1) A neural structure, stimulation of which evoked a postsynaptic potential in the apical dendrite of CA₁ or CA₂ was found within the rabbits hippocampus. The slow potential inhibited the spike of the apical dendrite. 2) It was found that the fornix contained at least two pathways to the hippocampus, one exciting and the other inhibiting the activity of the apical dendrite. The former was considered as the antidromic pathway, generating spike in the apical dendrite by way of the Schaffer collaterals. The latter was regarded as the same as that found by GREEN et al. in 1956. But as for its function, quite contrary to GREEN et al. it was found that impulses running this pathway inhibited the spike of the apical dendrite by generating a slow positive potential. 3) The inhibitory pathway was considered entering directly into the Ammon's horn, without changing synapses at the granule cells.

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1. The transmembrane action potentials driven by extracellular electrical stimulations were recorded with flexibly mounted microelectrode in the isolated uterine muscle of the mouse at latter half period of pregnancy.
2. Single action potential was usually produced by an electrical shock, but a series of discharges on some occasions. Magnitude of action potential was 38.2±0.38mV on an average, while that of resting potential was 51.3±0.35mV at this stage of pregnancy.
3. Duration of the action potential at 10% level of spike height was 69±0.40 msec. on an average but varied markedly in individual cases, mostly because of variable magnitude of the after-potential and of the peculiar slow potential superposed on the rising or falling phase of the spike.
4. With gradual increase in the intensity of extracellular stimulation, a peculiar slow potential first made its appearance and then a spike when the slow potential exceeded a critical depolarization. It was also at the threshold stimulus that two or three slow potentials were frequently produced.
5. Further increase in the intensity, however, usually caused a shortening of latency of both slow and spike potentials and finally set up a simple typical action potential.
6. When too strong stimulus was applied to a portion near the recordingelectrode, the action potential appeared mostly flattened and markedly deformed showing double peaks in some instances.
7. The refractory period was about 0.1sec. for producing an effective second response and 0.2sec. for producing the second full spike.
8. The conduction velocity of excitation was 10.2±0.41cm per second in the same muscle bundle, but much slower and variable between different muscle bundles.
9. Discussions were made on the nature of the peculiar slow potential.

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1. The effects of the mechanical stimulations on the nerve trunk were exarnined by recording propagated action currents from a single nerve fiber.
2. In the case of single brief mechanical shocks, the nerve fiber responded to them in the ratio of 1:1. A single strong shock produced invariably, repetitive excitation.
3. The response time of the mechanical stimulation was found to lie between those of short electrical pulse and of rheobasic stimulating current.
4. The effect of mechanical pressure on the nerve fiber was identified with the action of catelectrotonus. The pressure on the nerve fiber produced an increase in excitability, and the increased excitability in the portion stimulated with a brief mechanical subthreshold shock lasted about 15msec.

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Using the mechanoelectric transducer, the relaxation of the oyster heart muscle after the stimulation of anodal current pulse has been studied. The inhibition of spontaneous rhythmic contraction is greatly influenced by the phase of the cardiac cycle where the stimulation is applied. On the other hand, the relaxation of tension below the spontaneous diastolic tension is independent of the phase of the cardiac cycle and is dependent on the level of diastolic tension such as cardiac tone. The grade of anodal relaxation is dependent on the intensity of stimulation. The relaxation can be produced either by a steady current flow or by repetitious pulses, suggesting mechanisms different from the relaxation of mytilus adductor muscle. The grade and the rate of anodal relaxation are greater when the muscle is in the tonic state, than when it is in the relaxed state. These findings are not influenced by an application of a procain solution, thus suggesting the independency of this relaxation from neural inhibition.
The research reported in this document has been made possible through the suppor and sponsorship of the U. S. Department of Army through its Far East Research Office.

