Biomedical subjects

N Akaike

Publications and source records attributed to N Akaike.

At least 253 records · Page 14Linked to original sources

PubMed1991

Excitatory amino acid response in isolated spiral ganglion cells of guinea pig cochlea.

1. The physiological and pharmacological properties of excitatory amino acid (EAA)-induced responses were investigated in acutely isolated spiral ganglion cells of guinea pig by a conventional patch-clamp technique combined with a rapid drug application (Y-tube) method. 2. L-glutamate (Glu) and its agonists, quisqualate (QA) and kainate (KA), induced inward currents in a concentration-dependent manner at a holding potential (VH) of -70 mV. The values of half-maximal concentration (EC50) were 4.0 x 10(-4) M for Glu, 2.3 x 10(-5) M for QA, and 1.4 x 10(-4) for KA. The Hill coefficients were 0.96, 1.00, and 1.56 for Glu, QA, and KA, respectively. However, one of Glu agonists, N-methyl-D-aspartate (NMDA), and another excitatory amino acid, L-aspartate (Asp), did not induce any responses even in Mg2(+)-free external solution containing 10(-6) M glycine (Gly). 3. The current-voltage (I-V) relationships for the Glu-, QA-, and KA-induced responses were linear, and these reversal potentials were near 5 mV. 4. Kynurenic acid (Kyn), 6,7-dichloro-3-hydroxy-2-quinoxalinecarboxylic acid (diCl-HQC), and quinoxalinediones such as 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 6,7-dinitro-quinoxaline-2,3-dione (DNQX) suppressed the Glu-, QA-, and KA-induced currents in a concentration-dependent manner. The inhibitory potency was in the order of DNQX = CNQX greater than diCl-HQC greater than Kyn. 5. CNQX antagonized the Glu-, QA-, and KA-induced currents without affecting the maximum responses showing no voltage-dependency, indicating the competitive inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗

PubMed1991

Quinolones and fenbufen interact with GABAA receptor in dissociated hippocampal cells of rat.

1. Interaction of quinolone antibiotics and the anti-inflammatory agent fenbufen with the gamma-aminobutyric acid-A (GABAA) receptor-chloride channel complex in pyramidal neurons freshly dissociated from the hippocampal CA1 region of the rats was investigated in whole-cell mode, using the patch-clamp technique under voltage-clamp conditions. 2. Quinolones in clinical doses had no effects on the GABA-gated Cl- current (ICl) but slightly suppressed the response at concentrations greater than 10(-5) M. A metabolite of fenbufen, 4-biphenylacetic acid (BPA), also had little effect on the GABA response at therapeutic concentrations. 3. Coadministration of one of quinolones and BPA suppressed the GABA-gated ICl with increase in each of them in a concentration-dependent manner, and there was a parallel shift of the concentration-response curve for GABA to the right but with no effect on the maximum response, thereby indicating a competitive antagonism. The inhibitory potency of antibiotics in combination with BPA was in the order of norfloxacin much greater than enoxacin greater than cyprofloxacin greater than pipemidic acid much greater than ofloxacin greater than cinoxacin = piromidic acid = nalidixic acid = 0. 4. Norfloxacin and BPA, administered simultaneously, also strongly suppressed pentobarbital sodium (PB)-gated ICl, but they did not act on benzodiazepine (BZP) receptors. 5. Both GABA- and PB-induced ICls reversed at the Cl- equilibrium potential (ECl). In the presence of BPA, the quinolone-induced inhibition of GABA-gated ICls showed no voltage dependence. 6. It was concluded that, in the presence of an anti-inflammatory agent, the quinolone antibiotics decrease the affinity of GABAA receptors, the result being induction of epileptogenic neurotoxicities.

4-Quinolones↗

PubMed1991

Effects of two volatile anesthetics and a volatile convulsant on the excitatory and inhibitory amino acid responses in dissociated CNS neurons of the rat.

