An attempt was made to explain visual masking phenomenon in terms of single cell activity in the cat's striate cortex by means of three modes of light stimulation: a slit of light stimulus, a diffuse flash of light stimulus and a combination of these two. Only single cells responding well to a moving slit of light and having the distinct axis of receptive field were used for the analysis. These cells were classified into four groups by using flashing stationary slit of light stimulus: viz., ON, ON-OFF, OFF and an unclassified type.
The responses to the combined stimuli were observed in half the ON type cells and all the ON-OFF type cells but never in the OFF type cells. They consisted of two groups of bursts, one termed early response, appearing within300 msec, and the other late response, appearing about 700msec after onset of the diffuse flash of the combined stimuli.
The early response varied in firing pattern from unit to unit, and the latency tended to increase with increase in background luminance. It was very weak or absent in the ON type units, while it was brisk and stable in the ON-OFF type units. It was suggested that the early response may be correlated with the extinction of the maintained stationary slit of light caused by the bright diffuse flash.
The late response was observed in every cell of the ON and ON-OFF types. The firing pattern was a unimodal discharge lasting for a period of 300 to 400msec. The peak time and the spike frequency of the late response decreased almost linearly with increase in background luminance. On the other hand, a similar relationship was also found between log luminance and the reaction time of the human subject to reappearance of the slit of light after it was masked by the bright flash. Therefore, it was inferred that the peak time of the late response corresponds to the period of temporary impairment of perception of the stationary light stimulus by the flash (so-called visual masking).
A diffuse flash of light evoked little or no response from single units ofthe cat's primary visual cortex, in contrast to its effect on ganglion cells of the retina or the lateral geniculate body (BISHOP and RODIECK, 1965; HUBEL and WIESEL, 1959, 1961; HUBEL, 1960). For activation of the visual cortical units the light stimulus must be in elongated form (e. g., a slit of light) and attention must be paid tp such parameters as its orientation (HUBEL and WIESEL, 1962), contrast (BURNS and PRITCHARD, 1964), binocular disparity (BARLOW et al., 1967; NIKARA et al., 1968) and rate of movement (PETTIGREW et al., 1968). The importance of stimulus movement implies that cortical units in the paralyzed cat do not respond to stationary stimuli.
However, while a diffuse flash of light and a stationary slit of light stimulus are equally ineffective alone, a significant number of cortical units were found to respond to these stimuli when combined (NIKARA, 1970). This response was systematically examined. Dependence of the latency (or peak time) of the response upon the level of background illumination was compared with that of the reaction time of human subjects. Here, the reaction time means the period which elapses from the onset of a bright flash till the subject reacts to the reappearance of a slit of light after it has been masked for a while by the bright flash of light (visual masking effect). The results were discussed with reference to the psychophysical studies on visual masking effects.

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The excitation mechanisms of toothache caused by thermal changes were investigated on the canines of anesthetized mongrel dogs. Thermal stimulations were applied to the local tooth surface or the cavity floor made in dental tissues by a thermal stimulating equipment or cold and hot Ringer solutions. The potential difference between the cavity floor and the pulp transdentinal potential-and the action potentials of the odontoblast cell area and the alveolar nerve were recorded.
The results obtained were as follows: 1) Synchronous relation was found between the action potentials. 2) Two contradictory or single biphasic action potentials were recorded by large and small diameter micropipette electrodes. 3) Following the fall or rise of the stimulating temperature the transdentinal potential increased or decreased in inverse proportion to temperature variation. This potential was diminished by the administration of a narcotic agent to the pulp or cavity floor. The strength of these potentials was 50mV or more. 4) The action potentials were caused by the application of electrical current with the same intensity as the transdentinal potential. 5) It was found that the site most sensitive to thermal stimulation was the amelodentinal junction area and the areas least sensitive were the enamel and the dentin.

