATP. During hypotensive anesthesia, coronary blood flow, myocardial blood flow and cardiac index increased significantly in both groups. Lactic acid and uric acid increased significantly during hypotensive anesthesia in the group 1. Heart rate, MAP, systemic vascular resistance and coronary vascular resistance decreased significantly during hypotensive anesthesia in both groups. Mean pulmonary arterial pressure, pulmonary arterial wedge pressure and central venous pressure showed no significant changes in both groups. Base excess in the group 1 increased markedly compared with the group 2. We conclude that pretreatment with dipyridamole can prevent metabolic acidosis that occurs during hypotensive anesthesia induced by ATP.

Adenosine Triphosphate↗

PubMed1992

Cooperative regulation of calcitonin gene-related peptide levels in rat sensory neurons via their central and peripheral processes.

Calcitonin gene-related peptide (CGRP) is present in both motor and sensory neurons and transported in the somatofugal direction. CGRP levels in sensory neurons are assumed to be regulated by NGF supplied from their peripheral targets. In cultured sensory neurons, however, a basal level of CGRP persists even without NGF. This suggests that some additional factors may be involved in regulation of CGRP levels of sensory neurons. The present study shows that chronic section of the sciatic nerve in the rat reduces CGRP levels in the lumbar dorsal root ganglia (DRG), whereas section of dorsal roots increases CGRP levels in the DRG. This increased CGRP level by dorsal rhizotomy was associated with enhancement of the CGRP mRNA expression in the DRG. Thus, CGRP expression in DRG appears to be regulated reciprocally via their central and peripheral processes. When the sciatic nerve had been cut 1 week previously, however, dorsal rhizotomy no longer increased CGRP levels in the lumbar DRG. Therefore, stimulation of CGRP synthesis in the DRG by dorsal rhizotomy may require the integrity of the peripheral processes. When NGF had been infused into the central stump of the cut sciatic nerve, dorsal rhizotomy again increased CGRP levels in the DRG, despite prior section of the peripheral processes. We conclude that CGRP expression in sensory neurons may be regulated by cooperative action of some factors derived via their central processes and NGF supplied from the peripheral targets.

Animals↗

PubMed1991

Mast cell degranulating (MCD) peptide and its optical isomer activate GTP binding protein in rat mast cells.

The MCD peptide in bee venom induces degranulation in mast cells. The internal calcium concentration of mast cells increased and remained high following MCD stimulation. This calcium increase was blocked by pertussis toxin (Ptx) treatment, suggesting that MCD peptide activates Ptx-sensitive G-protein. Even in the absence of external calcium in the incubation medium, the calcium concentration increased by MCD treatment, but soon returned to the original level. D-MCD, the optical isomer of the MCD peptide, also increased the internal calcium concentration through a Ptx-sensitive pathway. We suggest that cationic clusters at one side of the surface are more important in activating the G-protein than the alpha-helix conformation.

Animals↗

PubMed1991

Release of calcitonin gene-related peptide from nerve terminals in rat skeletal muscle.

1. The amount of calcitonin gene-related peptide (CGRP) released from the isolated rat soleus muscle was measured by enzyme immunoassay. 2. When the soleus muscle was exposed to a solution containing high K+ (20-100 mM) in the presence of tetrodotoxin, the amount of CGRP released into the bathing medium increased with an increase in the K+ concentration. 3. The exposure to 100 mM-K+ did not increase CGRP release from chronically denervated soleus muscles or from pieces of the soleus nerve separated from the muscle. 4. The amount of CGRP released from the isolated muscle by 100 mM-K+ depended on the external Ca2+ concentration. The slope of the relation between the amount of CGRP release and the Ca2+ concentration was less than one on double logarithmic co-ordinates. 5. Following chronic section of the lumbar ventral roots, the mean amount of CGRP released from the soleus muscle by 100 mM-K+ was reduced by 28%, compared with that observed in normal muscle. 6. Antidromic stimulation of the lumbar dorsal roots at an intensity three times the threshold for most excitable sensory fibres failed to induce CGRP release from the soleus muscle, whereas stimulation at intensities 50-100 times the threshold increased significantly the amount of CGRP release from the muscle. 7. Stimulation of the muscle nerve at an intensity sufficient to activate the alpha-motor fibres did not release CGRP from the soleus muscle or from the diaphragm. 8. It is concluded that the major source of CGRP released from skeletal muscle is A delta- and/or C sensory terminals and that the Ca2+ dependence of CGRP release is less steep than that reported for acetylcholine release at neuromuscular junctions.

