Biomedical subjects

M Sasa

Publications and source records attributed to M Sasa.

At least 55 records · Page 3Linked to original sources

PubMed1998

5-HT1A receptor-mediated inhibition of nucleus accumbens neurons activated by stimulation of parafascicular nucleus of thalamus.

Electrophysiological studies using chloral hydrate-anesthetized rats were performed to elucidate the role of serotonin1A (5-HT1A) receptors in the regulation of neuronal activity of nucleus accumbens (Acc) neurons receiving input from the parafascicular nucleus of the thalamus (Pf). Extracellular neuronal activities were recorded in Acc using a glass microelectrode attached along a seven-barreled micropipette, each barrel of which was filled with dopamine, 5-HT, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT: 5-HT1A agonist) hydrobromide, 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]-piperazine (NAN-190: 5-HT1A antagonist) hydrobromide, glutamate and 2 M NaCl. These drugs were microiontophoretically applied to the immediate vicinity of the target neuron. Spikes elicited by Pf stimulation were inhibited by iontophoretically applied dopamine, 5-HT and 8-OH-DPAT in a dose-dependent manner. In these neurons, firing induced by iontophoretic application of glutamate was also suppressed by dopamine, 5-HT and 8-OH-DPAT. The 5-HT or 8-OH-DPAT-induced inhibitions of the glutamate-induced firing were antagonized by concomitant application of NAN-190. These findings suggest that the dopamine-sensitive Acc neurons receiving input from Pf are inhibited by 5-HT via 5-HT1A receptors located on postsynaptic Acc neurons.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1998

Cytochemical and patch-clamp studies of calcium influx through voltage-dependent Ca2+ channels in vestibular supporting cells of guinea pigs.

To clarify whether or not vestibular supporting cells have voltage-dependent Ca2+ channels, cytochemical and patch-clamp studies were performed using cells isolated from the ampullae of the semicircular canal of the guinea pig. Image analysis used fura-2 as a Ca(2+)-sensitive fluorescence dye and showed that the intracellular Ca2+ concentration ([Ca2+]i) increased with bath application of high (150 mM)K+, but was unaffected by 80 mM K+. The increase in [Ca2+]i induced by high K+ was completely blocked by 1 microM nifedipine as an L-type Ca2+ channel antagonist. In the patch-clamp whole-cell recording of the isolated supporting cells, the voltage-dependent inward current was induced by a depolarizing pulse lasting 2 s in a high (50 mM) Ca2+ and tetraethylammonium-containing external solution replaced by choline chloride and a Cs(+)-containing internal solution. The inward current was obtained when the membrane was depolarized to -50 mV and maximum current was observed at -10 to +10 mV. This inward current was completely blocked by 1 microM nifedipine. These findings strongly suggest that voltage-dependent Ca2+ channels exist in the vestibular supporting cells and regulate Ca2+ concentration in the vestibular endolymph.

Animals↗

PubMed1998

Induction of convulsive seizures by acoustic priming in a new genetically defined model of epilepsy (Noda epileptic rat: NER).

Noda epileptic rat (NER) is a mutant rat, found in a Crj: Wistar colony, which exhibits a tonic clonic convulsion spontaneously about once per 30 h from 14 weeks of age. We performed modified acoustic priming, that is, repeated weekly sound stimulations from 3 weeks of age. In addition, characteristics of audiogenic seizure (AGS), and ictal/interictal electroencephalograms (EEGs) were examined. We also studied the effect of repeated weekly stimulations from 14 weeks of age on AGS susceptibility in another NER. From 9 weeks of age, the NER primed from 3 weeks of age had a high incidence (100%) of AGS: a typical seizure was composed of sudden wild running and/or jumping (WRJ) followed by clonic or tonic-clonic convulsion. The severity and the duration of the AGS were intensified and prolonged with an increase in age, respectively. By contrast, the NER repeatedly stimulated from the age of 14 weeks, rarely showed AGS (20-40(%). The majority of the seizures in this NER were WRJ. The cortical and hippocampal EEG during the tonic convulsion showed a low-voltage spike-wave (5-7 Hz). This evolved into a high-amplitude spike- or polyspike-waves associated with the clonic convulsion. Immediately after cessation of the seizures, the EEG showed a flattening or diffuse slowing. In interictal EEG analysis, sporadic spikes predominantly in the hippocampus and spike-wave bursts in both the cortex and hippocampus occurred from 11 and 20 weeks of age, respectively. These results indicate that AGS susceptibility in NER can be induced consistently by modified acoustic priming and this rat strain is a new genetic model useful for experimental studies of human epilepsy.