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The pharmacological actions of guanidinoacetic acid, γ-guanidinobutyric acid and γ-guanidinobutyryl-methylester were investigated and compared with those of ω-aminoacids.
1. Guanidinoacetic acid had a considerable stimulant effect on the isolated guinea-pig ileum at 10^-4-10^-3M/l, while γ-guanidinobutyric acid produced rarely a very slight stimulant effect. Methylesterification of γ-guanidinobutyric acid strengthened markedly the stimulant effect. Its effect was weaker than that of γ-aminobutyryl-methylester and stronger than those of guanidinoacetic acid or ε-aminocapronyl-methyle ster.
2. Their stimulant effects on the guinea-pig ileum were antagonized by 0.1μg/ml. atropine sulfate, as was the case with those of ε-aminoacids and their methylester.
3. These guanidino-derivatives had the similar effects on the isolated rabbit ileum.
4. The anatognistic actions of guanidinoacetic acid against stimulants (ACh, 5-HT, nicotine) on the guinea-pig ileum were much weaker than those of GABA. Guanidinoacetic acid had practically an anti-5-HT only.γ-Guanidinobutyric acid and its methylester had not any antagonistic action to the stimulants.
5. Guanidinoacetic acid had a slight depressant effect on blood pressure of anesthetized rabbits, while γ-guanidinobutyric acid produced it hardly.γ-Guanidinobutyryl-methylester had a much stronger depressant effect than γ-guanidinobutyric acid. Its effect was weaker than γ-aminobutyryl-methylester and stronger than γ-aminocapronyl-methyiester. The effect of guanidinoacetic acid was farinferior to that of GABA.
6. In anesthetized cats, the depressant effects of these guanidino-derivatives were more pronounced than in rabbits. Guanidinoacetic acid had rather a stronger effect than GABA in the cat.
7. The similarity and difference in the pharmacological actions of guanidinoderivatives and simple ω-aminoacid-derivatives were discussed in some details.

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The effects of guanidinoacetic acid, γ-guanidinobutyric acid and γ-guanidinobutyryl-methylester on the direct cortical response and the transcallosal response were investigated in the rabbit and cat.
1. Guanidinoacetic acid suppressed the initial negative spike and augmented slightly the secondary negative wave of the direct cortical response in lower concentrations. In higher concentrations (0.5-1%), it abolished completely the initial negative spike. Disappearance of the initial negativity was accompanied by development of a surface positive wave.
2. The effects of guanidinoacetic acid on the transcallosal response consisted of three; 1) suppression of the surface negative wave, 2) augmentation and prolongation of the surface positive wave, 3) development of a late slow negative wave. Sometimes, there occurred repetitive positive shifts in potential following this late slow negativity.
3.γ-Guanidinobutyric acid augmented selectively the secondary negative wave, but did not affect directly the initial negative spike of the direct cortical response.
4.γ-Guanidinobutyric acid augmented the surface negative component of the transcallosal response, leaving the surface-positive component unchanged.
5. Methylesterification of γ-guanidinobutyric acid did not produce any change in the effects on cvoked potentials. Namely, γ-guanidinobutyryl-methylester augmented the secondary negative wave of the direct cortical response and the negative wave of the transcallosal response.
6. Guanidinoacetic acid, γ-guanidinobutyric acid and γ-guanidinobutyryl-methylester corresponded neuropharmacologically to GABA, ε-aminocaproic acid andε-aminocapronyl-methylester respectively.

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Applying repetitive stimuli to a single node of Ranvier of a myelinated nerve fibre of the toad, the relation between the response and the stimulus strength and frequency were investigated. Chief results obtained are as follows:
1. The case of subthreshold repetitive stimulation. 1) Several local responses (L. R.) appeared prior to the first spike. The L. R. became gradually larger in size towards a certain maximal value where a spike was fired suddenly. After the first spike, the same thing took place before the second spike appeared, or else each of the successive stimuli did evoke a spike, according to the stimulation frequency. 2) The spike height appeared smaller when preceded by a larger number of local responses. 3) The spike height got smaller while the maximal L. R. larger with time, especially in high stimulation frequency.
2. The case of weak suprathreshold repetitive stimulation. 1) In very high frequency stimulation, one and just one spike was evoked. 2) The value of Q in the final steady state got smaller with higher stimulation frequency.
3. The case of strong repetitive stimulation. 1) The spike appeared reduced in size when elicited by a stimulus more than several times stronger than the threshold. 2) Just one spike was evoked in very strong repetitive stimulation.
4. WEDENSKY'S inhibition was discussed.
5. The ratio Q as a safety factor of conduction was confirmed.

