Electrical responses to light flashes were recorded from single red rods in dark-adapted retinas of the bullfrog, Rana catesbeiana. When the flashes were ≤50ms in duration, plots of the peak amplitude of the responses as a function of log stimulus intensity were found to be parallel, and the stimulus intensity and duration required to elicit criterion-amplitude responses showed a linear relation with a negative unit slope. Furthermore the waveforms of equal-amplitude responses to flashes of different intensities and durations were superimposable. With increases in the stimulus duration beyond 50ms, however, the slopes of the response-log intensity curves for the higher stimulus intensities decreased, the slope of curves describing the intensity required to elicit criterion responses became less negative, and the responses of the rods decayed more slowly. These results indicate that within 50ms after the onset of flash stimuli, the effect of incident photons summate linearly to evoke rod responses of ertain sub-saturating amplitudes when assessed in terms of the peak response amplitude as well as the response waveform.

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Possible roles of smooth muscle contractions in the vascular dynamics were studied in the isolated rat large artery which has previously been shown to generate spontaneous rhythmic contractions depending upon the extracellular Ca²⁺. A cylindrical segment of the common carotid artery was superfused externally and perfused intraluminally by Tyrode solution, and the steady state intraluminal pressure (P)-volume (V) relationship of the vessel was obtained. The pressure buffering characteristic (Windkessel effect) of the vascular wall was evaluated by measuring the intraluminal pressure swing during application of external alternating pressure (semi-triangular pressure pulse, 0-120mmHg, 300cycle/min, "dynamic pressure load") to the intraluminal space. Effects on these vascular dynamics of inhibition of spontaneous smooth muscle contraction during superfusion of the preparation with nominally Ca²⁺-free Tyrode solution were investigated. Spontaneous rhythmic fluctuations of the intraluminal pressure (0.2-1.0mmHg, 2-25cycle/min), presumably due to contractions of vascular smooth muscles, were detected. The Ca²⁺-free solution abolished these spontaneous changes in the intraluminal pressure and reduced the baseline intraluminal pressure. The volume distensibility (ΔV/(V•ΔP)) of the preparation at higher intraluminal fluid volumes (or pressures, higher wall stretch) was increased by Ca²⁺-free solution. The magnitude of intraluminal pressure swing and the maximum rate of changes in the pressure during application of "dynamic pressure load" were decreased in Ca²⁺-free solution. The results suggest that the inhibition of spontaneous contractions of smooth muscle by Ca²⁺-free solution may increase the volume distensibility and pressure-buffering function of the large elastic artery.

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The effects of transient hypoxia on the responses of internal intercostal (IIC) muscle activity before and after surgical denervation of the carotid sinus nerves were studied in the bilaterally vagotomized rabbits. Bilateral vagotomy caused a complete inhibition of IIC activity in 11 of 13 animals. In the vagotomized animals with no expiratory activity in the IIC muscles, lung inflations with low O₂ gas mixture (6% O₂ in N₂) produced an increase in IIC activity, whereas these excitatory effects were remarkably reduced after sectioning the carotid sinus nerves. In addition, the effects of lung inflation with low O₂ gas mixture (6% O₂ in N₂) on carotid chemoreceptor activity were also studied in the vagotomized rabbits. Lung inflations with hypoxic gas caused an increase in carotid chemoreceptor activity. These results indicate that in the absence of proprioceptive input from the lungs, hypoxic stimulation of the carotid chemoreceptors is capable of activating the expiratory activity in the IIC muscles.

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The present work was undertaken to elucidate the underlying causative factors limiting survival in hypothermic rats (non-hibernator) and hamsters (hibernator). A variety of physiological and biochemical parameters were measured for 28 male Wistar rats (205-286g) and 26 male golden hamsters (85-118g) before and during induction of hypothermia to colonic temperature (Tco) of 18°C. With progressive decreases in Tco, parallel falls in V_O2, V_CO2, and heart rate were observed. In rats, plasma pH (pH_p) in arterial blood was significantly lowered from 7.453 at Tco of 38°C to 7.327 at Tco of 18°C (p<0.001). From the observations of increased arterial P_CO2 and bound CO₂ (bicarbonate ion) concentration, together with the unchanged blood lactate, respiratory acidosis caused by hypoventilation was suggested to be responsible for the decrease in pH_p. In contrast to rats, in hamsters pH_p was almost unchanged during the induction of hypothermia, while nearly complete depletion of blood glucose (-84.6%) and liver glycogen (-99.5%) were observed when Tco of 38°C was lowered to 18°C. It is concluded that the decrease in pH_p is a limiting factor for rats to survive the deep hypothermia at Tco of 18°C and the exhaustion of carbohydrates as an energy supply for hamsters.

