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K Shibuki

Publications and source records attributed to K Shibuki.

At least 37 records · Page 2Linked to original sources
PubMed1995

A quick test for sound discrimination ability of rats in a single session after preparatory training.

We developed a sound discrimination test combined with a preparatory training procedure. After water deprivation of 48 h, rats were trained to respond to a sound with pedal-pressing to receive a reward of water. Six of the eight trained rats showed pedal-pressing responses to the sound within 4 h of training, and these six were exposed to two different sounds, response to only one of which was rewarded with water. In a single session of 10 h, the rate and latency of pedal-pressing in response to the two sound stimuli were continuously monitored. All six tested rats showed behavioral discrimination between the rewarded and unrewarded sounds within 6 h.

Acoustic Stimulation↗
PubMed1995

Functional brain block preparation of the rat auditory cortex.

To maintain neural functions in brain block preparations of the rat auditory cortex in vitro, a pressurized oxygenated medium was injected into the blocks. Distribution of indigo carmine contained in the injection medium indicated that a columnar region of 1-2 mm in diameter was homogeneously perfused from the white matter to the pial surface. Stimulation of cortical layers just above the white matter produced supragranular field potentials of two negative peaks. They represented antidromic and postsynaptic activities, of which only the latter was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM). The depth profile and temperature-dependency of field potentials in the blocks were very similar to those recorded in usual slice preparations. The responses in blocks were recorded stably for several hours. The functional brain block preparation may be a useful tool for analyses of neocortical neural networks in vitro.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1994

Long-term potentiation in the auditory cortex of adult rats.

Long-term potentiation (LTP) in the auditory cortex was studied in slices obtained from adult rats. White matter stimulation produced field potentials in layers II/III, which were composed of two negative waves followed by a slow positivity. The second negative and third positive waves were blocked by a low Ca2+ (0.48 mM) medium or by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM), while the first negativity unchanged. D-2-amino-5-phosphonovalerate (D-AP5, 50 microM) showed no clear effect on the field potentials. Tetanic stimulation of the white matter produced potentiation in the second negativity, and the potentiation was maintained for at least 30 min. D-AP5 blocked this potentiation completely. These data indicate that LTP is evoked by activation of N-methyl-D-aspartate (NMDA) receptors in the auditory cortex of adult rats.

2-Amino-5-phosphonovalerate↗
PubMed1992

Cerebellar long-term potentiation under suppressed postsynaptic Ca2+ activity.

To study the roles of postsynaptic Ca2+ activity in cerebellar synaptic plasticity, we used a patch-recording technique in Purkinje cell dendrites. While the combination of parallel fibre stimulation and 8-bromo cyclic guanosine monophosphate (Br-cGMP) application produced long-term depression (LTD) of the parallel fibre/Purkinje cell transmission, the same stimuli evoked long-term potentiation (LTP) during postsynaptic injection of Ethyleneglycol-bis-(beta-amino-ethylether)-N, N, N', N'-tetraacetate (EGTA). Furthermore, in the presence of alpha-aminobutyric acid (GABA), parallel fibre stimulation plus Br-cGMP produced LTP of extracellular K+ increases following parallel fibre stimulation. These results suggest that postsynaptic Ca2+ activity in Purkinje cells is negatively correlated to the direction of plastic changes and that the Ca2+ changes and cGMP play distinct roles in cerebellar synaptic plasticity.

Animals↗
PubMed1991

Endogenous nitric oxide release required for long-term synaptic depression in the cerebellum.

Conjunctive stimulation of climbing and parallel fibres in the cerebellum evokes a long-term depression of parallel-fibre Purkinje-cell transmission, a phenomenon implicated as the cellular mechanism for cerebellar motor learning. It is suspected that the increase in cyclic GMP concentration that occurs after activation of climbing fibres is required to evoke long-term depression. Excitatory amino acids are known to cause the release of nitric oxide (NO), resulting in elevation of the cGMP level in the cerebellum. Here we report that endogenous NO is released after stimulation of climbing fibres, that long-term depression evoked by conjunctive stimulation of parallel and climbing fibres is blocked by haemoglobin (which strongly binds NO) or L-NG-monomethyl-arginine (an inhibitor of NO synthase), and that exogenous NO or cGMP can substitute for the stimulation of climbing fibres to cause long-term depression in rat cerebellar slices. These results demonstrate that the release of endogenous NO is essential for the induction of synaptic plasticity in the cerebellum.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1990

Long-term synaptic changes in rat cerebellar slices reflected in extracellular K+ activity.

