Microelectrode recordings of neuronal activities in the cat were made in the vestibular main nuclei and the y group cells in response to stimulation of the saccule and IIIrd (oculomotor) nuclei. A relatively new anaesthetic (Ketalar, Parke Davis Co.) that apparently did not suppress transmissions through the sacculo-oculomotor pathways was used. A special accessory arm to replace one side of the standard stereotaxic frame was designed to permit surgical access to the inner ear. Orthodromic focal potentials indicating monosynaptic activation were recorded in the region of the lateral and inferior vestibular nuclei in response to ipsilateral stimulation of saccule. Antidromic field potentials in response to IIIrd nuclear stimulation were also recorded. Similar results were obtained from the y group cells. Unit recordings demonstrated that neurones in the rostral part of the lateral vestibular nucleus received monosynaptic excitation from the saccule before projecting to the IIIrd nuclei. However, studies on the y group cells indicated the existence of a separate and distinct pathway in the sacculo-oculomotor reflex. This pathway involves at least three synapses before reaching the motoneurones.

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Effects of triiodothyronine (T₃)(100μg/100g, sc) on blood-free fatty acid (FFA) and glucose concentrations were investigated in warmand cold-adapted rats. Blood specimens were obtained from the tail locally anesthetized with lidocaine. In warm-adapted rats FFA rose 3 to 6hr after administration of T₃, but returned to the pre-injection level 12hr later. Thereafter, blood FFA level showed a repeated cyclical rise and fall every 12hr for up to 60hr, while blood glucose level did not increase until 12hr later and this level was maintained for up to 36hr. After that time it also showed a repeated rise and fall every 12hr for up to 60hr. Both FFA and glucose levels returned to the initial values after 72hr. Changes induced by T₃ in blood levels of these metabolites were reciprocal. In cold-adapted rats the patterns of responses to T₃ were essentially the same as those observed in warm-adapted ones, except that T₃ provoked a simultaneous rise in blood glucose as well as FFA 6hr after injection, although an extent of FFA increment was less than in warm-adapted rats. Reserpine pre-treatment caused a considerable reduction in the FFA mobilizing action of T₃. The FFA and glucose mobilizing action of T₃ was also observed at dosages of 25 and 6.25μg/100g, although to lesser extent. These results indicated for the first time the cyclical action of T₃ on blood FFA and glucose concentrations, and a changed sensitivity to T₃ in coldadapted animals.

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The slope of the in vivo CO₂ titration curve of blood (pH-[HCO₃^-] p relationship, in vivo slope, unit: slyke) expresses the buffering capacity of blood for CO₂ in vivo or the buffering capacity of extracellular fluid for CO₂. It depends on the extent of contributions by chemical and physiological buffering processes for CO₂ occurring during CO₂ titration. Theoretically, the in vivo slope obtained for mixed venous blood is independent of cardiac output during CO₂ titration. The present study was attempted to confirm this theoretical concept experimentally. Anesthetized dogs were allowed to breathe air and then 10% CO₂-25% O₂ in N₂ for 60min for the titration in vivo. During the CO₂ breathing period the legs were exercised through direct electrical stimulation of the muscles; this also induced an increase in cardiac output 130% above the air breathing period. The in vivo slope (Δ[HCO₃^-] P/ΔpH) of the mixed venous blood at an apparent steady state in the CO₂ breathing period was 16 slyke, which was 5 slyke higher than in other dogs breathing CO₂ at rest with a 60% increase in cardiac output observed in our previous study. This finding was discussed in relation to a greater contribution of tissue fluid for buffering of CO₂. The present study suggests that cardiac output is a significant determinant of the buffering capacity of extracellular fluid.

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In vivo effect of glucagon on blood-free fatty acid (FFA) concentration was investigated in rats adapted to 25°Cand to 5°C. Intraperitoneal injection of glucagon in 100 or 25μg/100g body weight doses was followed by a triphasic response in blood FFA concentration: an immediate and marked rise at 5min, a secondary depression at 60min and a final rise at 120 to 240min after the injection. For the 12.5 and 6.25μg/100g body weight injections, an initial increment was significantly lowered and no elevation at 240min was observed. Concomitant elevations of blood glucose concentration were shown 5min after glucagon injection of 100, 25, 12.5, and 6.25μg/100g body weight doses and their extents were not significantly different each other between these doses. However, rise in blood glucose level at 60min was not seen at the 12.5 and 6.25μg/100g body weight doses. Blood lactate concentrations did not show any significant variations by the injections of glucagon. In fasting rats, glucagon at the 100μg/100g body weight dose caused similar increase in blood FFA as that in fed ones.
In fed cold-adapted rats at 5°C glucagon at the dose of 100μg/100g body weight brought about similar effects in elevation of blood FFA level and its time-course as those in fed rats adapted to 25°C. However, under fasting condition cold-adapted animals exhibited greater increment in blood FFA level at 5min than those adapted to 25°C, while an elevation of blood FFA at 240min was not observed in the former animals.
These results indicate for the first time an in vivo lipolytic action of glucagon in rats and further suggest an enhanced sensitivity to lipolytic action of glucagon in cold adaptation.

