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Biomedical subjects

T Sunada

Publications and source records attributed to T Sunada.

At least 19 recordsLinked to original sources
PubMed1990

Intracellular response properties of neurons in the spinal trigeminal nucleus to peripheral and cortical stimulation in the cat.

The responses of the secondary neurons in the spinal trigeminal nucleus oralis (STNo) were recorded intracellularly to peripheral and cortical stimulation in chloralose-anesthetized cats. Electrical stimulation of the trigeminal sensory nerves (the frontal, infraorbital and inferior alveolar nerves) evoked an EPSP superimposed by one or a few spikes followed by a biphasic IPSP in one group of STNo neurons (Type I), and a prolonged EPSP superimposed by a burst of spikes in the other group of STNo neurons (Type II). Nearly half of Type I neurons were trigeminothalamic neurons projecting to the contralateral ventral posteromedial nucleus, while the remaining Type I and all the Type II neurons were non-projection neurons. A majority of Type I neurons responded with spike potentials to stimulation of only one sensory nerve, while most Type II neurons responded to stimulation of more than one nerve. Stimulation of the contralateral primary somatosensory cortex evoked IPSPs in most Type I projection neurons, and EPSPs in all Type II as well as most Type I non-projection neurons. In Type I neurons touch or pressure applied to a circumscribed area in the facial skin evoked an EPSP superimposed by one or a few spikes followed by a biphasic IPSP, and IPSPs were evoked from a wide surrounding area in the face by the same mechanical stimulation. In Type II neurons innocuous mechanical stimulation within a wide area evoked an EPSP, while IPSPs could not be induced from anywhere. The results indicate that postsynaptic inhibition is involved in the surround inhibition as well as corticofugal descending inhibition of sensory transmission in the trigeminal sensory nucleus.

Action Potentials↗
PubMed1988

Phase-linked modulation of excitability of presynaptic terminals of low-threshold afferent fibers in the inferior alveolar nerve during cortically induced fictive mastication in the guinea pig.

Excitability of presynaptic terminals of low-threshold primary afferent fibers in the inferior alveolar nerve was tested in the trigeminal spinal nucleus of the ketamine-anesthetized, paralyzed guinea pig, by Wall's method. Fictive mastication was induced by repetitive stimulation of the cortical masticatory area, and was monitored by rhythmical burst activity in the jaw-opening anterior digastric motoneuron pool. The excitability was rhythmically modulated in a phase-linked manner during the masticatory cycle: it was decreased coincidentally with the digastric burst activity (jaw-opening phase) and increased during the middle and late periods of the interburst phase (jaw-closing phase) of the masticatory cycle. The results imply that presynaptic modulation of synaptic transmission of peripheral inputs from primary afferents to interneurons in the jaw-opening reflex pathway may contribute to the rhythmical modulation of the jaw-opening reflex evoked by innocuous stimulation of the intraoral structures during mastication; presynaptic inhibition contributing to the depression of the jaw-opening reflex during the jaw-closing phase and presynaptic facilitation to its enhancement during the jaw-opening phase.

Afferent Pathways↗
PubMed1987

Cortically induced masticatory rhythm in masseter motoneurons after blocking inhibition by strychnine and tetanus toxin.

In the first series of experiments, we studied whether or not strychnine (STR)-resistant inhibition of masseter motoneurons (MASS . MNS) was involved in their rhythmical inhibition that occurs during masticatory activity, induced by repetitive stimulation of the cortical masticatory area (CMA) in the cat. After systemic STR injection, repetitive CMA stimulation induced rhythmically alternating activity in the masseteric and anterior digastric nerves with a shorter cycle time than before STR-administration. The short-latency IPSPS in the MASS . MNS evoked by single shocks applied to the CMA were abolished. In contrast, repetitive CMA stimulation still induced a rhythmical alternation of EPSPS and IPSPS in the MASS . MNS, although the IPSPS were significantly reduced in amplitude. In the second series, we attempted to abolish the STR-resistant component of the rhythmical IPSP with tetanus toxin (TT). This was injected into one superficial masseter muscle of the guinea pig. In the majority of animals, repetitive CMA stimulation induced a tonic EMG superimposed by rhythmical bursts in the TT-intoxicated masseter muscle. Repetitive CMA stimulation induced a rhythmical sequence of EPSPS and superimposed spikes in the MASS . MNS innervating the TT-intoxicated masseter muscle in paralyzed guinea pigs. It was concluded that: (1) the cortically-evoked short-latency inhibition of MASS . MNS is STR-sensitive, as is part of the rhythmical inhibition during CMA-induced mastication; and (2) rhythmical inhibition is not essential for the central generation of the rhythmical activity in the MASS . MNS.

Action Potentials↗
PubMed1978

[Analysis of the right ventricular function by simulation (author's transl)].