In rat cerebellar slices, a [K+]o increase evoked locally by molecular layer stimulation was recorded by a K(+)-sensitive microelectrode. This K+ response was reduced clearly during application of low-Ca2+ medium, kynurenate or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Sustained depression of the K+ response by about 20% was observed after simultaneously but not after alternately combined stimulation of the molecular layer and the white matter/granule cell layer. It is concluded from these results that long-term depression of parallel fiber-Purkinje cell transmission can be detected as depression of the K+ response.

Adaptation, Physiological↗
PubMed1990

An electrochemical microprobe for detecting nitric oxide release in brain tissue.

To detect the release of nitric oxide (NO) in brain tissue, an electrochemical microprobe was developed. The output current of the probe correlated linearly with the NO concentration at the tip, and the sensitivity of the probe was between 3.5 and 106 pA per 1 microM change in NO concentration. This probe showed no sensitivity to oxygen or to oxidized derivatives of NO. The NO release from sodium nitroprusside solution was successfully detected by the probe. An NO probe inserted into the molecular layer of a rat cerebellar slice detected a response corresponding to 8-58 nM of NO concentration following electrical stimulation of the white matter. This response was blocked reversibly by tetrodotoxin (1 microM) and was attenuated in the medium containing hemoglobin (1 or 10 microM). The dependence of the response amplitude on the voltage at the cathode in the probe was the same as that of the NO-induced probe current. These results ensure that the NO probes developed in this study effectively detect the endogenous NO release in brain tissue.

Animals↗
PubMed1990

Activation of neurohypophysial vasopressin release by Ca2+ influx and intracellular Ca2+ accumulation in the rat.

1. Isolated rat neurohypophyses were stimulated electrically in an in vitro perifusion system. A Ca2(+)-sensitive microelectrode was placed in the centre of each neurohypophysis and [Ca2+]o decrease evoked by the stimulation were determined. 2. In neurohypophyses injected with Fura-2 AM (acetoxymethyl ester), increases and decreases in fluorescence excited at 340 and 380 nm, respectively, were evoked by stimulation. The time course of the fluorescence changes was similar to that of [Ca2+]o decreases, suggesting that the [Ca2+]o changes mirrored [Ca2+]i increases. 3. Calcium influx into neurosecretory axons and terminals was estimated as the difference in [Ca2+]o decrease rates immediately before and after train pulse stimulation. 4. Vasopressin release from the neurohypophysis, measured by specific radioimmunoassay, was facilitated by stimulation in parallel with a parameter of [Ca2+]o decrease multiplied by Ca2+ influx. 5. The O2 consumption rate, estimated as rate of PO2 decrease in the tissue, was facilitated by stimulation in parallel with [Ca2+]o decreases. 6. Possible calcium-dependent mechanisms of vasopressin release, and the energy-dependent step of the release by Ca2+, are discussed.

Animals↗
PubMed1989

Demonstration of reversible membrane internalization after exocytosis in the rat neurohypophysis.

Isolated rat neurohypophysis was stimulated electrically in media containing fluid phase markers such as carboxyfluorescein and choline. After the markers in the extracellular space were washed out, release of the markers trapped in the tissue was evoked by stimulation. Both the uptake and the release of fluid phase markers were not observed in a Mn2+-containing medium. These results provide direct evidence that internalized vesicles have the function to fuse with plasma membrane in response to Ca2+ entry during electrical stimulation.

Animals↗
PubMed1989

Calcium-dependent and ouabain-resistant oxygen consumption in the rat neurohypophysis.