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To estimate the “resting potential ” of the sinoatrial node cell, membrane potentials in quiescent states under various conditions were compared with the holding potential at which no net membrane current flowed during the voltage clamp. The membrane potential of the rabbit sinoatrial node cell was recorded using a conventional microelectrode method. The single sucrose gap method and the double microelectrode method were employed for the voltage clamp. The membrane potential immediately before the resumption of the spontaneous activity in normal Tyrode solution after a quiescence in high K⁺ concentration, in low Na⁺ concentration or in low temperature was approximately-37mV and was similar to that of the temporarily quiescent sinoatrial node cells after dissection. The holding potential at which no net membrane current flowed was-38.4mV, which coincided with the membrane potential during, quiescence. The resting potential in quiescence increased by approximately 17mV for a tenfold decrease in the extracellular Na⁺ concentration, and 22mV for a tenfold increase in the K⁺ concentration. The relative membrane conductance decreased transiently on removing Na⁺ from the bathing medium. These findings suggest that a potential equivalent to the resting potential exists in the S-A node cell approximately 20mV positive to the maximum diastolic potential, and this low value might be due to the high Na⁺ conductance of the cell membrane.

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Glass microelectrodes were inserted into motoneurons innervating pectoral fin muscles to record action and synaptic potentials, evoked by electrical stimulation of ventral and dorsal roots, and the medulla oblongata. Ventral root stimulation evoked a small depolarizing response which had properties compatible with those of the EPSP; its amplitude changes were graded, being increased by membrane hyperpolarization and decreased by high frequency repetitive stimulation. The latency of the response was sufficiently longer than that of the antidromic spike to allow for a monosynaptic delay. Stimulation of the dorsal root produced EPSPs with relatively long latencies, suggesting mediation by a polysynaptic pathway. EPSPs with short latencies were evoked by stimulation of the medulla oblongata, indicating the presence of a monosynaptic excitatory connection. Action potentials, recorded from peripheral nerve after stimulation of the medulla oblongata, were facilitated by conditioning volleys via ventral roots. This facilitation was blocked by dihydro-beta-erythroidine hydrobromide and atropine sulphate, indicating the cholinergic nature of the EPSP of ventral root origin. The conduction velocities of motor axons and of the ventral root fibers responsible for production of EPSPs were about the same. The EPSP of ventral root origin had a slower rising time course and lesser sensitivity to shifts of membrane potential than the EPSP of medulla oblongata origin, suggesting that the sites of generation of the former EPSP were on the peripheral dendrites. From the above results, it was concluded that the EPSP of ventral root origin was mediated by recurrent axon collaterals of motoneurons.

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The responses of smooth muscle cell membrane of the guinea-pig stomach to field stimulation were investigated. In response to a single field stimulation (0.1-0.2msec), the longitudinal and circular muscles excised from the antrum of the stomach produced a small hyperpolarization which was blocked by treatment with tetrodotoxin. Repetitive stimulation at various frequencies lowered the amplitude of the slow potential change thus causing suppression of the spike generation and mechanical response. Phentolamine did not suppress the generation of the inhibitory junction potential produced by a single stimulation but did slightly suppress the hyperpolarization produced by repetitive stimulation. Tetrodotoxin suppressed the amplitude but not the frequency of the slow potential change, however repetitive field stimulation in the presence of tetrodotoxin did not reduce further the amplitude of the slow potential changes. After a single or repetitive field stimulation was applied, the muscle membrane produced a delayed excitation on the slow potential change. The delayed excitation, however, did not generate in the presence of tetrodotoxin or of atropine. Reversal potential level for the inhibitory junction potential was ranged between-80 and-85mV. Externally applied noradrenaline and ATP suppressed the generation of slow potential changes. Noradrenaline slightly hyperpolarized the membrane and increased the ionic conductance of the membrane but ATP neither modified the membrane potential nor increased the ionic conductance of the membrane.

