Biomedical subjects

Y Masuda

Publications and source records attributed to Y Masuda.

At least 271 records · Page 15Linked to original sources

PubMed1997

Dual effects of endothelins on the muscarinic K+ current in guinea pig atrial cells.

Effects of endothelins (ETs) on the acetylcholine receptor-operated K+ current (I(KACh)) were examined in isolated guinea pig atrial cells using patch-clamp techniques. ET-1 or ET-3 produced a transient activation of I(KACh) in atrial cells held at -40 mV. When I(KACh) was preactivated by 1 microM carbachol, however, both ETs produced a transient potentiation followed by a sustained inhibition of the current. When I(KACh) was maximally activated by 10 microM carbachol or 100 microM adenosine, these ETs produced only a sustained inhibition of the I(KACh). Their inhibitory effects on the preactivated I(KACh) were concentration dependent, and the half-maximal effective concentrations were 314 pM for ET-1 and 1.13 nM for ET-3. The inhibitory effect of ET-1 was antagonized by BQ-485, a specific ET(A) receptor antagonist, but not by BQ-788, a specific ET(B) receptor antagonist, indicating that the ET-1 effect is mediated by ET(A) receptors. On the other hand, the inhibitory effect of ET-3 was antagonized by BQ-788 and more effectively by BQ-485, suggesting the involvement of "atypical" ET receptors. Both ETs partly reversed the carbachol-induced shortening of the action potential recorded in the current-clamp mode. Inhibitory effects of ET-1 and ET-3 on the preactivated I(KACh) may contribute to the positive inotropic and chronotropic effects of ETs in atrial tissues.

Acetylcholine↗

PubMed1997

Modulation of jaw muscle spindle discharge during mastication in the rabbit.

Discharges of jaw muscle spindles were recorded during chewing carrot from mesencephalic trigeminal nucleus (Mes V) in the awake rabbit to evaluate contribution of the muscle spindles to the development of complete sequences of masticatory movements. The Mes V spindle units were divided into two types according to the maximum firing rates during mastication, with a dividing line at 200 Hz; high-frequency units and low-frequency units. Although both types of units fired maximally during the jaw-opening phase of chewing cycles, their firing rates and pattern varied according to three sequential stages of mastication (stages I, IIa, and IIb). The high-frequency units often increased firing before the start of mastication and built up firing in the first few chewing cycles. Their maximal firing rate was sometimes lower during stage IIa (chewing stage) than during stage I (ingestion stage) and stage IIb (preswallowing stage), although the jaw movements were greater in stage IIa than in other stages. The phase relationship of the firing to a jaw movement cycle in stage IIa was consistent in individual units. The low-frequency units did not build up activity before the onset of movements. They fired mostly during the jaw-opening phase, but the peak of firing did not necessarily coincide with the time of maximal opening. It was concluded that the difference in the firing pattern among masticatory stages may be ascribed to a stage-dependent modulation of both fusimotor activity and jaw movement pattern.

Animals↗

PubMed1997

Regulation of masticatory force during cortically induced rhythmic jaw movements in the anesthetized rabbit.

To examine the relationships between masticatory force, electromyogram (EMG) of masticatory muscles, and jaw movement pattern, we quantitatively evaluated the effects of changing hardness of a chewing substance on these three variables. Cortically induced rhythmic jaw movements of a crescent-shaped pattern were induced by electrical stimulation of the cerebral cortical masticatory area in the anesthetized rabbit. The axially directed masticatory force was recorded with a small force-displacement transducer mounted on the ground surface of the lower molars. EMGs were recorded from the masseter and digastric muscles simultaneously with jaw movements. Five test strips of polyurethane foam of different hardness were prepared and inserted between the upper molar and the transducer during the movements. The peak, impulse, and buildup speed of the masticatory force increased with strip hardness, whereas duration of the exerted force did not vary with strip hardness. The integrated activity and duration of the masseteric EMG bursts also increased with strip hardness. The integrated EMG activity of the digastric bursts was weakly related to strip hardness, whereas the duration was not. The minimum gape increased with strip hardness, but the maximum gape did not. The horizontal excursion of the jaw did not vary in a hardness-dependent manner, although it was greater in the cycles with strip application than in the cycles without strip application. Deprivation of periodontal sensation by cutting the nerves to the teeth reduced the buildup speed of the force, maximum gape, net gape, and horizontal jaw movements. The denervation also elongated the force duration and that of masseteric EMG bursts. However, the rate of the hardness-dependent changes in the above parameters did not alter after denervation. The latency of the masseteric EMG response to strip application was evaluated before and after denervation. In both conditions, it was > or = 6 ms in approximately 70% of the cycles and <6 ms in the remaining approximately 30%, which cannot be explained by a simple reflex mechanism. On the basis of the analysis of correlation coefficients, the masseteric integrated EMG seemed to be a good indicator of the peak and impulse of the masticatory force both before and after denervation. We conclude that periodontal afferents would be responsible for a quick buildup of masticatory force and that afferents other than those from periodontal tissue would contribute to the hardness-dependent change of masticatory force during cortically induced rhythmic jaw movements.