To analyze rapid changes in energy metabolism in the neurohypophysis, pO2 was measured in the tissue in vitro with a miniature O2 electrode (tip diameter less than 100 microns, 90% response time less than 3 s). Electrical stimulation (20 Hz, 5 s) evoked immediate pO2 decreases by 93.4 +/- 10.5 mm Hg (mean +/- S.E.M., n = 12) which lasted for about 1 min and were blocked by tetrodotoxin (1 microM) or sodium cyanide (1 mM). Replacement of Ca2+ in the perifusing medium with Mn2+ reduced the pO2 decreases to 23.1 +/- 4.9% (n = 5) of the value before the replacement. In normal medium, ouabain application (1 mM, 3 min) suppressed the electrically evoked pO2 decreases only slightly to 82.6 +/- 6.5% (n = 5). In the Mn2+ medium, the same ouabain application suppressed the pO2 changes to 28.8 +/- 1.4%. High K+ (70 mM) evoked pO2 decreases by 175.8 +/- 14.9 mm Hg (n = 5) within 1-2 min. These pO2 changes were reduced to 35.6 +/- 3.8% in an Mn2+ medium. Veratridine (100 microM) evoked pO2 decreases by 204.8 +/- 36.3 mm Hg (n = 5). During the pO2 decreases, the effects of electrical or high K+ stimulation on pO2 were blocked. These results indicate that O2 consumption was evoked by electrical stimulation, and probably that high K+ or veratridine application in the neurohypophysis is mainly dependent on extracellular calcium and resistant to ouabain. The relationship between O2 consumption and exocytotic release is discussed.

Animals↗
PubMed1988

Effects of naloxone and of intraperitoneal hypertonic saline upon oxytocin release and upon supraoptic neuronal activity.

Urethane anaesthetized male rats were given an i.p. injection of hypertonic saline to increase plasma osmotic pressure. This injection resulted in significantly elevated plasma oxytocin levels and increased discharge activity of putative oxytocin cells in the supraoptic nucleus. Subsequent injection of naloxone (1 mg/kg) i.v. resulted in a similarly large increase in plasma oxytocin, but did not affect the discharge activity of putative oxytocin neurones. The results suggest that, following an i.p. injection of hypertonic saline, endogenous opioids act at the neurosecretory terminals to partially inhibit oxytocin release.

Animals↗
PubMed1988

Effects of raised extracellular potassium on the excitability of, and hormone release from, the isolated rat neurohypophysis.

1. Single neurohypophyses from male rats were maintained in an in vitro perifusion chamber. Ion-sensitive microelectrodes were introduced into the tissue to measure changes in [K+]o and [Ca2+]o during electrical stimulation. 2. Electrical stimulation at 6 Hz for 1 min and 30 Hz for 12 s raised [K+]o by 5.4 +/- 0.4 and 13.5 +/- 0.5 mM (mean +/- S.E.M., n = 8) respectively. To investigate the effects of raised [K+]o on the excitability of the neurosecretory terminals, stimulations were repeated in media of altered K+ concentration. The increase in [K+]o evoked by 6 Hz stimulation was elevated in 10 mM-K+ medium (133% of that in 5 mM-K+ medium) and reduced in 0 mM-K+ medium and in 25 mM-K+ medium. Thus it appeared that stimulus-induced changes in [K+]o might enhance the excitability of the tissue during electrical activation. 3. To test this hypothesis, we measured the field potential responses evoked by 0.5 Hz stimulation in media of different K+ concentrations. The size of the field potential was enhanced in 10 mM-K+ medium and depressed in 0 mM-K+ medium and in 25 mM-K+ medium. 4. Electrical stimulation (6 Hz, 1 min) decreased [Ca2+]o by 10.9 +/- 1.8% (n = 6). This decrease was absent in the presence of 1 microM-tetrodotoxin or 1 mM-cadmium. Again, the [Ca2+] response to stimulation was enhanced in 10 mM-K+ medium and depressed in 0 mM-K+ medium or 25 mM-K+ medium. 5. The release of vasopressin and oxytocin evoked by stimulation at 6 or 30 Hz from isolated neurohypophyses was measured by radioimmunoassay in a separate series of experiments. Stimulation at 30 Hz for 1 min released 5- to 6-fold more hormone than stimulation at 6 Hz for 5 min. Release evoked by 6 Hz stimulation was enhanced in 15 mM-K+ medium and depressed in 25 mM-K+ medium. 6. We conclude that the rise in [K+]o that accompanies high-frequency activation of axons and terminals in the neurohypophysis contributes to the facilitation of hormone release with increasing frequencies of stimulation, and in particular to the efficiency of the milk-ejection burst discharge of oxytocin neurones for evoking oxytocin release.