1. Effects of two volatile anesthetics [halothane (Hal) and enflurane (Enf)] and a volatile convulsant [hexafluorodiethyl ether (HFE)] on amino acid-induced membrane currents in neurons dissociated from the nucleus tractus solitarius of the rat were examined. The dissociated neurons were voltage clamped in the whole-cell mode of the patch-clamp technique. All drugs were applied with a microperfusion system, termed the "Y-tube" method. 2. The glutamate (Glu)-induced excitatory response was slightly reduced by both the anesthetics. The responses to three agonists at Glu receptor were depressed by Hal (10(-3) M) in the rank order of quisqualate greater than N-methyl-D-aspartate greater than kainate. HFE slightly increased the Glu response at a high concentration of 2 x 10(-3) M. 3. The gamma-aminobutyric acid (GABA)-induced chloride current (ICl) was enhanced by both anesthetics. The dissociation constant (Kd) for the enhancement was 2.3 x 10(-4) M for Hal and 2.1 x 10(-4) M for Enf, and the Hill coefficient was 1.6 for Hal and 1.5 for Enf. HFE depressed the GABA response with a Kd of 8.7 x 10(-5) M and a Hill coefficient of 0.84. 4. Hal (10(-3) M) and Enf (10(-3) M) decreased the Kd of the GABA concentration-response curve from 3.5 x 10(-6) to 10(-6) and 1.9 x 10(-6) M, respectively, without changing the maximum response or the Hill coefficient (1.5). In the presence of HFE (10(-4) M), the Kd was increased to 1.4 x 10(-5) M and the Hill coefficient was slightly changed to 1.2.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗

PubMed1991

T-type calcium channel in mammalian CNS neurones.

1. In all neurones freshly isolated from various brain regions of newborn, adult and aged rats, the T-type Ca2+ currents were elicited by step depolarizations to potentials more positive than -60 mV from a holding potential of -100 mV, and reached a peak in the current-voltage relationship around -30 mV. 2. The activation and inactivation processes were highly potential-dependent, and the latter was fitted by a single exponential function. 3. It was concluded that mammalian brain neurones possess a definite class of T-type Ca2+ channel characterized by both current kinetics and ion selectivity for Ca2+, Ba2+ and Sr2+. However, the pharmacological nature of the T-type Ca2+ channel differed from that in other tissues such as cardiac and smooth muscle cells, peripheral neurones, and cultured cells.

Animals↗

PubMed1991

Calcium antagonist effects on low-threshold (T-type) calcium current in rat isolated hippocampal CA1 pyramidal neurons.

In CA1 pyramidal cells freshly isolated from the rat hippocampus, the low-threshold (T-type) Ca++ current was induced by step depolarization to potentials more positive than about -60 mV from a holding potential of -100 mV, and reached a peak in the current-voltage relationship around -30 mV. The activation and inactivation processes of the current were highly potential-dependent, and the latter was fitted by a single exponential function. Organic and inorganic Ca++ antagonists dose dependently blocked T-type Ca++ channel in the order of flunarizine greater than nicardipine greater than D600 greater than diltiazem and La greater than Zn++ greater than Cd++ greater than Ni++ greater than Co++, respectively. The inhibitory effects of flunarizine, nicardipine and D600 were voltage- and use-dependent. It was concluded that rat hippocampal neurons possessed a definite class of T-type Ca++ channel characterized by the current kinetics and the high sensitivity to organic Ca++ antagonists. The pharmacologic nature differed from that in other tissues such as cardiac and smooth muscle cells, peripheral neurons and cultured cells.

Animals↗

PubMed1990

Triphenyltin: a potent excitatory neurotoxicant. Its reciprocal effects on voltage-dependent Na and K currents of mammalian brain neuron.

Effects of triphenyltin (TPT) on voltage-dependent sodium current (INa) and two respective potassium currents (delayed and transient potassium currents, IKD and IA) were examined on hippocampal neurons acutely isolated from Wistar rats using a conventional suction pipette technique. TPT at concentrations of 10(-7) to 10(-5) M increased the peak amplitude of INa associated with a prolongation of current decay. On the other hand, TPT started to reduce the peak amplitude of IA at 10(-7) M and completely suppressed it at 10(-5) M or less. The peak amplitude of IKD was also reduced by TPT at 10(-6) M or more. Results suggest that TPT possesses an excitatory neurotoxic action and that TPT as a possible environmental hazard may be harmful for human health.

Animals↗

PubMed1990

GABA affects the glutamate receptor-chloride channel complex in mechanically isolated and internally perfused Aplysia neurons.

The effects of gamma-aminobutyric acid (GABA) on the glutamate receptor chloride ion (Cl-) channel complex were examined in mechanically isolated and internally perfused Aplysia neurons using a concentration clamp technique. GABA at concentrations of 3 x 10(-6) M or more, concentration dependently delayed the recovery of the glutamate response from desensitization. This effect was independent of the GABA response and Cl- redistribution. Muscimol (10(-4) M) mimicked the effect of GABA. However, this was not the case for baclofen (10(-3) M). In some isolated neurons, GABA at concentrations of more than 10(-4) M clearly induced an additional Cl- current, the current kinetics of which were different from those induced by lower concentrations of GABA. Even in the continued presence of 10(-4) M GABA, which desensitized the fast GABA response, higher concentrations of GABA (3 x 10(-4) M to 10(-2) M) elicited the additional current in a concentration-dependent manner. The presence of 10(-4) M glutamate completely abolished this current, indicating cross-desensitization between the glutamate and slow GABA responses. High concentrations of GABA (3 x 10(-2) M) did not activate the glutamate receptor coupled to the large cation channel. The results suggest that, in Aplysia neurons, the glutamate receptor-Cl- channel complex has some similarities to the GABA receptor-Cl- channel complex.