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Unitary discharges were recorded from the inferior mesenteric ganglion of decerebrate dogs. Eighty-one units were identified as sympathetic postganglionic neurons innervating the colon and rectum by collision test performed by stimulation of the lumbar colonic nerve. Discharges of four units were enhanced simultaneously with an increased outflow of the renal nerve by pinching a toe. Thus, those units were regarded as vasoconstrictors of colonic blood vessels. Sixty-five units whose discharges were depressed or not affected by the pinching were regarded as neurons innervating colonic smooth muscle or mucosa (colonic units). Discharges were enhanced in the majority of the colonic units by colonic, rectal, and vesical distension, and mechanical stimulation of the anal canal, while discharges were depressed in a few units by rectal and vesical distension, and the anal canal stimulation. The number and percentage of the depressed units increased not only after cutting the hypogastric nerves and descending branches of the lumbar colonic nerve but also after transection of the caudal pons. The reflex depressions disappeared after transection at the bulbospinal junction, but the reflex enhancements remained. These results indicate that the colonic units are enhanced through a spinal reflex by the inflows from the distal colon, rectum, anal canal, and urinary bladder through the lumbar colonic, hypogastric, pelvic, and pudendal nerves, while a few are inhibited through a supraspinal reflex by inflows through the pelvic and pudendal nerves.

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An electromagnetic flow probe was chronically implanted around the common carotid, superior mesenteric, or renal artery or the terminal aorta in deoxycorticostrerone acetate (DOCA) hypertensive rats (prepared with DOCA and saline after uninephrectomy) and uninephrectomized control rats. A catheter for pressure measurement was inserted into the terminal aorta through a femoral artery. At rest the carotid and hindquarter (measured at the terminal aorta) blood flows in DOCA hypertensive rats were similar to the respective, corresponding values in normal rats with intact bilateral kidneys. The group mean of superior mesenteric flow was about 70% and that of renal flow about 40% larger than in normal rats. Cardiac output was estimated to be greater in DOCA hypertensive rats than in normal rats. In uninephrectomized control rats, superior mesenteric flow was larger than in normal rats to such an extent that an increase in cardiac output was assumed as in DOCA hypertensive rats, but renal flow was normal (about twice the unilateral renal flow in normal rats). Estimation of regional sympathetic vasoconstrictor tone from the decrease in peripheral resistance with hexamethonium and vasopressin antagonist revealed a substantial tone also in the superior mesenteric and hindquarter areas, where the tone was estimated to be almost absent in normal rats and uninephrectomized rats. It is suggested that hypertension in DOCA hypertensive rats is sustained by an increase in cardiac output and an elevation of vasoconstrictor tone in resistance vessels. Since increase in cardiac output appears to be similarly present in uninephrectomized control rats, the elevation of sympathetic tone due to administration of DOCA and salt seems to be indispensable for DOCA hypertension.

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3, 5-Dimethyl-3′-isopropyl-L-thyronine (DIMIT)-induced fetal hyperthyroid rats showed a marked accumulation of intracellular tubulin content in the cerebral cortex, hypothalamus, and cerebellum at 1 day old. When the fetuses were transplacentally radio-thyroidectomized with the administration of [¹³¹I]-Na, the brain weight was not changed at 1 day old. The DNA content was not affected by the radio-thyroidectomy (Tx), but intracellular RNA concentration (per DNA) was increased in the hypothalamus and cerebellum at that age. The DIMIT-supplement to Tx-fetuses failed to restore these abnormal values to normal. Delayed effects of the fetal Tx were observed in 11-day-old infants. These neonates showed decreased weight gain in the body, brain, cerebral cortex, and cerebellum. The DNA content (per wet tissue) was higher in the hypothalamus and cerebellum. The intracellular concentrations of RNA and tubulin (per DNA) were significantly decreased in the hypothalamus. These values were restored to normal by the administration of L-thyroxine(T₄) to rats between 1 and 10 days old. These results demonstrate that fetal nervous tissues are sensitive to changes in thyroid functions. The different manner of response to the hormonal states among the brain areas may reflect that each nervous tissue has a specific critical period for thyroid hormones during development.