Animals↗

PubMed1997

Role of calcium conductances on spike afterpotentials in rat trigeminal motoneurons.

Intracellular recordings were obtained from rat trigeminal motoneurons in slice preparations to investigate the role of calcium conductances in the depolarizing and hyperpolarizing spike afterpotential (ADP and mAHP, respectively). The mAHP was suppressed by bath application of 1 microM apamin, 2 mM Mn2+, and 2 mM Co2+, and also by intracellular injection of ethylene glycol-bis(b-aminoethylenether)-N,N,N',N'-tetraacetic acid (EGTA), suggesting that the potassium conductance generating the mAHP is activated by Ca2+ influx. Mn2+ (2 mM) or Cd2+ (500 microM) reduced the ADP, whereas the ADP amplitude was increased by raising extracellular Ca2+ concentration from 2 to 8 mM by bath application of Ba2+ (0.5-5 mM) and by intracellular injection of EGTA. This would suggest that Ca2+ itself is likely to be the charge carrier generating the ADP. Focal application of omega-conotoxin GVIA (10-30 microM) suppressed the mAHP and enhanced the ADP, whereas focal application of omega-agatoxin IVA (10-100 microM) reduced the ADP amplitude without apparent effects on the mAHP. We conclude that Ca2+ influx through omega-agatoxin IVA-sensitive calcium channels is at least in part responsible for the generation of the ADP and that Ca2+ influx through omega-conotoxin GVIA-sensitive calcium channels contributes to the generation of the mAHP. Because of the selective suppression of the ADP and mAHP by omega-agatoxin IVA and omega-conotoxin GVIA, respectively, it is suggested that both calcium channels are separated geometrically in rat trigeminal motoneurons.

Animals↗

PubMed1997

Functional properties of neurons in the primate tongue primary motor cortex during swallowing.

Recent studies conducted in our laboratory have suggested that the tongue primary motor cortex (i.e., tongue-MI) plays a critical role in the control of voluntary tongue movements in the primate. However, the possible involvement of tongue-MI in semiautomatic tongue movements, such as those in swallowing, remains unknown. Therefore the present study was undertaken in attempts to address whether tongue-MI plays a role in the semiautomatic tongue movements produced during swallowing. Extracellular single neuron recordings were obtained from tongue-MI, defined by intracortical microstimulation (ICMS), in two awake monkeys as they performed three types of swallowing (swallowing of a juice reward after successful tongue task performance, nontask-related swallowing of a liquid bolus, and nontask-related swallowing of a solid bolus) as well as a trained tongue-protrusion task. Electromyographic activity was recorded simultaneously from various orofacial and laryngeal muscles. In addition, the afferent input to each tongue-MI neuron and ICMS-evoked motor output characteristics at each neuronal recording site were determined. Neurons were considered to show swallow and/or tongue-protrusion task-related activity if a statistically significant difference in firing rate was seen in association with these behaviors compared with that observed during a control pretrial period. Of a total of 80 neurons recorded along 40 microelectrode penetrations in the ICMS-defined tongue-MI, 69% showed significant alterations of activity in relation to the swallowing of a juice reward, whereas 66% exhibited significant modulations of firing in association with performance of the trained tongue-protrusion task. Moreover, 48% showed significant alterations of firing in relation to both swallowing and the tongue-protrusion task. These findings suggest that the region of cortex involved in swallowing includes MI and that tongue-MI may play a role in the regulation of semiautomatic tongue movement, in addition to trained motor behavior. Swallow-related tongue-MI neurons exhibited a variety of swallow-related activity patterns and were distributed throughout the ICMS-defined tongue-MI at sites where ICMS evoked a variety of types of tongue movements. These findings are consistent with the view that multiple efferent zones for the production of tongue movements are activated in swallowing. Many swallow-related tongue-MI neurons had an orofacial mechanoreceptive field, particularly on the tongue dorsum, supporting the view that afferent inputs may be involved in the regulation of the swallowing synergy.