Action Potentials↗
PubMed1988

Spike propagation and conduction failure in the rat neural lobe.

1. Single units were recorded from the rat hypothalamo-neurohypophysial system in vivo to test the hypothesis that action potential conduction failure might contribute to the relative inefficiency of neurohypophysial hormone release at low frequencies of stimulation, and following prolonged stimulation. 2. Recordings were made from the cell bodies of supraoptic neurones which project to the neural lobe of the pituitary. Stimuli applied to the neural lobe evoked antidromic action potentials (in ten of forty cells) at times when the axonal membrane at the site of stimulation should have been refractory following the passage of a spontaneous, orthodromically conducted action potential. This observation suggests that failure of orthodromic action potentials may occur intermittently in the neural lobe. 3. Recordings from single units in the neural lobe showed similar spontaneous patterns of activity to those seen from cell bodies in the supraoptic nucleus. 4. Stimuli applied to the neural stalk evoked orthodromically conducted spikes in these single units: evoked spikes followed stimulation faithfully at 50-80 Hz for 1 s or at 20 Hz for 1 min. Such stimulation was accompanied by a reduction in spike height and a prolongation of latency. 5. Comparable changes were seen in the latency and amplitude of evoked potentials recorded from the neural lobe with low-resistance electrodes. 6. Stalk stimulation at 50 Hz for 1 s was accompanied by a reduction in the threshold for initiation of action potentials, suggesting an increase in the excitability of neural lobe axons. 7. We conclude that, during low-frequency activation, spike failure occurs intermittently in neurohypophysial axons, and that changes in the excitability of the axons during activation at high frequencies may contribute to the facilitation of neurohypophysial hormone release that occurs with increasing frequencies of stimulation.

Action Potentials↗
PubMed1988

Endogenous opioid actions and effects of environmental disturbance on parturition and oxytocin secretion in rats.

Blood samples were taken from conscious, chronically-catheterized rats during parturition for measurement of oxytocin by specific radioimmunoassay. After the birth of the 3rd pup, rats were allowed to remain in their nesting cage (undisturbed rats) or were transferred for 45 min to a glass bowl (disturbed rats); at the time of transfer, rats were given an i.v. injection of the opioid antagonist naloxone or saline vehicle. Subsequent parturition was prolonged in saline-treated disturbed rats, but not in naloxone-treated disturbed rats. Parturition was significantly hastened in naloxone-treated undisturbed rats. Naloxone injections were followed by a large rise in plasma oxytocin concentrations in disturbed and undisturbed rats. We conclude, from a statistical analysis of the relationship within experimental groups between plasma oxytocin concentration and speed of parturition, that the effects of disturbance and of naloxone upon parturition may be accounted for, at least in part, by their effects upon oxytocin release. However, the effects of disturbance on parturition may not be mediated entirely by activation of opioid pathways. Naloxone did not potentiate oxytocin release in non-pregnant rats, or on Day 1 post partum, but did potentiate oxytocin release on Day 22 of pregnancy even in rats before the onset of parturition. Endogenous opioid pathways regulating oxytocin release therefore appear to be active during late pregnancy and during parturition itself.

Animals↗
PubMed1987

Synergistic interactions between footshocks and non-osmotic hypovolemia on vasopressin secretion in rats.