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The Haldane effect coefficient in vivo and arterial-venous O₂ content difference ((a-v)C_O2) are, more or less, influenced by the contact time (t_c), P_O2 and P_O2 differences between venous blood and alveolar air. To increase the accuracy of the (a-v)C_O2 and the cardiac output measured by means of the rebreathing technique, factors to correct the Haldane effect (F(H)) and (a-v)C_O2 (F(avC_O2)) were obtained theoretically from the numerical solutions of simultaneous O₂ and CO₂ diffusions in the red blood cell. Both the factors were complicated functions of t_c, the difference in P_CO2 between venous blood and alveolar air, as well as (a-v)C_O2. For simplicity, we eliminated t_c from the above functions by using the standardized relation between the t_c and (a-v)C_O2 measured from a rebreathing experiment in man. The F(H) was a linear function of (a-v)C_O2. The (a-v)C_O2 was calculated by dividing the product of F(H) and the slope of the CO₂ dissociation curve by that of a gas exchange ratio against the P_CO2 in rebreathing air. The F(avC_O2) was given by a ratio of (a-v)C_O2 at any alveolar P_CO2 to the standard one, in which arterial blood has the same intracellular pH as that in venous blood. It was a linear function of the difference in P_CO2 between venous blood and alveolar air, whose slope was inversely related to the (a-v)C_O2 itself.

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The gas exchange ratio (R) obtained from O₂ and CO₂ concentrations measured in rebreathing air usually shows a linear relation to the P_CO2. By referring to this relation and the R which equals the Haldane effect coefficient and zero, the true- and oxygenated-venous P_CO2 are obtained in addition to the alveolar P_CO2. When these P_CO2 are evaluated, the R-P_CO2 line can also be computed theoretically from a numerical solution on the overall O₂ and CO₂ diffusions in the red blood cell. By comparing both the experimental and theoretical R-P_CO2 lines with each other, we derived a contact time equation. Since the linear approximation of the R-P_CO2 relation gave rise to an error in the contact time (t_c), first a factor to correct the linearity of the R-P_CO2 line was derived. Next, using these parameter values, t_c was quantitatively determined from experimental data obtained during rebreathing in 5 normal subjects and it was compared with that estimated from the pulmonary diffusing capacity for CO in the same rebreathing experiment. When the extracellular HCO₃^- dehydration rate was taken to be 0.1s in time constant, the t_c, being ca. 0.7 and 0.4s at rest and during exercise, respectively, showed good agreement with those obtained from the diffusing capacity for CO.

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Quantitative relations between O₂ uptake (V_O2), arterial-venous O₂ content difference ((a-v)C_O2), and contact time (t_c) were measured at rest and during exercise in 7 normal subjects, using a rebreathing technique. By injecting a known amount of pure O₂ into a rebreathing circuit, the VO₂ was measured from the time interval during which the injected O₂ volume was consumed. From the O₂ and CO₂ concentrations in rebreathing air the gas exchange ratio (R), which was linearly related to the PCO2, was determined. By using the slope of the R-PCO₂ relation, the (a- v)CO₂ was evaluated from the slope of the C_O2 dissociation curve between the true- and oxygenated-venous PCO2. These two venous PCO₂ were estimated from the R-P_O2 relation by use of the Haldane effect coefficient and by extrapolating it to the abscissa, where R=0. Furthermore, tc was evaluated by inserting the above two venous PC_O2 together with the alveolar PC_O2 into a contact time equation. The mean (a-v)C_O2 and t_c had consistent relations to the VO₂ and (a-v)CO2, respectively: (a-v)CO2=9.5•V_O2 0.35, (vol%), and t_c=4.86•(a-v)C_O2-1.025, (s)

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To clarify the effect of a cholinergic agent on free-running period of circadian rhythm, locomotor activities were continuously recorded in the rat implanted with a paraffin pellet mixed with or without carbachol near the suprachiasmatic nucleus. Implantation of carbachol, but not paraffin alone, resulted in shortening of the free-running period under constant darkness.

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The time course of the current response produced by a prolonged application of dopamine (DA) was studied in Aplysia ganglion cells with different types of DA receptors. The Na⁺-dependent fast excitatory receptors were found to be more readily desensitized than K⁺-dependent inhibitory ones, whereas Na⁺-dependent slow excitatory ones showed little sign of desensitization.

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Isolated strips of the human tracheal muscle had slow fluctuations of membrane potential (slow wave), essentially similar to those of guinea-pig trachea. The average amplitude and frequency of slow wave were 7.7mV and 19.9/min (n=9), respectively. There was clear correlation between the electrical activity and mechanical response during the excitation caused by tetraethylammonium (TEA), carbachol, and noradrenaline and also during the inhibition by isoprenaline. The slow wave seems to be related to the basal muscle tone, which is probably maintained by endogenous leukotrienes in human and by prostaglandins in guinea-pig.

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A novel apparatus for detecting a subtle decrease in erythrocyte deformability was developed. The oscillatory shape change of erythrocytes was monitored under an oscillatory shear stress (modulating the oscillation frequency in the range of 9-90dyn/cm²). The ellipsoidal deformation of intact erythrocytes perfectly followed the oscillatory force of up to about 2Hz, but the diamide-treated cells showed a phase difference of the oscillatory deformation at 1.7Hz.

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