Animals↗

PubMed1990

Serotonin suppresses N-methyl-D-aspartate responses in acutely isolated spinal dorsal horn neurons of the rat.

In acutely isolated spinal dorsal horn neurons of the rat, effects of serotonin (5-hydroxytryptamine, 5-HT) on inward current induced by excitatory amino acids were studied under whole-cell voltage-clamp condition. 5-HT suppressed the response to N-methyl-D-aspartate (NMDA), but not the response to kainate or quisqualate. This inhibitory effect of 5-HT on NMDA response was present at 5-HT concentrations as low as 10(-15) M. Although the 5-HT effect exhibited similar pharmacology to the 5-HT1A-type receptors, it was not mimicked by increasing intracellular concentration of adenosine 3',5'-cyclic monophosphate that is the common second messenger for 5-HT1A receptors in the mammalian central nervous system. Glycine strongly antagonized this inhibitory effect of 5-HT, and 5-HT reduced opening of NMDA-gated single channels recorded from the outside-out membrane patch. These lines of evidence are consistent with a possibility that 5-HT might directly modulate the NMDA receptor-ion channel complex, either by interacting with the regulatory site(s) or by acting on a distinct site.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1990

The regional difference of neuronal susceptibility in the dentate gyrus to hypoxia.

The effects of hypoxia on neuronal activity in dentate gyrus granule cells were studied in submerged guinea pig hippocampal slices. In all regions of the dentate gyrus granule, the amplitude of the population spike recorded from the dentate granule cell layers, in response to electrical stimulation of the perforant path, decreased during hypoxia and recovered during reoxygenation. However, the ventral dentate gyrus granule cells (upper blade) were more susceptible to hypoxia than the dorsal ones (lower blade), indicating regional differences of neuronal susceptibility to hypoxia in the dentate gyrus.

Action Potentials↗

PubMed1990

Effects of antagonists on N-methyl-D-aspartate response in acutely isolated nucleus tractus solitarii neurons of the rat.

The effect of antagonists on N-methyl-D-aspartate (NMDA)-induced response was investigated in isolated nucleus tractus solitarii (NTS) neurons freshly isolated from the rat using a conventional pathclamp technique. The NMDA-induced inward current consisted of an initial peak followed by a steady-state component. The competitive antagonists of NMDA receptor, D-2-amino-5-phosphonovalerate (APV), D-2-amino-4-phosphonoheptanoate (APH) and 3-3(2-carboxypiperazine-4-yl)propyl-1-phosphate (CPP), selectively suppressed the initial peak of NMDA-induced current more than the steady-state component at low concentrations. The non-competitive antagonists, MK-801, ketamine, Zn2+ and Mg2+, equally blocked both peak and steady-state components.

2-Amino-5-phosphonovalerate↗

PubMed1990

Inhibition of nicotinic acetylcholine response by atropine in frog isolated sympathetic neurons.

The effect of atropine on nicotinic acetylcholine (ACh) response was studied in frog isolated sympathetic ganglion cells using a 'concentration clamp' technique which combines intra-cellular perfusion with a rapid external solution change within 3 ms. When atropine (more than 6 x 10(-7) M) was simultaneously applied to neurons with ACh (6 x 10(-6) M), the current amplitude was instantaneously reduced in a dose-dependent fashion. Further decreases in the current amplitude were observed in a time-dependent manner during about 20 min after the start of drug-application. Thereafter the current amplitude gradually restored toward the control level in the following 90-120 min in spite of the continuous presence of atropine. However, because d-tubocurarine greatly inhibited the 'restored' current, the last-mentioned is suggested to be also mediated by nicotinic ACh receptor-ionophore complex. Therefore, the inhibitory action of atropine on the peak amplitude of ACh response was examined at 15-20 min after adding the agent. It was dose-dependent but not voltage-dependent. Respective concentrations of atropine and d-tubocurarine causing half the maximum inhibition (IC50) of the peak current evoked by ACh (6 x 10(-6) M) were 1.8 x 10(-5) M and 1.8 x 10(-6) M. Thus, the inhibitory potency was 10 times less than that of d-tubocurarine, an antagonist of nicotinic ACh receptors. The blockade of ACh response by d-tubocurarine was competitive while that by atropine was non-competitive. The current elicited by ACh consisted of two (fast and slow) exponential components plus a steady-state one in the control period.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1990

Effect of temperature on the inhibition of the GABA-gated response by intracellular calcium.