Acoustic Stimulation↗

PubMed1998

Enhancement of GABA-mediated inhibition of rat medial vestibular nucleus neurons by the neurosteroid 20-hydroxyecdysone.

In vivo electrophysiological and patch-clamp studies were performed to determine whether 20-hydroxyecdysone (20-HE), a neurosteroid, influenced neuronal activities of the medial vestibular nucleus (MVN) using chloral hydrate-anesthetized rats and dissociated MVN neurons, respectively. Single neuronal activities of MVN were extracellularly recorded with a glass-insulated silver wire microelectrode attached along a seven-barreled micropipette. Each micropipette was filled with 20-HE, glutamate, bicuculline or 2 M NaCl. These chemicals were applied microiontophoretically to the immediate vicinity of the target neurons. Microiontophoretically applied 20-HE (20-80 nA) dose-dependently decreased rotation-induced firings of both type I and II neurons, which were identified according to their responses to horizontal sinusoidal rotations. Microiontophoretically applied bicuculline, a GABAA receptor antagonist, inhibited 20-HE-induced decreases in neuronal firing of MVN. These findings suggest that 20-HE potentiates the action of GABA, probably by acting directly on the GABAA receptor of MVN neurons. In addition, microiontophoretically applied 20-HE decreased firings induced by glutamate in both type I and II neurons. This decrease by 20-HE was also antagonized with bicuculline. Furthermore, the effects of 20-HE on GABA-induced currents in acutely dissociated MVN neurons were investigated using the whole-cell patch-clamp technique. Under voltage-clamp conditions, GABA (10 microM)-induced currents were potentiated in the presence of 20-HE (100 microM). These findings suggest that 20-HE inhibits MVN neurons by acting on the modulatory site on GABA receptor-ion channel complexes to potentiate GABA inhibition.

Animals↗

PubMed1998

NER rat strain: a new type of genetic model in epilepsy research.

PURPOSE: We characterized and evaluated as an animal model of epilepsy NER, a new epileptic rat strain, which was developed by inbreeding rats with spontaneous tonic-clonic seizures in a stock of Crj:Wistar. METHODS: Animals were monitored through the inbreeding course, and video-EEGs were recorded selectively. External seizure-provoking stimuli were applied to NER and to a control parental strain. F1, F2, and backcross progenies were produced between NER and a nonepileptic unrelated strain. Pathologic study included hematoxylin-and-eosin (HE), Klüver-Barrera's, modified Bodian silver, and neo-Timm's staining. RESULTS: After the F9 generation, 94%-98% of NER exhibited spontaneous tonic-clonic convulsions, beginning with neck and forelimb clonus, wild jumping/running, opisthotonic posturing, and evolving to tonic, then clonic convulsion, followed by postictal flaccidity. Most seizure onsets occurred between 2-4 months of age, and the incidence was 0.45 +/- 0.21 seizures in 12 h. Ictal cortical and hippocampal EEGs were characterized by high-voltage spikes followed by diffuse spike-and-wave or polyspike-and-wave complexes. NER revealed seizure susceptibility to pentylenetetrazol, tossing, and transcorneal electroshock, but not to tactile, photic, or acoustic stimuli, or to transauricular electroshock. Mating experiments revealed that 0% (0/46) of the animals in F1, 25.5% (13/51) in F2, and 63.6% (56/88) in backcross progenies exhibited spontaneous tonic-clonic convulsions without sex difference. For all these epileptic traits, no pathologic changes were demonstrated in the CNS. CONCLUSIONS: NER frequently exhibited spontaneous convulsions, controlled by a major autosomal recessive gene for epilepsy, that are comparable to generalized tonic-clonic seizures in humans. This can serve as a new genetic model in epilepsy research.