Animals↗

PubMed1991

Membrane currents recorded from sexually dimorphic motoneurones of the bulbocavernosus muscle in neonatal rats.

1. The electrophysiological properties were compared between sexually dimorphic motoneurones in the spinal nucleus of the bulbocavernosus (SNB) and those innervating hindlimb muscles by the whole-cell recording technique in thin slices of the neonatal rat spinal cord. 2. The mean duration of action potentials in SNB motoneurones was significantly longer than that in hindlimb motoneurones. 3. The spike duration of motoneurones was inversely related to the magnitude of transient K+ currents (IA), and in this relation, there was a continuous gradation between SNB and hindlimb motoneurones. 4. The mean duration of spike after-hyperpolarization (AHP) in female SNB motoneurones was significantly longer than that in male SNB motoneurones. 5. In both SNB and hindlimb motoneurones, sustained, Ca(2+)-dependent K+ currents (IAHP) appear to be responsible for the generation of AHP. When IAHP was recorded as a tail current following an identical depolarizing pulse, the magnitude and time course of IAHP were relatively uniform, regardless of the type of motoneurone. 6. In both SNB and hindlimb motoneurones, voltage-gated Ca2+ currents showed an initial transient phase followed by a sustained phase. The mean magnitude of sustained Ca2+ currents was larger in female SNB motoneurones than in male SNB motoneurones, whereas the mean magnitude of transient Ca2+ currents showed no significant different between male and female SNB motoneurones. 7. It is concluded that SNB and hindlimb motoneurones cannot be classified into two distinct neurone types in terms of their electrophysiological properties. 8. It is suggested that the predominant occurrence of natural cell death in female SNB motoneurones during early development may be due in part to high densities of sustained Ca2+ channels in these neurones.

Action Potentials↗

PubMed1991

Target-dependent hormonal control of neuron size in the rat spinal nucleus of the bulbocavernosus.

The spinal nucleus of the bulbocavernosus (SNB) in the rat is a cluster of sexually dimorphic motoneurons that innervate perineal muscles. In adult male rats, the size of SNB neurons is reduced following castration, and this effect is reversed by treatment with testosterone. However, androgen receptors are present in the perineal muscles as well as in SNB neurons. Therefore, it is not clear whether the neuronal size is regulated by direct action of the hormone on SNB neurons or by a target-derived factor that may be controlled via hormonal action on the innervated muscle. To address this question, the peripheral (pudendal) nerve of SNB neurons on one side was cut and united to the grafted soleus muscle, which lacks androgen sensitivity. On the control side, the pudendal nerve was similarly cut but was allowed to reinnervate the perineal muscles. The size of SNB neurons was measured on both sides after a postoperative period of 10 weeks, during which the animal had been castrated or treated with testosterone after castration. The size of SNB neurons that had reinnervated perineal muscles was reduced following castration and enlarged by testosterone treatment. In contrast, the size of SNB neurons that had innervated the soleus muscle remained unaltered in response to testosterone manipulation. It is concluded that hormonal regulation of the size of SNB neurons in adult rats is mediated by their target muscles.

Animals↗

PubMed1990

Target dependence of motoneuronal survival: the current status.

The concept that target-derived molecules are essential for the maintenance of motoneuronal survival has now received considerable support from different sources. One source of information arises from the target-related motoneuron death that occurs naturally at early developmental stages. Another source of information arises from axotomy-induced motoneuron death in adulthood. During development, the survival of motoneurons is initially target-independent. Its target dependence is expressed at a certain embryonic stage and, subsequently, motoneuronal survival becomes less dependent upon the target. It is not known how the state-switch of motoneurons is induced during development. Also, it is not certain whether naturally occurring motoneuron death during development and axotomy-induced motoneuron death in adulthood are based on the same mechanisms. Axotomy induces injury-associated disturbance in the motoneurons, in addition to elimination of the target-derived trophic supply. At present, there is no direct evidence that axotomy-induced motoneuron death in adulthood results solely from the deprivation of trophic factors from the target. The survival of motoneurons in adulthood appears to be maintained by multiple mechanisms. Some of the tropic factors that are involved in the maintenance of neuronal phenotypic expression are distinct from those involved in the maintenance of neuronal survival. There are multiple target-derived trophic factors for a given neuron.