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Effects of prostaglandin E₂(PGE₂) and oxytocin on the membrane activity of pregnant mouse myometrium were investigated with the microelectrode method. Sensitivity of the myometrium to oxytocin increased only during the last stage of gestation, however sensitivity to PGE₂ gradually increased beginning at the middle stage of gestation. Prolonged treatment with PGE₂ but not with oxytocin produced desensitization of the myometrium. When the membrane potential was electrically displaced to the resting level after the membrane had been markedly depolarized by either PGE₂ or oxytocin, spike activity was restored. However with PGE₂ there was continuous spike generation and with oxytocin periodic burst discharges with silent periods. In Ca-free Locke solution, PGE
2 and oxytocin still produced depolarization of the membrane, however, oxytocin produced larger depolarization. The different responses of the membrane to PGE₂ and oxytocin are discussed in relation to the roles of Ca ion and to the ovarian and placental hormones during gestation.

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Effects of prostaglindin E₁ (PGE₁) on the myometrial activity of the pregnant rat were investigated by recording the contractile response and intracellular electrical activity. PGE₁ (10^-9-10^-6g/ml) caused a depression of the contractile activity in the fresh preparations of either longitudinal or circular muscle strip (within 2-5hr after exposure to the artificial saline media). However neither membrane potential nor action potential was significantly affected by the treatment with the agents. By contrast, in the aged preparations (bathed in the saline media longer than 2-5hr), an increase in the contractile response dose-dependently was caused. The generation of action potential was facilitated without depolarization of the membrane. The inhibitory response induced by PGE₁ in the fresh preparation was converted to an excitatory response when treated with bretylium. The discussion covers the inhibitory effect of PGE₁ which is mediated through intrauterine adrenergic system, and is perhaps due to the focal hyperpolarization block of the conduction of excitation. The excitatory effect is very likely caused by a direct action on myometrial cell membrane.

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An isolated preparation formed exclusively of the specific conducting tissue of the A. V. node, bundle of His and bundle branches was dissected from the dog heart and studied using the microelectrode technique. The preparation, being completely isolated from the normal neighboring conducting tissues, can be turned over or twisted, so as to stimulate and record either separately or simultaneously the electrical activity of the dorsal and ventral surfaces of the bundle of His. The preparation showed spontaneous activity and maintained its physiological properties for long periods of time.
Morphological and electrophysiological evidence was found to differentiate two functional strands within the common trunk of the bundle of His. These two strands appear in different planes: The anterior or ventral strand starts in the superior part of the atrioventricular node and continues to form the right bundle branch; the posterior or dorsal strand begins in the inferior part of the A. V. node and runs underneath the ventral strand to form later the left bundle branch.
The two strands can be separated from each other, so as to have two functional preparations: one formed of the superior part of the A. V. node, the anterior strand and the right bundle branch; the other constituted by the inferior part of the A. V. node, the posterior strand and the left bundle branch.
Some of the electrophysiological properties of both strands are similar, except for the conduction velocity, which appears to be faster in the posterior strand than in the anterior. Transversal propagation occurs between the two strands and is slower than the longitudinal propagation that takes place along the parallel fibers of each strand.
The presence of cellular transversal bridges between the strands assures the activation of the two strands as if they were a single conducting cable. These characteristics are discussed in relation to some disturbances in propagation.

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Introduction: The effects of hypertonic urea solution on the excitation-contraction coupling of the bullfrog's heart muscle were investigated. Materials and Methods: Small strips obtained from the ventricular wall of Rana catesbiana were used. Contractile tension as well as transmembrane action potential were recorded in the single sucrosegapped arrangement. The muscle weight was measured in order to check the changes in the dimension of muscle fiber both during isotonic and hypertonic perfusions. Light microscopic study was also performed to compare the effect of hyperosmolar urea with that of sucrose. Results and Conclusions: 3.0 T-urea solution exerted a triphasic change in twitch tension during hypertonic perfusion and a biphasic change during the recovery perfusion. An initial rapid decline was restored to the original level within 10min and after an overshoot a secondary gradual decrease was observed during hypertonic perfusion. In spite of parallel change in the action potential duration with the time to peak tension there was an increase in dp/dt during the restoration phenomenon. The calcium sensitivity was altered in the 3.0 T-urea solution and thus in Ca-free solution the rate constant of the slow component of twitch decline was decreased. The muscle weight remained decreased during the whole period of hypertonic perfusion. Histological study revealed that the fiber bundles soaked in hypertonic urea solution show normal appearance whereas those in sucrose exhibit a marked shrinkage. These results show that urea can penetrate the heart muscle membrane easily and that urea has some augmenting action on the E-C coupling process.

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