This paper describes the effects of varying the time between excitations on the configuration of the action potential of the rabbit atrium which was not spontaneously active. Whenever the preparation had been kept at rest for a long period, the plateau phase of the first action potential was diminished and a spike-like potential with a long-lasting after-depolarization was obtained. The plateau phase appeared in the action potential elicited by the second shock at the stimulus interval of less than 30 sec. The duration of the plateau phase increased as the interval decreased until it reached about 0.5 sec. Differences in the rate of depolarization between the first and second action potentials thus obtained were very small when the second action potential was elicited beyond the refractory period of the first. By repetitive stimulation at definite intervals, a more prominent plateau phase was developed through a transient period, starting from the first spike-like potential to the final potential with a constant configuration corresponding to the particular stimulus interval. From these results, it is suggested that a prolonged action potential of a periodically excited heart may result from the longlasting small after-depolarization following each preceding action potential. Some possible underlying mechanisms were discussed.

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The effect of d-tubocurarine on the release of ACh from guinea pig phrenic nerve-diaphragm preparations was reinvestigated at high frequency of stimulations (50 cps). Various types of anticholinesterases, including DFP, Mipafox, Echothiophate and neostigmine, were used as cholinesterase inhibitors. The results show that in no case d-tubocurarine appeared to reduce the ACh release. Thus, our result confirms the earlier finding of DALE et al.(1936) but is contradictory to that of BEANI et al.(1964) although essentially similar procedure was followed. In contrast, Hemicholinium-3 reduced the ACh output to less than 20 per cent of control levels. Nerve terminal spikes of rat diaphragm preparations recorded with extracellular microelectrodes were not affected by d-tubocurarine whether with single or repetitive stimulations. The size of successive end-plate potentials evoked by repetitive stimulation at 100 cps in the preparation treated with Hemicholinium-3 declined more rapidly than that of curarized muscle. It is concluded that d-tubocurarine does not influence the presynaptic event of neuromuscular transmission even at high frequency of stimulation and that the Wedensky inhibition in curarized muscles is not due to a pharmacological effect of d-tubocurarine.

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The functional relationship between thyroid hormone and interscapular brown adipose tissue with respect to cold exposure was studied in the mouse.
1. Cold exposure for 5 days produced a significant increase in fat-free dry matter of interscapular brown adipose tissue in the mouse. Concurrent rise in oxygen consumption of this tissue was found, while that of epididymal white fat tissue remained unchanged.
2. Following single injection of thyroxine both fat-free dry matter and Qo₂ increased gradually and showed the peak at 96 hours.
3. The effect of norepinephrine on the oxygen consumption of brown adipose tissue was rather transient. The stimulatory effect of cold exposure and norepinephrine on the oxygen consumption of brown adipose tissue was abolished by methylthiouracil treatment. Administration of thyroxine into the hypothyroid mice restored the response to norepinephrine.
4. The hypothyroid mice showed a significant hypertrophy of brown adipose tissue when the animals were exposed to cold.

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Blood flow through interscapular brown adipose tissue and white epididymal or perirnetrial fat was estimated by the Sapirstein's radioactive isotope indicator method in the rat. Chronic cold exposure at 4-5°C for 2 weeks as well as acute exposure at 3°C for 30min resulted in a marked increase in the blood flow in brown adipose tissue, 14.7-fold and 2.8-fold respectively, while no significant effect was observed in the white adipose tissue.
Intravenous infusion of norepinephrine (2μg/min for 10min) into normal rats produced 6.4-fold increase in the blood flow through brown adipose tissue. Hexamethonium bromide could not prevent the increase of blood flow through brown adipose tissue caused by acute cold exposure. In cold-acclimated rats the infusion of norepinephrine failed to produce further increase in the blood flow of brown adipose tissue.
Thyroidectomy, methylthiouracil treatment and adrenalectomy did not affect the response of blood flow through brown adipose tissue to acute cold exposure nor to norepinephrine infusion. Thyroidectomized and methylthiouraciltreated rats failed to respond to chronic cold exposure in increasing the blood flow through brown adipose tissue.

