Shin-ichiro Katsuda

Overall open-loop gain of rapidly acting arterial pressure control system in rabbits.

We estimated the overall open-loop gain of the rapidly acting arterial pressure control system without surgically or pharmacologically opening the reflex loop in rabbits. Animals anesthetized by intravenous injection of Nembutal (27.5 mg·kg−1 body weight) and heparinized were bled by 2 ml·kg−1 body weight within 1–2 s through a catheter inserted into the aortic arch. Arterial pressure change after the quick mild hemorrhage was monitored via a catheter placed in the right subclavian artery for more than 2 min. The overall open-loop gain of the lumped arterial pressure control system determined from the mean arterial pressure response to the hemorrhage was 7.3. It was almost constant over the range between 12.9 and 22.2 kPa systemic pressure.

Comparative responsiveness of the rapidly acting arterial pressure control system to quick mild hemorrhage and infusion in conscious rabbits

The responsiveness of the rapidly acting arterial pressure control system to hemorrhage and infusion was investigated. Two catheters, one for pressure measurement and the other for inducing hemorrhage and infusion, were chronically implanted in 19 rabbits. A few days after the operation, each animal was quickly bled and transfused (2 ml/kg body weight) at intervals of 5 min while it was conscious. The hemorrhage-infusion experiment was repeated 16 times in each animal. The 16 strings of data were pooled for each animal. The overall open-loop gains (G) of the rapidly acting arterial pressure control system were estimated from the individually pooled responses to hemorrhage and infusion. There was no significant difference between the G-values, i.e., 7.2±1.2 by hemorrhage and 7.1±1.2 by infusion (mean ±SD), as evaluated by the paired t-test (p>0.5). Thus, the responsiveness of the rapidly acting arterial pressure control system to quick mild hemorrhage and to infusion appears to be similar.

Studies on the off-response of the rod photoreceptors in the isolated frog retina

Transretinal potential changes induced by a 30 sec exposure to 503 nm light were studied in the dark-adapted frog isolated retina. The retina was treated with aspartate and 0.5 mM Ba2+ to suppress the PII and slow PIII components of the electroretinogram, and therefore the response to the light stimulus consisted of the on-response (fast PIII response) and the off-response. The amplitude of the off-response was proportional to that of the on-response when the stimulus intensity was weak. The amplitude ratio of the off-response to the on-response was unaffected by partial bleachings of rhodopsin. In the presence of 700 nm background illumination, the amplitude of the on-response was decreased, whereas that of the off-response was increased. The amplitude of the off-response increased to about four-fold that of the original response at 3 hr after turning on the background illumination, but the effects of 480 nm background light were less remarkable. Both the on- and off-response, however, had a peak spectral sensitivity at about 500 nm, regardless of the presence of background light. From these findings, it was suggested that the red rods contribute to the development of the off-response, but the cones would also contribute through small focal gap junctions between the cones and the red rods.

Functional disorders in the peripheral neuromuscular system induced by gonyautoxins in rabbits.

The effects of gonyautoxins (GTXs) on the neuromuscular system in rabbits were examined. M waves were evoked by electric stimulation on the tibial nerve and recorded mainly from the plantar interosseous muscle. Intravenous administration of GTXs decreased the amplitude and prolonged both latency and duration of M waves, while showed little effect on the motor nerve conduction velocity. These results suggest that GTXs have inhibitory effects on the peripheral neuromuscular system, mainly on the neuromuscular transmission.

Arrhythmic and hypotensive actions of gonyautoxins in rabbits.

The effects of gonyautoxins (GTXs), the major component of paralytic shellfish poison in Japan, on cardiovascular system in rabbits were examined by means of the electrocardiogram (ECG) pattern and the arterial pressure changes. The intravenous administration of GTXs produced transient arrhythmia and hypotension. GTXs induced prolongation of P-R and QRS intervals in the ECG, which was prone to initiate paroxysmal ventricular tachycardia, fibrillation and flutter in a large amount of GTXs. Similar results were observed in vagotomized rabbits.