Animals↗

PubMed1998

Inhibition by gamma-aminobutyric acid system activation of epileptic seizures in spontaneously epileptic rats.

The effects of muscimol, a gamma-aminobutyric acid (GABA)A-receptor agonist, and aminooxy-acetic acid (AOAA), an inhibitor of GABA-converting enzyme, on tonic and absence-like seizures in spontaneously epileptic rats (SER: zi/zi, tm/tm) were investigated to elucidate whether GABAergic function operates normally in these animals. Muscimol at doses of 1 and 3 mg/kg (i.p.) induced high-voltage slow waves in the cortical and hippocampal EEG of SER, although the behavioral observation suggested inhibition of absence-like seizures. Similar high-voltage slow waves were also observed in the cortical and hippocampal EEG of normal rats with muscimol (1 and 3 mg/kg). Tonic convulsions in SER were dose-dependently inhibited by muscimol. AOAA (3 and 10 mg/kg, i.v.) inhibited both tonic and absence-like seizures in SER, although there were no obvious changes in EEG pattern. The inhibitory effects of AOAA on tonic convulsions appeared more slowly and lasted longer than those on absence-like seizures. Cerebral, hippocampal and cerebellar GABA levels were significantly higher in SER than the normal Kyo:Wistar and zitter rat (zi/zi), which were both the parent strains. These findings suggest that GABA receptors and GABAergic neurons are functional in SER and that the GABA system is involved in the inhibition of both seizures.

4-Aminobutyrate Transaminase↗

PubMed1998

Protection against glutamate neurotoxicity in retinal cultures by acidic conditions.

We evaluated the effects of extracellular acidic conditions on glutamate-induced death in cultured retinal neurons. Primary retinal cultures, obtained from 3- to 5-day-old Wistar rats, were estimated to be consisted of mainly amacrine cells (90%) together with a small population of horizontal (8%) and ganglion cells (2%). We examined the effects of acidic pH (pH 6.0 to 7.0) on glutamate neurotoxicity by monitoring the delayed death of retinal neurons induced by brief (10 min) exposure to 1 mM glutamate followed by a 24-hr incubation. The glutamate-induced delayed death of cultured retinal neurons was attenuated with an acidic pH between 6.0 and 7.0. Furthermore, whole-cell patch-clamp recordings were taken from retinal neurons to examine the effects of acidic pH on N-methyl-D-aspartate (NMDA) or kainate receptor-mediated currents. NMDA- and kainate-induced currents were suppressed at pH 6.0 to 7.0 and pH 6.0 to 6.5, respectively. The acidity of the medium protected the retinal neurons from glutamate-induced delayed death, probably by inhibiting NMDA and/or kainate receptor activation.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1998

Effects of talipexole on contraversive rotation and functional impairment in MPTP-induced chronic hemiparkinsonian monkeys.

The effects of talipexole on functional motor improvement in comparison with contraversive circling were studied in five chronic (5-7 years post MPTP-lesioned) hemiparkinsonian Macaca nemestrina monkeys. Talipexole induced contraversive rotations in a dose of 32 microg/kg for about 1 hr after i.m. injection. Larger doses (56 and 100 microg/kg, i.m.) produced less effect due to sedation. Three different rating scales were used to assess functional improvement, including a clinical parkinsonism rating scale, volitional responses to fruit presentations, and number of significant hand movements. The optimal dose of talipexole was 32 microg/kg, i.m. Functional improvement by talipexole, including clinical parkinsonian rating scales and significant hand movements, as well as contraversive circling in hemiparkinsonian monkeys, confirm that this chronic animal model is useful in preclinical testing of drugs for the treatment of human parkinsonism.