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1. Using a coaxial microelectrode, intra- and extra-cellular potentials were recorded from “idle” cells in the cerebral cortex of the cat. Records were made during repetitive stimulation of the cortical surface and during Metrazol induced paroxysmal activity.
2. The intra- and extra-cellular potentials induced by either stimulation of cortical surface or Metrazol injection were of opposite polarity, revealing that the intracellularly recorded potential was a change in membrane potential of the impaled cell and not a field potential generated by other elements.
3. The extracellular potential elicited during stimulation of the cortical surface was an approximate mirror image of the intracellular one, and thus accounted for the slow depolarization of the “idle” cell.
4. Following Metrazol injection, the extracellular potential, although opposite in polarity to the intracellular one, showed oscillation which had no counterpart in the intracellular record. Similar recordings made from cortical neurons showed intracellularly recorded oscillations which corresponded to extracellular ones. Therefore, the extracellular potential recorded immediately outside an “idle” cell following Metrazol is viewed as reflecting a composite of both glial and neuronal membrane changes.
5. Iontophoretic staining of “idle” cells suggests that they are probably glia.

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1. The membrane potentials, currents and contractile responses were measured in the bullfrog ventricular trabeculae under voltage clamp conditions by means of double glycerol-gap technique.
2. The threshold potential for sodium inward current was -62mV and that for tetrodotoxin insensitive current, -58mV. At stronger depolarization up to +20mV, the contractile tension increased, showing a sigmoid curve in the presence of tetrodotoxin.
3. The tension development depended strongly on the duration of depolarization. Below a critical duration, neither active current nor tension was elicited (Phase I). Slightly longer depolarization, up to about 100msec, produced an all-or-none inward current and small tension in normal conditions (Phase II). This changed into graded responses after tetrodotoxin.
4. Further increase in duration of depolarization augmented the peak tension, first by increasing the rate of rise of tension (Phase III) and later by prolonging the time to peak tension (Phase IV). After reaching the peak the tensionde creased gradually when the depolarization was continued further (Phase V). No second rise of tension was observed for long and strong depolarizations.
5. Differences in characteristics of the bullfrog ventricle from those of mammalian myocardium were discussed, and a role of sarcotubular systems in the relation between the action potential and tension development was suggested.

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An electrophysiological study has been made on the central relay pathway of the vago-vagal reflexes with special reference to those evoked by afferent stimulation of the abdominal vagus in cats under chloralose (50mg/kg i.v.) anesthesia.
1. Stimulation of the central cut end of the cervical or thoracic vagus nerve produced three mass reflex discharges in the contralateral cervical vagus nerve. On the other hand, stimulation of the abdominal vagal branch caused only the most delayed mass discharge.
2. Among the three mass discharges caused by cervical or thoracic vagal stimulation, at least the third one was regarded as the same discharge as that caused by afferent stimulation of the abdominal vagus nerve.
3. The maximum conduction velocity of the afferent fibres which caused the third response ranged between 1.0-1.4m/sec.
4. Transection of the medulla oblongata at the level of 5-6mm rostral to the obex did not abolish the vagal mass discharges but transection at the level of 4mm abolished or markedly reduced all of them.
5. The third mass discharge and sometimes the second ones were abolished by a superficial dorsal sagittal section (1-2mm deep) of the obex with its immediate caudal region. On the other hand, the first and sometimes the second were still recorded after such a section.
6. The possibility of the existence of the specific reflex pathway at least for the mass reflex discharge caused by afferent stimulation of the abdominal vagus nerve was discussed.

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1. Attempts were made to clarify the mechanism of lipolytic effect of excess potassium on rat brown adipose tissue in vitro.
2. The lipolytic effect of excess potassium on brown adipose tissue was almost completely eliminated in both reserpinized and denervated brown adipose tissues, whereas the lipolytic effect of norepinephrine was rather enhanced.
3. The lipolytic effect of excess potassium as well as of norepinephrine on brown adipose tissue was markedly inhibited by propranolol. A similar inhibitory effect of propranolol on the lipolytic effect of norepinephrine was also demonstrated in epididymal adipose tissue. However, the same dose of propranolol had no influence on the lipolytic action of ACTH and theophylline in epididymal adipose tissue.
4. Barium ions showed some small but intrinsic lipolytic effect on brown adipose tissue. This lipolytic effect was evidenced by combining theophylline and was markedly increased in an excess potassium medium.
5. Excess potassium in the medium caused a marked increase in the disappearance rate of norepinephrine from brown adipose tissue.
6. The lipolytic effect of norepinephrine on reserpinized rat brown adipose tissue was markedly increased in an excess potassium medium.
7. From these results, it is suggested that the lipolytic effect of excess potassium on brown adipose tissue was mediated through norepinephrine release from adrenergic nerve endings within the tissue. In addition, the possibility of potentiation of the norepinephrine effect per se in the presence of excess potassium was briefly discussed.