Animals↗

PubMed1997

Setting up and features of a database of images of plastinated materials.

A database of plastinated materials was set up and distributed with a CD-ROM on the Internet. A total of 197 specimens, prepared at the Medical Museum of the University of Tokyo between 1991 and 1995, were catalogued in the database on a personal computer with commercial and original software. The database was originally designed to catalogue anatomical specimens and drawings for curators and researchers, but it also services as a worldwide digital museum.

Anatomy↗

PubMed1997

Immunohistochemical localization of manganese superoxide dismutase in rat vestibular dark cell regions.

A modified immunoglobulin peroxidase bridge sequence method was used to detect the localization of manganese superoxide dismutase (MnSOD), a superoxide radical (O2-) scavenging enzyme locating in mitochondrial matrix, in the vestibular labyrinth of pigmented rats. Strong positive MnSOD immunostaining was demonstrated in the dark cell regions of the ampullae, utricle, and common crus. The result provides for the first time direct evidence demonstrating the existence of mitochondrial O2- scavengers in the vestibular labyrinth and illustrates that the specific sites for vestibular MnSOD immunolocalization are the dark cell regions. This site specificity of MnSOD immunolocalization suggests that dark cell regions may possess high metabolic activity and may encounter constant threat from O2-. We assume MnSOD is needed in protecting some physiologic functions of the dark cell regions. Cell types showing negative MnSOD immunostaining may conceivably be relatively vulnerable to acute O2- damage.

Animals↗

PubMed1997

Clinical effect of low-dose, long-term roxithromycin chemotherapy in patients with chronic sinusitis.

We studied the clinical efficacy of roxithromycin (RXM) administered at the daily dosage of one tablet (150 mg) for 3 months in 30 patients with chronic sinusitis. The effectiveness of this drug was evaluated on a four-point scale. Subjective and objective symptoms disappeared or decreased markedly, especially postnasal drip and nature of discharge in 80 percent or more of the patients. All symptoms significantly decreased (P < 0.001; headache P < 0.05), except for the sensation of foul odor. Symptoms improved even in those cases in which Haemophilus influenzae was detected. It is suggested that RXM produce some clinically beneficial effect through an immunological and or anti-inflammatory mechanisms in addition to its antibiotic effect.

Adolescent↗

PubMed1997

Determination of ventilatory volume in mice by whole body plethysmography.