Animals↗

PubMed1998

Cold exposure enhances nitroxidergic nerve-mediated vasodilatation in canine nasal mucosa.

We have previously reported that there is non-adrenergic, non-cholinergic (NANC) innervation in canine nasal mucosa and that the relaxation response to electrical stimulation of the NANC nerve is mainly mediated by nitric oxide (NO). In the present study, we examined the effect of cold exposure (24 degrees C) on nitroxidergic nerve-mediated vasodilatation in isolated canine nasal mucosa. Nasal mucosa strips, prepared from canine nasal septum and moderately precontracted with methoxamine in the presence of atropine and guanethidine, relaxed in response to transmural electrical stimulation (square pulses of 0.5-msec duration, at 5 Hz and 25 V). The degree of relaxation at 24 degrees C (55.4+/-13.2% of methoxamine-induced contraction, mean+/-S.D., n=6) was significantly greater than that at 34 degrees C (33.8+/-8.6%, n=6). This phenomenon was reversible. In contrast, the magnitude of relaxation responses to an NO donor (sodium nitroprusside of 0.1 and 1 microM) remained unchanged by cold exposure. These results suggest that the release of NO from the nitroxidergic nerve endings is augmented by cold exposure and, thus, vasodilatation of the nasal blood vessel is enhanced, thereby contributing to the swelling of the nasal mucosa in cold conditions.

Animals↗

PubMed1998

Ethanol reduces spontaneous firing and potentiates GABA-induced currents in acutely dissociated rat medial vestibular nucleus neurons.

Effects of ethanol on acutely dissociated medial vestibular nucleus (MVN) neurons were examined using whole-cell patch clamp technique to elucidate the mechanism underling the inhibitory effects of this drug on the neurons observed in in vivo studies. Dissociated MVN neurons obtained from male Wistar rats were superfused with extracellular solution continuously at a flow rate of 1-3 ml/min. Whole-cell patch clamp recording was performed according to standard procedures. GABA was applied by pressure from a pipette placed near the neuron recorded. Ethanol was applied via pipette by pressure or through bath perfusion. Acutely dissociated MVN neurons regularly showed spontaneous firing. Under current-clamp conditions, bath application of ethanol at 0.1% caused hyperpolarization and reduced spontaneous firing in MVN neurons, while 0.1% ethanol did not affect spontaneous firing. Pulse application of higher concentrations of ethanol (0.1-1%) caused similar hyperpolarization. Under voltage-clamp conditions at a holding potential of -30 mV, GABA induced outward currents in a concentration-dependent manner. GABA-induced currents were potentiated in the presence of 0.01% ethanol. These results indicate that high concentrations of ethanol (0.1-1%) directly induce inhibition of spontaneous firing and low concentrations (0.01%) enhance GABA-induced inhibition in the MVN neurons.

Action Potentials↗

PubMed1998

Effects of pramipexole on contraversive rotation and functional motor impairments in 1-methyl-4-phenyl1,2,3, 6-tetrahydropyridine-induced chronic hemiparkinsonian monkeys.

Rotational and functional motor behavioral changes were studied in five MPTP lesioned chronic hemiparkinsonian Macaca nemestrina monkeys after i.m. pramipexole, a predominant D2 subfamily agonist. Pramipexole induced contraversive rotations in a dose-dependent manner with an optimal dose of 56 microg/kg for approximately 2 to 4 hr after injection. Three different rating scales were used to determine drug-induced functional improvement. They included a monkey parkinsonism rating scale, volitional responses to fruit presentations, and number of hand movements that appeared volitional. A dose of 56 microg/kg of pramipexole produced functional improvements on hand disability, and on a parkinsonian rating scale for monkeys in a dose-dependent manner from 32 to 100 microg/kg. These doses produced an increase in significant hand movements in the affected (contralateral) as well as in the normal (ipsilateral) hand to the side of the brain lesion compared with 5% dextrose in water vehicle control. With a dose of 100 microg/kg, the therapeutic effects of pramipexole on hand movements were less than with 56 microg/kg, due to side effects such as scratching.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1997

Mutations of the p53 gene in human lung cancer from chromate-exposed workers.