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1. Rat soleus (SOL) and extensor digitorum longus (EDL) muscles, stored for 2-6hrs at 30°C in Krebs' solution with rat serum in higher concentration than 2%, showed low internal Na and high internal K concentrations as compared with control muscles stored in the normal saline solution. Such a serum effect on the EDL muscles decreased with lowering of temperature of the external solution.
2. The rabbit, cow and cat serum in concentration of 5% as well as rat serum had a beneficial effect on the maintenance of electrolyte concentrations in EDL muscles.
3. In addition, the resting potential of EDL muscles stored in Krebs' solution with 5% rat serum at 30°C for 4 hrs was slightly greater than that in control muscles. A significant increase was found in the magnitude of action potential of the serum-treated muscles.

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In order to develop an applicable H₂ Pt electrode for the determination of average blood flow through organs, a catheter tip electrode covered with a Teflon membrane was designed. The properties of the covered electrode were studied polarographically mainly with reference to the effects of the applied voltage on the linearity, reproducibility and response time of the H₂ current against P_H2. Next the coronary blood flow was measured by placing an electrode in the coronary sinus and also in the aorta. In a wide range of the applied voltage an addition of H₂ to the solution caused an increase in the positive current through the electrodes. But the H₂ current was influenced to a considerable extent by the applied voltage. It was observed that a linear relation between the H₂ current and PH₂ was obtained in a range of applied voltage of -0.1 to +0.3V, when the external resistance was fixed at 5MΩ. However, at the applied voltage of +0.3V the response time was found to be markedly prolonged. Thus, the following conditions were selected as reasonable for practical use in vivo: 1) The platinisation was performed for 10 seconds with -1.5V in an 1% H₂ (PtCl₆) 6H₂O solution with 0.01% Pb (CH₃COO) ₂3H₂O, 2) the applied voltage was about -0.1V against an Ag-AgCl electrode, and 3) the external resistance was 5MΩ. Even under these conditions the H₂ current was influenced by P_O2 the stirring of the medium and the temperature. Therefore, to obtain reproducibility, these factors should be kept unchanged.
In order to ascertain the applicability of the present method to blood flow measurement, coronary blood flow was simultaneously determined by use of the H₂ and N₂O methods. The values obtained by both methods were in fairly good agreement, with only a small difference. The H₂ currents alone were then recorded at various inspired P_H2's and the coronary blood flow was calculated by using the saturation and desaturation curves of PH2. It was revealed that the change in the inspired P_H2 caused no remarkable influence on the calculated value, and that the desaturation curve gave more reliable values for the blood flow than the saturation curve. As an application of this electrode the coronary blood flow was measured under hypoxia over a 2 hour interval. As the result it was shown that the coronary blood flow was significantly increased during continuous hypoxia of over 2 hours compared with that in air respiration.

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The H₂ catheter electrode was applied for the determination of the coronary blood flow to ascertain its applicability. First, a modified catheterization technique was newly introduced to facilitate the placing of the catheter tip in the coronary sinus. Secondly, using this technique, the catheter electrode was inserted into the coronary sinus of dogs. Then, the H₂ currents were measured in the aorta, coronary sinus and right atrium during the H₂ inhalation to obtain the blood flow rate per unit volume of the heart tissue. This flow measurement was performed under three different experimental conditions of hypoxic respiration, epinephrine infusion and intravenous injection of carbochromen.
In comparison of the present results with the previous data obtained by other authors, it was demonstrated that the H₂ current had sufficient accuracy and reproducibility to show the changes in coronary blood flow continuously over the long run of the experiment lasting for several hours. Unlike the results in the N₂O method based on the coronary sinus blood sampling, the H₂ desaturation curves recorded in the coronary sinus formed a straight line on the semilogarithmic scale. This suggested that the coronary blood flow observable in the coronary sinus might be almost uniform.

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