Animals↗

PubMed1990

PT pretreatment inhibits 48/80-induced activation of Ca(+)-permeable channels in rat peritoneal mast cells.

We recently reported that the secretagogue, compound 48/80, activated Ca2(+)-permeable channels of mast cells possibly via a second messenger [Kuno, Okada, and Shibata. Am. J. Physiol. 256 (Cell Physiol. 25): C560-C568, 1989]. The effects of pretreatment with pertussis toxin (PT) on compound 48/80 (48/80)-induced activation of the Ca2(+)-permeable channel have now been investigated by measuring Ca2+ signals of cell suspensions using the Ca2+ indicator fura-2 and by recording Ba2+ currents through the channel using the patch-clamp technique. In the presence of extracellular Ca2+, the fluorescence change was biphasic, with an immediate rise and a delayed peak at room temperature. The delayed peak, mainly due to Ca2+ entry through plasma membranes, was greatly reduced by pretreatment with PT. The quenching of the fluorescence by 48/80-induced Mn2+ influx was also decreased by PT, whereas the Ca2+ transients due to Ca2+ release from the intracellular stores apparently did not change. In patch-clamp recordings from cell-attached patches with pipettes containing isotonic Ba2+, the 48/80-induced Ba2+ currents were either suppressed or delayed in the PT-treated cells, under conditions where degranulation was absent. These results suggest that PT-sensitive GTP-binding protein is involved in activating the Ca2(+)-permeable channel in mast cells during stimulus-secretion coupling.

Animals↗

PubMed1990

Terminal sprouting is not responsible for enhanced transmitter release at disused neuromuscular junctions of the rat.

Chronic block of nerve-muscle activity is known to induce sprouting of motor nerve terminals and to enhance transmitter release at the neuromuscular junction. Increased transmitter release has been assumed to be a physiological correlate of disuse-induced sprouting of nerve terminals. We examined this assumption in the rat extensor digitorum longus muscle following chronic conduction block of the sciatic nerve with TTX. The minimal period of nerve block required for the expression of terminal sprouting was 3 d, whereas transmitter release, measured by the quantal analysis of end-plate potentials, was already enhanced within 24 hr of nerve block. Following 6 d of nerve block, sprouting was observed in about 35% of the motor nerve terminals examined. Under this condition, the total length of individual terminals was significantly greater in the terminals with sprouts than those without sprouts. However, enhancement of transmitter release occurred uniformly at these junctions regardless of the presence or absence of terminal sprouts. Also, transmitter release enhanced by nerve block for 2 d remained elevated for at least 4 d even after resumption of nerve activity without the formation of terminal sprouts. It is concluded that terminal sprouting and increased transmitter release induced in disused neuromuscular junctions are not causally related and that the signals for inducing these 2 events are at least quantitatively different.

Animals↗

PubMed1989

Triggering of T-lymphocytes via either T3-Ti or T11 surface structures opens a voltage-insensitive plasma membrane calcium-permeable channel: requirement for interleukin-2 gene function.

Stimulation of human T-lymphocytes via either the surface T3-Ti antigen-major histocompatibility complex receptor complex or the T11 molecule results in clonal proliferation through a calcium-dependent mechanism. To investigate this signal transduction, plasma membrane calcium-permeable channels were characterized in T-lymphocytes by means of whole cell or single channel patch-clamp recordings. Stimulation of T-lymphocytes via either structure results in opening of an identical set of voltage-insensitive plasma membrane Ca2+-permeable channels through the action of a diffusible second messenger. Previous work with excised inside-out patches suggests that inositol 1,4,5-trisphosphate is the activating second messenger of the voltage-insensitive T-cell Ca2+-permeable channel. Since there is a significant increase in phosphoinositide turnover after stimulation via either the T3-Ti or T11 pathway, it is suggested that triggering of either structure opens a common set of channels through this mechanism. Furthermore, currents flowing through Ca2+-permeable channels are apparently autoregulated, as inward conductance is abolished by elevation of Ca2+ concentration in the bathing solution. In particular, the steady-state rise in interleukin-2 (T-cell growth factor) mRNA is dependent on the rise of [Ca2+]i resulting from ion movement across this channel.

Antigens, Differentiation, T-Lymphocyte↗

PubMed1989

A patch-clamp study: secretagogue-induced currents in rat peritoneal mast cells.