We examined p53 mutations in 20 cancer samples from 19 chromate workers with lung cancer by Polymerase chain reaction-Single strand conformation polymorphism analysis and direct sequencing. Six missense mutations were identified in 4 (20%) of the 20 chromate lung cancer samples. Fewer mutations were found in the patients with lung cancers who had been exposed to chromate than in those who had not. However, the pattern of p53 mutations in lung cancer patients exposed to chromate differed from that of common lung cancers in 3 respects. There were no apparent G to T transversions, which are common base changes in lung cancers. Half of the mutational sites (3/ 6) had changes of AT base-pairs, and 2 of 4 mutational tumor samples had double missense mutations. Our results suggested that chromate exposure may induce point mutation of the p53 gene.

Adenocarcinoma↗

PubMed1997

Glutamate as a primary afferent neurotransmitter in the medial vestibular nucleus as detected by in vivo microdialysis.

An in vivo microdialysis study using alpha-chloralose-anesthetized cats was performed to elucidate whether glutamate is actually released from the vestibular nerve terminals in the medial vestibular nucleus (MVN) with electrical stimulation of the vestibular nerve. When repetitive stimuli composed of rectangular pulses (200 micros in duration, 0.5 mA, and 0.1-50 Hz) were applied to the vestibular nerve for 10 min, a significant frequency-dependent increase in the release of glutamate was observed in the MVN. However, the levels of other amino acids such as aspartate, glycine and GABA remained unaltered with the stimuli. These findings indicate that glutamate is the primary afferent neurotransmitter from the vestibular nerve to the MVN neurons.

Animals↗

PubMed1997

Talipexole or pramipexole combinations with chloro-APB (SKF 82958) in MPTP-induced hemiparkinsonian monkeys.

The effects of two predominant dopamine D2-like receptor agonists, talipexole (6-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo [4,5-d]-azepine dihydrochloride, B-HT 920 CL2) and pramipexole (S(-)2-amino-4,5,6,7-tetrahydro-6-propyl-aminobenzothiazole dihydrochloride, SND 919 CL2Y), were studied alone and in combination with the selective dopamine D1-like receptor agonist chloro-APB ((+/-)6-chloro-7-8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-benz azepine hydrobromide, SKF 82958) in five chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesioned hemiparkinsonian Macaca nemestrina monkeys. Talipexole induced contraversive rotation in a dose-dependent manner up to 32 microg/kg, i.m. Talipexole was more potent than pramipexole (10 vs. 32 microg/kg, i.m.), but pramipexole was more efficacious in producing contraversive rotational behavior and significant hand movements in the afflicted limb. Larger doses of chloro-APB also produced contraversive rotation. Combinations of each dopamine D2-like receptor agonist in a median effective dose with chloro-APB (23.4 and 74.8 microg/kg, i.m.) had synergistic effects, producing either addition or potentiation, depending upon the dose used. The effects noted with these combinations were less than the effect of a large dose (100 microg/kg) of pramipexole. Talipexole, in the largest dose studied (100 microg/kg, i.m.), produced sedation which was not seen with the same dose of pramipexole. No significant extrapyramidal side effects were noted with either agent.

Animals↗

PubMed1997

Existence of voltage-dependent Ca2+ channels in vestibular dark cells: cytochemical and whole-cell patch-clamp studies.