The effects of i.p. injected hypertonic NaCl and polyethylene glycol on the magnitude of increase in plasma vasopressin after footshocks were studied in male rats, to determine whether hypovolemia and body fluid osmolality interact with noxious stimuli on vasopressin secretion. Present data have demonstrated that non-osmotic hypovolemia but not body fluid hyperosmolarity interact significantly and synergistically with footshocks to potentiate vasopressin secretion.

Animals↗
PubMed1987

Extracellular potassium changes in the rat neurohypophysis during activation of the magnocellular neurosecretory system.

1. Potassium-sensitive microelectrodes were used to measure extracellular [K+] in the isolated rat neurohypophysis maintained in vitro. Electrical stimulation of the neurohypophysial stalk (20 Hz 5 s) increased the inferred extracellular [K+] by 9.2 +/- 0.4 mM (mean +/- S.E. of mean; n = 21). 2. Veratridine (10 microM) enhanced the response to stalk stimulation, and at a higher concentration (50 microM) increased extracellular [K+] in the absence of stimulation. By contrast, tetrodotoxin (1 microM) blocked the [K+] increase completely and reversibly in each of five experiments, indicating that the increase was a consequence of action potential generation. 3. At the end of brief periods of stimulation, the raised extracellular [K+] returned to pre-stimulation levels within 30 s. In the presence of ouabain (100 microM), the recovery was slower: the half-decay time was extended by 150-300% in each of three experiments. 4. Replacement of calcium in the medium with cobalt, cadmium or magnesium reduced the amplitude of the [K+] increase by 26-30%, indicating that the [K+] increase was largely independent of events subsequent to evoked release of hormone and/or transmitters. 5. Potassium-sensitive microelectrodes were placed in the neurohypophysis of rats anaesthetized with urethane. Electrical stimulation of the pituitary stalk (50 Hz, 5 s) produced transient voltage increases of 7.6 +/- 0.9 mV (mean +/- S.E. of mean of seven experiments). These voltage increases were similar in magnitude to the response of the electrodes to the addition of 7.6 +/- 1.0 mM-K+ to rat plasma. 6. In seven lactating rats, the suckling of a litter of hungry pups evoked periodic reflex milk ejections, as detected by increases in intramammary pressure. Potassium-sensitive microelectrodes in the neurohypophysis recorded transient voltage increases prior to each milk ejection (0.4-5.5 mV). Each increase preceded an increase in intramammary pressure by 12-30 s. 7. Thus synchronized high-frequency activation of magnocellular neurones can produce large changes in extracellular [K+]. The implications of these findings for stimulus-secretion coupling in the neurohypophysis are discussed in the light of previous reports that hormone release from the neurohypophysis is highly dependent on the frequency and pattern of electrical stimulation.

Animals↗
PubMed1986

Synergistic activation of rat supraoptic neurosecretory neurons by noxious and hypovolemic stimuli.

The effects of saphenous nerve stimulation on discharge activity of supraoptic neurosecretory (NS) cells were studied in anesthetized rats. Of 112 supraoptic neurosecretory cells, 62 exhibited a 'phasic' discharge pattern. The nerve stimulation transiently excited 46 of these 62 'phasic' units, as well as 35 of the 50 remaining 'non-phasic' units. No appreciable blood pressure change was noted using PSTHs with 1-ms resolution. Though the nerve stimulation also evoked a flexor reflex of the ipsilateral hind limb, blockage of the hind limb movement with gallamine did not alter the amplitude of the supraoptic cell excitation. The threshold of the nerve stimulation was higher for the excitation than for the flexor reflex. Effects of hypovolemic and hyperosmotic stimuli on discharge activity of 'phasic' cells during saphenous nerve stimulation were studied to find a possible interaction between these stimuli. Hemorrhage potentiated the transient excitation evoked by the nerve stimulation in all of the 8 'phasic' cells tested, while no such effect was seen after an injection of hypertonic sodium chloride solution in the 7 'phasic' cells tested. These electrophysiological data suggest that hypovolemic and noxious stimuli potentiate VP secretion in a synergistic manner but that hyperosmotic and noxious stimuli do not.

Animals↗