The effects of the voltage-dependent Ca2+ inward current (ICa) on gamma-aminobutyric acid (GABA)-induced Cl- current (ICl) in isolated frog sensory neurons were examined at different temperatures and with different concentrations of external Ca2+ using the 'concentration-clamp' technique. The total amount of inhibition of GABA-induced ICl by a preceding ICa increased in a hyperbolic manner with increasing Ca2+ influx. The time course of recovery of the GABA response after inhibition by Ca2+ influx followed a single exponential and was facilitated by warming but slowed dramatically by a slight cooling from 20 to 15 degrees C in spite of a decrease in Ca2+ influx. It is discussed that the energy-dependent, temperature-sensitive ionic pump and exchange systems at the surface membrane and intracellular organelles regulate the cytoplasmic free Ca2+, thus explaining the quantitative effects of Ca2+ influx and temperature on the inhibition of the GABA-gated Cl- channel.

Animals↗

PubMed1990

Glycine-insensitive desensitization of N-methyl-D-aspartate receptors in acutely isolated mammalian central neurons.

Acutely isolated rat central neurons were recorded by whole-cell voltage-clamp and responses to a class of excitatory amino acid N-methyl-D-aspartate (NMDA) were examined. Rapid application of NMDA evoked inward current consisted of a fast initial peak followed by a sustained component. Glycine potentiated both initial and desensitized states of the NMDA response with identical concentration-dependence. The initial response, but not the sustained component, was abolished when low concentration of NMDA was pre-applied, and glycine could not reverse the desensitization. This evidence suggests that the NMDA receptor desensitization is sensitive to NMDA but not to glycine, and support the hypothesis that glycine initiates the activation of NMDA receptors rather than that glycine prevents desensitization at NMDA receptors in these cells.

Animals↗

PubMed1990

Cerebral ischemia model with conscious mice. Involvement of NMDA receptor activation and derangement of learning and memory ability.

During anesthesia in mice, both common carotid arteries were tied loosely with an overhand knot suture (an occluder), while two snares (releasers) were placed in the knot so that it could be repeatedly tightened to occlude the arteries and loosened again to allow for reperfusion while the mice were conscious and unrestrained. The incidence of mortality as well as impairment of brain metabolism depended upon the length of cerebral ischemia. Cortical electroencephalogram (EEG) clearly reflected the regional ischemia as evidenced by electrical quiescence. Less mortality was observed with ischemic mice treated with dextrorphan (30 mg/kg p.o.). On day 1 (24 hr after ischemia), there were impairments in complex motor coordination, multichoice swim performance, and step-through or thermal pain-motivated avoidance responses. Thereafter, the battery of tests progressively improved. This improvement depended on the period of resumption of cerebral blood flow; the 7-day, postischemic lapse significantly reduced the deficit observed. Reduction in the degree of habituation of exploratory activity was also clearly observed following ischemic insult. Dextrorphan (1-30 mg/kg i.p.) given to ischemic mice was effective in the habituation and step-through-type passive avoidance test paradigms. In conclusion, 1) the decline in cognition as observed with ischemic mice is due to the temporal and reversible derangement of their neuronal networks; 2) excessively released glutamate is probably of major pathogenic importance in the consequences of cerebral ischemia based on the positive results of the N-methyl-D-aspartate receptor antagonist, dextrorphan; 3) the simple technique could be useful in elucidating the pathophysiologic mechanisms of ischemically elicited derangement of the cerebral organization; and 4) the model could be used to assess the efficiency of drugs with high clinical predictivity.

Animals↗

PubMed1990

Hypothalamic warm-sensitive neurons possess a tetrodotoxin-sensitive sodium channel with a high Q10.

We have investigated the ionic current responses to temperature of dissociated cells from the preoptic and anterior hypothalamus (PO/AH) of rat, using the 'whole-cell' configuration. The majority of the recorded neurons showed a linear increase in a non-inactivating inward current during warming (30-40 degrees C), and the Q10 was about 2. However, about 24% of PO/AH neurons were markedly sensitive to warming and the increase in non-inactivating inward current to a rise in temperature in the hyperthermic range (35-40 degrees C) had a high Q10 (4.3-7.0). This increase in current in the hyperthermic range was reversibly blocked by tetrodotoxin (TTX). The inward current in neurons with a Q10 of 2 was not affected by TTX. The results show that some neurons in the PO/AH possess a non-inactivating sodium channel that is highly temperature-sensitive in the hyperthermic range. These neurons are presumably the 'primary' warm-sensitive neurons.