We examined the reliability of whole-body plethysmography (WBP) for determining the ventilatory volume in mice. The degree of agreement of tidal volume (VT) determined consecutively by WBP with that by direct plethysmography (DP) or pneumotachography (PT) was analyzed using urethane-anesthetized young male 129/Sv mice. Between WBP and DP, the mean difference of VT was 0.000 ml with a 95% confidence interval of -0.003 to 0.002, whereas that between WBP and PT was 0.000 ml (-0.004 to 0.003). The limits of agreement, or mean +/- 2SD of the difference, were -0.008 and 0.008 ml in WBP vs. DP, and -0.011 and 0.010 ml in WBP vs. PT. These values were 5.1-6.6% of the average VT (0.157 ml in WBP and DP, and 0.165 ml in WBP and PT). Thus, VT can be determined by WBP without any bias and with a systemic error of less than 7% of that measured by the other direct methods examined. Through applying WBP to conscious 129/Sv and 129/SvJ-ICR hybrid mice, we further studied the effects of differences in mouse strain, age and sex on respiratory rate (f) and minute volume (V = VT.f), and their reflex changes in responses to systemic hypoxia and hypercapnia. V was significantly greater in young (10-16 weeks old) male 129/Sv than in young male 129/SvJ-ICR hybrids (139 +/- 11 and 73 +/- 8 ml/min/100 g, respectively), while the pattern of reflex responses was similar. In aged (32-44 weeks old) male 129/Sv, the basal level of V and its reflex increases were all diminished as compared to those in their young counter parts. However, we were unable to find significant differences between aged male and female 129/Sv mice. In conclusion, WBP is a useful and reliable method to determine ventilatory parameters in conscious and anesthetized mice. Furthermore, there are considerable strain- and age-related differences in baseline ventilation and reflex responses to hypoxia and hypercapnia.

Age Factors↗

PubMed1997

An in vitro brainstem-heart preparation of the neonatal rat with intact right vagus nerve.

An in vitro brainstem preparation of the neonatal rat with intact right vagal (X) innervation of the right atrium, and intact medullary roots of the left X and glossopharyngeal (IX) nerves for stimulation was developed. The preparation was continuously superfused with artificial CSF at 25 degrees C. The electrical activity of the right atrium was recorded to determine the heart rate. Applications of atropine or propranolol to the superfusate did not alter the heart rate. Electrical stimulation (0.5 ms pulse, 20 Hz) of the left IX and X afferents elicited a reduction in the heart rate from 70.3 +/- 13.2 to 50.6 +/- 13.2 beats/min (mean +/- SD, p < 0.05), which was abolished after division of the right X or application of atropine to the superfusing solution. A similar reflex bradycardia was seen in a preparation with intact left vagal-right atrium innervation during right IX and X afferent stimulation. Cervical spinal cord transection affected neither the baseline heart rate nor the magnitude of the reflex bradycardia. Longitudinal sectioning of the medulla oblongata in the mid-line down to the level of the posterior inferior cerebellar artery abolished the heart rate response. After bilateral cervical vagotomies, electrical stimulation (0.5 ms pulse, 20 Hz, up to 100 microA) of the ventrolateral medulla oblongata, lateral funiculus at C2 or intermediate nucleus of the spinal cord at Th1-4 did not affect the heart rate. These results indicate that the functions in the lower brainstem are preserved in this preparation, at least in regard to the generation of reflex bradycardia. The results also suggest that the laterality of cardiac vagal innervation and sympathetic innervation will develop during the postnatal period. This preparation may be useful for the study of the central neuronal network controlling the heart rate.

Animals↗

PubMed1997

Electron spin resonance spin trapping assay and immunohistochemical localization of superoxide dismutases in the rat nasal mucosa.

The immunohistochemical method and electron spin resonance (ESR) spin trapping assay were employed to detect the localization and biochemical activity of superoxide dismutases (SODs) in the rat nasal mucosa. Manganese SOD and copper-zinc SOD were immunohistochemically illustrated to be richly expressed in the epithelial cells and the subepithelial glands of nasal mucosa. The olfactory vesicles also showed positive immunostaining for manganese SOD and copper-zinc SOD. ESR spin trapping assay revealed that SOD activity in the mucosa of olfactory areas was significantly higher than in the mucosa of respiratory areas; however, the ratio of SOD activity in the mitochondrial fraction to SOD activity in the cytosolic fraction was similar, approximating 17:83 in the mucosa of both the olfactory and respiratory areas. The predominant localization of SODs in epithelial cells of nasal mucosa suggests the importance of mucosal epithelium in protecting nasal mucosa against cytotoxic superoxide (O2-) radicals. Epithelial goblet cells and the connective tissue of lamina propria, which showed no positive immunostaining for SODs, are considered to be vulnerable to oxidative insults implicated in the generation of O2- radicals. The higher SODs activity in the mucosa of olfactory areas implies that there is a different requirement of SOD in mucosa of the respiratory and olfactory areas on scavenging microenvironmental O2- radicals.