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Employing toad's myelinated fibres as material, the responses of a single node of Ranvier to direct repetitive stimulation were examined. The chief results obtained are as follows:
1. The spike height gets larger (smaller) and the duration gets shorter (longer) in A. E. T.(C. E. T.).
2. Generally, the spike height gets gradually smaller with time. The rate of decrease is larger (smaller) than normal under C. E. T.(A. E. T.).
3. Repetitive subthershold stimulation under C. E. T. evokes a spike after evoking several local responses, as in normal conditions. Thereby, the necessary number of stimulus decreases with strength of C. E. T. towards “one”. The size of the spike is a little larger when evoked after repetition of stimulus than when evoked by a single stimulus (FIG. 4, C. E. T.). Under A. E. T., on the other hand, a just suprathreshold stimulus becomes subthreshold, the number of stimulus necessary for initiation of spike increases with strength of the tonus, until finally just local responses are produced without evoking any spike. The size of thespike is somewhat larger when evoked by a single stimulus than when evoked by some repetitive stimuli (FIG. 4, A. E. T.).
4. The local response can be summated in sufficiently high frequency stimulation.
5. There is some after-effect of electrotonus upon the spike height. It is the same, not reversed, in quality with the effect during the tonus-on.
6. There are differences between the attitudes of spike and local response to stimulation under E.T at least with regard to the response size
7. The ratio Q (spike height/max. L. R height) was large in long pulse stimulation and in A. E. T. and smaller in short pulse stimulation and in C. E. T.

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The afferent innervation of the splanchnic nerve has been studied by recording the impulse discharges from the splanchnic, mesenteric and several other nerves. The results are summarized as follows:
1. As the splanchnic afferent nerve fiber has many branchings on its course, it can innervate many different abdominal viscera and several parts of these organs in common.
2. Many of these branchings may be localized near the bifurcation of the nerve trunk.
3. Every myelinated afferent fiber branched at the node of Ranvier, and daughterfibers generally had smaller diameters than those of parent-fibers.
4. Afferent impulses from peripheral mechanoreceptors were conducted not only in a central direction but also to a peripheral direction through branchings.
5. Each abdominal organ is innervated by several different splanchnic afferent fibers in an overlapped manner.

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1. Single spinal motoneurons of the cat were directly stimulated with linearly increasing currents flowing through an intracellular micropipette. Intensities of currents of varying slopes at the moment of spike generation were measured on the oscilloscopic records and compared with the rheobase.
2. According to different courses of the threshold-latency curves, the motoneurons can be classified into two groups. In the first group motoneurons, the threshold current intensity is progressively increased, to attain a certain final value, with decreasing rate of current rise. Electrical differentiation of the spike potentials reveals that they are initiated at the initial segment when the rise of current is rapid, and from the soma when the rise of current is slow enough. These motoneurons are characterized by relatively short after-hyperpolarization and considered to be phasic or fast mtoneurons.
3. The second group motoneurons have a threshold current intensity almost constant within a wide range of slopes of current rise. The spikes are initiated always at the initial segment. They are considered functionally to be tonic or slow motoneurons with the after-hyperpolarization of rather long duration.
4. Deeper Nembutal anesthesia and reduced synaptic inflow to the motoneuron seem to favor the chance to encounter the first group motoneurons. Accommodation of the initial segment is in general faster than that of the soma, but the former may change its rate with ease depending on the environmental conditions.
5. Two alternative interpretations of the threshold-latency curve of the first group motoneuron were proposed and their implications were discussed. The hypothesis admitting a transition zone between the initial segment and the soma seems to be preferable, being consistent with an assumption of constant threshold depolarization at fixed areas of the motoneuron.

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Using the isolated frog skin, the effects of ouabain on active as well as on passive ion transport were investigated under short-circuit conditions. The drug decreased the short-circuit current and the electrical conductance, but it enhanced the Na and SO₄ outfluxes. When the concentration of Na in the fluid outside the skin was low, the electrical conductance did not change by application of the drug. In some skins it was observed that before the addition of ouabain, the conductance for the passive Na transport was negligibly small compared with the total electrical conductance. These facts were explained by assuming that the electrical conductance of the frog skin depended on the active Na transport process as well as on the passive diffusion of ions.

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