To determine whether functional Ca2+ channels are present in vestibular dark cells, changes in intracellular Ca2+ concentration ([Ca2+]i) due to K+ applications were measured using the Ca(2+)-sensitive dye (fura-2) and patchclamp whole-cell recordings were made in dark cells isolated from the ampullae of the semicircular canal of the guinea pig. Exchange of the external solution with a buffer medium containing a high K+ concentration (80 mM K+ or 150 mM K+) caused a concentration-dependent increase in [Ca2+]i in vestibular dark cells. Application of 1 microM nifedipine as a Ca2+ channel antagonist completely blocked the increase in [Ca2+]i. Further treatment with 10 microM BAY K 8644 as a Ca2+ channel agonist caused an increase in [Ca2+]i. In the patch-clamp whole-cell recordings a 1-s depolarizing pulse given into the dark cell in the presence of a high barium concentration (50 mM Ba2+) induced an inward current. In determining the current-voltage relationship, a current was detected at a potential that depolarized at-50 mV and was maximal at +10 mV. This inward current was completely blocked by 1 mM La3+ as a Ca2+ channel antagonist. These findings suggest the presence of voltage-dependent Ca2+ channels in dark cells, which have a presumed function in the regulation of [Ca2+]i in the vestibular endolymph.

Animals↗

PubMed1997

Behavioral LTP during learning in rat hippocampal CA3.

Behavioral long-term potentiation (LTP) of the potentials with the advance of learning were investigated in hippocampal mossy fiber (MF)-CA3 synapses. In both acute and chronic experiments, control and test groups of rats were used. Daily learning tasks in the radial arm maze were given to animals in the test groups. Complete acquisition of learning was observed on day 5. In acute experiments, when MF stimulation-induced population spikes (PS) were examined on day 7 of learning task, relatively higher PS were observed in the test group than those in the control group, and tetanic stimulation (TS)-induced LTP was still observed from the increased PS before TS in the test groups. In chronic experiments, in which the MF stimulation-induced PS were recorded daily after the learning tasks with implanted electrodes, amplitude of PS of the test groups, but not the control, increased concomitantly with the progress in learning. The PS potentiation persisted steadily from day 4 to day 7 of training. The fact that LTP in the MF-CA3 system coincided well with the advance of learning suggests that the MF-CA3 system is involved in the acquisition of learning and/or memory storage.

Anesthesia↗

PubMed1997

Potentiation by ethanol of GABA-induced current and facilitation of its desensitization in cultured rat cortical neurons.

1. Patch-clamp whole cell recording was performed to elucidate whether or not ethanol, at low concentration, has an effect on the GABAA receptor in cultured rat cortical neurons as compared with flunitrazepam. 2. Bath application of ethanol (0.01%) or flunitrazepam (1 mM) potentiated the peak amplitude of GABA-induced (10 microM) current without affecting the equilibrium potential. 3. The decay time constant and time to peak of GABA-induced current were shortened in the presence of ethanol or flunitrazepam. 4. These findings indicate that a low concentration of ethanol and flunitrazepam potentiates the GABA-induced current concomitantly with acceleration of desensitization to the drug.

Animals↗

PubMed1997

Nonadrenergic, noncholinergic inhibitory innervation in the longitudinal muscle of the rabbit portal vein.

1. We examined whether nitric oxide (NO) and ATP take part in inhibitory nonadrenergic, noncholinergic (NANC) neurotransmission in the portal vein of Japanese White rabbits. Longitudinal strips of the vein were suspended in organ baths containing Krebs bicarbonate solution. Preparations relaxed in response to electrical field stimulation (EFS) (25 V, 0.5 msec in duration, 1-50 Hz) and exogenous ATP (1-300 microM) after contraction was induced with 10 microM ergotamine in the presence of 3 microM guanethidine and 0.1 microM atropine. 2. The relaxation response to EFS was abolished by addition of 100 microM NG-nitro-L-arginine, an NO synthase inhibitor. This abolition was partly reversed by 10 mM L-arginine, a substrate for NO synthase. 3. The relaxation response to exogenous ATP was significantly inhibited by 1 mM suramin, a P2X- and P2Y-purinoceptor antagonist, whereas relaxation response to EFS was not inhibited by 1 mM suramin. 4. From the results of this study, we conclude that the inhibitory NANC neurotransmission is mediated by NO alone and does not involve ATP in the portal vein of Japanese White rabbits under our experimental conditions.

Adenosine Triphosphate↗