Animals↗

PubMed1997

[Changes in the extent of mitral regurgitation during hemodialysis: color Doppler echocardiographic study].

The changes in the extent of mitral regurgitation (MR) during maintenance hemodialysis patients were studied in six patients with MR by color Doppler echocardiography. M-mode, two-dimensional and color Doppler echocardiography were performed before and every hour during hemodialysis. The severity of MR was evaluated by a semiquantitative grading system and maximal MR area. Hemodialysis removed 2.1 +/- 0.9/body fluid. Blood pressure and heart rate did not change systematically by hemodialysis. Left atrial, left ventricular end-diastolic and end-systolic dimensions were significantly decreased by hemodialysis (p < 0.05). Stroke volume and left ventricular wall stress were also significantly decreased (p < 0.01). MR area was significantly smaller at the end of hemodialysis compared to pre-hemodialysis (49.0 +/- 20.5 vs 171.0 +/- 49.2 mm2, p < 0.05). During hemodialysis, the extent of MR was continuously decreased. In two out of six patients, the MR jet disappeared. The extent of MR may depend on the fluid volume removed by hemodialysis because the MR area diminished more as more fluid was removed. No major disorders of the mitral complex were detected when the MR area was decreased rapidly to less than 60 mm2 in response to the removal of a small amount of fluid. The dry weight should be determined as the body weight when MR is as small as possible by color Doppler echocardiography.

Adult↗

PubMed1997

[Is it allowed to have a public open exhibition of human plastinated specimens in Japan?].

This survey was conducted to know what inhibits the public open exhibitions of human anatomical specimens. Questionnaires were handed to 1,035 visitors to the public open exhibition of plastinated specimens at the University of Tokyo between March 30 and April 4, 1995. Five hundred and twenty-two responses were analyzed. The survey revealed following responses of medial and non-medical visitors. 1) Over 90 percent of the visitors welcomed to the public open exhibition of human anatomical specimens. 2) Visitors concerned about the aim of the exhibition and hoped explanations of exhibited specimens. They thought it is necessary to pay attention to the privacy of the cadavers and their families. 3) The most impressive specimens to the visitors were whole body silicone specimens and a series of slices of a whole body for both medical and non-medical visitors. 4) Medical visitors evaluated specimens high for medical education to understand three dimensional structures. On the contrary, non-medical visitors are astonished to encounter the whole body specimens not the dissected ones, and found the identity and human beings in the specimens. 5) Some anatomists strongly stand against the public open exhibitions of anatomical specimens because the plastinated specimens are quite different from ordinary hormaline fixed specimens and they expect that non-medical people must get upset about the specimens.

Anatomy↗

PubMed1997

[Respiratory arrest after a ventriculoscopic surgery in infants: two case reports].

Case-1: A 4 month old, 7120 g, girl with hydrocephalus underwent endoscopic fenestration of the septum pellucidum. Her development had been normal without signs or symptoms of intracranial hypertension. She had no history of convulsion or apnea. Ventriculoscopic diagnosis was complete obstruction of the right foramen of Monro and partial defect of right ependyma. Intraoperative course was uneventful under general anesthesia. She had two episodes of respiratory arrest accompanied with myoclonus and the left conjugate deviation 15 min after extubation. Postoperative CT scan showed no abnormal findings such as intracranial hemorrhage. The respiratory arrest and conjugate deviation disappeared after phenobarbital administration. She had no further respiratory arrest. Case-2: A 1-month old boy with congenital hydrocephalus underwent endoscopic third ventriculostomy. He had no signs or symptoms of intracranial hypertension. CT scan showed enlargement of lateral ventricle and third ventricle due to aqueductal stenosis. Respiratory arrest was noted 10 min after extubation in the recovery room. His anterior fontanel sank abnormally and rigidity of the extremities was observed. His trachea was reintubated and he was transferred to ICU. After 24 h of respiratory care in the ICU he was extubated and discharged to the ward. He had no further episodes of respiratory arrest. We believe that postanesthetic apnea monitoring is mandatory in young infants who undergo ventriculoscopic surgery.

Anesthesia, General↗

PubMed1997