Action Potentials↗

PubMed1990

Excitatory amino acid response in isolated nucleus tractus solitarii neurons of the rat.

The excitatory amino-acid-induced currents in nucleus tractus solitarii neurons freshly isolated from rats were investigated in a whole-cell recording mode using a conventional patch-clamp technique. At a holding potential of -70 mV, L-glutamate (Glu), N-methyl-D-aspartate (NMDA) with 10(-9) M glycine, kainate (KA), quisqualate (QA) and L-aspartate (Asp) evoked inward currents. The currents increased in a sigmoidal fashion with increasing agonists concentration. The half-maximum concentration (EC50) values were 5 x 10(-5) M for Glu, 10(-6) M for QA, 10(-4) M for KA, 6 x 10(-5) M for NMDA and 5 x 10(-5) M for Asp. The Hill coefficients of the Glu-, QA-, KA-, NMDA- and Asp-induced responses were 1.0, 1.3, 1.1, 1.3 and 1.1, respectively. The Glu-, QA-, NMDA- and Asp-induced currents consisted of a transient initial peak and a successive steady-state component showing no desensitization. These currents had the same reversal potential near +5 mV. In the current-voltage (I-V) relationships for the Glu-, NMDA- and Asp-induced currents, slight outward rectifications were observed in Mg2(+)-free external solution at membrane potentials negative to 0 mV. In the presence of extracellular Mg2+, the currents induced by Glu, NMDA and Asp were suppressed at negative membrane potentials, but the suppression was less for the Glu response. The I-V relationships for QA- and KA-induced responses were almost linear at a membrane potential between -90 and +50 mV with or without the presence of Mg2+.

Amino Acids↗

PubMed1990

Nicergoline inhibits T-type Ca2+ channels in rat isolated hippocampal CA1 pyramidal neurones.

1. The effects of nicergoline on the T- and L-type Ca2+ currents in pyramidal cells freshly isolated from rat hippocampal CA1 region were investigated by use of a 'concentration-clamp' technique. The technique combines a suction-pipette technique, which allows intracellular perfusion under a single-electrode voltage-clamp, and rapid exchange of extracellular solution within 2 ms. 2. T-type Ca2+ currents were evoked by step depolarizations from a holding potential of -100 mV to potentials more positive than -70 to -60 mV, and reached a peak at about -30 mV in the current-voltage relationship. Activation and inactivation of T-type Ca2+ currents were highly potential-dependent. 3. Nicergoline and other Ca2+ antagonists dose-dependently blocked the T-type Ca2+ channel with an order of potency nicardipine greater than nicergoline greater than diltiazem. 4. The L-type Ca2+ channel was also blocked in the order nicardipine greater than nicergoline greater than diltiazem, although the T-type Ca2+ channel was more sensitive to nicergoline. 5. The inhibitory effects of nicergoline and nicardipine on the T-type Ca2+ current were voltage-, time-, and use-dependent, and the inhibition increased with a decrease in the external Ca2+ concentration. Diltiazem showed only a use-dependent block.

Animals↗

PubMed1990

Augmentation of GABA-induced current in frog sensory neurons by pentobarbital.

The effect of pentobarbital sodium (PB) on the gamma-aminobutyric acid (GABA)-induced macroscopic and microscopic Cl- currents (ICl and iCl, respectively) was studied in the soma membrane of isolated frog sensory neurons using a rapid concentration-jump and patch-clamp technique. The GABA-induced ICl was composed of a transient peak and a steady plateau. PB shifted the concentration-response curve of the GABA-induced peak ICl to the left without affecting the maximum value. The apparent dissociation constant (KD) decreased from 13 microM at control to 8.0, 4.8, and 2.9 microM by adding 10, 30, and 100 microM PB, respectively. PB also shifted the concentration-response curve for the plateau ICl to the left and augmented the maximum value of the plateau, indicating an increase in the available receptor-channel complex. The Hill coefficient (n = 2) in concentration-response curves of both peak and plateau responses was not changed by adding PB. Both the activation and desensitization phases of GABA-induced ICl consisted of two exponential components. PB significantly increased the time constant of slow desensitization component at all concentrations of GABA used. In the "inside-out" configuration, PB markedly increased the open probability (Po) of a GABA-gated single Cl- channel having a conductance of 14.57 +/- 2.3 pS (n = 123) without affecting the single-channel conductance. The increase of Po was due to the prolongation of mean open time (tau of the tau os) and shortening of mean closed time (tau cf and tau cs), resulting in the increase of channel-opening events.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