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1. In anesthetized open-chested dogs, relations of electrically paced heart rate to cardiac output and to other related variables were studied before and after changing one of the following four parameters: cardiac sympathetic activity, cardiac vagal activity, venous return and arterial resistance.
2. When heart rate was elevated from 40 to 60/min in control experiments, cardiac output kept increasing until the rate reached approximately 110/min, remained almost constant between 110 and 200/min, and decreased above 200/min.
3. At every pacing rate a marked augmentation of cardiac output and stroke volume occurred with curtailed ejection time following stimulation of the left stellate ganglion. The faster the rate, the more prominent augmentation was observed. Cardiac output thus maintained the maximum level even at rates beyond 200/min. The marked augmentation of peak flow velocity seemed to be responsible for the increased stroke volume.
4. Vagal stimulation usually caused, exclusively over a high heart rate range (usually beyond 180/min), a slight but definite fall in cardiac output and stroke volume with decreased peak flow velocity and unchanged ejection time. Since the ventricular contractility was found unaffected, the observed fall was ascribed to the inhibitory vagal action on the atrium.
5. An increase in cardiac output and stroke volume was observed at every pacing rate following infusion of dextran saline solution. Ejection time and peak flow velocity were both increased by infusion.
6. Cardiac output and stroke volume were always decreased by compression of the descending aorta. The decrease was marked at high heart rates and associated with diminished peak flow velocity and prolonged ejection time.

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The experiments were performed on the false tendon from the right ven-tricle of a dog heart. The transmembrane potentials from the Purkinje fiberswere recorded through glass micropipettes.
The Purkinje action potentials may appear with a steep slope of the diastolic depolarization (pacemaker fibers) or with a slight diastolic depolarization (non-pacemaker fibers). Under different experimental conditions one type ofaction potential may be transformed into the other.
When the false tendon, with spontaneous activity, was stimulated duringbrief periods with progressively increasing frequencies, its automatism de-creased immediately after the period of stimulation. The magnitude of thereduction in spontaneity varied according to the parameters of the stimuli, but in every case the automatism recovered gradually.
After the period of high frequency stimulation, the corresponding transmembrane potentials of the first and subsequent spontaneous responses, had aslighter slope of their diastolic depolarization as compared to the spontaneouscontrol responses. The amplitude of the action potentials and the restingmembrane potential were also reduced during the recovery of the spontaneity.
After the period of high frequency stimulation, small rhythmic potentialswith slow rate of rise appeared during the abolition of the automatism. Theamplitude of those potentials augmented gradually and when they reached acertain value, an active response occurred.
An increase in the external KCl concentration (3.4 or 4.1mM) produced alarger reduction in the automatism than that obtained under normal KCl con-centration. The opposite effect was observed when the KCl concentration ofthe Tyrode solution was lowered. A decrease in the external NaCl concentra-tion (120.5, 109.6 or 102.7mM) provoked changes in the automatism of the Purkin je fibers similar to those described for the high KCl concentrations.
During spontaneous activity the increase in the external KCl concentrationproduced, concomitantly with the reduction in the frequency of the automatism, a decrease in the rate of diastolic depolarization. Similar effects were ob-served during the diminution in external NaCl concentration.
The reduction in automatism produced by high frequency stimulation isdiscussed in terms of the ionic theory and tentatively explained as due to anincreased efflux of potassium combined with a reduced sodium ions influx.