In the previous experiments it was reported that either the interventricular septum of the free wall of the right ventricle was replaceable with a non-contractile prosthesis. It was also reported that a new chamber constructed on the epicardium had capability of producing a pulsatile pressure. This study was to determine contribution of the septum and the free wall on performance of the right ventricle by using a simulator. Left-ward shift of the interventricular groove was not found along the basal half of the long axis and was limited only along the apical half. Bulging of the septum toward the right ventricular cavity did not occur at all, but on contrary the septum moved toward left, denying contribution of the septal movement to pump action of the right ventricle.

Animals↗
PubMed1977

Myocardial protection during open-heart surgery: intermittent aortic crossclamping versus coronary perfusion.

Twenty-seven patients undergoing open-heart surgery were divided into three groups, i.e., control, intermittent aortic crossclamping and coronary perfusion groups. Myocardial oxygen extraction, lactate extraction, arterial-coronary sinus hydrogen ion difference, potassium difference and glucose difference were determined during the operation, as well as, postoperative stroke and cardiac indices and comparisons were made. When the ascending aorta was not crossclamped, myocardial metabolism was well preserved during and after the perfusion at a flow rate of 2.0 L./min/m2. Intermittent aortic crossclamping for 15 minutes alternating with a period of perfusion for five minutes at 30 degrees C was sufficient to protect the myocardium from ischemia. Perfusion of the left coronary artery alone at a flow rate of six per cent of total body perfusion (150 to 200 ml per minute) at 30 degrees C was sufficient to protect the myocardium when the aorta was opened. Since intermittent perfusion of the left coronary artery may produce myocardial derangement, coronary perfusion should be continuous. Otherwise topical cardiac cooling or other means of myocardial protection should be used.

Adolescent↗
PubMed1977

Mechanodynamics at the interventricular sulcus--reciprocal effect of the ventricles on the ventricular function.

The forces acting on IVS were analyzed to delineate reciprocal effects of the two ventricles on the ventricular fucntion as a whole. The resultant force (FT) was dependent on the LV pressure but independent on the RV pressure. But the composite forces (F1 and F2) of FT were affected by the LV and RV pressures. In a normal heart F1 increased with increasing LV and/or RV pressures. But in F2 increase occurred only with increasing RV pressure. In the LV pressure increase occurred only when the RV pressure was 10 mmHg and decrease did when the RV pressure was 50 mmHg, while stable at 30 mmHg. Directions of both the forces (F1 and F2) diverged as the RV pressure increased and the LV pressure decreased. When FRV was hypertrophic, increases of the magnitudes of the forces were decreased when the pressures of the LV and RV were higher. The angle between the forces was also decreased so that the efficiency of the forces was risen. When a portion of the ventricles lost its contractility, FT increased, particularly, when FLV lost its contractility. But these increases seemed to well be within range of compensation.

Biomechanical Phenomena↗
PubMed1976

Total parenteral nutrition after small intestinal bypass operation in rats.

A jejuno-ileal bypass operation which excluded about 85% of the small intestine was conducted in two groups of rats to evaluate the effects of oral feeding versus total parental nutrition (TPN). One group received food orally while another group received TPN. Two other groups of nutritive control animals underwent laparotomy and suture markings on the intestine. Animals were sacrificed two weeks after the shunt or sham operation. The liver, kidneys, pancreas and spleen were weighed. The wet and dry weights and the villus height of small intestinal segments were also determined. The shunt-operated TPN rats showed a body weight gain of 28% over the initial body weight while the orally fed animals showed an increase of 3.2%. The TPN controls had a negative nitrogen balance only on the day of the sham operation, whereas the TPN shunt-operated animals changed to positive nitrogen balance on the second postoperative day. The wet weights of the liver, kidneys and spleen were significantly higher in TPN animals. The functioning region of the small intestine in the shunt-operated animals was hypertrophic in both the orally fed and the TPN animals, but there were greater quantitative changes in the orally fed animals. The experiments demonstrated the beneficial effect in rats of TPN over oral nutrition for the treatment of surgically induced malabsorption. The studies also showed that the small intestine is capable of developing compensatory mucosal action without intraluminal nutritive content, although the presence of food in the lumen appears to stimulate morphological changes to a greater extent after massive small bowel resection.

Animals↗
PubMed1976

Total correction of Ebstein's anomaly by replacement with a biological aortic valve without plication of the atrialized ventricle.

For the surgical management of Ebstein's anomaly, the preferred operation will be Hardy's procedure, which preserves the patient's valve. However, we have encountered 3 cases of this disease in which the downward displacement of the tricuspid valve was so severe and the functioning right ventricle was so small that Hardy's method could not be adapted without causing tricuspid regurgitation and making the right ventricular chamber more narrow. We treated these patients by replacing the tricuspid valve with an inverted aortic valve with a stent and not plicating the atrialized ventricle. The results have been proved satisfactory through about 7 years' follow-up, suggesting that our technique will be remarkably effective as a radical corrective operation for Ebstein's anomaly with severe intracardiac abnormalities.

Adolescent↗