Ca2+ entry through plasma membrane has been considered to play a significant role in elevating cytosolic free Ca2+ concentrations during stimulus-secretion coupling in mast cells, but electrophysiological evidence of the Ca2+ channels is lacking. We examined the properties of secretagogue (compound 48/80)-induced currents in rat peritoneal mast cells, using the patch-clamp technique. In the whole cell recordings, the addition of compound 48/80 induced transient currents that were suppressed by Cd or reduced by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). In Ringer solution containing 2 mM Ca2+, the current-voltage relation was fairly linear from -100 to 50 mV and the reversal potential was 14 +/- 10.1 mV (n = 9). When the external Ca2+ was approximately 1 microM, the compound 48/80-induced currents were marginal, but readmission of Ca2+ or Ba2+ to the bath solution led to an appearance of the currents. In the cell-attached patches, the stimulation enhanced the activity of inward current mediated by Ba2+. The unitary inward Ba2+ current was characterized by the unitary conductance of 10.5 +/- 2.0 pS (n = 10) with isotonic BaCl2 pipette solution, the extrapolated reversal potential of 60.7 +/- 16.0 mV (n = 10) positive to the resting membrane potentials. The percent open time of the inward Ba2+ current channel was not appreciably changed by voltage. In some whole cell recordings, an increase in openings of the cation-selective channel (20-45 pS) was identified in the stimulated cells. When the external Na+ was completely replaced by choline+, the compound 48/80-induced currents had a fairly linear current-voltage relation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Axonal transport and distribution of endogenous calcitonin gene-related peptide in rat peripheral nerve.

Calcitonin gene-related peptide (CGRP) has been found in both sensory and motor neurons. It has been suggested that CGRP is transported from neuron cell bodies to their terminals, where it may act as an anterograde trophic factor. However, it is not known how fast CGRP is transported or whether CGRP found in the innervated target organ indeed originated in neural tissues. We have quantified endogenous CGRP in the rat peripheral nerve by a newly developed enzyme immunoassay. The CGRP immunoreactive material obtained from neural tissues coincided with synthetic rat CGRP in fractional distributions separated by gel filtration. After ligation of the sciatic nerve, tissue CGRP accumulated in the segment central to the ligature. The rate of anterograde transport of CGRP was about 1 mm/hr in both sensory and motor fibers. In the sciatic nerve, only a small fraction of CGRP measured was found to originate from the motor nerve fibers. This may be due in part to the disproportionately large number of sensory fibers in the sciatic nerve and in part to the possible presence of CGRP in sympathetic nerve fibers. The CGRP content in the dorsal root fibers was significantly lower than that in the peripheral processes of the sensory neurons. The CGRP content in the hind leg muscle was much higher than that expected from the amount of CGRP per nerve fiber in the sciatic nerve. Most CGRP in muscle disappeared following denervation. It is concluded that CGRP highly concentrated in nerve terminals is supplied by axonal transport from the neuron cell bodies.

Animals↗

PubMed1989

Disuse-induced enhancement of Ia synaptic transmission in spinal motoneurons of the rat.

Monosynaptic excitatory postsynaptic potentials (EPSPs) evoked in rat spinal motoneurons by stimulation of a muscle nerve are enhanced during the first few days after section of the muscle nerve before subsiding to subnormal levels. We have examined whether this biphasic alteration results from changes of different factors involved in the regulation of central synaptic function. We chronically blocked the conduction of the intact peripheral nerve with tetrodotoxin (TTX). Under this disuse condition, enhancement of monosynaptic EPSPs was fully expressed within 2 d, and synaptic function remained elevated for at least 3 d, even after resumption of the impulse activity following discontinuance of the TTX. The magnitude of synaptic enhancement and the minimal period of nerve block required for synaptic enhancement were both comparable to those observed following nerve section. Thus, the early synaptic enhancement produced by section of the peripheral nerve could be accounted for entirely by the deprivation of sensory impulse activity. However, a prolonged nerve block up to 6 d still maintained synaptic enhancement. This was in contrast with synaptic depression observed after the first 3-4 d following section of the peripheral nerve. The late synaptic depression can thus be attributed to changes in some factors other than sensory impulse activity. Therefore, sensory impulse activity and the peripheral axonal continuity of sensory fibers appear to be 2 distinct factors for the regulation of central synaptic function.

Animals↗