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1. Effects of static pressure changes on sound reception were studied withneurophysiological techniques in goldfish. Static pressure changes were appliedon the fish's abdomen in order to make the saccular otolith deviate from itsnormal position.
2. Microphonic potentials as recorded with microelectrodes from the saccularmacula were evoked at twice the frequency of the sound. When the pressureon the abdomen was increased, peaks of the microphonic that corresponded tothe compression phase of the sound were augmented and those which corre-sponded to the rarefaction phase were suppressed. The effect of a decreaseof the pressure took place in an opposite direction.
3. Action potentials were recorded intracellularly from single saccular nervefibers. Effects of pressure changes on the activity of these fibers were different depending on the direction of the pressure change and on the response typeof individual nerve fibers.
4. One type of fiber responded with graded depolarization only to an increaseof the pressure but did not respond to its decrease. When sound stimulus wasapplied with pressure changes, response of the fiber to sound stimulus wasfacilitated during a rise of the pressure, but it was suppressed during a pressuredecrease. There were also fibers that responded only to a decrease of thepressure. Behavior of these fibers was just the opposite to that describedabove.
5. The other type of fibers responded to both an increase and a decrease ofthe pressure. They correspond to fibers that set up discharges at a rate twicethe frequency of the sound. In this type of fibers, responses to the compression phase of the sound were facilitated and responses to the rarefactionphase were suppressed during a rise of the pressure. A decrease of the pressure produced an opposite effect.
6. Mechanisms of interaction between pressure changes and sound stimuliwere discussed.

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It has been observed that adrenalectomized rabbit are extremely susceptible to hypercalcemia. Intravenous infusion of CaCl₂ solution induced easilya lethal hypotention accompanied by cyanosis before cardiac disturbancesdue to extreme hypercalcemia ensued. Autopsy showed a pronounced dilatation of pulmonary artery and right heart, suggesting pulmonary arteriolarspasm. Examination of the cerebrospinal fluid in the shocked state revealeda marked elevation of calcium concentration. In intact animals no suchelevation occurred and cardiac death followed in extreme hypercalcemia.Intracisternal injection of small amounts of CaCl₂ solution in intact animalswas found to induce a quite similar type of shock observed in adrenalectomizedanimals in hypercalcemia. Thereby, bilateral cervical vagotomy could preventthe appearance of the shock, indicating that the shock was due to activationof pulmonary vagal vasoconstrictors.
Pretreatment with glucocorticoid which completely reversed the increasedsusceptibility of adrenalectomized rabbits to intravenous infusion of CaCl₂ solution was found also effective in preventing the entrance of calcium ioninto the cerebrospinal fluid. Thus it has been deduced that the hypercalcemicshock in the absence of glucocorticoid might be the result of the enhancedpermeability of the blood-cerebrospinal fluid barrier to calcium ion. Thesignificance of glucocorticoid for the maintenance of blood-cerebrospinal fluidbarrier and the central action of calcium ion in this animal species havebeen discussed.

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1. The excitability changes of pre- and postgeniculate neurons werestudied during reversible retinal inactivation achieved by application of highintraocular pressure (IOP) in the cat with midpontine pretrigeminal transections and in the dark-adapted state.
2. Pregeniculate neurons spontaneously discharged at a relatively highrate (mean, 38.0/sec). The discharge stopped completely upon application ofhigh IOP. The postgeniculate neurons discharged at a low rate (mean, 19.9/sec) compared with pregeniculate neurons. The postgeniculate neurons did notcompletely stop their spontaneous activity on high IOP, but continued firingat a reduced rate.
3. Retinal blockade obtained by application of a high IOP gave rise toan increase in the responsiveness of postgeniculate neurons during the timewhen a decrease in responsiveness of pregeniculate neurons was present.
4. Possible mechanisms responsible for their changes of responsivenessin the pre-and postgeniculate neurons during application of high IOP arediscussed.

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1) Single spike activities of the primary ending of the muscle spindle ofankle flexors and extensors were recorded in the unanesthetized chronic cat, keeping the muscle slightly and constantly stretched, with particular referenceto the natural sleep. Three different kinds of influences attributable to the fusimotor neuron activity were differentiated during the para-sleep: tonicdepression, phasic depression and phasic facilitation.
2) In awake state the muscle spindle activity changed its rate, continuously, being higher or lower. During ortho-sleep the rate was more regular andrelatively lower than in awake state.
3) In the para-sleep state, compared with ortho-sleep, the rate of the spontane-ous activity of muscle spindle afferents became irregular and decreased in 12units out of tested 14 units (tonic depression).
4) In addition to the tonic depression during para-sleep there was transientburst pattern of the firing with or without muscle twitching (phasic facilita-tion) and there was the transient depression without co-contractions (phasicdepression). The latter often associated with the rapid eye movement phase.

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